Solar Thermal Final

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solar thermal energy




Global environmental issues, such as climate change and deforestation, have
emerged as new challenges to people throughout the world. Many countries with aims to
become a low-carbon society through green growth achieved via green technologies and
green industries which enhance eco-efficiency while minimizing adverse environmental
The field of green technology encompassed a continuously evolving groups or
materials, from techniques for generating energy to non- toxic cleaning products. Green
Technology is the development and application of products, equipment and systems used to
conserve the natural environment and resources, which minimize and reduces the negative
impact of human activities. By definition, green technology is the technology that
environmental friendly and is created and used in a ways that conserves natural resources
and environment.
As we know green technology had rapidly developed. The goals that inform
developments in this rapidly grow field include sustainability, “Cradle to cradle” design,
source reduction, innovation, and viability. Sustainability is the meeting the need of human
need without compromising the future generation’s ability to meet their own needs. “Cradle
of cradle” design is the ending the “cradle to grave” cycle of manufactured products by
creating product that can be fully reclaimed or re-used. Source of reduction is changing the
patterns of production and consumption to reduce waste and pollution. Innovation is
developing alternative technology to replace the technologies that have damage human
health and environment. Meanwhile viability is creating a centre of economic activities
around technologies and products that benefit to the environment, speeding their
implementation and creating new careers that protect the earth.
Five criteria that mention the products, equipments or system was a green
technology is it minimize the degradation of the environment, it has zero or low green house
gas (GHG) emission, it is safe for use and promotes healthy and improved environment for
all forms of life, it conserves the use of energy and natural resources, and it promotes the
use of renewable resources. The four key area that significant progress and major
improvement is energy, building, water and waste management and transportation.
Nowadays, green technology is use into two categories. Firstly, those intended to deal with
global warming by either reducing greenhouse effect or potential harmful on the planet.
Second, that technology associated with establishing economic “sustainable growth”.


It is important to understand that solar thermal energy is not the same as solar panel
or photovoltaic technology. Solar thermal is a renewable energy that often known as the
other solar power. It is a carbon-free, renewable alternative to the power we generate with
fossil fuels like coal and gas. Solar thermal uses mirrors to focus sunlight on a liquid that turn
into steam and power a turbine. Solar thermal energy does not use heat directly from the
sun in order to produce energy and there are relatively simple process can store energy for
several hours after sundown. Solar thermal energy concentrates light from the sun to create
heat and the heat is use to generate engine, which turn the turbine to produce electricity.
The fluid used can be either liquid or gas. Steam engine, gas turbines, and stirling engines is
always used to move the turbine.
To produce solar thermal energy in a large quantity, there is a various technique use
to concentrate heat energy from the sun. The heat that we obtain is then used to boil water
to drive a steam turbine that generates electricity in much the same way as coal and nuclear
power plants, supplying electricity for thousands of people. To obtain solar thermal energy,
panels that contain tubing which water circulates through it are positioned to maximise the
absorption of heat from the sun. The first technique, long troughs of U-shaped mirrors focus
sunlight on a pipe of oil that runs through the middle. The hot oil then boils water for
electricity generation. Another technique uses moveable mirrors to focus the sun's rays on a
collector tower, where a receiver sits. Molten salt flowing through the receiver is heated to
run a generator.
Solar energy panels are used to collect solar energy for heat. USA Energy
Information Administrator classified solar thermal collector into low-, medium-, and high-
temperature collectors. Low temperature collector is a flat plate that uses to heat swimming
pools. Medium temperature collectors also a flat plate but is used for heating water or air for
residential and commercial use. Meanwhile high temperature collectors concentrate sunlight
using mirrors or lenses and are generally used for electric power production. The most
common uses of these solar thermal panels are heating, drying and water distillation.
Water heating is the most common and widely used especially in the area that
receive high solar isolation. Domestic water heaters are usually found amongst wealthier
sections of the communities in developing countries. Many of the solar water heaters


available consists of a series of pipes that are painted black, sitting inside an insulated box
fronted with a glass panel. The pipe that is painted black is known as solar panel which is
function as heat collector. The fluid that is heated by the sun is then circulated through the
tank several times to raise the heat of the fluid to the required temperature.
Controlled drying is necessary for various types of products and crops including
grain, coffee, tobacco as well as some fruits, vegetables and fish. Many times drying is done
to enhance the quality of the product. Solar thermal energy is used to assist in the drying of
such products. As the temperature is raised, air passed through the compartment to remove
moisture from the fruit. Via solar drying crops can improve and protect the beneficial effects
of the health and nutrition of the crop.
Distillation or desalination used to purify drinking water in remote regions where
needed removing impurities such as fluoride and salt. This is done so by placing a glass or
transparent plastic cover over a shallow tray of water which has a black backing to trap the
solar energy. When the sun heats the water up it evaporates which then condenses on the
underside of the glass covering, this covering is at an angle so water drains off and the
impurities are trapped below, thus providing clean drinking water.
Heat in a solar thermal system is guided by five basic principles: heat gain; heat
transfer; heat storage; heat transport; and heat insulation. Here, heat is the measure of the
amount of thermal energy an object contains and is determined by the temperature, mass
and specific heat of the object. Solar thermal power plants use heat exchangers that are
designed for constant working conditions, to provide heat exchange.
Heat gain is the heat accumulated from the sun in the system. Solar thermal heat is
trapped using the greenhouse effect; the greenhouse effect in this case is the ability of a
reflective surface to transmit short wave radiation and reflect long wave radiation. Heat and
infrared radiation (IR) are produced when short wave radiation light hits the absorber plate,
which is then trapped inside the collector. Fluid, usually water, in the absorber tubes collect
the trapped heat and transfer it to a heat storage vault.
Heat is transferred either by conduction or convection. When water is heated, kinetic
energy is transferred by conduction to water molecules throughout the medium. These
molecules spread their thermal energy by conduction and occupy more space than the cold
slow moving molecules above them. The distribution of energy from the rising hot water to


the sinking cold water contributes to the convection process. Heat is transferred from the
absorber plates of the collector in the fluid by conduction. The collector fluid is circulated
through the carrier pipes to the heat transfer vault. Inside the vault, heat is transferred
throughout the medium through convection.
Heat storage enables solar thermal plants to produce electricity during hours without
sunlight. During days, heat is transfer to thermal storage medium in an insulated reservoir
and will be generate when there is low density of sunlight. Thermal storage mediums will be
discussed in a heat storage section. Rate of heat transfer is depending on the conductive
and convection medium as well as the temperature differences. High temperature difference
lead the heat transfer is faster than the low temperature difference.
Heat transport refers to the activity in which heat from a solar collector is transported
to the heat storage vault. Heat insulation is vital in both heat transport tubing as well as the
storage vault. It prevents heat loss, which in turn relates to energy loss, or decrease in the
efficiency of the system.
Heat storage allows solar thermal plant to produce electricity throughout day and
night. So, it potentially to replace both coal and natural gas fired power plants. In addition,
the utilization of generator is higher that reduce the cost. Heat is transferred to a thermal
storage medium in an insulated reservoir during the day, and withdrawn for power
generation at night. Thermal storage media include pressurized steam, concrete, a variety of
phase change materials, and molten salts such as sodium and potassium nitrate.
Steam accumulator
Heat that stores in tank by solar power tower is pressurized steam at 50 bars and
285 °C. When the temperature is higher, the steam will condense, but as the temperature is
lowered it will flashed back to steam. Storage is for one hour and not proven yet that the
storage more than one hour.
Molten salt storage
Molten salt is used in solar power systems because it is liquid at atmosphere
pressure, provide an efficient, low-cost medium in which to stored thermal energy, it
operating temperatures are compatible with today’s high temperature and high pressure
steam turbine and it is non-flammable and nontoxic. In de-coupling the collection of solar


energy from producing power, electricity can be generated in periods of inclement weather
or even at night using stored thermal energy in the hot salt tank and normally the tank can
stored the energy for a week.

Graphite heat storage
I. Direct
The proposed power plant in Cloncurry Australia will store heat in purified graphite.
The plant has a power tower design. The graphite is located on top of the tower. Heat
from the heliostats goes directly to the storage. Heat for energy production is drawn
from the graphite. This simplifies the design.
II. Indirect
Molten salt coolants are used to transfer heat from the reflectors to heat storage
vaults. The heat from the salts is transferred to a secondary heat transfer fluid via a
heat exchanger and then to the storage media, or alternatively, the salts can be used
to directly heat graphite. Graphite is used as it has relatively low costs and
compatibility with liquid fluoride salts. The high mass and volumetric heat capacity of
graphite provide an efficient storage medium.
Phase-change materials for storage
Phase Change Material (PCMs) offers an alternate solution in energy storage. Using
a similar heat transfer infrastructure, PCMs have the potential of providing a more efficient
means of storage. PCMs can be either organic or inorganic materials. Advantages of organic
PCMs include no corrosives, low or no under cooling, and chemical and thermal stability.
Disadvantages include low phase-change enthalpy, low thermal conductivity, and
flammability. Inorganic are advantageous with greater phase-change enthalpy, but exhibit
disadvantages with under cooling, corrosion, phase separation, and lack of thermal stability.
The greater phase-change enthalpy in inorganic PCMs make hydrate salts a strong
candidate in the solar energy storage field.


Solar Thermal Energy involves the technological process of heating water by utilizing
energy from the sun . Prior to the mid-2000s many solar experts had overlooked the benefits
of solar thermal as solar electric has been a high profile technology for commercial use. After
a series of studies by solar trade associations in Austria in 2004, these organizations began
to recognize that the potential of solar thermal has been greatly underestimated. By January
2005, Green Markets International found solar thermal energy is suitable used in wind farms
and hydro electric facilities as it will reduce the emission of greenhouse gas. They also
discovered that water heating is more cost-effective at reducing greenhouse gases rather
than solar electric.
Solar Water Heating has 4 to 5 times the power density of PV. An average 40
square foot Skyline Water Heater produces thermal energy in an amount equal to the energy
of a 2kW Photovoltaic system at a fraction of the cost. Solar Water Heating is a perfect
complement to a Photovoltaic system because it doubles the energy ouput of an average
2kW system, at a fraction of the cost.




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