Offshore Wind Turbine

CHAPTER 1
H ISTORY
1.0 INTRODUCTION
Since early recorded history, people have been harnessing the energy of the wind. Wind
energy propelled boats along the Nile River as early as 5000 B.C. By 200 B.C., simple windmills
in China were pumping water, while vertical-axis windmills with woven reed sails were grinding
grain in Persia and the Middle East.
New ways of using the energy of the wind eventually spread around the world. By the
11th century, people in the Middle East were using windmills extensively for food production;
returning merchants and crusaders carried this idea back to Europe. The Dutch refined the
windmill and adapted it for draining lakes and marshes in the Rhine River Delta. When settlers
took this technology to the New World in the late 19th century, they began using windmills to
pump water for farms and ranches, and later, to generate electricity for homes and industry.
Industrialization, first in Europe and later in America, led to a gradual decline in the use
of windmills. The steam engine replaced European water-pumping windmills. In the 1930s, the
Rural Electrification Administration's programs brought inexpensive electric power to most rural
areas in the United States.
However, industrialization also sparked the development of larger windmills to generate
electricity. Commonly called wind turbines, these machines appeared in Denmark as early as
1890. In the 1940s the largest wind turbine of the time began operating on a Vermont hilltop
known as Grandpa's Knob. This turbine, rated at 1.25 megawatts in winds of about 30 mph, fed
electric power to the local utility network for several months during World War II.
The popularity of using the energy in the wind has always fluctuated with the price of
fossil fuels. When fuel prices fell after World War II, interest in wind turbines waned. But when
the price of oil skyrocketed in the 1970s, so did worldwide interest in wind turbine generators.
The wind turbine technology R&D that followed the oil embargoes of the 1970s refined
old ideas and introduced new ways of converting wind energy into useful power. Many of these
approaches have been demonstrated in "wind farms" or wind power plants — groups of turbines
that feed electricity into the utility grid in the United States and Europe.

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Today, the lessons learned from more than a decade of operating wind power plants,
along with continuing R&D, have made wind-generated electricity very close in cost to the
power from conventional utility generation in some locations. Wind energy is the world's fastestgrowing energy source and will power industry, businesses and homes with clean, renewable
electricity for many years to come.
Wind power has been used as long as humans have put sails into the wind. For more than
two millennia wind-powered machines have ground grain and pumped water. Wind power was
widely available and not confined to the banks of fast-flowing streams, or later, requiring sources
of fuel. Wind-powered pumps drained the polders of the Netherlands, and in arid regions such as
the American mid-west or the Australian outback, wind pumps provided water for livestock and
steam engines.
With the development of electric power, wind power found new
applications in lighting buildings remote from centrallygenerated power. Throughout the 20th century parallel paths
developed small wind plants suitable for farms or residences,
and larger utility-scale wind generators that could be connected
to electricity grids for remote use of power. Today wind powered
generators operate in every size range between tiny plants for
battery charging at isolated residences, up to near giga watt
sized offshore wind farms that provide electricity to national
electrical networks.

1.1 Antiquity:
Sailboats and sailing ships have been using wind power for at least 5,500 years and
architects have used wind-driven natural ventilation in buildings since similarly ancient times.
The use of wind to provide mechanical power came somewhat later in antiquity.
The Babylonian emperor Hammurabi planned to use wind power for his ambitious
irrigation project in the 17th century BC.
The wind wheel of the Greek engineer Heron of Alexandria in the 1st century AD is the
earliest known instance of using a wind-driven wheel to power a machine. Another early
example of a wind-driven wheel was the prayer wheel, which was used in
ancient Tibet and China since the 4th century.

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1.2 Early Middle Ages:
The first practical windmills were in use in Sistan, a region in Iran and
bordering Afghanistan, at least by the 9th century and possibly as early as the 7th century. These
"Panemone windmills" were horizontal windmills, which had long vertical drive shafts with six
to twelve rectangular sails covered in reed matting or cloth. These windmills were used to grind
corn and pump water, and in the grist milling and sugarcane industries. The use of windmills
became widespread use across the Middle East and Central Asia, and later spread to China and
India. Vertical windmills were later used extensively in Northwestern Europe to grind flour
beginning in the 1180s, and many examples still exist. By 1000 AD, windmills were used to
pump seawater for salt-making in China and Sicily.
Wind-powered automata are known from the mid-8th century: wind-powered statues that
"turned with the wind over the domes of the four gates and the palace complex of the Round City
of Baghdad". The "Green Dome of the palace was surmounted by the statue of a horseman
carrying a lance that was believed to point toward the enemy. This public spectacle of windpowered statues had its private counterpart in the 'Abbasid palaces where automata of various
types were predominantly displayed."

1.3 Late Middle Ages:
The first windmills in Europe appear in sources dating to the twelfth century. These early
European windmills were sunken post mills. The earliest certain reference to a windmill dates
from 1185, in Weedley, Yorkshire, although a number of earlier but less certainly dated twelfthcentury European sources referring to windmills have also been adduced.While it is sometimes
argued that crusaders may have been inspired by windmills in the Middle East, this is unlikely
since the European vertical windmills were of significantly different design than the horizontal
windmills of Afghanistan. Lynn White Jr., a specialist in medieval European technology, asserts
that the European windmill was an "independent invention;" he argues that it is unlikely that the
Afghanistan-style horizontal windmill had spread as far
west as the Levant during the Crusader period. In
medieval England rights to waterpower sites were often
confined to nobility and clergy, so wind power was an
important resource to a new middle class.In addition,
windmills, unlike water mills, were not rendered
inoperable by the freezing of water in the winter.
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By
the
14th
century
Dutch windmills were in use to drain areas
of the Rhine River delta.

1.4 18th Century:
Windmills were used to pump water
for salt making on the island of Bermuda,
and on Cape Cod during the American
revolution.

1.5 19th century:
In Denmark there were about 2,500 windmills by 1900, used for mechanical loads such
as pumps and mills, producing an estimated combined peak power of about 30 MW.In the
American midwest between 1850 and 1900, a large number of small windmills, perhaps six
million, were installed on farms to operate irrigation pumps. Firms such as Star,
Eclipse, Fairbanks-Morse and Aeromotor became famed suppliers in North and South
America.The first windmill used for the production of electricity was built in Scotland in July
1887 by Prof James Blyth of Anderson's College, Glasgow (the precursor of Strathclyde
University). Blyth's 10 m high, cloth-sailed wind turbine was installed in the garden of his
holiday cottage at Marykirk in Kincardineshire and was used to charge accumulators developed
by the Frenchman Camille Alphonse Faure, to power the lighting in the cottage, thus making it
the first house in the world to have its electricity supplied by wind power. Blyth offered the
surplus electricity to the people of Marykirk for lighting the main street, however, they turned
down the offer as they thought electricity was "the
work of the devil." Although he later built a wind
turbine to supply emergency power to the local Lunatic
Asylum, Infirmary and Dispensary of Montrose the
invention never really caught on as the technology was
not considered to be economically viable.
Across the Atlantic, in Cleveland, Ohio a larger
and heavily engineered machine was designed and
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constructed in the winter of 1887-1888 by Charles F. Brush, this was built by his engineering
company at his home and operated from 1886 until 1900.
The Brush wind turbine had a rotor 17 m (56 foot) in diameter and was mounted on an
18 m (60 foot) tower. Although large by today's standards, the machine was only rated at 12 kW;
it turned relatively slowly since it had 144 blades. The connected dynamo was used either to
charge a bank of batteries or to operate up to 100 incandescent light bulbs, three arc lamps, and
various motors in Brush's laboratory. The machine fell into disuse after 1900 when electricity
became available from Cleveland’s central station and was abandoned in 1908.
In 1891 Danish scientist, Poul la Cour, constructed a wind turbine to generate electricity,
which was used to produce hydrogen by electrolysis to be stored for use in experiments and to
light the Askov High school. He later solved the problem of producing a steady supply of power
by inventing a regulator, the Kratostate, and in 1895 converted his windmill into a prototype
electrical power plant that was used to light the village of Askov.

1.6 20th century:
Development in the 20th century might be usefully divided into the periods:


1900–1973, when widespread use of individual wind generators competed against fossil
fuel plants and centrally-generated electricity



1973–onward, when the oil price crisis spurred investigation of non-petroleum energy
sources

1.7 (1900–1973) Danish development:
In Denmark wind power was an important part of a decentralized electrification in the
first quarter of the 20th century, partly because of Poul la Cour from his first practical
development in 1891 at Askov. By 1908 there were 72 wind-driven electric generators from
5 kW to 25 kW. The largest machines were on 24 m (79 ft) towers with four-bladed 23 m (75 ft)
diameter rotors. In 1957 Johannes Juul installed a 24 m diameter wind turbine at Gedser, which
ran from 1957 until 1967. This was a three-bladed, horizontal-axis, upwind, stall-regulated
turbine similar to those now used for commercial wind power development.
A giant change took place in 1978 when the world's first multi-megawatt wind
turbine was constructed. It pioneered many technologies used in modern wind turbines and
allowed Vestas, Siemens and others to get the parts they needed. Especially important was the
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novel wing construction using help from German aeronautics specialists. The power plant was
capable of delivering 2MW, had a tubular tower, pitch controlled wings and three blades. It was
built by the teachers and students of the Tvind school. Before completion these "amateurs" were
much ridiculed. The turbine still runs today and looks almost identical to the newest most
modern mills.
Danish commercial wind power development stressed incremental improvements in
capacity and efficiency based on extensive serial production of turbines, in contrast with
development models requiring extensive steps in unit size based primarily on theoretical
extrapolation. A practical consequence is that all commercial wind turbines resemble the Danish
model, a light-weight three-blade upwind design.

1.8 Farm power and isolated plants
In 1927 the brothers Joe Jacobs and Marcellus Jacobs opened a factory, Jacobs
Wind in Minneapolis to produce wind turbine generators for farm use. These would typically be
used for lighting or battery charging, on farms out of reach of central-station electricity and
distribution lines. In 30 years the firm produced about 30,000 small wind turbines, some of
which ran for many years in remote locations in Africa and on the Richard Evelyn
Byrd expedition to Antarctica. Many other manufacturers produced small wind turbine sets for
the same market, including companies called Wincharger, Miller Airlite, Universal Aeroelectric,
Paris-Dunn, Airline and Wind power.
In 1931 the Darrieus wind turbine was invented, with its vertical axis providing a
different mix of design tradeoffs from the conventional horizontal-axis wind turbine. The vertical
orientation accepts wind from any direction with no need for adjustments, and the heavy
generator and gearbox equipment can rest on the ground instead of atop a tower.
By the 1930s windmills were widely used to generate electricity on farms in the United
States where distribution systems had not yet been installed. Used to replenish battery storage
banks, these machines typically had generating capacities of a few hundred watts to several
kilowatts. Besides providing farm power, they were also used for isolated applications such
as electrifying bridge structures to prevent corrosion. In this period, high tensile steel was cheap,
and windmills were placed atop prefabricated open steel lattice towers.
The most widely used small wind generator produced for American farms in the 1930s
was a two-bladed horizontal-axis machine manufactured by the Win charger Corporation. It had
a peak output of 200 watts. Blade speed was regulated by curved air brakes near the hub that
deployed at excessive rotational velocities. These machines were still being manufactured in the
United States during the 1980s. In 1936, the U.S. started a rural electrification project that killed

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the natural market for wind-generated power, since network power distribution provided a farm
with more dependable usable energy for a given amount of capital investment.
In Australia, the Dunlite Corporation built hundreds of small wind generators to provide
power at isolated postal service stations and farms. These machines were manufactured from
1936 until 1970.

1.9 Utility-scale Turbines
A forerunner of modern horizontal-axis utility-scale wind generators was the WIME D-30
in service in Balaklava, near Yalta, USSR from 1931 until 1942. This was a 100 kW generator on
a 30 m (100 ft) tower, connected to the local 6.3 kV distribution system. It had a three-bladed 30
metre rotor on a steel lattice tower. It was reported to have an annual load factor of 32 per
cent, not much different from current wind machines.
In 1941 the world's first megawatt-size wind turbine was connected to the local electrical
distribution system on the mountain known as Grandpa's Knob in Castleton, Vermont, USA. It
was designed by Palmer Cosslett Putnam and manufactured by the S. Morgan Smith Company.
This 1.25 MW Smith-Putnam turbine operated for 1100 hours before a blade failed at a known
weak point, which had not been reinforced due to war-time material shortages. No similar-sized
unit was to repeat this "bold experiment" for about forty years.

1.10 Fuel-saving Turbines
During the Second World War, small wind generators were used on German U-boats to
recharge submarine batteries as a fuel-conserving measure. In 1946 the lighthouse and residences
on the island Insel Neuwerk were partly powered by an 18 kW wind turbine 15 metres in
diameter, to economize on diesel fuel. This installation ran for around 20 years before being
replaced by a submarine cable to the mainland.
The Station d'Etude de l'Energie du Vent at Nogent-le-Roi in France operated an
experimental 800 KVA wind turbine from 1956 to 1966.

1.11 (1973–2000) US development
States government worked with industry to advance the
technology and enable large commercial wind turbines.
The NASA wind turbines were developed under a program to
create a utility-scale wind turbine industry in the U.S. With
funding from the National Science Foundation and later
the United States Department of Energy (DOE), a total of 13
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experimental wind turbines were put into operation, in four major wind turbine designs. This
research and development program pioneered many of the multi-megawatt turbine technologies
in use today, including: steel tube towers, variable-speed generators, composite blade materials,
partial-span pitch control, as well as aerodynamic, structural, and acoustic engineering design
capabilities. The large wind turbines developed under this effort set several world records for
diameter and power output. The MOD-2 wind turbine cluster of three turbines produced 7.5
megawatts of power in 1981. In 1987, the MOD-5B was the largest single wind turbine operating
in the world with a rotor diameter of nearly 100 meters and a rated power of 3.2 megawatts. It
demonstrated an availability of 95 percent, an unparalleled level for a new first-unit wind
turbine. The MOD-5B had the first large-scale variable speed drive train and a sectioned, twoblade rotor that enabled easy transport of the blades. The 4 megawatt WTS-4 held the world
record for power output for over 20 years. Although the later units were sold commercially, none
of these two-bladed machines were ever put into mass production. When oil prices declined by a
factor of three from 1980 through the early 1990s, many turbine manufacturers, both large and
small, left the business. The commercial sales of the NASA/Boeing Mod-5B, for example, came
to an end in 1987 when Boeing Engineering and Construction announced they were "planning to
leave the market because low oil prices are keeping windmills
for electricity generation uneconomical."
Later, in the 1980s, California provided tax rebates for wind
power. These rebates funded the first major use of wind power
for utility electricity. These machines, gathered in large wind
parks such as at Altamont Pass would be considered small and
un-economic by modern wind power development standards.

1.12 Self-sufficiency and back-to-the-land
In the 1970s many people began to desire a selfsufficient life-style. Solar cells were too expensive for
small-scale electrical generation, so some turned to
windmills. At first they built ad-hoc designs using wood
and automobile parts. Most people discovered that a
reliable wind generator is a moderately complex
engineering project, well beyond the ability of most
amateurs. Some began to search for and rebuild farm
wind generators from the 1930s, of which Jacobs Wind
Electric Company machines were especially sought after.
Hundreds of Jacobs machines were reconditioned and
sold during the 1970s.
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All major horizontal axis turbines today rotate the same way (clockwise) to present a
coherent view. However, early turbines rotated counter-clockwise like the old windmills, but a
shift occurred from 1978 and on. The individualist-minded blade supplier Økær made the
decision to change direction in order to be distinguished from the collective Tvind and their
small wind turbines. Some of the blade customers were companies that later evolved
into Vestas, Siemens, Enercon and Nordex. Public demand required that all turbines rotate the
same way, and the success of these companies made clockwise the new standard.
Following experience with reconditioned 1930s wind turbines, a new generation of
American manufacturers started building and selling small wind turbines not only for batterycharging but also for interconnection to electricity networks. An early example would be
Enertech Corporation of Norwich, Vermont, which began building 1.8 kW models in the early
1980s.
In the 1990s, as aesthetics and durability became more important, turbines were placed
atop tubular steel or reinforced concrete towers. Small generators are connected to the tower on
the ground, and then the tower is raised into position. Larger generators are hoisted into position
atop the tower and there is a ladder or staircase inside the tower to allow technicians to reach and
maintain the generator, while protected from the weather.

1.13 21th century:

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As the 21st century began, fossil fuel was still
relatively cheap, but rising concerns
over energy security, global warming, and
eventual fossil fuel depletion led to an
expansion of interest in all available forms
of renewable
energy.
The
fledgling
commercial wind power industry began
expanding at a robust growth rate of about
25% per year, driven by the ready availability
of large wind resources, and falling costs due to improved technology and wind farm
management. The steady run-up in oil prices after 2003 led to increasing fears that peak oil was
imminent, further increasing interest in commercial wind power. Even though wind power
generates electricity rather than liquid fuels, and thus is not an immediate substitute for
petroleum in most applications (especially transport), fears over petroleum shortages only added
to the urgency to expand wind power. Earlier oil crisis had already caused many utility and
industrial users of petroleum to shift to coal or natural gas. Natural gas began having its own
supply problems, and wind power showed potential for replacing natural gas in electricity
generation.
Technological innovations continues to drive new developments in the application of wind power

1.14 Floating wind turbine technology:
Offshore wind power began to expand beyond fixed-bottom, shallow-water turbines
beginning late in the first decade of the 2000s. The world's first operational deep-water largecapacity floating wind turbine, Hywind, became operational in the North Sea off Norway in late
2009 at a cost of some 400 million kroner (around US$62 million) to build and deploy.
These floating turbines are a very different construction technology—closer to floating
oil rigs rather—than traditional fixed-bottom, shallow-water monopile foundations that are used
in the other large offshore wind farms to date.
By late 2011, Japan announced plans to build a multiple-unit floating wind farm, with six
2-megawatt turbines, off the Fukushima coast of northeast Japan where the 2011 tsunami and
nuclear disaster has created a scarcity of electric power. After the evaluation phase is complete in
2016, "Japan plans to build as many as 80 floating wind turbines off Fukushima by 2020" at a
cost of some 10-20 billion Yen.

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1.15 Airborne turbines:
Airborne wind energy systems use airfoils or turbines supported in the air by buoyancy or
by aerodynamic lift. The purpose is to eliminate the expense of tower construction, and allow
extraction of wind energy from steadier, faster, winds higher in the atmosphere. As yet no gridscale plants have been constructed. Many design concepts have been demonstrated.

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CHAPTER 2
WIND TURBINE
2.1 What Is Wind?
Wind is moving air and is caused by differences in air pressure within our atmosphere. Air under
high pressure moves toward areas of low pressure. The greater the difference in pressure, the
faster the air flows.

2.2 The Fastest Winds:
In 1934, on the roof of a little wooden building atop Mount Washington, in New
Hampshire, an instrument to measure wind speed, called an anemometer, made history. It
recorded a wind speed of 231 miles per hour (mph) during a huge spring storm, the fastest wind
gust ever recorded with the instrument!
More recently, sophisticated Doppler radar has been used to measure winds, recording a
wind speed of 318 mph in an Oklahoma tornado in 1999. That’s faster than the top speeds of
Japanese bullet trains and over three times quicker than the fastest baseball pitch.
The strongest wind gust ever was registered in the automatic weather station of Barrow
Island, Australia, on the 10th April 1996. The local anemometer marked 408 km/h (220 knots,
253 mph) and was mounted 10 meters above sea level.
The windiest region in the world is Cape Farewell, in Greenland. Planes only flew over
this Arctic spot, for the first time, in 2008, because of the strong blows that inhabit the place.

2.3 Describing Wind:
Wind is described with direction and speed. The direction of the wind is expressed as the
direction from which the wind is blowing. For example, easterly winds blow from east to west,
while westerly winds blow from west to east. Winds have different levels of speed, such as
“breeze” and “gale”, depending on how fast they blow. Wind speeds are based on the
descriptions of winds in a scale called the Beaufort Scale, which divides wind speeds into 12
different categories, from less than 1 mph to more than 73 mph.
Wind can blow anywhere, anytime and in any direction. The official measurement format
for grading the power of winds is knots.

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2.4 Measurement:
If you want to measure wind speed, it is important to use an
accurate digital anemometer.

2.5 What causes wind?
To understand what makes the wind blow, we first need to understand what atmospheric
pressure is. Pressure at the earth's surface is a measure of the 'weight' of air pressing down on it.
The greater the mass of air above us, the higher the pressure we feel, and vice-versa. The
importance of this is that air at the surface will
want to move from high to low pressure to
equalize the difference, which is what we
know as wind.
So wind is caused by differences in
atmospheric pressure - but why do we get
these differences? It's down to the rising and
sinking of air in the atmosphere. Where air is
rising we see lower pressure at the earth's
surface, and where it's sinking we see higher pressure. In fact if it weren't for this rising and
sinking motion in the atmosphere then not only would we have no wind, but we'd also have no
weather.
This can be explained in simple terms by the daily wind cycle.
The earth's surface has both land and water. When the sun comes up, the air over the land heats
up quicker than that over water. The heated air is lighter and it rises. The cooler air is denser and
it falls and replaced the air over the land. In the night the reverse happens. Air over the water is
warmer and rises, and is replaced by cooler air from land.
2.5.1 Small scale winds:
This rising and sinking of air in the atmosphere takes place both on a global scale and a
local scale. One of the simplest examples of a local wind is the sea breeze. On sunny days during
the summer the sun's rays heat the ground up quickly. By contrast, the sea surface has a greater
capacity to absorb the sun's rays and is more difficult to warm up - this leads to a temperature
contrast between the warm land and the cooler sea.
As the land heats up, it warms the air above it. The warmer air becomes less dense than
surrounding cooler air and begins to rise, like bubbles in a pan of boiling water. The rising air
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leads to lower pressure over the land. The air over the sea remains cooler and denser, so pressure
is higher than inland. So we now have a pressure difference set up, and air moves inland from the
sea to try and equalize this difference - this is our sea breeze. It explains why beaches are often
much cooler than inland areas on a hot, sunny day.
2.5.2 Large scale winds:
A similar process takes place on a global scale. The sun's rays reach the earth's surface in
Polar Regions at a much more slanted angle than at equatorial regions. This sets up a temperature
difference between the hot equator and cold poles. So the heated air rises at the equator (leading
to low pressure) whilst the cold air sinks above the poles (leading to high pressure). This pressure
difference sets up a global wind circulation as the cold polar air tries to move southwards to
replace the rising tropical air. However, this is complicated by the earth's rotation (known as the
Coriolis Effect).
Air that has risen at the equator moves pole wards at higher levels in the atmosphere then
cools and sinks at around 30 degrees latitude north (and south). This leads to high pressure in the
subtropics - the nearest of these features that commonly affects UK weather is known as the
Azores high. This sinking air spreads out at the earth's surface some of it returns southwards
towards the low pressure at the equator (known as trade winds), completing a circulation known
as the Hadley Cell.
Another portion of this air moves pole wards and meets the cold air spreading southwards
from the Arctic (or Antarctic). The meeting of this subtropical air and polar air takes place on
latitude close to that of the UK and is the source of most of our weather systems. As the warm air
is less dense than the polar air it tends to rise over it - this rising motion generates low pressure
systems which bring wind and rain to our shores. This part of the global circulation is known as
the mid-latitude cell, or Ferrell Cell.
Another important factor is that the coriolis effect from the earth's rotation meaning that
air does not flow directly from high to low pressure - instead it is deflected to the right (in the
northern hemisphere - the opposite is true in the southern hemisphere). This gives us our
prevailing west to southwesterly winds across the UK.

2.6 Wind Energy Conversion/ Wind Turbine:
A wind turbine is a device that converts kinetic energy from the wind into electrical
power. A wind turbine used for charging batteries may be referred to as a wind charger.
The terms "wind energy" or "wind power" describe the process by which the wind is used
to generate mechanical power or electricity. Wind turbines convert the kinetic energy in the wind
into mechanical power. This mechanical power can be used for specific tasks (such as grinding
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grain or pumping water) or a generator can convert this mechanical power into electricity to
power homes, businesses, schools, and the like.
The terms wind energy or wind power describes the process by which the wind is used to
generate mechanical power or electricity. Wind turbines convert the kinetic energy in the wind
into mechanical power. This mechanical power can be used for specific tasks (such as grinding
grain or pumping water) or a generator can convert this mechanical power into electricity.

Wind Turbines
Wind turbines, like aircraft propeller
blades, turn in the moving air and power an
electric generator that supplies an electric
current. Simply stated, a wind turbine is the
opposite of a fan. Instead of using
electricity to make wind, like a fan, wind
turbines use wind to make electricity. The
wind turns the blades, which spin a shaft,
which connects to a generator and makes
electricity. Wind turbines operate on a
simple principle. The energy in the wind
turns two or three propeller-like blades
around a rotor. The rotor is connected to the
main shaft, which spins a generator to create electricity.

2.7 Design and Construction:
1. Anemometer:
Measures the wind speed and transmits wind speed data to the controller.
2. Blades:
Most turbines have either two or three blades. Wind blowing over the blades causes the blades to
“lift” and rotate.
3. Brake:
A disc brake, which can be applied mechanically, electrically, or hydraulically to stop the rotor in
emergencies.
4.Controller:
The controller starts up the machine at wind speeds of about 8 to 16 miles per hour (mph) and
shuts off the machine at about 55 mph. Turbines do not operate at wind speeds above about 55
mph because they might be damaged by the high winds.
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5. Gear Box:
Gears connect the low-speed shaft to the high-speed shaft and increase the rotational speeds from
about 30 to 60 rotations per minute (rpm) to about 1000 to 1800 rpm, the rotational speed
required by most generators to produce electricity. The gear box is a costly (and heavy) part of
the wind turbine and engineers are exploring “direct-drive” generators that operate at lower
rotational speeds and don’t need gear boxes.
6. Generator:
Usually an off-the-shelf induction generator that produces 60-cycle AC electricity which is
approximately 34% of the wind turbine cost.
7. High Speed Shaft:
Drives the generator.
8. Low Speed Shaft:
The rotor turns the low-speed shaft at about 30 to 60 rotations per minute.
9. Nacelle:
The nacelle sits atop the tower and contains the gear box, low- and high-speed shafts, generator,
controller, and brake. Some nacelles are large enough for a helicopter to land on.
10. Pitch:
Blades are turned, or pitched, out of the wind to control the rotor speed and keep the rotor from
turning in winds that are too high or too low to produce electricity.
11. Rotor:
The blades and the hub together are called the rotor. which is approximately 20% of the wind
turbine cost.
12. Tower:
Towers are made from tubular steel, concrete, or steel lattice. Because wind speed increases with
height, taller towers enable turbines to capture more energy and generate more electricity. which
is approximately 15% of the wind turbine cost.
13. Wind Direction:
This is an “upwind” turbine, so-called because it operates facing into the wind. Other turbines
are designed to run “downwind,” facing away from the wind.
14. Wind Vane:
Measures wind direction and communicates with the yaw drive to orient the turbine properly
with respect to the wind.
15. Yaw Drive:

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Upwind turbines face into the wind; the yaw drive is used to keep the rotor facing into the wind
as the wind direction changes. Downwind turbines don’t require a yaw drive; the wind blows the
rotor downwind.
16. Yaw Motor:
Powers the yaw drive.

2.8 Turbine Configurations:
Wind turbines are often grouped together into a single
wind power plant, also known as a wind farm, and generate
bulk electrical power. Electricity from these turbines is fed
into a utility grid and distributed to customers, just as with
conventional power plants.

2.9 How Wind Turbines Work:
A wind turbine works the opposite of a fan. Instead of
using electricity to make wind, like a fan, wind turbines use
wind to make electricity. The wind turns the blades, which
spin a shaft, which connects to a generator and makes
electricity.
How wind turbines work can be explained as a conversion of kinetic energy (wind) to
mechanic energy (turbine). Wind energy is essentially a form of solar energy since it is the sun
that heats unevenly the Earth's surface causing the breeze to blow.
There are two basic types of wind generators including the horizontal axis wind
turbine and the vertical axis wind turbine. Understandably one turns on a horizontal axis (or axel)
and the other one upon a vertical axis (or axel).
Each type of wind turbine works in similar fashion. Basically, the wind blows past the
wind generator blades or rotors causing a low pressure system on the trailing edge of the blades
similar to a wing of an airplane. Utility scale wind turbine blades may need a wind speed of 10
mph or more to start turning while residential wind turbines may start rotating at speeds of 7 mph
or less.
Smaller wind turbines will use a tail fan and larger devices
will use computerized tracking to keep the blades pointing into the
wind for optimal efficiency. Utility wind turbine blades are
connected to shafts, gears, generators and electrical control
systems. These systems then interface with high-voltage
transformers and then to the grid.

17

Small wind turbines such as those used at residences usually have the blades connected to
a DC generator, power inverter, AC generator and bank of batteries. The home wind turbine is
used to power the batteries, which in turn power the residence. An electrical contractor can tie in
the home wind generator to the grid if desired.
How wind turbines work efficiently have to do with the size and shape of the rotors, the
location of the turbine including geography and height and other basic mechanics that either
cause more drag or less drag on the system. Many assume that the old style windmill with many
blades is more efficient because of the number of rotors.
But, the number of rotors can actually add more drag, more weight and get in the way of
wind flowing through the blade area. Two or three bladed turbines are most popular now days
because of more thrust and less wind resistance.
One of the main factors that contribute to how wind turbines work is the kind of
electromagnetic system that is used to generate electricity. The wind turbine blades are usually
tied into something akin to the alternator in one's car.
The alternator works because many loops of copper wire spin around at high speeds
around an iron core, producing an electromagnetic current (electricity). The kind of
electromagnetic induction can vary depending upon the size of the wind turbine and the
manufacturer's specifications and design.
How wind turbines work has changed over the years. The history of wind power starts
with these renewable energy devices being used to grind grains and pump water. Over the years,
the need to use wind turbines for electrical generation has come to the forefront and which is
why so much development is taking place right now.

2.10 Efficiency:
Not all the energy of blowing wind can be harvested, since conservation of mass requires
that as much mass of air exits the turbine as enters it. Betz' law gives the maximal achievable
extraction of wind power by a wind turbine as 59% of the total kinetic energy of the air flowing
through the turbine.
Further inefficiencies, such as rotor blade friction and drag, gearbox losses, generator and
converter losses, reduce the power delivered by a wind turbine. Commercial utility-connected
turbines deliver about 75% of the Betz limit of power extractable from the wind, at rated
operating speed.

18

Efficiency can decrease slightly over time due to wear. Analysis of 3128 wind turbines
older than 10 years in Denmark showed that half of the turbines had no decrease, while the other
half saw a production decrease of 1.2% per year.

2.11 Yaw Mechanism
The yaw system of wind turbines is the component responsible for the orientation of the
wind turbine rotor towards the wind.

2.12 History:
The task of orientating the rotor into the wind was a complicated issue already for
historical windmills. The first windmills able to rotate in order to "face" the wind appeared in the
mid-18th century. Their rotatable nacelles were mounted on the main structure of
the windmill using primitive wooden gliding bearings lubricated with animal fat. The necessary
yawing torque was created by means of animal power, human power or even wind
power (implementation of an auxiliary rotor known as fantail).
Vertical axis wind turbines (VAWT) do not need a yaw system since their vertical rotors
can face the wind from any direction and only their self-rotation gives the blades a clear direction
of the air flow. Horizontal axis wind turbines however need to orient their rotors into and out of
the wind and they achieve that by means of passive or active yaw systems.
Horizontal axis wind turbines employ some sort of yaw system which can be passive or
active. Both passive and active systems have advantages and disadvantages and various design
solutions (both active and passive) are being tried in order to find the optimal design for each
wind turbine depending on its size, cost and purpose of operation.

2.13 Types:
2.13.1 Active yaw system:
The active yaw systems are equipped with some sort of torque producing device able to rotate
the nacelle of the wind turbine against the stationary tower based on automatic signals from wind
direction sensors or manual actuation (control system override). The active yaw systems are
considered to be the state of the art for all the modern medium and large sized wind turbines,
with a few exceptions proving the rule (e.g. Vergnet). The various components of the modern
active yaw systems vary depending on the design characteristics but all the active yaw systems
include a means of rotatable connection between nacelle and tower (yaw bearing), a means of
active variation of the rotor orientation (i.e. yaw drive), a means of restricting the rotation of the

19

nacelle (yaw brake) and a control system which processes the signals from wind direction
sensors (e.g. wind vanes) and gives the proper commands to the actuating mechanisms.
The most common types of active yaw systems are:


Roller yaw bearing - Electric yaw drive - Brake: The nacelle is mounted on a roller
bearing and the azimuth rotation is achieved via a plurality of powerful electric drives. A
hydraulic or electric brake fixes the position of the nacelle when the re-orientation is
completed in order to avoid wear and high fatigue loads on wind turbine components due
to backlash. Systems of this kind are used by most of the wind turbine manufacturers and are
considered to be reliable and effective but also quite bulky and expensive.



Roller yaw bearing - Hydraulic yaw drive: The nacelle is mounted on a roller bearing and
the azimuth rotation is achieved via a
plurality of powerful hydraulic motors or
ratcheting hydraulic cylinders. The benefit
of the yaw system with hydraulic
drives has to do with the inherent benefits
of the hydraulic systems such as the
high power-to-weight
ratio and
high reliability. On the downside however
the hydraulic systems are always troubled
by leakages of hydraulic fluid and
clogging of their high pressure hydraulic
valves. The hydraulic yaw systems often
(depending on the system design) also
allow for the elimination of the yaw brake
mechanism and their replacement with cut-off valves.



Gliding yaw bearing - Electric yaw drive: The nacelle is mounted on a friction
based gliding bearing and the azimuth rotation is achieved via a plurality of powerful electric
drives. The need for a yaw brake is eliminated and depending on the size of the yaw system
(i.e. size of the wind turbine) the gliding bearing concept can lead to significant cost savings.



Gliding yaw bearing - Hydraulic yaw drive: The nacelle is mounted on a friction
based gliding bearing and the azimuth rotation is achieved via a plurality of
powerful hydraulic motors or ratcheting hydraulic cylinders. This system combines the
characteristics of the aforementioned gliding bearing and hydraulic motor systems.

2.13.2 Passive Yaw System:
20

The passive yaw systems utilize the wind force in order to adjust the orientation of
the wind turbine rotor into the wind. In their simplest form these system comprise a simple roller
bearing connection between the tower and the nacelle and a tail fin mounted on the nacelle and
designed in such a way that it turns the wind turbine rotor into the wind by exerting a
"corrective" torque to the nacelle. Therefore the power of the wind is responsible for the rotor
rotation and the nacelle orientation. Alternatively in case of downwind turbines the tail fin is not
necessary since the rotor itself is able to yaw the nacelle into the wind. In the event of skew
winds the "wind pressure" on the swept area causes a yawing moment around the tower axis (zaxis) which orients the rotor.
The tail fin (or wind vane) is commonly used for small wind turbines since it offers a low
cost and reliable solution. It is however unable to cope with the high moments required to yaw
the nacelle of a large wind turbine. The self-orientation of the downwind turbine rotors however
is a concept able to function even for larger wind turbines. The French wind turbine
manufacturer Vergnet has several medium and large self-orientating downwind wind turbines in
production.
Passive yaw systems have to be designed in a way that the nacelle does not follow the
sudden changes in wind direction with too fast a yaw movement, in order to avoid high
gyroscopic loads. Additionally the passive yaw systems with low yaw-friction are subjected to
strong dynamic loads due to the periodic low amplitude yawing caused by the variation of
the inertia moment during the rotor rotation. This effect becomes more severe with the reduction
of the number of blades.
The most common passive yaw systems are:


Roller Bearing (free system): The nacelle is mounted on a roller bearing and it is free to
rotate towards any direction. The necessary moment comes from a tail fin or the rotor
(downwind wind turbines)



Roller Bearing - Brake (Semi-active system): The nacelle is mounted on a roller
bearing and it is free to rotate towards any direction, but when the necessary orientation is
achieved an active yaw brake arrests the nacelle. This prevents the
uncontrolled vibration and reduced gyroscopic and fatigue loads.



Gliding Bearing/Brake (Passive system): The nacelle is mounted on a gliding bearing and
it is free to rotate towards any direction. The inherent friction of the gliding bearing achieves
a quasi-active way of operation.

2.14 Component:
21

2.14.1 Yaw Bearing:
One of the main components of the yaw
system is the yaw bearing. It can be of the
roller or gliding type and it serves as a rotatable
connection
between
the
tower
and
the nacelle of the wind turbine. The yaw
bearing should be able to handle very high
loads, which apart from the weight of
the nacelle and rotor (the weight of which is in
the range of several tenths of tons) include also
the bending moments caused by the rotor
during the extraction of the kinetic energy of
the wind.
2.14.2 Yaw drives:
The yaw drives exist only on the active yaw systems and are the means of active rotation
of the wind turbine nacelle. Each yaw drive consists of powerful electric motor (usually AC)
with its electric drive and a large gearbox, which increases the torque. The maximum
static torque of the biggest yaw drives is in the range of 200.000Nm with gearbox reduction
ratios in the range of 2000:1.Consequently the yawing of the large modern turbines is relatively
slow with a 360° turn lasting several minutes.

2.14.3Yaw brake:
In order to stabilize the yaw bearing against rotation a means of braking is necessary. One
of the simplest ways to realize that task is to apply a
constant small counter-torque at the yaw drives in order
to eliminate the backlash between gear-rim and yaw
drive pinions and
to
prevent
the nacelle from oscillating due to the rotor rotation.
This operation however greatly reduces the reliability of
the electric yaw drives, therefore the most common
solution is the implementation of a hydraulically
actuated disk brake.
The disk brake requires a flat circular brake
disk and
plurality
of
brake calipers with
hydraulic pistons and brake pads. The hydraulic yaw
brakes are able to fix the nacelle in position thus
22

relieving the yaw drives from that task. The cost however of the yaw brake in combination with
the requirement of a hydraulic installation (pump, valves, pistons) and its installation in the
vicinity of brake pads sensitive to lubricant contamination is often an issue.
A compromise that offers several advantages is the use of electric yaw brakes. These
replace the hydraulic mechanism of the conventional brakes and with electro-mechanically
actuated brake calipers. The use of electric yaw brakes eliminates the complexity of the hydraulic
leakages and the subsequent problems that these cause to the yaw brake operation.
Several wind turbine design and manufacturing companies experiment with alternative
yaw breaking methods in order to eliminate the drawbacks of the existing systems and to reduce
the cost of the system. One of these alternatives involves the use of air pressure in order to
achieve the necessary yaw braking moment. In this case, some of the gliding surface (usually the
axial, due to higher available surface) is utilized in order to accommodate the yaw brake pads
and the pneumatic brake mechanism. The pneumatic actuator can be a conventional pneumatic
cylinder or even a flexible air chamber which inflates when supplied with pressurized air. Such a
device is able to exert very high braking forces due to the high active surface. This is achieved
with a simple industrial air pressure compression system (6-10 bars) which is a reliable and low
cost solution. Furthermore in the even of leakage, the environmental impact is practically zero
compared to hydraulic oil leakages. Finally brake actuators can be produced with very low cost
from lightweight plastic materials thus significantly reducing the overall cost of the system.

2.14.4 Yaw vane (passive systems):
The yaw vane (or tail fin) is a component of the yaw system used only on small wind
turbines with passive yaw mechanisms. It is nothing more than a flat surface mounted on the
nacelle by means of a long beam. The combination of the large surface of the fin and the
increased length of the beam create a considerable torque which is able to rotate the
nacelle despite the stabilizing gyroscopic effects of the rotor. The required surface however for a
tail fin to be able to yaw a large wind turbine is enormous thus rendering the use of such a device
un-economical.

2.15 Yaw Error:
The wind turbine is said to have a yaw error, if the rotor is not perpendicular to the wind.
A yaw error implies that a lower share of the energy in the wind will be running through the rotor
area. (The share will drop to the cosine of the yaw error, for those of you who know math).
If this were the only thing that happened, then yaw control would be an excellent way
of controlling the power input to the wind turbine rotor. That part of the rotor which is closest to
23

the source direction of the wind, however, will be subject to a larger force (bending torque) than
the rest of the rotor. On the one hand, this means that the rotor will have a tendency to yaw
against the wind automatically, regardless of whether we are dealing with an upwind or a
downwind turbine. On the other hand, it means that the blades will be bending back and forth in
a flap wise direction for each turn of the rotor. Wind turbines which are running with a yaw error
are therefore subject to larger fatigue loads than wind turbines which are yawed in a
perpendicular direction against the wind.

2.16 Types of Generators used for Wind Turbines
There are many different kinds of generators that could be used in a wind turbine; right
now I am going to just group them in three different types.
2.16.1 Induction Generator:
An induction generator is a type of electrical generator that is mechanically and
electrically similar to an induction motor. Induction generators produce electrical power when
their shaft is rotated faster than the synchronous frequency of the equivalent induction motor.
Induction generators are often used in wind turbines and some micro hydro installations.
Induction generators are mechanically and electrically simpler than other generator types. They
are also more rugged, requiring no brushes or commutator.
Induction generators are not self-exciting, meaning they require an external supply to
produce a rotating magnetic flux, the power required for this is called reactive current. The
external supply can be supplied from the electrical grid or from the generator itself, once it starts
producing power or can you can use a capacitor bank to supply it. The rotating magnetic flux
from the stator induces currents in the rotor, which also produces a magnetic field. If the rotor
turns slower than the rate of the rotating flux, the machine acts like an induction motor. If the
rotor is turned faster, it acts like a generator, producing power at the synchronous frequency. In
the United States it would be 60hz.
The common down side of using an induction generator in a wind turbine is gearing.
Typically you need an induction motors to run 1500+ RPM to meet the synchronous so a gearing
is almost always needed.
2.16.2 Permanent Magnet Alternators:
Permanent magnets alternators (PMA) have one set of electromagnets and one set of
permanent magnets. Typically the permanent magnets will be mounted on the rotor with the
electromagnets on the stator. Permanent magnet motor and generator technology has advance
greatly in the past few years with the creation of rare earth magnets (neodymium, samariumcobalt, and alnico). Generally the coils will be wired in a standard three phase wye or delta.

24

Permanent magnet alternators are can be very efficient, in the range of 60%-95%,
typically around 70% though. As a generator they do not require a controller as a typical three
phase motor would need. It is easy to rectify the power from them and charge a battery bank or
use with a grid tie.
It is easy to build a permanent magnet alternator, even for beginners. This is a common
choice for home builders. I will have some great information on this site a little later that will
take you through the design and building process. You just need to understand a little science and
have some sort of mechanical competency.
Note: Car alternators are not PMA but actually have a field coil instead of permanent
magnets, and are typically very inefficient around 50%. They typically need to be spun
1500+RPM to get any real power out of them, but with a belt or gear arrangement can still do a
decent job.
2.16.3 Brushed DC Motor:
Brushed DC Motors are commonly used for home built wind turbines. They are
backwards from a permanent magnet generator. On a brushed motor, the electromagnets spin on
the rotor with the power coming out of what is known as a commutator. This does cause a
rectifying effecting outputting lumpy DC, but this is not an efficient way to “rectify” the power
from the windings, it is used because it’s the only way to get the power out of the rotor. A good
brushed motor can reach a good efficiency, but are typically at most 70%.
There are many great advantages to using a brushed motor. One of the biggest reasons is
because typically you can find one not requiring any gearing and still get a battery charging
voltage in light wind. They are also quite easy to find, they can be purchased from eBay, surplus
supply stores, industrial supply stores, and can find them on different things that might get
thrown away or given away (like a treadmill).
2.17 Advantages:
Wind Energy offers many advantages, which explains why it’s the fastest-growing energy
source in the world. Research efforts are aimed at addressing the challenges to greater use of
wind energy.
Wind energy is fueled by the wind, so it’s a clean fuel source. Wind energy doesn’t
pollute the air like power plants that rely on combustion of fossil fuels, such as coal or natural
gas. Wind turbines don’t produce atmospheric emissions that cause acid rain or greenhouse
gasses. Wind energy is a domestic source of energy, produced in the United States. The nation’s
wind supply is abundant. Wind energy relies on the renewable power of the wind, which can’t be
used up. Wind is actually a form of solar energy; winds are caused by the heating of the
atmosphere by the sun, the rotation of the earth, and the earth’s surface irregularities. Wind
25

energy is one of the lowest-priced renewable energy technologies available today, costing
between 4 and 6 cents per kilowatt-hour, depending upon the wind resource and project
financing of the particular project. Wind turbines can be built on farms or ranches, thus
benefiting the economy in rural areas, where most of the best wind sites are found. Farmers and
ranchers can continue to work the land because the wind turbines use only a fraction of the land.
Wind power plant owners make rent payments to the farmer or rancher for the use of the land.
2.18 Challenges:
Wind power must compete with conventional generation sources on a cost basis.
Depending on how energetic a wind site is, the wind farm may or may not be cost competitive.
Even though the cost of wind power has decreased dramatically in the past 10 years, the
technology requires a higher initial investment than fossil-fueled generators. Good wind sites are
often located in remote locations, far from cities where the electricity is needed. Transmission
lines must be built to bring the electricity from the wind farm to the city. Wind resource
development may compete with other uses for the land and those alternative uses may be more
highly valued than electricity generation. Although wind power plants have relatively little
impact on the environment compared to other conventional power plants, there is some concern
over the noise produced by the rotor blades, aesthetic (visual) impacts, and sometimes birds have
been killed by flying into the rotors. Most of these problems have been resolved or greatly
reduced through technological development or by properly siting wind plants.

CHAPTER 3
TYPES OF WIND TURBINE

Wind turbines can be separated into two basic types determined by which way the turbine
spins. Wind turbines that rotate around a horizontal axis are more common (like a wind
mill), while vertical axis wind turbines are less frequently used (Savonius and Darrieus are
the most common in the group).

3.1 Horizontal Axis Wind Turbines (HAWT)

26

Horizontal axis wind turbines, also shortened to HAWT, are the common style that most of us
think of when we think of a wind turbine. A HAWT has a similar design to a windmill; it has
blades that look like a propeller that spin on the horizontal axis.
Horizontal axis wind turbines have the main rotor shaft and electrical generator at the top of a
tower, and they must be pointed into the wind. Small turbines are pointed by a simple wind vane
placed square with the rotor (blades), while large turbines generally use a wind sensor coupled
with a servo motor to turn the turbine into the wind. Most large wind turbines have a gearbox,
which turns the slow rotation of the rotor into a faster rotation that is more suitable to drive an
electrical generator.
Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the tower.
Wind turbine blades are made stiff to prevent the blades from being pushed into the tower by
high winds. Additionally, the blades are placed a considerable distance in front of the tower and
are sometimes tilted up a small amount.
Downwind machines have been built, despite the problem of
turbulence, because they don't need an additional mechanism for
keeping them in line with the wind. Additionally, in high winds the
blades can be allowed to bend which reduces their swept area and
thus their wind resistance. Since turbulence leads to fatigue
failures, and reliability is so important, most HAWTs are upwind
machines.

3.2 HAWT advantages:
The tall tower base allows access




The tall tower base allows access to stronger wind in sites
with wind shear. In some wind shear sites, every ten meters
up the wind speed can increase by 20% and the power
output by 34%.
High efficiency, since the blades always move
perpendicularly to the wind, receiving power through the
whole rotation. In contrast, all vertical axis wind turbines,
and most proposed airborne wind turbine designs, involve
various types of reciprocating actions, requiring airfoil
surfaces to backtrack against the wind for part of the cycle.
Backtracking against the wind leads to inherently lower
efficiency.

27

3.3 HAWT disadvantages








Massive tower construction is required to support the heavy blades, gearbox, and
generator.
Components of a horizontal axis wind turbine (gearbox, rotor shaft and brake assembly)
being lifted into position.
Their height makes them obtrusively visible across large areas, disrupting the appearance
of the landscape and sometimes creating local opposition.
Downwind variants suffer from fatigue and structural failure caused by turbulence when
a blade passes through the tower's wind shadow (for this reason, the majority of HAWTs
use an upwind design, with the rotor facing the wind in front of the tower).
HAWTs require an additional yaw control mechanism to turn the blades toward the wind.
HAWTs generally require a braking or yawing device in high winds to stop the turbine
from spinning and destroying or damaging itself.

3.4 Cyclic stresses and vibration
When the turbine turns to face the wind, the rotating blades act like a gyroscope. As it pivots,
gyroscopic precession tries to twist the turbine into a forward or backward somersault. For each
blade on a wind generator's turbine, force is at a minimum when the blade is horizontal and at a
maximum when the blade is vertical. This cyclic twisting can quickly fatigue and crack the blade
roots, hub and axle of the turbines.

3.5 Vertical axis:
Vertical axis wind turbines, as shortened to VAWTs, have the main rotor shaft arranged vertically.
The main advantage of this arrangement is that the wind turbine does not need to be pointed into
the wind. This is an advantage on sites where the wind direction is highly variable or has
turbulent winds.

28

With a vertical axis, the generator and other primary components
can be placed near the ground, so the tower does not need to
support it, also makes maintenance easier. The main drawback of
a VAWT generally creates drag when rotating into the wind.
It is difficult to mount vertical-axis turbines on towers, meaning
they are often installed nearer to the base on which they rest, such
as the ground or a building rooftop. The wind speed is slower at a
lower altitude, so less wind energy is available for a given size
turbine. Air flow near the ground and other objects can create
turbulent flow, which can introduce issues of vibration, including
noise and bearing wear which may increase the maintenance or
shorten its service life. However, when a turbine is mounted on a
rooftop, the building generally redirects wind over the roof and
this cans double the wind speed at the turbine. If the height of the rooftop mounted turbine tower
is approximately 50% of the building height, this is near the optimum for maximum wind energy
and minimum wind turbulence.

3.6 VAWT subtypes:
3.6.1 Darrieus wind turbine
Darrieus wind turbines are commonly called "Eggbeater" turbines, because they look like a giant
eggbeater. They have good efficiency, but produce large torque ripple and cyclic stress on the
tower, which contributes to poor reliability. Also, they generally require some external power
source, or an additional Savonius rotor, to start turning, because the starting torque is very low.
The torque ripple is reduced by using three or more blades which results in a higher solidity for
the rotor. Solidity is measured by blade area over the rotor area. Newer Darrieus type turbines are
not held up by guy-wires but have an external superstructure connected to the top bearing.
3.6.2 Savonius wind turbine
A Savonius is a drag type turbine; they are commonly used in cases of high reliability in many
things such as ventilation and anemometers. Because they are a drag type turbine they are less
efficient than the common HAWT. Savonius are excellent in areas of turbulent wind and selfstarting.
3.7 VAWT advantages





No yaw mechanisms are needed.
A VAWT can be located nearer the ground, making it easier to maintain the moving parts.
VAWTs have lower wind startup speeds than the typical the HAWTs.
VAWTs may be built at locations where taller structures are prohibited.
29



VAWTs situated close to the ground can take advantage of locations where rooftops,
mesas, hilltops, ridgelines, and passes funnel the wind and increase wind velocity.

3.8 VAWT disadvantages





Most VAWTs have a average decreased efficiency from a common HAWT, mainly
because of the additional drag that they have as their blades rotate into the wind. Versions
that reduce drag produce more energy, especially those that funnel wind into the collector
area.
Having rotors located close to the ground where wind speeds are lower and do not take
advantage of higher wind speeds above.
Because VAWTs are not commonly deployed due mainly to the serious disadvantages
mentioned above, they appear novel to those not familiar with the wind industry. This has
often made them the subject of wild claims and investment scams over the last 50 years.

3.9 Offshore Wind:
Offshore wind is similar to terrestrial wind technologies, as a large windmill-like turbine located
in a fresh or saltwater environment. Wind causes the blades to rotate, which is then turned into
electricity and connected to the grid with cables. The advantages of offshore wind are that winds
are stronger and more consistent, allowing turbines of much larger size to be erected by vessels.
The disadvantages are the difficulties of placing a structure in a dynamic ocean environment. The
turbines are often scaled-up versions of existing land technologies. However, the foundations are
unique to offshore wind and are listed below:

3.10 Types With Respect to Foundation:
There are mainly two types of offshore wind turbine with respect to foundation.



Floating
Fixed

There are three main types of floating foundation:

30

3.11 Spar:
The main advantage of the spar design over other floating platforms is
its small cross-section at the water's surface, which makes it less
sensitive to wave motion
The main disadvantage is the cost. The structure requires roughly five
times as much steel as a standard monopile.
The spread mooring system of a Spar does not influence the waveinduced motions of the platform. Instead, the Spar relies on its deep
draft and large effective mass to keep vertical motions within an
acceptable range.
3.11.1 Advantages of the Spar
 Less sensitive than TLPs to water depth and payload
 Allows surface wellheads (dry trees)
 Vertical access to wells
 Support of remote wells
 Drilling and workover capability
 Active lateral mooring system can provide drilling access to a large well pattern
3.11.2 Limitations of the Spar
 More extensive offshore campaign for integration and installation


Sensitive to long period waves



Support of TTRs in very deep water



Limited centerwell space for large numbers of TTRs

The Spar configuration typically includes a buoyant upper section (hard tank), a deep lower
section to contain permanent solid ballast material (keel tank), and a structural connection
between the hard tank and keel tank that may take the form of a truss structure (for a Truss Spar)
or a flooded circular cylinder (Classic Spar).

3.12 Tension leg platform (TLP):
A tension-leg platform (TLP) or extended tension leg platform (ETLP) is a vertically moored
floating structure normally used for the offshore production of oil or gas, and is particularly

31

suited for water depths greater than 300 metres (about 1000 ft) and less than 1500 metres (about
4900 ft). Use of tension-leg platforms has also been proposed for wind turbines.
The mooring system of a TLP is vertically oriented and consists of tubular steel members called
tendons. The group of tendons at each corner of the structure is called a tension leg. The tendon
system is highly tensioned due to excess buoyancy of the platform hull. The high tension limits
horizontal offsets to a small percentage of water depth. Vertical motions of the TLP are nearly
non-existent due to the tendon’s high axial stiffness (low elasticity). Roll and pitch motions are
also negligible.

3.14 Cost effective:
Although the Massachusetts Institute of Technology and the National Renewable Energy
Laboratory explored the concept of TLPs for offshore wind turbines in September 2006,
architects had studied the idea as early as 2003. [1] Earlier offshore wind turbines cost more to
produce, stood on towers dug deep into the ocean floor, were only possible in depths of at most
50 feet (15 m), and generated 1.5 megawatts for onshore units and 3.5 megawatts for
conventional offshore setups. In contrast, TLP installation was calculated to cost a third as much.
TLPs float, and researchers estimate they can operate in depths between 100 and 650 feet (200
m) and farther away from land, and they can generate 5.0 megawatts.
3.14.1 Advantages of the Tension Leg Platform:
Surface wellheads (dry trees)
Vertical access to wells through TTRs
Support of remote wells through SCRs
Drilling and workover capability
Improved motion characteristics compared to Spars and Semisubmersibles
Full integration and commissioning prior to installation
Proven performance record
3.14.2 Limitations of the Tension Leg Platform
Water depth / payload limited

32

Cost of tendon system
Vertical mooring system does not provide active control of horizontal position (e.g., for
well access)
The TLP is very effective once installed. However, the tendon system is critical to performance
and must be carefully designed, fabricated, inspected and installed to ensure long term
performance and robustness. Tendon installation requires specialized equipment and careful
execution.
The platform is permanently moored by means of tethers or tendons grouped at each of the
structure's corners. A group of tethers is called a tension leg. A feature of the design of the tethers
is that they have relatively high axial stiffness (low elasticity), such that virtually all vertical
motion of the platform is eliminated. This allows the platform to have the production wellheads
on deck (connected directly to the subsea wells by rigid risers), instead of on the seafloor. This
allows a simpler well completion and gives better control over the production from the oil or gas
reservoir, and easier access for downhole intervention operations.
TLPs have been in use since the early 1980s. The first tension leg platform [1] was built for
Conoco's Hutton field in the North Sea in the early 1980s. The hull was built in the dry-dock at
Highland Fabricator's Nigg yard in the north of Scotland, with the deck section built nearby at
McDermott's yard at Ardersier. The two parts were mated in the Moray Firth in 1984.
The Hutton TLP was originally designed for a service life of 25 years in Nord Sea depth of 100
to 1000 metres. It had 16 tension legs. Its weigh varied between 46,500 and 55,000 tons when
moored to the seabed, but up to 61,580 tons when floating freely.[1] The total area of its living
quarters was about 3,500 square metres and accommodated over a 100 cabins though only 40
people were necessary to maintain the structure in place.[1]
Larger TLPs will normally have a full drilling rig on the platform with which to drill and
intervene on the wells. The smaller TLPs may have a workover rig, or in a few cases no
production wellheads located on the platform at all.
The deepest (E) TLPs measured from the sea floor to the surface are:[2]


4,674 ft. (1,425 m) Magnolia ETLP. Its total height is some 5,000 feet (1,500 m).



4,300 ft. (1,300 m) Marco Polo TLP



4,250 ft. (1,300 m) Neptune TLP



3,863 ft. (1,177 m) Kizomba A TLP
33



3,800 ft. (1,200 m) Ursa TLP. Its height above surface is 485 ft (148 m) making a total
height of 4,285 ft. (1,306 m).



3,350 ft. (1,020 m) Allegheny TLP



3,300 ft. (1,000 m) W. Seno A TLP

3.15 Semi-submersible:
Similar to the Truss Spar, the spread mooring of a Semi does not influence the wave-induced
motions of the platform. The Semi relies on its small waterplane area to help minimize vertical
motions. Vertical motions of the many typical Semi designs in the GoM prohibit the platform
from supporting top tensioned risers.

3.15.1 Advantages of the Semisubmersible:
Less sensitive to water depth than TLPs
Wide range of payload capacity
Installed as a fully integrated system
Maximum execution plan flexibility
Support of remote wells
Drilling and work over capability
(using subsea BOP)
Can be easily redeployed
3.15.2
Limitations
Semisubmersible

of

the

Platform motions
Cannot support TTRs (Target
Tracking Radars)

34

SCR fatigue (Steel Catenary Riser)
The above mentioned limitations are general in nature. The critical objective when developing a
Semi configuration is to minimize motions to meet functional requirements such as SCR support
and processing up time.
The Semi is perhaps the least complex to integrate and install but the overall motions
performance is less favorable than the Spar or TLP. The motions therefore have more impact to
functional capability and performance

3.16 Buoyancy Concept:
In science, buoyancy is an upward force exerted by a fluid that opposes the weight of an
immersed object. In a column of fluid, pressure increases with depth as a result of the weight of
the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences
greater pressure at the bottom of the column than at the top. This difference in pressure results in
a net force that tends to accelerate an object upwards. The magnitude of that force is proportional
to the difference in the pressure between the top and the bottom of the column, and (as explained
by Archimedes' principle) is also equivalent to the weight of the fluid that would otherwise
occupy the column, i.e. the displaced fluid. For this reason, an object whose density is greater
than that of the fluid in which it is submerged tends to sink. If the object is either less dense than
the liquid or is shaped appropriately (as in a boat), the force can keep the object afloat. This can
occur only in a reference frame which either has a gravitational field or is accelerating due to a
force other than gravity defining a "downward" direction (that is, a non-inertial reference frame).
In a situation of fluid statics, the net upward buoyancy force is equal to the magnitude of the
weight of fluid displaced by the body.
The center of buoyancy of an object is the centroid of the displaced volume of fluid.

3.17 How do Mooring Systems Work?





35



A mooring system is made up of a mooring line, anchor and connectors, and is used for station
keeping of a ship or floating platform in all water depths. A mooring line connects an anchor on
the seafloor to a floating structure. We will focus on mooring Mobile Offshore Drilling Units and
Floating Production Systems.
The mooring line can be made up of synthetic fiber
rope, wire and chain or a combination of the three.
Environmental factors - wind, waves and currents determine which materials make up the mooring
system.
Chain is the most common choice for permanent
moorings in shallow water up o 100 m, whereas steel
wire rope is lighter weight and has a higher elasticity
than chain, which is a better choice in water depths
greater than 300 m. However, synthetic fiber rope is
the lightest weight of all three. Configurations
include all chain, chain and wire rope (conventional
mooring line to 2,000 m), chain and synthetic fiber
rope, and chain, wire rope and synthetic fiber rope
combinations are used in ultra-deepwater (greater
than 2,000 m).

3.18 Anchors:
The mooring system relies on the strength of the anchors. The holding capacity of anchors
depends on the digging depth and the soil properties. The mooring lines run from the vessel to
the anchors on the seafloor. Anchor types include: drag embedment, suction and vertical load.
A drag embedment anchor (DEA) is the most utilized anchor for mooring floating MODUs in the
Gulf of Mexico. The drag anchor is dragged along the seabed until it reaches the required depth.
As it penetrates the seabed, it uses soil resistance to hold the anchor in place. The drag
embedment anchor is mainly used for catenary moorings, where the mooring line arrives on the
seabed horizontally. It does not perform well under vertical forces.
Suction piles are the predominant mooring and foundation system used for deepwater
development projects worldwide. Tubular piles are driven into the seabed and a pump sucks out
the water from the top of the tubular, which pulls the pile further into the seabed. Suction piles
36

can be used in sand, clay and mud
soils, but not gravel, as water can
flow through the ground during
installation, making suction difficult.
Once the pile is in position, the
friction between the pile and the soil
holds it in place. It can resist both
vertical and horizontal forces.
Vertical load anchors are similar to
drag anchors as they are installed in
the same way. However, the vertical
load anchor can withstand both
horizontal and vertical mooring forces. It is used primarily in taut leg mooring systems, where
the mooring line arrives at an angle the seabed.

3.19 Mooring Systems:
There are six types of mooring systems discussed below. They include
1. catenary
2. taut leg
3. semi-taut
4. spread
5. single point
6. dynamic positioning
The catenary mooring system is the most
commonly used system in shallow water. It gets its
name from the shape of the free hanging line as its
configuration changes due to vessel motions. At the
seabed, the mooring line lies horizontally; thus the
mooring line has to be longer than the water depth. Increasing the length of the mooring line also
increases its weight. As the water depth increases, the weight of the line lessens the working
payload of the vessel. In that case, synthetic ropes are used. As water depth increases,
conventional, catenary systems become less and less economical.

37

The tout leg system typically uses polyester rope that is pre-tensioned until taut. The rope comes
in at a 30 to 45 degree angle on the seabed where it meets the anchor (suction piles or vertically
loaded anchors), which is loaded vertically. When the platform drifts horizontally with wind or
current, the lines stretch and this sets up an opposing force.
The semi-taut system combines taut lines and catenary lines in one system. It is ideally
used in deep-water.
A spread mooring system is a group of mooring lines distributed over the bow and stern
of the vessel to anchors on the seafloor. The vessel is positioned in a fixed heading, which is
determined by the sea and weather conditions. The symmetrical arrangement of anchors helps to
keep the ship on its fixed heading location. The spread mooring system does not allow the vessel
to weathervane, which means to rotate in the horizontal plane due to wind, waves or current.
Spread mooring is versatile as it can be used in any water depth, on any vessel, in an equally
spread pattern or a group.
A single point mooring system connects all the lines to a single point. It links subsea
manifolds connections and weathervaning tankers, which are free to rotate 360 degrees. The
single point system includes a buoy, mooring and anchoring elements, product transfer system
and other components.
Dynamic positioning does not use mooring lines. Instead a computer controls the vessel's
thrusters and propellers to maintain position. DP can be used in combination with other mooring
systems to provide additional redundancy.

3.20 Some other Offshore Floating Concepts:
3.20.1 IDEOL Floating Foundation for Offshore Wind Turbine
Based on the Damping Pool system and concrete fabrication, the IDEOL foundation
solution enables to install wind turbine without the usual shallow water limitations, at costs
more competitive than bottom-fixed foundation beyond 35-40 meters depth, where winds
are better and noise/visual/fishing conflicts much lower.

38

3.21Ty
pes of
off
Shore
Fixed Foundation:
1.
2.
3.
4.
5.

Monopile
Tripode
Gravity
Gravity trpode
Jacket

Monopile Foundation:
Monopile foundations are used in
shallow depth applications (0-30 m) and
consist of a pile being driven to varying
depths into the seabed (10-40 m)
depending on the soil conditions. The
pile-driving construction process is an
environmental concern as the noise
produced is incredibly loud and
propagates far in the water, even after
mitigation strategies such as bubble
shields, slow start, and acoustic
cladding. The footprint is relatively
small, but may still cause scouring or
artificial reefs. Transmission lines also
produce an electromagnetic field that may be harmful to some marine organisms.
39

Tripod Fixed Bottom
Tripod fixed bottom foundations are used
in transitional depth applications (20-80
m) and consist of three legs connecting to
a central shaft that supports the turbine
base. Each leg has a pile driven into the
seabed, though less depth is necessary
because of the wide foundation. The
environmental effects are a combination
of those for monopile and gravity
foundations.

   Gravity Foundation
Gravity foundations are used in shallow depth applications (0-30 m) and consist of a large and
heavy base constructed of steel or
concrete to rest on the seabed. The
footprint is relatively large and may
cause scouring, artificial reefs, or
physical destruction of habitat upon
introduction. Transmission lines also
produce an electromagnetic field that
may be harmful to some marine
organisms.
 Gravity Tripod
Gravity tripod foundations are used in
transitional depth applications (10-40
m) and consist of two heavy concrete
structures connected by three legs, one
structure sitting on the seabed while
the other is above the water. As of
2013, no offshore wind farms are
currently using this foundation. The
environmental concerns are identical
to those of gravity foundations,
though the scouring effect may be less
significant depending on the design.

40

Floating Structure
Floating structure foundations are used in deep depth applications (40-900 m) and consist of a
balanced floating structure moored to the seabed with fixed cables. The floating structure may be
stabilized using
1. mooring lines
2. ballast
3. buoyancy
The mooring lines may cause minor scouring or a potential for collision. Transmission lines also
produce an electromagnetic field that may be harmful to some marine organisms.

3.22
Jacket structure:
There are many variants of the three or four-legged jacket/lattice structure typically consisting of
corner piles interconnected with bracings with diameters up to 2m. The soil piles are driven
inside the pile sleeves to the required depth to gain adequate stability for the structure. The
tubular joints are welded.
These types of structures are considered well suited
for sites with water depth ranging from 20-50m
according to the DNV. The minimum is 3.5m at the
South Korean offshore wind farm Tamra and the
maximum depth for an operational project is 45m on
the Beatrice Demonstration project. Other projects in
the planning pipeline are suggestion using jackets in
water dephs up to 60-70m but these have yet to be
consented
The transition piece forms the connection between the
main jacket and the tower of the wind turbine. Loads
are transferred through the members mainly in axial
direction. The large base of the jacket structure offers
large resistance to overturning.
The secondary steel includes the work platform,
ladders and stairs, access systems, J-tube, cables, and corrosion protection systems.
3.22.1 Advantages of the jacket structures as:
• Low wave loads in comparison to monopiles (the jacket structure is very stiff and the area
facing
the
wave
movement
is
smaller
than
monopiles)
• Fabrication expertise is widely available, in part due to Offshore Oil and Gas industry supply
chain
41

3.22.2 Disadvantages as:
•
•

High initial construction costs and potentially
Transportation is moderately difficult and expensive

higher

maintenance

costs

CHAPTER 4
WIND ENERGY RESOURCE POTENTIAL
Global distribution of annual average onshore wind power potential (W/m2) for 2006
accounting for Spatial limitations on placement without limitations on potential realizable
capacity factors.

Annual
wind
energy potential country by country, restricted to installations with capacity factors >20%
with siting limited.
One of the questions most often asked about wind power is ‘what happens when the wind
doesn’t blow’. On a local level, this is mainly a question of grid integration, but in the big picture
the wind is a vast untapped resource capable of supplying the world’s electricity needs many
times over. In practical terms, in an optimum, clean energy future, wind will be an important part
of a mix of renewable energy technologies, playing a more dominant role in some regions than in
42

others. However, it is worthwhile to step back for a minute and consider the enormity of the
resource.
Researchers at Stanford University’s Global Climate and Energy Project recently did an
evaluation of the global potential of wind power, using five years of data from the US National
Climatic Data Center and the Forecasts Systems Laboratory. They estimated that the world’s
wind resources can generate more than enough power to satisfy total global energy demand.
After collecting measurements from 7,500 surface and 500 balloon-launch monitoring stations to
determine global wind speeds at 80 meters above ground level, they found that nearly 13% had
an average wind speed above 6.9 meters per second , sufficient for economical wind power
generation. Using only 20% of this potential resource for power generation, the report concluded
that wind energy could satisfy the world’s electricity demand in the year 2000 seven times over.
North America was found to have the greatest wind power potential, although some of
the strongest winds were observed in Northern Europe, whilst the southern tip of South America
and the Australian island of Tasmania also recorded significant and sustained strong winds. To be
clear, however, there are extraordinarily large untapped wind resources on all continents, and in
most countries; and while this study included some island observation points, it did not include
offshore resources, which are enormous.

43

For example, looking at the resource potential in the shallow waters on the continental
shelf off the densely populated east coast of the US, from Massachusetts to North Caroline, the
average potential resource was found to be approximately four times the total energy demand in
what is one of the most urbanized, densely populated and highest-electricity consuming regions
of the world.
A study by the German Advisory Council on Global Change (WBGU), “World in
Transition – Towards Sustainable Energy Systems” (2003) calculated that the global technical
potential for energy production from both onshore and offshore wind installations was 278,000
TWh (Terawatt hours) per year. The report then assumed that only 10–15% of this potential
would be realizable in a sustainable fashion, and arrived at a figure of approximately 39,000
TWh supply per year as the contribution from wind energy in the long term, which is more than
double current electricity demand.
The WBGU calculations of the technical potential were based on average values of wind
speeds from meteorological data collected over a 14 year period (1979–1992). They also
assumed that advanced multi-megawatt wind energy converters would be used. Limitations to
the potential came through excluding all urban areas and natural features such as forests,
wetlands, nature reserves, glaciers and sand dunes. Agriculture, on the other hand, was not
regarded as competition for wind energy in terms of land use.

4.1 OFFSHORE:
Offshore wind power installations are
on track to hit a seventh consecutive
annual record in 2013. Developers
added 1,080 megawatts of generating
capacity in the first half of the year,
expanding the world total by 20
percent in just six months. Fifteen
countries host some 6,500 megawatts
of offshore wind capacity. Before the
year is out, the world total should
exceed 7,100 megawatts. Although
still small compared with the roughly
300,000 megawatts of land-based
wind power, offshore capacity is
growing at close to 40 percent a year.
In 1991, Denmark installed the world’s first offshore wind farm, a 5-megawatt project in
the Baltic Sea. The country’s offshore wind sector has since alternated between lulls and bursts
of activity. Since 2008, Denmark’s offshore wind capacity has more than tripled, topping 1,200
44

megawatts by mid-2013. Over 350 megawatts of offshore wind power were plugged into the grid
in the first half of the year—all of it to complete the 400-megawatt Anholt project, which is
expected to meets 4 percent of Danish electricity needs.
Denmark already gets more than 30 percent of its electricity from wind—onshore and
offshore—and aims to increase that share to 50 percent by 2020. At about one third the size of
New York State, Denmark has the world’s
highest wind power capacity per square
mile, so it will rely mostly on offshore
expansion to hit the 2020 target. Denmark
was first to put wind turbines in the sea,
but today it ranks a distant second to the
United Kingdom in total offshore wind
generating capacity.
More than 500 megawatts of new
offshore wind power went online in U.K.
waters in the first half of 2013, bringing
the country’s grand total to over 3,400
megawatts—enough to power more than
2 million U.K. homes. The bulk of this
new offshore capacity went to completing the
630-megawatt first phase of the London Array,
now the world’s largest offshore wind farm. It
overtook another U.K. project, the 500megawatt Greater Gabbard wind farm, which
was finished in 2012. In all, the United
Kingdom has some 12,000 megawatts of
offshore wind capacity under construction or in
earlier development stages. Belgium’s offshore
wind capacity grew 20 percent to 450
megawatts in the first half of 2013, placing it
third in the world rankings. Germany reached
380 megawatts of offshore wind and will have at least 520 megawatts by year’s end.
Beyond this, the German offshore industry expects another 1,000 megawatts will connect to the
grid in both 2014 and 2015. Countries in Asia are starting to make offshore wind power more
than just a European affair. China, for example, brought its first offshore wind farm online in
2010. Since then, China has quickly climbed to fourth in the world, with 390 megawatts.
The official goal is for 5,000 megawatts of wind capacity in Chinese waters by 2015,
ballooning to 30,000 megawatts by 2020. In Japan, where land is at a premium and where the
future of nuclear energy is in question, offshore wind is gaining attention as a potentially huge
45

domestic, carbon-free power source. A 16-megawatt project inaugurated in the first half of 2013
bumped Japan’s offshore wind capacity to 41 megawatts. Because Japan lacks much shallow
seabed in which to fix standard offshore turbines, new floating turbine technology is likely the
future for offshore wind there. Off the coast of Fukushima prefecture, a 2-megawatt floating
turbine will begin generating electricity in November 2013, the first stage of a 16-megawatt
demonstration project. If it performs well, the hope is to expand the project’s capacity to up to
1,000 megawatts by 2020.
Floating turbines may actually be a big part of future offshore wind development at the
global level. Not only do they greatly expand the area available for wind farms, they also have
the potential to dramatically reduce the cost of offshore wind generation, which today is more
than twice as expensive as that from turbines on land. While offshore wind manufacturers have
managed to achieve cost reductions for the turbines themselves—through lighter, stronger
materials and increased efficiency, for example—these savings have thus far been offset by the
rising cost of installing and maintaining turbines fixed to the seabed as projects move into deeper
waters.
The renewable energy consultancy GL Garrad Hassan notes that working around harsh
weather becomes much easier with floating turbines: when conditions are favorable, relatively
cheap tugboats can bring a turbine to the project site for quick installation, avoiding the need for
specialized installation vessels.
The turbine developer, Deep Cwind, a consortium led by the University of Maine, plans
to deploy two much larger versions, 6 megawatts each, in 2016. The first full-fledged offshore
wind farm in the United States, though, will likely be of the traditional variety fixed to a
foundation in the seabed. Three proposals—Massachusetts’ 470-megawatt Cape Wind project,
Rhode Island’s 30-megawatt Block Island Wind Farm, and New Jersey’s 25-megawatt
Fisherman’s Energy I project—are the closest to beginning construction. U.S. offshore wind’s
potential is staggering.
According to the U.S. Department of Energy, shallow waters along the eastern seaboard
could host 530,000 megawatts of wind power, capable of covering more than 40 percent of
current U.S. electricity generation. Adding in deeper waters and the other U.S. coastal regions
boosts the potential to more than 4.1 million megawatts. This is consistent with the findings of
a 2009 Harvard study that calculated wind energy potential worldwide.
The authors estimated that in most of the world’s leading carbon dioxide-emitting
countries, available wind resources could easily meet national electricity needs. In fact, offshore
wind alone would be sufficient. Clearly, the world has barely begun to realize its offshore
potential. Indeed, in some countries, regulatory and policy uncertainty seem to be sapping
offshore wind’s momentum just as it really gets going, clouding the picture for future
development.

46

The U.K. government, concerned about costs, recently changed its target date for 18,000
megawatts of offshore wind from 2020 to 2030. In Germany, turbine orders are scarce as
developers await the new coalition government’s plans for regulations and incentives. And in
China, offshore wind companies say the guaranteed price for the electricity they generate is set
too low to stimulate rapid growth, calling into question whether the country can hit its ambitious
goals for 2015 and 2020.
Reflecting the hazy outlook in these and other key countries, projections for global
offshore wind capacity over the next decade or so—from research and consulting firms and from
industry publications—range anywhere from 37,000 to 130,000 megawatts. Despite the
impressive growth of recent years, it seems that the lower end of these forecasts is much more
likely. We know there is practically no limit to the available resource. What remains to be seen is
how quickly the world will harness it and give offshore wind power a more prominent place in
the new energy economy.

4.2 Some Notable off Shore Wind Turbine Farms:
There are top 25 offshore wind farms that are currently operational rated by nameplate
capacity. It also lists the 10 largest offshore wind farms currently under construction, the largest
proposed offshore wind farms, and offshore wind farms with notability other than size.

Coun
t.
1

Wind Farm

2

Greater
Gabbard
Bird OffShore 1
Anholt

3
4

London Array

Total
(MW)
630

Location

Turbine & Model

UK

504

UK

400
400

Germany
Denmark

175 × SIEMENS 3.6120
140 × SIEMENS 3.6107
80 × BARD 5.0
111 × SIEMENS 3.6-

Commissionin
g Date
2012
2012
2013
2013
47

5

Walney Phases
1&2

376.2

UK

6

Thorntonebank
Phases(1-3)

235

Belgium

7

315

UK

8

Sheringham
shoal
Thanet

300

UK

9
10

Lincs
Horns Rev 2

270
209.3

UK
Denmark

11

Rodsand 2

207

Denmark

12
13

201
194

China
UK

14

Chenjiagang
Lynn & Inner
Dowsing
Robin Rigg

180

UK

15

Gunfleet Sands

172

UK

16
17

Nysted
Bligh Bank

166
165

Denmark
Belgium

18

Horns Rev 1

160

Denmark

19
20

Ormonde
Longyuan
Rudong
Intertidal
Demonstration

150
150

UK
China

21

Princess Amalia

120

22

Donghai Bridge

110.6

Netherlan
ds
China

23

Lillgrund

110

Sweden

120
102
× SIEMENS SWT3.6-107
6 × REPOWER 5MW,
48× REPOWER 6.15
MW
88 × SIEMENS 3.6107
100 × VESTAS V903MW
75 × 3.6MW
91 × SIEMENS 2.393
90 × SIEMENS 2.393
134 × 1.5MW
54 × SIEMENS 3.6107
60 × VESTAS V903MW
48 × SIEMENS 3.6107
72 × SIEMENS 2.3
55 × VESTAS V903MW
80 × VESTAS V802MW
30 × RE POWER 5M
21 × SIEMENS 2.393;
20
× GOLDWIND 2.5M
W
17 × SINOVEL 3W
2 × CSIC HZ 5.0154 PROTOTYPE
60 × VESTAS V802MW
34
× SINOVEL SL3000/
90
1 × SINOVEL SL
5000
1 × S HANGHAI
E LECTRIC
W3600/116
48 × SIEMENS 2.393

2011(phase 1)
2012(phase 2)
2009(P1)
2012(P2)
2013(P3)
2012
2012
2013
2009
2010
2010
2008
2010
2010
2003
2010
2002
2012
2011
2012

2008
2010
2011

2007

48

24

Egmond aan
Zee

108

Netherlan
d

36 × VESTAS V903MW

2006

25

Borkum Riffgat

108

Germany

30 × SIEMENS 3.6MW

2014

4.3 Top 10 Under Construction:

4.4 Top 3 Biggest producers of Energy:

Count.

Wind
Farm

Production

Total
Production

Country

Turbine
Model

1

HORNS
R EV 1

676

5877

DENMAR

NYSTED
1

575

HORNS
R EV 2

956

80
× 2002
VESTAS
V80
2.0
MW
72
× 2003
BONUS 2.3
MW
91
2009
X S IEMENS
2.3 MW

2

3

K

5097

DENMAR
K

2959

DENMAR
K

Official
Start

49

CHAPTER 5
CHALLENGE AND CONSIDERATION FOR OFFSHORE WIND INCLUDE

5.1 Costs:
The installed cost of an offshore wind plant can be 50 to 100 percent higher than an equivalent
onshore plant. Offshore costs are much more dependent on site-specific factors than land-based
projects. Access to financing is typically more difficult due to the higher perceived investment
risk.
Economics plays a critical role when assessing the overall feasibility of offshore wind energy.
This chapter identifies the major cost variables comprising a wind project investment and
estimates the cost of energy derived from a hypothetical ocean-based project in New Jersey.
Financial incentives for wind development are also discussed.

5.2 Offshore Project Costs:
The offshore wind industry is
gaining momentum in Europe
where several countries are
promoting offshore installations.
According to published figures
available from trade journals and
web sites for several existing and
planned projects, offshore capital
costs range between $1700 and
$2500 per kW, with a mean value of
$1950 per kW (see Figure 9.1). This
compares with total installed costs
for land-based projects of $1100 to
$1300 per kW, indicating that
offshore installations cost roughly
50 to 100% more than land projects.

5.3 Transmission System Assessment:
5.3.1 Scope of Required Facilities
An offshore wind facility must transmit power to shore in order to interconnect with existing grid
infrastructure. While such facilities have yet to be deployed in the US for the purpose of offshore
wind power transmission such facilities would be identical to the submarine power transmission
facilities deployed throughout the US and the world. The scope of these transmission facilities
would typically include one or more armored cables that would be buried in the seabed to a
depth sufficient to ensure they remained covered through natural sediment shift or external
aggression from anchors, fishing gear or otherwise. Through the surf zone and across the beach
and dune areas it has become common practice to install a directionally bored conduit, through
50

which the transmission cable would be fed, to eliminate the need for surface disturbance of the
dune and beach areas. Once onshore the transmission cable would proceed to the interconnection
point via direct burial, conduit, or aerially as conditions dictate.
5.3.2 Interconnection Requirements:
To be economically feasible, offshore wind projects generally need to be large in terms of both
the number of turbines and total installed capacity (> 100 MW). The thermal capability of
existing lines must therefore be sufficient to deliver the power from an offshore wind project to
the utility’s load centers. The thermal capability of transmission lines rated at 138 kV and higher
meet this requirement. Lower voltage lines (69 kV and below) would need to be upgraded to at
least 138 kV in order to inject large amounts of wind generation from a single offshore location
into the existing bulk power system. 26 Other factors affecting the choice of potential injection
points include landfall locations that offer a low-impact route for marine cable, the lack of
transmission congestion or the need for costly upgrades, and substation capacity.
5.3.3 Availability, Reliability and Access
High availability is crucial for the economics of any wind farm. This depends primarily on high
system reliability and adequate maintenance capability, with both being achieved within
economic constraints on capital and operational costs.
Key issues to be addressed for good economics of an offshore wind farm are:
5.3.4 Minimization of maintenance requirements; and Maximization of access feasibility.
The dilemma for the designer is how best to trade the cost of minimizing maintenance by
increasing reliability - often at added cost in redundant systems or greater design margins against the cost systems for facilitating and increasing maintenance capability. Previous studies
within the EU research programmers, such as OptiOWECS, have considered a range of strategies
from zero maintenance (abandonment of faulty offshore turbines) to highly facilitated
maintenance.
Access is critical as, in spite of the direct cost of component or system replacement in the
difficult offshore conditions, lost production is often the greatest cost penalty of a wind turbine
fault. For that reason much attention is given to access. Related to the means of access is the
feasibility of various types of maintenance activities and the need or not for support systems
(cranes and so on) and other provisions in the wind turbine nacelle systems.
5.5 IMPACT ON NACELLE DESIGN
The impacts of maintenance strategy on nacelle design relate to:




Provision for access to the nacelle;
Systems in the nacelle for handling components; and
The strategic choice between whether the nacelle systems should be (a) designed for long
life and reliability in an integrated design that is not particularly sympathetic to local
maintenance and partial removal of sub-systems or (b) designed in a less cost-effective modular
way for easy access to components.
5.6 LOCATION OF EQUIPMENT:
51

Transformers may be located in the nacelle or inside the tower base. Transformer failures have
occurred in offshore turbines, but it is not clear that there is any fundamental problem with
location either in the nacelle or the tower base.
5.7 IMPORTANCE OF TOWER TOP MASS:
The tower top mass is an important influence on foundation design. In order to achieve an
acceptable natural frequency, greater tower top mass may require higher foundation stiffness,
which could significantly affect the foundation cost for larger machines.
5.8 INTERNAL CRANES:
One option is to have a heavy duty internal crane. Siemens and Vestas have adopted an
alternative concept, which in general consists of a lighter internal winch that can raise a heavy
duty crane brought in by a maintenance vessel. The heavy duty crane may then be hoisted by the
winch and set on crane rails provided in the nacelle. Thus it may be used to lower major
components to a low-level platform for removal by the maintenance vessel.
Critical and difficult decisions remain about which components should be maintained offshore in
the nacelle, which can be accessed, handled and removed to shore for refurbishment or
replacement, and when to draw a line on component maintenance capability and accept that
certain levels of fault will require replacement of a whole nacelle.
5.9 MEANS OF ACCESS
The costs of turbine downtime are such that an effective access system offshore can be relatively
expensive and still be justified.
Source: Windcat Workboats, Unifly

52

Helicopter access to the nacelle top has been provided in some cases. The helicopter cannot land
but can lower personnel. Although having a helipad that would allow a helicopter to land is a
significantly different issue, the ability to land personnel only on the nacelle top of a wind
turbine has very little impact on nacelle design. Although adopted for the Horns Rev offshore
wind farm, helicopter access is probably too expensive as a routine method of transporting
personnel to and from offshore wind turbines, assuming current project sizes and distance from
shore. However, as projects grow in size and go further offshore, this will be a credible option.

5.10
ACCESS FREQUENCY:
At Horns Rev, which is the first major offshore wind farm in the North Sea, a vast number of
worker transfers have taken place since construction, and this is a concern for the health and
safety of personnel. It is expected (and essential) that the required number of transfers for the
establishment and commissioning of offshore wind plant will reduce as experience is gained.
5.11 ACCESS IMPEDIMENTS
In the Baltic Sea especially, extensive icing occasionally takes place in some winters. This
changes the issues regarding access, which may be over the ice if it is frozen solid or may use
icebreaking ships. Also, the ice in general is in motion and may be quite unstable. Lighthouses
have been uprooted from their foundations and moved by pack ice. The wind turbine foundation
design used by Bonus in the Middelgrunden offshore wind farm, situated in shallow water
between Denmark and Sweden, provides for a section at water level with a bulbous shape. This
assists in ice breaking and easing the flow of ice around the wind turbine, thereby reducing loads
that would tend to move the whole foundation.

53

In the European sites of the North Sea, the support
structure design conditions are more likely to relate
to waves than ice, and early experience of offshore
wind has shown clearly that access to a wind turbine
base by boat is challenging in waves of around 1m
height or more.
Currently most standard boat transfers cannot – and
should not – be performed in sea states where the
significant wave height is greater than 1.5m and
wind conditions are in excess of 12 m/s. This sea
state constraint is generally not an onerous parameter
for wind farms located in the Baltic region.
However, in more exposed locations, such as in UK
and Irish waters, the average number of days where
the wave height is greater than 1.5 m is considerably
greater.
Source: Vattenfall

5.12 FEASIBILITY OF ACCESS:
Operating in concert with the wave height restrictions are restrictions from the water depth, swell
and underwater currents. As an example, UK wind farms are generally sited on shallow
sandbanks, which offer advantages in easier installation methods, scaled reductions in foundation
mass requirements and in the tendency of shallow sandbanks to be located in areas away from
shipping channels. However, shallow waters, particularly at sandbank locations where the
seabed topography can be severe, amplify the local wave height and can significantly change the
wave form characteristics. Generally speaking, where a turbine in a wind farm is located in the
shallowest water, this turbine will present the most access problems.
Wave data that is representative of UK offshore wind farm sites shows that access using a
standard boat and ladder principle (significant wave heights up to 1.5m) is generally possible for
approximately 80 per cent of the available time. However this accessibility rate is too low for
good overall wind farm availability. In winter, accessibility is typically worst when there is the
greatest likelihood of turbine failures; yet at these times there are higher winds and hence
potentially higher levels of production loss. Accessibility can be improved to above 90 per cent
if access is made possible in significant wave heights between 2.0 and 2.5m. Providing access in
yet more extreme conditions is probably too challenging considering cost, technical difficulty
and safety. A safety limit on sea conditions has to be set and rigidly adhered to by the wind farm
operator. This implies that 100 per cent accessibility to offshore wind plant will not be
achievable and 90 per cent accessibility seems a reasonable target. Improvements in availability
thereafter must be achieved through improved system reliability.
Safe personnel access is currently one of the most important topics under discussion in offshore
wind energy. For example, the British Wind Energy Association, in consultation with the UK
Health and Safety Executive, has produced guidelines for the wind energy industry (BWEA,
2008). These guidelines were issued as general directions for organisations operating or
considering operating wind farms.

54

5.13 ACCESS TECHNOLOGY DEVELOPMENT
There may be much benefit to be gained from the general knowledge of offshore industries that
are already developed, especially the oil and gas industry. However, there are major differences
between an offshore wind farm and, for example, a large oil rig.
The principal issues are:


There are multiple smaller installations in a wind farm and no permanent (shift based) manning,
nor the infrastructure that would necessarily justify helicopter use; and



Cost of energy rules wind technology, whereas maintenance of production is much more
important than access costs for oil and gas.
Thus, although the basis of solutions exists in established technology, it is not the case that the
existing offshore industry already possesses off-the-shelf solutions for wind farm construction
and maintenance. This is evident in the attention being given to improved systems for access,
including the development of special craft.
5.14 CONCLUSIONS REGARDING ACCESS ISSUES
There appears to be a clear consensus on offshore wind turbine access emerging for current
generation sites. Purpose-built aluminum catamaran workboats are currently in use for the
several wind farms. Catamarans generally provide safe access in sea conditions with a
maximum significant wave height up to 1.5m. On occasion this figure has been exceeded by
skippers experienced in offshore wind transfers on a particular site.
In most current projects the standard boat and ladder access principle is practicable for
approximately 50-80 per cent of the available service time, depending on the site. However
when this accessibility figure is considered in concert with the overall wind farm availability
equation, there is scope for improvement. The main reason for improvement is that winter
accessibility rates are typically much worse than for the summer period. This is compounded
with a higher likelihood of turbine failures in winter and also higher winds, hence higher levels
of production loss.
With some effort this accessibility figure can be improved markedly - that is to say, where access
can be made possible in significant wave heights of between 1.5m and 2.0m. Providing access
above 2.0m becomes an economically and technically challenging decision. It is likely that
significant expenditure and technical resources would be necessary to gain modest incremental
improvements in access rates above the 2.5m significant wave threshold.
Projects soon to come online and those planned for the next decade may have a new driver
distance to shore. For these, transit times by vessel become impractical for day-workers, and in
these cases solutions using helicopters or offshore accommodation platforms (or vessels) will
come to the fore.
5.16 Noise
Offshore wind turbines can and do propagate noise through the air and surrounding water. the
underwater noise propagation of an operating wind park is a function of seabed conditions,
foundation type, turbine design and other factors. The results of these studies and reports are
forming a base for the evaluation of noise on marine wildlife and the nearest land residents.
55

5.17 Maintenance and Availability:
Early experiences in Europe have shown that wind turbines may be accessible only 80% of the
time during good weather in the summer, and significantly less often during other times of the
year. This is due to variable sea states, which can limit safe access to a wind project by work
crews via boat or helicopter. As a result, turbine maintenance needs will take longer to address,
potentially leading to longer down times and lost production.
5.18 Limited Experience:
The siting, permitting, construction and operation of offshore wind projects are still undergoing
development. Equipment, techniques and infrastructure have yet to be developed or adapted in
the U.S. for all aspects of offshore wind development.
5.19 Marine Environment:
Hydrodynamic structure and foundation loading, water depth, collisions from air- and waterborne vessels, waves, currents, scour and sand waves, severe weather and high seas, logistics (of
installation and operation and maintenance), corrosive marine environment, marine growth –
these are all issues unique in an offshore environment.
5.20 Infrastructure:
An extensive on- and offshore infrastructure is required to construct and operate an offshore
project. Some of the necessary items include: port with deep draft facilities, large staging area
with appropriate loading equipment, dedicated fleet of maintenance and construction vessels
(possibly including a helicopter), reliable communication system, appropriate safety and rescue
provisions, and skilled personnel.
The Offshore Wind Infrastructure research initiative consists in the realisation of a number of
investments allowing for the monitoring and modelling of offshore wind energy resources and of
the behaviour of systems components in offshore wind farms. On the short term, the project aims
at the setup of a complete windmonitoring and testing infrastructure. It aims at improving the
lifetime of offshore wind turbine components, at optimising the Operation and Maintenance
strategies for offshore wind parks and maximising the energy output of offshore wind farms\
5.21 Environmental Impact:
Although research into wind turbine impacts on marine habitats, avian use and fisheries is
ongoing, site-specific concerns must be addressed.
5.22 Aesthetics:
A common concern regarding any wind project is its visibility. Depending on weather and sea
conditions, tall turbines can be seen up to 20 miles away. Aesthetic impact is an issue that has led
to the denial of some offshore project permit applications in Europe.
5.23 Foundations:
Foundation design is a site-specific concern and represents a much larger portion of a project’s
installed cost compared to land-based installations. Water depth, extreme wind/wave loading
conditions, and seabed geology dictate the design of the foundation

CHAPTER 6
56

FUTURE CONCEPTS

6.1 Flying Wind Farms
This could very well be a true picture of future power
harvesters according to NASA. A federal fund of $100,000 is
being reserved for exploring these high-altitude, nano-tube cable
tethered, above-ground wind farms. The project will check all
aspects as well as weigh the pros and the cons of a wind farm
this one.

such

as

6.1.1 Envisioned Research by NASA

Mark Moore, aerospace engineer at NASA, outlined this research as a study to look at the
practicalities of the idea of air-borne turbines. To know the challenges that will be faced when
turbines are working at 30,000 feet above ground level and what the effect will be on airspace
and unmanned aircraft is what the project is aiming to uncover.

6.1.2 Features of Flying Wind Farms

A prototype planned by Italian startup TWIND has a pair of balloons at 2,600 feet. The
open sails move antagonistically so while one moves
downwind the other moves upwind. This movement
spins a turbine to generate power. The option of
offshore flying wind turbines is also being explored to
solve the airspace competition issue.

6.1.3 Advantages Presented

57

At higher altitudes, wind has more power and velocity and is more consistently
predictable. As power generated goes up because of higher wind resistance proportional to the
cube of relative velocity, more power can be generated. That works out to be some 8 – 27 times
the power produced at ground level. The tethers can haul in the kites/balloons housing the
turbines during storms or for general maintenance work. Less pollution is an advantage, as well
as the fact that it will not take up much precious ground space for installation.

6.1.4 Challenges Presented
This plan certainly presents plenty of challenges for air traffic and other unmanned aircraft by its
need of a minimum 2-mile no-fly zone. The offshore option also has the extra effort of
transporting the energy from sea to land-based power plants.
6.1.5 Need for Government Involvement
Since this plan of flying wind farms involves diverse major aspects like sharing airspace,
geography, and technology, Moore says that there is a genuine need for government involvement
to make this a viable plan. In his words, “We’re trying to create a level playing field of
understanding, where all of the concepts and approaches can be compared.”

6.2 Increasing The Efficiency Of Wind turbine Blades
To ensure wind turbines that are big in size work in a better manner, a new kind of airflow technology may soon be introduced. Apart from other aspects, it will focus on efficiency of
blades used in the wind turbines. The technology will help in increasing the efficiency of these
turbines under various wind conditions. This is a significant development in the area of
renewable energy after new wind-turbine power generation capacity got added to new coal-fired
power generation in 2008.
Testing new systems to optimize the efficiency of wind turbines and their blades
Syracuse University researchers Guannan Wang, Basman El Hadidi, Jakub Walczak,
Mark Glauser and Hiroshi Higuchi are testing new intelligent-system based active control
methods with the support from the U S Department of Energy through the University of
Minnesota Wind Energy Consortium. They record data in an intelligent controller after getting a
58

rough idea of the flow conditions over the blade surfaces from surface measurement. This helps
them implement real-time actuation on the blades. In this way, not only the efficiency of wind
turbine system is increased but the airflow can also be managed.
Advantages of new systems to optimize the efficiency of wind turbines and their blades



They reduce noise.
They reduce vibration.

New developments that are being worked out to make wind turbines and blades more
efficient





The overall working scope of the wind turbine can be enlarged by using the flow control
on the outboard side of the blade beyond the half radius. Attempts are being made to
increase the rated output power without increasing the level of operating range.
An anechoic chamber is being set-up to measure and define the effects of flow control on
the noise spectrum of the wind turbine.
To know the airfoil lift and drag characteristics with suitable flow control while exposed
to large-scale flow unsteadiness, efforts are being made to characterize airfoil in an
anechoic wind tunnel facility at Syracuse University.
Scientists are also trying to attain a greater efficiency by placing blades at various angles
through wind tunnel tests of 2.5 megawatt turbine airfoil surfaces and computer
simulations.

Drawbacks of wind energy turbines and their blades
The blades face a lot of challenge while beating the air. Scientists at the University of
Minnesota are looking forward to erect this process called drag by placing these small grooves or
triangular riblets scored into a coating on the surface of the turbine blade. The small groves of
the size between 40 to 225 microns make the blade look smooth. When used in an aero plane, the
riblets were very successful. With their basic structure being the same as the wings of the plane,
they were able to reduce the drag by 6 percent in aircrafts. But since the turbine blades have a
thick cross section close to the hub and there is a lot of chaos at the ground, this technology
failed in wind turbines.
Anything working on wind energy including wind turbines needs a steady wind flow to
function properly. The wind turbine blades, when confronted with extreme conditions, wear out
very fast.
The design of wind turbines is not considered appropriate, despite the fact that the cost of
making power through them has reduced.
Though wind energy turbines, their blades and the riblets may have some drawbacks,
they can still be considered as a very efficient and reliable source of energy. Keeping this in
mind, a meeting has been arranged in Long Beach, CA by American Physical Society Division of
Fluid Dynamics to assess the ways to enable the best use of wind turbines. Also, a project to use
59

riblets to increase wind turbine efficiency by 3 percent is being worked upon by Roger Arndt,
Leonardo P. Chamorro and Fotis Sotiropoulos from University of Minnesota.

6.3 South Korea Planning Massive Offshore Wind Form
Wind energy currently meets a mere 1.5% of global electricity generation. But
scientists foresee a lot of potential in this alternative energy source. Asian
countries are also trying to embrace clean and green energy. South Korea is going
for an ambitious off-shore wind farm amounting to $8.3 billion. This
project will be executed at the western coast of the Korean peninsula
taking a time period of ten years.
Currently South Korean companies such as Hyundai Heavy
Industries, Samsung Heavy Industries, Doosan Heavy
Industries & Construction, and Hyosung Corp. are taking keen
interest in the production of wind turbines.
According to the Ministry of Knowledge Economy (MKE) this project will erect 500
wind turbines in the West Sea off the Jeolla province. All these turbines are supposed to produce
2,500 megawatts of energy a year. This amount of electricity will be sufficient for 3.5 million
Busan residents for a full month. MKE director general Kang Nam-hoon says, “Basically, the
scheme is composed of three phases. By 2013, we will have raised 20 5-megawatt turbines and
add 180 by 2016 and 300 more by 2019.”
Kang Nam-hoon is quite hopeful that South Korea will register its entry into clean and
green fuel with the completion of this project. He states, “On the back of the mega-sized project,
we strive to preempt the ever-growing global green market and become one of the three
powerhouses in the offshore wind power generation.”
Kang also thinks that this massive wind farm will force the world to sit up and take notice
of the Korean technology and other countries will be glad to apply the advanced technology
exhibited by this country. Kang also feels that South Korea will be able to fulfill the ever
growing demands of alternative energy market. He expresses his views, “Many domestic
companies are working on large-sized wind turbines. Offshore wind power generation has a shot
at becoming the country’s future cash cow when it becomes mainstream technology.”
But MKE is not providing all the funds. They are hoping for the private companies to
pool in their own money to complete the requirement of the $ 8.3 billion. The MKE will fund
just the 0.3% of the overall cost of the project. In fact they are financing the research and
development of specific technologies. This can cast a shadow on the execution of the project.
But the ministry is hopeful that major Korean shipbuilders and heavy machinery makers
will be interested in trapping the profitable global alternative energy market. So those
manufacturers will need to build their reputation on something massive and awe-inspiring and
this project is supposed to yield 153.9 gigawatts of electricity. Kang confirms, “Many domestic
companies are working on large-sized wind turbines. Offshore wind power generation has a shot
at becoming the country’s future cash cow when it becomes mainstream technology.”

6.4 Solar Wind Power In the future:
60

As the world discovers new ways to meet its growing energy needs,
energy generated from Sun, which is better known as solar power and
energy generated from wind called the wind power are being considered as a
means of generating power. Though these two sources of energy
have attracted the scientists for a very long time, they are not able to
decide, which of the two is a better source to generate power. Now
scientists are looking at a third option as well. Scientists at Washington
State University have now combined solar power and wind power to
produce enormous energy called the solar wind power, which will
satisfy all energy requirements of human kind.

Advantages of Solar wind power.








The scientists say that whereas the entire energy generated from solar wind will not be
able to reach the planet for consumption as a lot of energy generated by the satellite has
to be pumped back to copper wire to create the electron-harvesting magnetic field, yet the
amount that reaches earth is more than sufficient to fulfill the needs of entire human,
irrespective of the environment condition.
Moreover, the team of scientists at Washington State University hopes that it can generate
1 billion billion gigawatts of power by using a massive 8,400-kilometer-wide solar sail to
harvest the power in solar wind.
According to the team at Washington State University, 1000 homes can be lit by
generating enough power for them with the help of 300 meters (984 feet) of copper wire,
which is attached to a two-meter-wide (6.6-foot-wide) receiver and a 10-meter (32.8-foot)
sail.
One billion gigawatts of power could also be generated by a satellite having 1,000-meter
(3,280-foot) cable with a sail 8,400 kilometers (5,220 miles) across, which are placed at
roughly the same orbit.
The scientists feel that if some of the practical issued are solved, Solar wind power will
generate the amount of power that no one including the scientists working to find new
means of generating power ever expected.

How does the Solar wind power technology work?
The satellite launched to tap solar wind power, instead of working like a wind mill, where
a blade attached to the turbine is physically rotated to generate electricity, would use charged
copper wire for capturing electrons zooming away from the sun at several hundred kilometers
per second.

Disadvantages of Solar wind power
61

But despite the fact that Solar wind power will solve almost all the problems that we were to
face in future due to power generating resources getting exhausted, it has some disadvantages as
well. These may include:
 Brooks Harrop, the co-author of the journal paper says that while scientists are keen to
tap solar wind to generate power, they also need to keep provisions for engineering
difficulties and these engineering difficulties will have to be solved before satellites to tap
solar wind power are deployed.
 The distance between the satellite and earth will be so huge that as the laser beam travels
millions of miles, it makes even the tightest laser beam spread out and lose most of the
energy. To solve this problem, a more focused laser is needed.
 But even if these laser beams reach our satellites, it is very doubtful that our satellites in
their present form will be able to tap them. As Greg Howes, a scientist at the University
of Iowa puts it, “The energy is there but to tap that energy from solar wind, we require
big satellites. There may be practical constraints in this.”

6.5 Fresh Water Wind Farm on Lake Erie:
A fresh-water wind farm is taking shape at Lake Erie and
when completed will provide 20 megawatts and get on to about one
gigawatt power by 2020. Huge individual turbines 300 feet tall, to be built by GE will
be erected off Ohio, Cleveland. Better designs: These are special gearless superefficient turbines, with three 176-foot long blades, which run with the help of a giant
ring of magnets. The blades are longer due to strategically placed
carbon fibre, and lighter too. Many moving parts like gearbox, coils and starter
brushes are eliminated with resultant reduced maintenance. The giant magnetic
ring array helps the turbine generate power even at very low
speed.

Rejuvenating wind energy industry:
As land-based turbines are facing a lack of interest and demand, wind energy industry is
facing a setback. This new-design turbines to tap the energy from off-shore wind can bring about
a positive tilt to the industry. It has been estimated that off-shore wind potential from Great
Lakes area only is 321,936 megawatts which is about 10 times the energy from all sources put
together.

Farm partners:
This wind farm project is resulting from a partnership between Lake Erie Energy
Development Corporation (LEEDCo) of Northern Ohio and General Electric Co.(NYSE:GE).
Costing US $100 million, this project will light up 16,000 homes. General Electric (GE) has been
asked to supply the 5 turbines for this project. This project can be the harbinger of good times of
GE along with another $300 million Saudi contract in the times of overall financial setback.

Perfect balance:
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As per the report of National Renewable Energy Laboratory (NREL) on offshore
wind, an interesting factor came to surface. Wind blows strongest at midnight and with least
force at midday and solar power is strongest at noon and almost nil at midnight. So with windpower at night and solar power at day, we can have continuous generation of clean, renewable
energy.

6.6 Air Born Wind Turbines:
Yes, the day is not far off when reaching for sky is the new motto for generating costeffective renewable energy. Initially it was considered to be technically non-viable to tap highaltitude winds. But today, technically-advanced materials and innovative computer know-how
are giving new life to this scheme with innovative autonomous aerial structures using wind
energy to generate power.

Joby Energy, Inc. model:
Joby Energy Inc., exploring wind turbine technology, has developed a computercontrolled multi-winged kite-like structure which floats around 2000ft height for generating
power. Mr Bevirt is the inventor of this aerial kite. The DC power generated is transferred to
ground through tether to a ground station to be converted to AC power ready for consumption via
a power grid.
Advantages of high altitude wind turbines:
Extolling the virtues of these autonomous aerial power generators, Mr. Bevirt said,
“Operating at five times the height of a conventional turbine increases both wind speed and
consistency resulting in more power, more often.” Professor William Moomaw, Director,Centre
for International Environment and Resource Policy at Tufts University, Massachusetts, agreed,
“The higher speeds at the greater altitudes should produce significantly more electricity.”
Mega source up above:
Actually statistics is strongly in favor of these air-borne wind turbines because globally
tropospheric winds carry nearly carry potential to produce 870 terawatts of energy whereas our
total demand put together is only 17 terawatts. Along with Joby Energy Inc., other companies
like Kitegen focusing on power kites, Magenn Power’s Air Rotor System called (MARS) with a
helium filled blimp design and Sky WindPower with flying electric generators are trying to tap
this mega source to produce clean and cost effective power.
Tread with care:
US Federal Aviation Administration has asked the
flying altitudes restricted to 2000 ft or less in spite of the
potential to reach heights up to 35,000. Also Professor Mick
Womersely, Director of Sustainability, Unity College, Maine,
expressed the obvious concerns about possible hazards and
reliability of these prototypes.

63

Reassurance about safety:
Mr. Bevrit confirmed about the safety measures like ability to ground the turbines in galeforce-type winds, multiple motor designs to circumvent motor failure and on-board stand-by
batteries to land the system in case of tether malfunction. He assured that road-testing in
sparsely-populated areas with good strong wind is being planned and all safety measures will be
paid attention to.
Joby Energy’s aim:
Joby Energy aims to create enough systems to power 150 homes (about 300kW) and
move on to larger systems producing 3MW or more. In Mr. Bevirt’s words, “Our goal is to
deploy airborne wind turbines globally to produce cheap, consistent, and abundant electricity for
a prosperous planet.

6.7 Bladeless Wind Turbine:
A research company in New Hampshire recently patented its bladeless wind
turbine, which is based on a patent issued to Nikola Tesla in 1913. This wind turbine
is christened as the Fuller Wind Turbine. This turbine is developed
by Solar Aero. The specialty of Fuller Wind Turbine is it has only one
rotating part, known as the turbine-driveshaft. The entire machinery is
assembled inside a housing. Wind turbines are often disliked by
environmentalists because they kill birds and bats and often
generate noise for the residents living nearby.
The wind industry is trying to find a solution to the
problem by working with environmental groups, federal
regulators, and other interested parties. They are trying to develop
measuring and mitigating wind energy’s effect on birds. The Fuller
offers hope to bird lovers and environmentalists.
Fuller Wind Turbine has several advantages over the
ones having blades. Fuller Wind Turbine has a screened inlet and
you try to get a closer look at this wind turbine you can see the only
visible is as it adjusts to track the wind. This wind turbine can be
utilized by the military surveillance and radar installations because
there are no moving blades to cause difficulties.

methods
of
Wind Turbine
traditional
outlet. If
movement

Another plus attached to this wind turbine is that it won’t cost a heaven
when you get its power. According to manufacturers this turbine is expected to deliver power at a
cost at par with the coal-fired power plants. If you want to probe deeper, its good news that total
operating costs over the lifetime of the unit are expected to be about $0.12/kWh.
If we take the maintenance angle it won’t cause much headache because it’s a bladeless
turbine. The turbine maintenance requirements are not colossal and it would result in lower
lifetime operating costs. The turbine is mainly supported on magnetic bearings. Another
advantage is all of the generating equipments are kept at ground level. This will lead towards
64

easy maintenance of equipments. The company comes out with encouraging figures and
proclaims “final costs will be about $1.50/watt rated output, or roughly 2/3 the cost of
comparable bladed units.”
If we take a look at the Tesla turbine patented in 1913, it operates using the viscous flow
of a fluid to move the turbine and as a result generates energy. The Tesla turbine has a set of
smooth disks fitted with nozzles that send out a moving gas to the edge of the disk. The gases
drag on the disk by following the principle of viscosity and the adhesion of the surface layer of
the gas. As the gas slows and adds force to the disks, it twirls in to the center exhaust. Because
the rotor has no projections, it is very strong and sturdy. One has to be careful about the disk
space because disks in the turbine need to be closely spaced so that they can trap the viscous
flow. The Tesla turbine has extremely thin disks to reduce turbulence at the edges and that makes
them effective. In 1913, Tesla was unable to find metals of adequate quality to make this work
effectively. But now almost a century later, those limitations have been surmounted.
Solar Aero’s current prototype is a modest trailer-mounted unit. But inventor says that
their other models “should be capable of 10kW output with no problem.” If this technology takes
off smoothly it would remove many hurdles attached with conventional wind turbines and more
environments friendly.

6.8 Jet Engines the Inspiration for New Wind Power Technology
Wind power has recently received a nice boost as one of the hottest forms of energy on
the market. When comparing the recent market growth
against all forms of energy, both renewables and nonrenewables, wind turbines seem to be jumping to the
head of the pack. While it still has a way to go before it
catches up to solar, it is gaining ground rather quickly.
Something that will help pick up the pace even further
is new technology that is coming from FloDesign. Their
truly unique wind turbine is actually based on the
design of a jet engine instead of the traditional
windmills that we see all across the country. Their
concept seems to be a simple one, but it extremely
effective.
The design concept is based on capturing the
wind through a small hole that powers a turbine that
looks almost identical to a jet engine. They claim that
the design makes the turbine as much as 4 times as
effective as the current turbines that are being used.
Judging by the $34.5 million financing that they have just received, it would seem that they have
convinced more than one person that this is the real deal.
65

Along with being more efficient, it is also less expensive. This is a rather large
development as wind energy was already growing in acceptance and following and with this turn
of events, it could really start to gain some momentum. Proof of this is the $8.3 million grant that
was awarded to the company from the US Dept of Energy.
FloDesign has a very hot product on their hands right now. More efficient, less cost and
more of them can occupy the same space that the traditional design was capable of occupying. If
this design is launched and experiences success, the energy world will literally change right
before our eyes.

6.9 The Kite Wind Generator
It’s an expert estimation that the total energy stored in wind is 100 times higher than actually
needed by humans on this earth. The catch is that we have to learn and devise
ways to trap this wind power blowing across the planet earth.
Experts tell us one more thing that most of the wind energy is
available at high altitude and we can’t manufacture turbines of
that height. So we have to think of new ways to trap that wind
power blowing at a significant height. Some experts estimate
that the total energy contained in wind is 100 times the amount
needed by everyone on the planet. However, most of this
energy is at high altitudes, far beyond the reach of any wind
turbine.
Now researchers want to create something like a kite that can float
at a higher altitude to trap the wind energy.

Kite Wind Generator
The Kite Wind Generator simply known as KiteGen is an Italian company. They are
installing kites that sprout from funnel like structures. They are mounted on giant poles. When
wind blows these kites come out of funnels. For short, use kites that spring from funnels on the
end of giant poles when the wind blows. For each kite, winches release a pair of high-resistance
cables to control direction and angle. These kites are light and ultra-resistant. These kites are
similar to those used for kite surfing – light and ultra-resistant, capable of flying up to a height of
2,000 meters.
KiteGen people have thought of new ways to exploit the wind power existing at an
altitude. They have discarded the usual heavy and static plants like current wind turbines, but
opted for light, dynamic and intelligent ones. They have installed all the light devices in the air
and heavy ones on the ground for generating power. The basics of the wind turbines and KiteGen
are same. But they have moved the heaviest parts to the ground. They claim that the resulting
structure, base foundation included, is much lighter and cheaper. They have also provided
flexibility regarding the height of kites. If the wind is strong at certain height, the height of the
kite too can be adjusted accordingly. If today wind if blowing nicely at 1000m, say, kites can be
adjusted at the same height. If tomorrow the strong wind is blowing at certain other height, wind
kites can be flown at that height to gain maximum advantage of the wind power.
66

The swirling kites prompt KiteGen’s core in motion, and the rotation activates large
alternators producing a current. They also have a control system on autopilot. This control
system manipulates the flight pattern so that maximum power can be generated be it night or day.
The KiteGen people are concerned with the environment too. They don’t want the lives of birds
to be affected by their flying kites. So they have installed the advanced radar system that can
redirect kites within seconds in case they detect flying of birds.
The cost of the technology is US$750,000 and it won’t takes acres and acres of space like
a wind farm. You can install the whole machinery within a diameter of just 100 meters. KiteGen
claim that they can produce half a GW of energy, and produce it at a cost of US$2.5 per GW. Its
creators, Sequoia Automation, say a 2,000 meter-version would generate 5GW of power.

6.10 Wind Turbine Power Goes Portable with Foldable Wind Generator
Renewable energy is one of the hottest things on the market right now but until recently,
solar power has been getting most of the attention. While there are plenty of techno gadgets, like
solar briefcases and solar laptop chargers, that can have solar power on the run, very few if any
items exist for other sources of renewable energy to become portable. The foldable wind
generator has all the right ideas, but may still be just a bit ahead of its time.
The Eolic is a very interesting design, but it is very questionable
as to whether or
not their foldable wind generator is capable of doing the job that it is there
for. The Eolic
looks great and is an incredible idea, but can it actually create enough
energy to
power anything and is it durable enough to actually hold its ground in a
wind strong enough to create electricity? At this point, it is probably nothing
more than wishful thinking.
The designers’ concepts behind the foldable wind generator are to be
supply power on the go in areas that do not have access to electricity.
was the beginning of a construction project or a community that lacked
these portable units could be put up to supply the necessary power to that
area. As we see it, the thing that makes this item so appealing is probably its
link.

able
to
Whether it
electricity,
specific
weakest

The Eolic is made of very light-weight materials that
are going to have a tough time standing tall in any wind that would be strong enough
to actually generate the power that they are talking about. If the item were anchored
into the ground, and by this we mean a solid foundation, not staked like a tent, it would be fine.
However, this being a portable unit, that luxury is not possible. While the overall ambitions of
the designers may be a bit unrealistic, the Eolic foldable wind generator can still serve a purpose.
As many of the smaller, portable solar devices are touted to provide outside lighting or
provide electricity on a camping trip, this device should be up to the task. If it actually works in
these scenarios, it could truly bring wind power into the picture as a primary renewable energy. It
would have a distinct advantage over solar power at that point as it could work all day long
versus needing to recharge. On the other hand, they could also be sold as a package to ensure
67

constant renewable energy on the go. That would be a two-pack that people would surely stand
in line for.

6.11 Energy Grid Could Make Offshore Wind Power More Reliable
Scientists believe that natural resources can meet the energy needs of the entire human
population. Wind energy too has huge potential to generate power for us. Researchers are trying
to trap offshore wind power. But there are still many hiccups that are preventing us from utilizing
natural resources for our needs. Wind turbines produce intermittent power because the direction
and strength of the wind varies. Scientists are trying to generate more or less consistent power
from offshore winds.
The researchers are focusing their efforts on more consistent offshore wind power supply.
They are of the view that production of energy can be more consistent if project locations can be
chosen by observing regional weather patterns. They are also proposing to connect the wind
power generators with a shared power line. The
fund was provided by the Delaware Sea Grant
College Program and CAPES, a Brazilian research
council.
Researchers from the University of
Delaware and Stony Brook University are trying to
generate a steady power supply from offshore
winds. They have published their work in the
Proceedings of the National Academy of Sciences.
The members of the research team are UD alumnus
Felipe Pimenta, UD research faculty member Dana
Veron, and Brian Colle, associate professor in the
School of Marine and Atmospheric Sciences at
Stony Brook University. Willett Kempton is the
UD professor of marine policy in the College of
Earth, Ocean, and Environment and director of its
Center for Carbon-free Power Integration. Willett
Kempton the lead author of the paper, says,
“Making wind-generated electricity more steady
will enable wind power to become a much larger
fraction of our electric sources.” The research team presented various designs of how offshore
wind power projects can reduce the nuisances of local weather on power fluctuations.
The researchers analyzed five years of wind observations from 11 monitoring stations
along the U.S. East Coast from Florida to Maine. Based on wind speeds at each location, they
estimated electrical power output from a hypothetical five-megawatt offshore turbine. After
analyzing the patterns of wind energy among the stations along the coast, the team explored the
seasonal effects on power output. Kempton talks about his work, “Our analysis shows that when
transmission systems will carry power from renewable sources, such as wind, they should be
designed to consider large-scale meteorology, including the prevailing movement of high- and
low-pressure systems.”
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Scientists are working on this project for the last five years. They have never found the
power output of their simulated grid to come to a standstill in this time period. The researchers
created their own hypothetical power generation site. They showed power fluctuations too like
any wind based powerhouse. But when they simulated a power line connecting grids, they
received a steady power supply without extremes. Until now the USA doesn’t have any offshore
energy plants. But many are in the pipeline waiting to be implemented off the coasts of many
Atlantic states. These proposed projects can take help in the selection of sites. Colle talks about
the ideal configuration. “north-south transmission geometry fits nicely with the storm track that
shifts northward or southward along the U.S. East Coast on a weekly or seasonal time scale,” he
said. “Because then at any one time a high or low pressure system is likely to be producing wind
(and thus power) somewhere along the coast.”

6.12 What factors affect the output of wind turbines?
Wind energy is undoubtedly one of the cleanest forms of
producing power from a renewable source. There is no
pollution, there is no burning of fossil fuels, and unless something very drastic
happens, you don’t run out of wind. But it’s not like you can erect
a wind turbine anywhere and it will start generating power for you.
There are lots of factors that can make an impact on the amount of
energy you can generate out of wind.
Wind
It being a wind turbine, its output first most depends on the wind. Both the speed and
force of the wind can be deciding factors. The more wind speed and force you have got, the
greater is the amount of power your wind turbine generates. Different regions have different
wind speeds. You can gather the available wind dynamics data and using a model like Webull
Distribution you can calculate how effective the wind of a particular region is going to be.
Height
Places of higher altitudes have more wind due to various atmospheric factors. Besides, at
higher places there is less obstruction from the surrounding hills, trees and building. In fact the
height is so important that alternative energy scientists and engineers are trying to use kites (due
to the heights they can easily reach) to tap the wind power.
Rotor
The amount of energy produced by your wind turbine is proportional to the size of the
rotor used, when all other factors have been taken into consideration. A bigger rotor certainly
generates more power. Although it may cost more, in the long run, whenever you are getting a
wind turbine erected, go for a big a rotor as possible.
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6.13 Storing Wind Power as Ice
Of the total amount of electricity generated by all
sources, about 75% is used by buildings, a major fraction
of which is consumed by air conditioners. With the
demand of renewable energy increasing with every passing
day, inventors are trying to find the best possible means to
store the generated energy during the best time, to provide
power when the generators aren’t getting the resources
they need. It is a natural phenomenon that the wind blows
stronger at night than in the day. We don’t need that extra
energy during nighttime. We can store this energy and use it
during daytime when the load is too much on the grid.
When we utilize alternative sources of energy, how to store the energy poses a big
problem. Scientists often create giant sized batteries or compressed air and hydroelectric storage.
But now a company, Calmac Booth is thinking of storing extra power in ice!
Air conditioning in the summer consumes the lion’s share of a building’s energy cost.
Calmac Booth is manufacturing a hybrid cooling system. This system exploits an ice bank
thermal energy storage tank known as IceBank. IceBank makes and stores ice for use in air
conditioning systems when the wind is blowing a bit faster or the sun isn’t shining, that is, at
night.
Heavily insulated polyethylene is used to manufacture the IceBank tanks. They also
contain a spiral-wound, polyethylene-tube heat exchanger surrounded with water. The tanks are
available in a variety of sizes. According to one’s need it is available from 45 to over 500 tonhours. When the charging cycle is going on, a solution containing 25% ethylene or propylene
glycol is cooled by a chiller. In the next step this solution is circulated through the heat
exchanger inside the IceBank tank. It has to be noted that the ethylene-based or propylene-based
is an industrial coolant. These coolants are particularly devised for low viscosity and superior
heat-transfer properties.
The unique property of the Ice Bank is that the ice is built uniformly throughout the tank.
Charging cycle of an Ice Bank tank takes about 6 to 12 hours. This device can also be utilized in
conjunction with a solar panel array.
During summer time the entire system tries to survive during peak hours. Ice Bank
simply prepares ice at night, when electricity is cheaper and it is cooler. During afternoon, this
stored energy can be consumed by running air conditioning. At that time it is hot and electricity
is in short supply. Ice Bank can help in reducing the load on the grids during peak hours.
According to the company reducing electricity demand for cooling can cut energy costs by 20 –
40 percent. That reduction also translates into fewer emissions from power plants.
This system can be applicable to those buildings too which are without on-site renewable
energy power generation. Ice can be prepared during night i.e. off-peak time. During off-peak,
electricity is cheaper and cleaner base load generation can be used. Calmac explains that for
70

every kilowatt-hour of energy that is shifted from on-peak usage to off-peak, there is a decrease
in the source fuel needed to generate it. This reduction can be between 8 and 30%.

6.14 Using Radar to Protect Birds from Wind Farms
The new Penascal wind farm in Texas hopes to become a model for responsible
development by installing new radar technology to protect migratory birds
and
wildlife. According to recent studies, wind farms kill about 7,000
birds a year, although actual numbers are thought to be much
higher. The new 202MW wind farm, operated by
Spanish firm Iberdrola Renewables, uses radar
technology developed by Florida based DeTect, Inc.

The same technology was originally developed for NASA
and the US Air Force. It can detect approaching birds up to four miles away and assess their
altitude, numbers and visibility. It then analyzes weather conditions to determine if they are in
danger of flying into wind turbine blades. If so, the turbines are programmed to automatically
shut down and restart once the birds are a safe distance away.
The Penascal wind farm is located on the Central Flyway, a main route for migratory
birds in the Americas. Millions of birds funnel through the narrow air corridor during the
semiannual migration. A study in the autumn of 2007 found 4,000 birds an hour passing
overhead.
Conservationists who have fought against wind farms because of their impact on wildlife
remain skeptical of this apparent ‘easy fix’. They argue that wind farms should be placed away
from migratory routes to begin with, and that the new technology still does not address the
disturbance of wildlife habitat and nesting grounds in the vicinity.

6.15 Improvements in Wind Speed Forecasting
Sources of alternative energy are still in infancy stage and taking
nascent steps towards the future. So there are ample scopes
for scientists to improve upon the various aspects of
existing models of alternative sources of energy. There is so much
untapped, and so much to explore in this sector. That’s why we are daily
flooded with information in the alternative energy field. But sometimes we
hear about the improvement in the existing models itself. Researchers from
the University of Alcala (UAH) and the Complutense University in Madrid
(UCM) have devised a new method for predicting the wind speed of wind
farm aero generators.
Why wind speed forecasting is necessary? Why should one be accurate while forecasting
the wind speed? We know that an electricity grid can develop disturbances in power supply if the
balance between demand and supply is disturbed. Power generation from wind is entirely
dependent on wind speed and is not easily dispatchable. Various factors affect the wind speed
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such as season, temperature variation, pressure variation etc. So accurate forecast of wind speed
is not easy. But when wind farms are contributing considerably in the energy mix of the grid then
it becomes necessary to know that how much power will be produced by the wind farm. They
have to behave like conventional power generator units. These forecasts are used to schedule the
operations of other plants, and are also used for trading purposes.
How this neural network was developed? Researchers have taken the help from Global
Forecasting System from the US National Centers for Environmental Prediction. They provide
the data of entire planet earth with a resolution of approximately 100 kilometres. The best thing
is one can access all the data for free on the Internet. But researchers went a step further and for
more detailed predictions they integrated the ‘fifth generation mesoscale model’ (MM5), from
the US National Center of Atmospheric Research. It has a resolution of 15×15 kilometres.
Sancho Salcedo, an engineer at the Escuela Politécnica Superior and co-author of the
study, published online in the journal Renewable Energy explained, “This information is still not
enough to predict the wind speed of one particular aerogenerador, which is why we applied
artificial neural networks.” These neural networks are automatic information learning and
processing systems. While doing their work the neural networks imitate the mechanisms of
animal nervous systems. Neural networks utilize the temperature, atmospheric pressure and wind
speed data already fed to them by forecasting models and data collected from the aerogenerators.
All these data are used to acclimatize the systems so that they can predict the wind speed in the
time range of one and forty eight hours. Wind farms are bound by law to provide these forecasts
to Red Eléctrica Española, the company that delivers electricity and runs the Spanish electricity
system.
Salcedo states that the method can be applied immediately: “If the wind speed of one
aerogenerator can be predicted, then we can estimate how much energy it will produce.
Therefore, by summing the predictions for each ‘aero’, we can forecast the production of an
entire wind farm.” They have already applied this method at the wind farm in Fuentasanta, in
Albacete. The trial was very successful.
This neural network for wind speed forecasting can save millions of Euros. They have
detected an improvement of 2% in predictions as compared to the existing models. But this
improvement is really significant if we see it in totality because it will lead to the amount of
energy production that can save millions of euros. Scientists are trying to improve the method.
They want to incorporate several global forecasting models that will result in several sets of
observations. These observations will be applied to banks of neural networks to achieve a more
accurate prediction of aerogenerator wind speeds. It will naturally lead to more accurate
forecasting of wind speed.

6.16 Interactive Renewable Energy Map
These days we are incessantly debating over one of the hottest issues, i.e. environmental
pollution and rise in temperature throughout the world. An intelligent person always likes to
72

foresee the near future a bit and try to prepare himself /herself for the impending battle raising
from the horizons of the past. He or she won’t start
digging a well
when the thirst strikes. Most of us want to do
something about this and contribute positively to
make this earth a better place to live. But we are most
of the time clueless. We don’t know from where to
begin? Where we can find relevant information? If
we are able to track down information then how to
process it for our own and community’s good?
If you empathize with above-mentioned
feeling you can take the help of the renewable
maps introduced by the Natural Resources Defense
Council (NRDC). Nathanael Greene, who is the director of renewable energy policy at NRDC,
explains enthusiastically, “You can find your county on the appropriate map, select the different
map layers to see current renewable energy sites and resource potential, and then read about the
latest technologies to see what mix of energy opportunities might work for you and your
community.”
You can find detailed information about the alternative energy scene about Florida, Ohio,
Nebraska, Pennsylvania and Tennessee. NRDC considers these states as “key battlegrounds” in
the alternative energy scenario. They are trying to include statistics of other states in near future
soon. The Natural Resources Defense Council has introduced maps showing the correlation
between natural resources (sunlight, wind, crops and livestock) and the renewable energy
potential that can be trapped from a particular area.
The map on NRDC’s Renewable Energy for America site colors the different regions of
the country differently, according to regional resources and shows the sites of existing and
planned wind, biofuel and biodigester plants. If you want to know about the energy mix of any
state, the information is just a mouse click away. If you feel lost in the vast states of the country
and want to view the stats of a particular area enter the zip code.
Nathanael Greene wrote on his blog about the objective of introducing such idea, “We
definitely plan to use the site as a tool for getting people excited about what they can do in their
state with renewables”.
Right now the map on NRDC’s Renewable Energy for America site is still in the process
of development. NRDC is gearing up to add data on solar, geothermal power projects and
potential in the other fields in the coming months. They are updating state-by-state features
continuously. Soon you will be able to view data of states like Michigan, Missouri, Indiana,
Virginia and Nevada too. NRDC has gathered much of its data for the new map from the
National Renewable Energy Laboratory. They are collecting data on solar energy for decades.
Other maps and online tools highlight energy efficiency data too. The Green Grid, an industry
group formed to encourage energy efficiency in data centers, has online tools, including a map,
to show which parts of the country hold the greatest potential for using outside air to cool data
centers (see Green Grid: Free Cooling for Data Centers).
This map service is not for investors or research purposes only. Everyone, be it a farmer,
politician, financier or a scholar, can benefit from it. This site (http://www.nrdc.org/renewables/)
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can help you in taking a decision that from various energy options (solar, wind, geothermal,
biomass or anaerobic digesters) which one will best suit you or your community. You can watch
the current and proposed renewable energy projects in your area; get yourself acquainted with
new technology and legislations debated by the politicians and arrive at the right decision you a
right kind of energy mix for yourself or your area.
The objective of such a step is to be self-reliant and use local resources for one’s energy
need. They have conviction that local action can make a difference. Ideal renewable energy mix
technology will help in improving the environment, less dependence on fossil fuel, create
employment opportunities during the time of recession and outsourcing and protect natural
resources of the country.

6.17 New Revolution in Wind Power
As soaring oil prices and greenhouse gas emissions fuel
the search for cheaper and cleaner sources of energy, a
Japanese aerospace manufacturer may have found the
right stuff for a solution. It’s a windmill you can call your very
own. Yokohama-based aerospace manufacturer,Nippi Corporation,
has developed a revolutionary 20 kW wind turbine power
generation system that’s turning heads everywhere.
Well known in Japan as a manufacturer of
precision aerospace components, Nippi’s launch of this proprietary wind power system marks the
company’s first foray into the field of commercial wind power applications. The same cuttingedge ingenuity that goes into its aircraft parts can be seen at work behind the new windmill
known as a vertical axis wind turbine (VAWT). If you’ve never seen a VAWT, imagine one of
those fashionable plastic pop bottle wind spinners sported by many a tree throughout suburbia,
only a lot bigger and with 20 kW of power, a whole lot better. This is definitely not your garden
variety whirligig. Its small, sleek, aerodynamic design makes it the perfect fit for the city
landscape with the potential for installations on building rooftops as well as in harbors, parks and
maybe even your backyard. You don’t have to worry about the neighbors complaining either. The
system’s airfoils rotate at such a low speed, it’s as quiet as can be. Like other VAWTs, the system
doesn’t depend on which way the wind is blowing and has a generator and gearbox that sits close
to the ground to make repairs and maintenance easy.
Nippi’s wind power system has been up and running at a site located next to Japan’s
Nikaho Highland Wind Farm in Aichi Prefecture where Japan’s National Institute of Polar
Research (NIPR) will put it to the test before installing it at its Antarctic research station. The
NIPR deal is all part of Japan’s goal under the Kyoto Protocol to tap renewable energy sources
and bring its greenhouse gas emissions down 6% below 1990 levels. As part of that equation
Japan had hoped to produce 3,000 MW of wind power annually by 2010 but with only 1,880
MW of annual output under its belt as of 2008 it is woefully shy of the mark. According to
statistics from the Global Wind Energy Council, Japan doesn’t even make it to the top ten list of
world wind power producers. Among the major obstacles to wind power in this resourcestrapped island nation, including typhoons, grid integration, and red tape, is a dearth of local
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turbine suppliers. Nippi should give the country a leg up in overcoming that last hurdle as the
aerospace company aims to take wind power in Japan to new heights.

6.18 Is It Possible To Convert To 100% Wind Power?
With all the talk of going green, the question had been thrown out many times
will ever be a time that we can use nothing but renewable energy to power our world.
small island in Denmark is trying answer that question with a resounding yes as they
up every single day via nothing but wind power. The Danish island is the ideal
setting as the wind literally never stops blowing. The North Sea offers the
perfect opportunity to capitalize on the winds that come off of the
sea and for them to use wind power as their primary source
power. As a matter of fact, the wind power that they are
using is
ONLY source of power.

if there
A
power

of
their

Samso Island has about 4,000 people who
reside on the island and they have a direct stake in
how well this project works out. You see, the residents are the ones
that own shares in most of the windmills that are being used to power the island. That being the
case, they don’t mind the noise of the windmills as the blades are whipping around to create
electricity.
While the naysayers of the world would argue that this is great on an island, but how
would it work in a city, they need only know that this “island” is far larger than Manhattan, NY.
It gives hope that one day, regardless of the location or size, that an entire US city can use some
sort of renewable energy to get their power. To be able to erase the entire carbon footprint can
actually become a reality.
The one thing that holds many of these projects back is the financing of them. They can
be quite expensive to get rolling, but because of islands like Samso, improvements will continue
to be made and over time, these prices will come down. We just need to keep plugging away and
sooner or later the world is going to come around to greener way of thinking

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CHAPTER 7
ASSESSMENT OF WIND POWER POTENTIAL FOR COASTAL AREAS OF
PAKISTAN
Introduction
There is rising need for alternate and renewable sources of energy, especially in developing
countries,
Whose progress and economic growth may strongly be indexed to its development. With the ever
increasing growth in energy consumption and rapidly depleting fossil fuel reserves, it is feared
the world will soon exhaust its fossil fuel reserves.
Pakistan is an energy deficient country and each year spends a large amount of its foreign
exchange to
import oil, to meet its energy requirements [1]. Thus the need to develop alternate energy
resources has
become inevitable. The oldest and most widely used renewable energy resources are solar and
wind, which have shown prospects and potential for efficient utilization. In the recent past, wind
energy has emerged as clean, abundant, affordable, inexhaustible and environmentally benign
source of energy. This is getting worldwide attention with the development and availability of
inexpensive technology that allow its easy conversion into useful energy [2, 3].
Wind energy has the advantage that it can be utilized independently, and deployed locally in rural
and remote areas. Thus the location far away from the main grid finds wind suitable for
generating electricity and pumping water for irrigation purpose [4]. Unfortunately, at present
there is no share of wind energy in the energy mix of Pakistan, whereas countries like Germany,
United States, India and China have successfully setup wind energy sources.
Coastal areas and mountains with high wind potential are considered most suitable for wind
energy utilization. Therefore this study aims in investigating the prospects of harnessing and
useful conversion of wind energy potential for the coastal area of Pakistan.
The coast of Pakistan is about 1,120 kilometer long and has a population of about 10 million
people [5].
It is very expensive to connect small villages to
the national electric grid because of the huge
infrastructure costs involved. According to the
experts,
WAPDA
(Water
and
Power
Development Authority, Pakistan) does not have
enough electricity to supply them. The only way
many in the coastal areas can be supplied is
through the use of wind power, because high
wind is always available nearly all year round in
these areas. [5]
Table 1 lists the geographic locations involved this study; and Table 2 gives the monthly mean,
maximum, minimum and annual wind speeds.
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Table 2. Monthly mean, maximum, minimum and annual wind speed for coastal locations of
Pakistan. in m/sec
This study gives a preliminary investigation of the potential of wind power generation employing
wind speed data of six years (1995-2000) for selected coastal areas of Pakistan. The maximum
available and extractable wind power is also calculated employing different blade diameters for
slow and fast wind machines.
To test the power generation feasibility, two test aero generators are considered: one having
Vci = 2.5 msec−1
and
Vr = 5.3 msec−1;
the other having
Vci = 3.5 m_sec−1 and Vr = 8.5.
Parameters Vci and Vr are the cut-in speed and rated speed of the wind machine, respectively

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7.1 Data and Methodology
The data for this study was obtained from Pakistan Meteorological Department, Karachi. The
data consisted of six years duration (1995 to 2000): monthly average wind speed measured at a
height of 10 meters.
Generation of power from a windmill requires continuous flow of wind at a rated speed. This is
difficult to accomplish because wind by its very nature is not constant and does not prevail at a
steady rate, but in fact fluctuates over short periods of time. The speed of wind is also dependent
on height above the ground.
In order to estimate the wind speed at any height, we employ the Hellmann exponent law [6]:
V (h)/V10 = (h/10) α

(1)

where V (h )is the wind speed at height h, and V10 is the wind speed at 10 m height and α is the
Hellmann exponent. For flat and open areas, α = 1/7. The available power in the wind per unit
area at any wind
speed may be estimated as [7]
P = 1/2ρV3

(2)

where ρ is the air density, which was assumed to be 1.225 Kgm−3and V3 is monthly mean wind
speed in
msec−1. This available power cannot be totally extracted by any wind machine. The maximum
extractable power from any wind machine is limited by the Betz relation [8], which assigns the
power coefficient
C = 16/27
for the maximum performance of a wind machine.
Maximum extractable power per meter is given as
Pmax = 1/2ρCpV3 Wm−2

(3)

7.2 Statistical models
For the prediction of energy output of a wind energy conversion system, among the most
important of data is the wind speed frequency distribution. Among the statistical models
developed so far, Weibull function gives good fit to the observed wind speed data [9]. Wentink
[9], after comparing the Weibull function with other distribution, such as Rayleigh distribution,
Planck's frequency distribution, and Gamma function, concluded that Weibull distribution gave
the best _t to the wind speed data. Other investigators,
Justus et al. [10], Peterson et al. [11] and Rehman [12] also confirmed the superiority of Weibull
distribution function over others by testing it for a number of stations in U.S.A. and Saudi
Arabia.

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7.3 Weibull distribution function
Weibull distribution function is a two-parameter function expressed a
P (V) = k/c (v/c) k-1 exp{−(v/c)k}
(4)
where k is the shape factor, c is the scale parameter and v is the average wind speed.
There are several methods to calculate these parameters as reported by Stevens and Smulders
[13]. They employed five different methods (method of energy pattern factor, the maximum
likelihood method, Weibull distribution function, percentiles, etc.) for the purpose and obtained
the same results in each case. The method adopted in this paper is due to Hennessey [14], for
being simple and easily available, employing the values of mean wind speed v and standard
deviation σ. Using v and σ via the relation
k = (σ/v)-1.086
(5)
one obtains the shape factor k, from which scale parameters c is calculated as
c = v/ Ƭ (1 + 1/k)
(6)
where Ƭ is the gamma function.
7.3.1 Results and Discussion
Since the second half of the 19th century, multi-bladed low speed wind turbines have been used
in Europe and North America. In this type of machine, the number of blades varies from 12 to 24
and it covers the whole face of the wheel, and equipped with a tail vain to keep the machine
facing the wind. Slow wind machines (SWM) are well adapted to low wind speed. They start
easily with wind speeds ranging from 2 to 3 m sec−1; however, the starting torque is relatively
high. SWM is most often used for the extraction of water from deep wells. The optimal rotational
speed N (in rotations per m−1) is 19V /D where V is the wind speed in m_sec−1 and D is the
diameter [15].
An 18 bladed horizontal axis slow wind turbine having blade diameters 5 to 10 m was selected
for the study. The maximum power likely to be produced by this type of machine can be
calculated via the equation
P = 0.15D2 V3
(7)
where P is power in watts, D is diameter in meters and V is in m_sec−1.Of fast wind machines
(FWM), the number of blade is much more limited, usually varying from two to four. These
wind machines are much lighter than SWM, and they need a higher wind speed to start up,
usually 4 to 5 m sec−1 being necessary. As expected, the rotational speed is much faster than
SWM. FWM is usually employed in the generation of electricity. The optimal rotational speed N
(revolutions per minute) for FWM is 115V /D, where V is the wind speed in msec−1 and D the
diameter in meters.
A three-bladed horizontal axis fast wind machine having blade diameters 5 to 10 m has been
chosen.
The maximum power likely to be produced by this machine can be calculated by using the
equation [15]
P = 0.20 D2 V3
(8)
where P is expressed in watts, D is in meters, and V is in msec−1. The power output for slow and
fast wind machine using different blade diameter for all stations are shown in Tables 3 and 4. The
power output has been estimated using maximum and minimum wind speeds per the locations.
79

Figures 1 and 2 gives the power curve for 4 KW and 20 KW aero-generators, where the rated
wind speed has been estimated using the expression [16]
Vci = (0.15)1/3 Vr
(9)
Here Vci is the cut-in and Vr is rated wind speed of the machine. The rated wind speed for a 4
KW wind machine is 5.3 msec−1 and for 20 KW wind machine it is 8.5 msec−1. While the cutin speed Vci of these machines are 2.5 msec−1, 3.5 msec−1, respectively [16]. The generator
will not generate power below Vci and wind machine output will be constant at the rated speed.
Shown in Figure 3 is the variation of mean monthly wind speed for the selected coastal areas:
Karachi, Ormara, Jivani & Pasni. For Karachi the wind speed is lower during the period
November, December and January. It is higher during monsoon months, i.e. June, July, August
and September. The maximum value of 5.9 msec−1 is recorded in June.

80

81

The wind speed pattern for Karachi and Ormara is nearly identical. It is observed that the wind
speed at Jivani is higher during the period of March to August, when it ranges from 5.3 msec−1
to 6 msec−1; and at Pasni the peak months are April, May and June [17] as these months show
the maximum wind speed of
8.5 msec−1 whereas annual average is 6.3 msec−1 and the lowest observed value is 3.9 msec−1.
The coastal areas exhibit strong variations during their seasonal cycle: the wind speed being
lower during September to January, and high from February to August. This trend is peculiar for
the coastal locations as also shown by Rehman [18] and Ramachandra et al. [4] for coast of
Saudi Arabia and Southern India. The annual wind speed pattern is shown in Figure 4. Among
annual averages, Pasni shows higher value of wind speed, and thus can be rated a better choice
for wind energy utilization in comparison to other coastal sites such as Ormara, Jivani and
Karachi. Table 5 shows the shape and parameters k and c for these stations under study, whereas
Figure (5) shows the monthly variation of k for all these coastal stations. From figure it is
apparent that for Karachi, Ormara and Pasni the shape factor k does not remain stable throughout
the year. The fluctuation is high. For Karachi, the minimum k is 3.1 in the month of January and
maximum value is 17.4 for August. For Ormara the minimum is 2.2 in December and the
maximum is 8.4 in June, while for Pasni minimum is 6.7 in March and maximum is 12.6 in June.
For Jivani the wind speed remains smooth throughout the year. The minimum k is 2.6 in March
and maximum is 4.6 in April. From Figures (6) and (7) It is observed that a 4 KW wind machine
can work efficiently for all the coastal stations whereas
20 KW wind machine will only be useful for Pasni and Jivani since the wind speed for Karachi
and Ormara is below the cut-in speed of the machine.

82

83

84

7.3.2 Conclusion
Start here next from the assessment of wind power potential for four coastal locations of Sindh
and
Baluchistan (Karachi, Ormara, Jivani and Pasni) it is observed that the annual wind speed pattern
in
Karachi is same (though on the lower side); and Pasni and Jivani are observed to have the higher
wind speeds. The expected power output of slow and fast wind machines is also higher for these
stations.
Although a 4 KW wind generator can be used efficiently throughout the year for all locations,
there is a limitation for the use of 20 KW generators. This generator can only be used for Pasni
and Jivani, as it requires high wind speed for operation. In the final conclusion, Pasni and Jivani
are recommended as the most prospective sites for use with a 4 KW and 20 KW wind machines.
The locations of Karachi and
Ormara can utilize wind power throughout the year using 4 KW wind machines only.
Utilization of wind energy potential for the coastal sites to optimal conversion, using proper wind
machine will be beneficial and economically feasible for water lifting and small scale power
generation.

7.4 Acknowledgement
The Authors are thankful to Pakistan Meteorological Department, Karachi Office, for providing
wind data for coastal areas.

85

7.5 References
[1] Pakistan Energy Year Book, Ministry of Petroleum & Natural Resources, Hydrocarbon
Development Institute of Pakistan, (Govt. of Pakistan. 2004).
[2] W. E Alnaser and A. Al. Karaglisuli, Renewable Energy, 21, (2000), 247.
[3] W. E Alnaser, Renewable Energy, 3(2/3), (1993), 185.
[4] T. V. Ramachandra, D.K. Subramanium and N.V.Joshi, Renewable Energy, 2, (1997), 585.
[5] J. A. Khan, Rehber Publisher, The Climate of Pakistan, (Pakistan. 1993).
[6]
P.
J.
Musgrove,
Solar
and
Wind
Technology,
4,
(1987),
37.
[7]
M.
Rizk,
Solar
and
Wind
Technology,
4,
(1987),
491.
[8] A. Betz, Windenergie und Ihre Anwendung Durch Wind Muhler Vanderhoeck and Ruprecht,
(Gottingen. 1942).
[9] Wentink, Final Report, (1976), Report no.
NSF/RANN /SE/AER 74-0039 /R-76/1, Geophysical Institute, University of Alaska.
[10] B. Justus, W. R. Hangraves and A. Yaleen, J. Appl. Meteor., 15, (1976), 673.
[11] F. I. Peterson, I. Frocus, S. Frandsen and K. Hedyard., Wind Atlas for Denmark, RISO,
(Denmark. 1981).
[12] Sha_qur Rehman, T. O. Halwani and Tahir Hussain, Solar Energy, 53, 6, (1994), 473.
[13] M. J. Stevens and P. T. Smulders, Wind Engg., 3, (1979), 132.
[14] J. P Hennessey, Wind Engg., 2, (1978), 156.
[15] Dessire LE, Gouries Wind Power Plant, Theory & Design, (Pergamon Press, New York,
U.S.A. 1982), p. 47.
[16] M. M. Pandey and P. Chandra, Solar & Wind Technology., 3, (1986), 135.
[17] M. Akhlaque Ahmed and Firoz Ahmed, Journal of Research Science, 15, 4, (2004), BZU,
455.
[18] Sha_qur Rehman and Aftab Ahmed, Energy, 29, (2004), 1105.

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