Fuel cell
Content
Fuel cell
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a
chemical reaction with oxygen or another oxidizing agent. The first fuel cells were invented in
1838. The first commercial use of fuel cells came more than a century later in NASA space
programs to generate power for probes, satellites and space capsules. Since then, fuel cells have
been used in many other applications. Fuel cells are used for primary and backup power for
commercial, industrial and residential buildings and in remote or inaccessible areas. They are
also used to power fuel-cell vehicles, including forklifts, automobiles, buses, boats, motorcycles
and submarines. Fuel cells are different from batteries in that they require a continuous source of
fuel and oxygen/air to sustain the chemical reaction whereas in a battery the chemicals present in
the battery react with each other to generate an electromotive force. Fuel cells can produce
electricity continuously for as long as these inputs are supplied.
Every fuel cell also has an electrolyte, which carries electrically charged particles from one
electrode to the other, and a catalyst, which speeds the reactions at the electrodes. Hydrogen is
the basic fuel, but fuel cells also require oxygen. One great appeal of fuel cells is that they
generate electricity with very little pollution–much of the hydrogen and oxygen used in
generating electricity ultimately combines to form a harmless byproduct, namely water. Fuel
cells are a promising technology for use as a source of heat and electricity for buildings, and as
an electrical power source for electric motors propelling vehicles. Fuel cells operate best on pure
hydrogen. But fuels like natural gas, methanol, or even gasoline can be reformed to produce the
hydrogen required for fuel cells. Some fuel cells even can be fueled directly with methanol,
without using a reformer.
The purpose of a fuel cell is to produce an electrical current that can be directed outside the cell
to do work, such as powering an electric motor or illuminating a light bulb or a city. There are
several kinds of fuel cells, and each operates a bit differently. But in general terms, hydrogen
atoms enter a fuel cell at the anode where a chemical reaction strips them of their electrons. The
hydrogen atoms are now "ionized," and carry a positive electrical charge. The negatively charged
electrons provide the current through wires to do work. If alternating current (AC) is needed, the
DC output of the fuel cell must be routed through a conversion device called an inverter.
Types of fuel cells
1. Alkali fuel cells
Alkali fuel cells operate on compressed hydrogen and oxygen. They generally use a solution of
potassium hydroxide (chemically, KOH) in water as their electrolyte. Efficiency is about 70
percent, and operating temperature is 150 to 200 degrees C, (about 300 to 400 degrees F). Cell
output ranges from 300 watts (W) to 5 kilowatts (kW). Alkali cells were used in Apollo
spacecraft to provide both electricity and drinking water. They require pure hydrogen fuel,
however, and their platinum electrode catalysts are expensive. And like any container filled with
liquid, they can leak.
2. Molten carbonate fuel cells
Molten Carbonate fuel cells (MCFC) use high-temperature compounds of salt (like sodium or
magnesium) carbonates (chemically, CO3) as the electrolyte. Efficiency ranges from 60 to 80
percent, and operating temperature is about 650 degrees C (1,200 degrees F). Units with
output up to 2 megawatts (MW) have been constructed, and designs exist for units up to 100
MW. The high temperature limits damage from carbon monoxide "poisoning" of the cell and
waste heat can be recycled to make additional electricity. Their nickel electrode-catalysts are
inexpensive compared to the platinum used in other cells. But the high temperature also
limits the materials and safe uses of MCFCs–they would probably be too hot for home use.
Also, carbonate ions from the electrolyte are used up in the reactions, making it necessary to
inject carbon dioxide to compensate.
3. Phosphoric acid fuel cells
Phosphoric Acid fuel cells (PAFC) use phosphoric acid as the electrolyte. Efficiency ranges
from 40 to 80 percent, and operating temperature is between 150 to 200 degrees C (about 300
to 400 degrees F). Existing phosphoric acid cells have outputs up to 200 kW, and 11 MW
units have been tested. PAFCs tolerate a carbon monoxide concentration of about 1.5 percent,
which broadens the choice of fuels they can use. If gasoline is used, the sulfur must be
removed. Platinum electrode-catalysts are needed, and internal parts must be able to
withstand the corrosive acid.
4. Proton exchange membrane fuel cells
Proton Exchange Membrane (PEM) fuel cells work with a polymer electrolyte in the form of
a thin, permeable sheet. Efficiency is about 40 to 50 percent, and operating temperature is
about 80 degrees C (about 175 degrees F). Cell outputs generally range from 50 to 250 kW.
The solid, flexible electrolyte will not leak or crack and these cells operate at a low enough
temperature to make them suitable for homes and cars. But their fuels must be purified, and a
platinum catalyst is used on both sides of the membrane, raising costs.
5. Solid oxide fuel cells
Solid Oxide fuel cells (SOFC) use a hard, ceramic compound of metal (like calcium or
zirconium) oxides (chemically, O2) as electrolyte. Efficiency is about 60 percent, and
operating temperatures are about 1,000 degrees C (about 1,800 degrees F). Cells output is up
to 100 kW. At such high temperatures a reformer is not required to extract hydrogen from the
fuel, and waste heat can be recycled to make additional electricity.
Fuel cells today
The concept of a fuel cell was demonstrated in the early nineteenth century by a number of
scientists including Humphry Davy and Christian Friedrich Schönbein. William Grove, a
chemist, physicist and lawyer, is generally credited with inventing the fuel cell in 1839. Fuel
cell technology offers clean, efficient, reliable power generation to almost any device
requiring electrical power. Fuel cells are used in a wide range of portable, stationary and
transport applications, from battery chargers to home heating and power to cars. Arguably,
fuel cells represent the most versatile energy solution ever invented. Fuel cells are used in a
large number of different applications. It is mostly used for portable power generation,
stationary power generation, and power for transportation.
Fuel cells are applicable in following areas:
a. Residential heat and power
A wide variety of technologies are available to provide heating and electricity to our homes.
In countries with a stable electricity grid, lighting and heating are taken for granted; but the
desire for cleaner energy is highlighting how dirty grid electricity is around the world, and
concerns over the future of nuclear power are adding to the debate. Many countries also have
a network that distributes natural gas, and off-grid options such as heating oil or LPG are
available, but when burned in conventional boilers these fuels only produce heat.
Combined heat and power (CHP) is the term used for when electricity and heat are coproduced from a single source of fuel, such as natural gas, and when done on a residential
scale this is known as micro-CHP. Micro-CHP can replace or supplement grid electricity as a
form of distributed generation of power in customers’ homes, and producing energy at the
point of use avoids transmission losses.
b. Uninterruptible power supply
Events such as Hurricane Katrina in 2005 have focused attention on the availability and
reliability of telecommunications services worldwide. Both wireless and wireline
communications are expanding globally, so the provision of reliable, economical power is
vital. Terrestrial Trunked Radio (TETRA) networks in use by emergency services, military
personnel and government agencies require total system reliability during emergencies, when
loss of communication would exacerbate an already critical situation. The rapid expansion of
cellular networks in countries without more traditional land-based telephone systems is also
demanding the provision of reliable power supplies and this market is one of the fastest
growing worldwide. The choice of backup power technology for telecommunications
therefore has a direct impact on the everyday life of people around the world. Traditional
solutions have included generators and batteries, but issues of maintenance, noise, pollution,
size, insufficient runtime, remote monitoring difficulties and operation under extreme
conditions all pose problems for these technologies. This has led to interest in fuel cell
technology for this application, and fuel cell backup power units are now being installed in a
number of countries.
c. Converting waste to energy
Waste management is a necessity wherever people live, but traditionally waste is viewed as a
problem, something that pollutes and needs reducing or mitigating. What if this mindset
could be changed such that we value our waste as a source of bioenergy? Waste contains
significant quantities of energy and, if we could harness this close to where the waste is
generated and convert it to a useable form, it could provide both a distributed source of
electricity and contribute to solving the global problem of waste.
Biogas is widely produced from processed municipal waste using anaerobic digesters and
then is usually combusted. However, biogas can be fed to a fuel cell to produce electricity
and heat.
d. Renewable energy system
Generating renewable electricity is an important way to reduce carbon dioxide (CO2)
emissions and many countries are installing wind and solar power plants to help meet targets
for cutting CO2. One drawback of these energy sources is their variability: the wind tends to
blow intermittently and solar power is only available during the daytime. Hence renewable
power plants either have to be over-engineered to take account of this lower capacity factor,
or they must be supported by spinning reserve power stations, typically fast-response opencycle gas turbines – which goes against the environmental aims of the projects.
Ideally, excess renewable energy generated during times of plenty can be stored for use
during periods when sufficient electricity is not available. But storing this energy is a difficult
task: batteries and similar technologies perform well over short timescales, but over periods
of weeks or months a different approach is necessary. Energy storage in the form of hydrogen
is one such possibility: excess electricity is fed into an electrolyser to split water into its
constituent parts, oxygen and hydrogen. The hydrogen is then used in fuel cells to produce
electricity when needed, releasing the stored energy back to the grid.
e. Prime power generation
A national electricity grid must always be able to meet the needs of its users. This requires it
to be: stable, maintaining the required electrical frequency (50 Hz in the UK); balanced,
continuously matching supply to demand; and adequate, ensuring total generation capacity is
never outstripped by demand.
Grid supply is split into three tiers: base, intermediate, and peak load. Baseload is a
permanent minimum amount of electricity that is required at all times and is met by
predictable, long-running power sources, usually coal-fired plants. Intermediate power plants
are more flexible and can vary output to suit the needs of the grid, but at a cost to the system
operator. These include nuclear, hydroelectric and gas/diesel combined cycle turbine plants.
Finally, peak power generators are called upon to meet short-term spikes of requirement and
as such must be able to start up and provide power instantaneously.
f. Vaolrising By Product Hydrogen
Electrochemical processes, such as the industrial production of caustic soda and chlorine, use
large quantities of electricity which contribute significantly to production costs, up to 70% in
some cases. They also produce hydrogen as a waste product (see diagram), which is either
combusted or vented to the atmosphere. Fuel cells offer a highly efficient method of utilizing
this hydrogen to produce electricity, offsetting much of a plant’s electrical demand whilst at
the same time reducing emissions.
Applications
a. Transport
Fuel Cell today defines fuel cells for transport as any units that provide propulsive power to a
vehicle, directly or indirectly (i.e. as range extenders). This includes the following
applications for the technology:
Forklift trucks and other goods handling vehicles such as airport baggage trucks etc.
Two- and three-wheeler vehicles such as scooters
Light duty vehicles (LDVs), such as cars and vans
Buses and trucks
Trains and trams
Ferries and smaller boats
Manned light aircraft Unmanned aerial vehicles (UAVs) and unmanned undersea
vehicles (UUVs), for example, for reconnaissance.
The fuel cell bus sector is showing year-on-year growth, with more prototypes being
unveiled. Successful deployments have taken place in Europe, Japan, Canada and the USA but
the high capital cost is still a barrier to widespread adoption. However, it is hoped that soon after
2014 fuel cell bus prices will be comparable to diesel-hybrid bus prices.
b. Portable
Fuel Cell today defines portable fuel cells as those which are built into, or charge up, products
that are designed to be moved. These include military applications (portable soldier power, skid
mounted fuel cell generators etc.), Auxiliary Power Units (APU) (e.g. for the leisure and trucking
industries), portable products (torches, vine trimmers etc.), small personal electronics (mp3
players, cameras etc.), large personal electronics (laptops, printers, radios etc.), education kits
and toys.
Fuel cells are being sold commercially for these applications, APU, small personal electronics,
education kits and toys (these we classify as micro fuel cells). Fuel Cell today defines a micro
fuel cell as a unit with a power output of less than 5 W. The difference between small and large
personal electronics is that the smaller devices, such as cameras or mobile phones only draw
around 3 W of power, whereas a laptop can use up to 25 W, requiring a fuel cell of higher power
density. Portable fuel cells typically replace or augment battery technology and exploit either
PEM or DMFC technology. PEM fuel cells use direct hydrogen, with no point-of-use emissions,
whereas DMFCs emit small quantities of CO2. The main drivers for fuel cells in portable
applications are as follows:
c.
Off-grid operation
Longer run-times compared with batteries
Rapid recharging
Significant weight reduction potential (for soldier-borne military power)
Convenience, reliability, and lower operating costs also apply
Stationary
Fuel Cell today defines stationary fuel cells as units which provide electricity (and sometimes
heat) but are not designed to be moved. These include combined heat and power (CHP),
uninterruptible power systems (UPS) and primary power units.
CHP units are sized between 0.5 kW and 10 kW, use either PEM or SOFC technology and take
advantage of the fact fuel cells generate heat alongside electricity. By making use of this heat, for
example to make hot water, the overall efficiency of the system increases. Fuel cells are also
more efficient at generating electricity which gives CHP units overall efficiencies of 80-95%.
Residential CHP units have been deployed extensively in Japan with more than 10,000
cumulative units by the end of 2010 providing home power and heating. South Korea has also
deployed CHP units for residential use but, as in Japan, their purchase still relies upon
government subsidies.
UPS systems provide a guaranteed supply of power in the event of grid interruption; this market
can be divided into five sub-sectors:
Off-line short run-time systems for telecommunication base stations
Off-line extended run-time systems for critical communication base stations such as
Terrestrial Trunked Radio (Tetra) networks
Off-line extended run-time rack mountable systems for data centers
On-line rack mountable systems for data centers
Off-line systems for residential use.
Large stationary refers to multi-megawatt units providing primary power. These units are being
developed to replace the grid, for areas where there is little or no grid infrastructure, and can also
be used to provide grid expansion nodes.
Fuel cell development in China
Fuel cells are not a new technology to China, but in fact have been researched and developed
since the 1970s, when a prototype alkaline fuel cell was developed for use in its domestic space
program. This unit never left the confines of the laboratory, but the interest in fuel cells remained
with PEMFC technology emerging as the dominant technology. Through the 1990s research
focused on automotive applications, but attempts to gain interest from commercial partners
proved fruitless. Around 1999, the government extended the electric vehicle R&D investment to
include fuel cell technology, and since 2000, a number of demonstration programs have taken
place raising the profile of fuel cells in the eyes of both the government and the public. Current
academic and commercial interest in fuel cells ranges from very small portable units for
powering torches and consumer electronics, through larger stationary systems for backup power
and all the way up to fuel cell electric vehicles and fuel cell buses.
Opportunities for fuel cells in China Stationary Systems
The market for stationary power has huge potential in China and in the backup sector for
telecommunications power it is beginning to gather momentum. China is home to the world’s
most rapidly expanding mobile phone network, but at the same time does not have an integrated
national grid system. China’s disjointed, and in some areas unreliable, grid system is composed
of power clusters spread across eight regions and controlled by three main companies. Backup
power cannot therefore be guaranteed and so battery backup is widely used in the
telecommunications industry. There are 30 to 50 billion RMB ($4.7 to $7.9 billion) of battery
sales per year in China for the telecoms industry alone, and currently more than one million cell
sites in the country. Growth of new cell sites currently runs at ten to twenty thousand per year.
Fuel cells in electric power train
Fuel cell and battery electric vehicles both use electric drivetrains, but where battery
electric vehicles (BEV) power their motors solely with batteries, fuel cell electric vehicles
(FCEV) are hybrids, powered by a hydrogen fuel cell with a small battery. Both vehicle types
benefit from near-silent operation, excellent drivability and no tailpipe emissions, or indeed no
tailpipe at all.
BEV is best realized as smaller cars in applications that require a continuous range of less than
200 kilometers (125 miles): city run-arounds and second cars. Restricted range and long
recharging times have limited their uptake to date. Plug-in hybrid electric vehicles (PHEV)
provide a bridge between conventional cars and electric vehicles, offering an electric drivetrain
with the convenience of using conventional fuel; however they can never be truly zero-emission.
FCEV provide all of the benefits of electric vehicles combined with the utility of a combustionengine car: they can be refueled in minutes by the driver using a nozzle similar to a conventional
fuel pump and then driven for hundreds of kilometers before they need refueling again. A large
proportion of road fuel is used in large and high-mileage vehicles and only fuel cells are proven
as a zero-emission power source for these vehicles. The mix of conventional conveniences and
electric advantages that FCEV can offer is a compelling proposition for personal transportation.
Solid oxide fuel cells: Most widely used fuel cells
SOFCs have recently emerged as a serious high temperature fuel cell technology. They promise
to be extremely useful in large, high-power applications such as full scale industrial stations and
large-scale electricity-generating stations. Some fuel cell developers see SOFCs being used in
motor vehicles. A SOFC system usually utilizes solid ceramic as the electrolyte and operates at
extremely high temperatures (600–1000°C). This high operating temperature allows internal
reforming, promotes rapid electro catalysis with non-precious metals, and produces high quality
byproduct heat for co-generation. Efficiencies for this type of fuel cell can reach up to 70% with
an additional 20% as heat recovery. SOFCs are best suited for provision of powering utility
applications due to the significant time required to reach operating temperatures.
Solid oxide fuel cell history
Emil Baur, a Swiss scientist and his colleague H. Preis experimented with solid oxide
electrolytes in the late 1930s, using such materials as zirconium, yttrium, cerium, lanthanum, and
tungsten oxide. The operation of the first ceramic fuel cell at 1000°C, by Baur and Preis, was
achieved in 1937. In the 1940s, O. K. Davtyan of Russia added monazite sand to a mix of
sodium carbonate, tungsten trioxide, and soda glass, in order to increase the conductivity and
mechanical strength. Davtyan’s design, however, also experienced unwanted chemical reactions
and short life ratings. By the late 1950s, research into solid oxide technology began to accelerate
at the Central Technical Institute in The Hague, Netherlands, Consolidation Coal Company, in
Pennsylvania, and General Electric, in Schenectady, New York. A 1959discussion of fuel cells
noted that problems with solid electrolytes included relatively high internal electrical resistance,
melting, and short-circuiting, due to semi conductivity. Not everybody gave up on solid oxides,
however. The promise of a high temperature cell that would be tolerant of carbon monoxide and
use a stable solid electrolyte continued to draw modest attention. Researchers at Westinghouse,
for example, experimented with a cell using zirconium oxide and calcium oxide in 1962.More
recently, climbing energy prices and advances in materials technology have reinvigorated work
on SOFCs, and a recent report noted about 40 companies working on these fuel cells that include
Global Thermo electric’s Fuel Cell Division, which is developing cells designed at the Julich
Research Institute in Germany. Cermatec Advanced Ionic Technologies is working on units up to
10 kW in capacity, running on diesel fuel, which would be used for mobile power generation.
The US Department of Energy announced that a SOFC-micro turbine co-generation unit has
been evaluated, since April 2000, by the National Fuel Cell Research Center and Southern
California Edison. The fuel cell was built by Siemens Westinghouse and the micro turbine by
Northern Research and Engineering Corporation. In a year of actual operating conditions, the
220 kW SOFC, running on natural gas is achieving an efficiency of 60%. Also, a world record
for SOFC operation, roughly eight years, still stands, and the prototype cells have demonstrated
two critical successes: the ability to withstand more than 100 thermal cycles, and voltage
degradation of less than 0.1% per thousand h. Moreover, a 140 kW peak power SOFC
cogeneration system, supplied by Siemens Westinghouse, is presently operating in the
Netherlands. This system has operated for over 16,600 h, becoming the longest running fuel cell
in the world. The first demonstration of the commercial prototype cells in a full scale SOFC
module is equally significant.
Design and operation of SOFCs
SOFCs differ in many respects from other fuel cell technologies. First, they are composed of allsolid-state materials. Second, the cells can operate at temperatures as high as 1000°C,
significantly hotter than any other major category of fuel cell. Third, the solid state character of
all SOFC components means that there is no fundamental restriction on the cell configuration.
Cells are being constructed in two main configurations, i.e., tubular cells or rolled tubes, such as
those being developed at Westinghouse Electric Corporation since the late 1950s, and a flatplates configuration adopted more recently by many other developers and employed today by the
electronics industry.
A SOFC consists of two electrodes sandwiched around a hard ceramic electrolyte such as the
remarkable ceramic material called zirconia.Hydrogen fuel is fed into the anode of the fuel cell
and oxygen, from the air, enters the cell through the cathode. By burning fuel containing
hydrogen on one side of the electrolyte, the concentration of oxygen is dramatically reduced. The
electrode on this surface will allow oxygen ions to leave the electrolyte and react with the fuel
which is oxidized, thereby releasing electrons (e). On the other side of the plate, which is
exposed to air, an oxygen concentration gradient is created across the electrolyte, which attracts
oxygen ions from the air side, or cathode, to the fuel side, or anode. If there is an electrical
connection between the cathode and the anode, this allows electrons to flow from the anode to
the cathode, where a continuous supply of oxygen ions (O2) for the electrolyte is maintained,
and oxygen ions from cathode to anode, maintaining overall electrical charge balance, thereby
generatinguseful electrical power from the combustion of the fuel.
Fuel for SFOCs
SOFCs require only a single partial oxidation reformer to pre-process their fuel, which can be
gasoline, diesel, natural gas, etc. The nature of the emissions from the fuel cell will vary
correspondingly with the fuel mix. Using hydrocarbons, for which a supply infrastructure is
currently available, offers a variety of advantages over446 A.B. Stambouli, E. Traversa /
Renewable and Sustainable Energy Reviews 6 (2002) 433–455using hydrogen. First of all,
hydrocarbons are much easier to transport and to store because they are in a stable state which
requires no processing before use. They are also more efficient at producing energy. Methane for
example yields eight electrons per molecule whereas hydrogen only yields two electrons energy.
This advantage could be magnified with the use of more complex hydrocarbons, such as pentane.
Benefits of SFOCs
Energy security: reduce oil consumption, cut oil imports, and increase the amount of the
country’s available electricity supply.
Reliability: achieves operating times in excess of 90% and power available99.99% of the
time.
Low operating and maintenance cost: the efficiency of the SOFC system will drastically
reduce the energy bill (mass production) and have lower maintenance costs than their
alternatives.
Constant power production: generates power continuously unlike backup generators,
diesel engines or Uninterrupted Power Supply (UPS).
Choice of fuel: allows fuel selection, hydrogen may be extracted from natural gas,
propane, butane, and methanol and diesel fuel.
SOFCs and their environmental impact
Recently, it created attention towards the utility industries especially for generation of heat and
power. The environmental impact of SOFC use depends upon the source of hydrogen-rich fuel
used. If pure hydrogen is used, fuel cells have virtually no emissions except water and heat. As
mentioned earlier, hydrogen is rarely used, due to problems with storage and transportation, but
in the future many people have predicted the growth of a solar hydrogen economy. In this
scenario, photovoltaic cells would convert sunlight into electricity. This electricity would be used
to split water (electrolysis) into hydrogen and oxygen, in order to store the sun’s energy as
hydrogen fuel. In this scenario, SOFCs generating stations would have no real emissions of
greenhouse or acid gases, or any other pollutants.
It is predominantly during the fuel processing stage that atmospheric emissions are released by a
fuel cell power plant. However, the high efficiency of SOFC results in less fuel being consumed
to produce a given amount of electricity, which corresponds to a lower emission of carbon
dioxide CO2, the main greenhouse gas responsible for global warming. When hydrogen from
natural gas is used as a fuel, SOFCs have no net emissions of CO2because any carbon released is
taken from the atmosphere by photosynthetic plants. A reduction of carbon dioxide emissions by
more than 2 million kg per year can be obtained. Moreover, emissions from SOFC systems will
be very low with near-zero levels of NOx, Sox and particulates, therefore eliminates 20,000 kg
of acid rain and smog-causing pollutants from the environment. In any case SOFCs generally
provide the lowest emissions of any non-renewable power generation method such as traditional
thermal power plants. This is very important with regard for energy related environment
concerns. When combined with a heat engine that uses any waste heat, SOFCs are the most clean
and efficient devices available for this purpose.
SOFC can also provide high-quality waste heat that can be used to warm the home or provide
refrigeration and air conditioning without harming the environment. If CO2 can be removed at
the source for disposal elsewhere, the SOFC really would become the ultra-high efficiency, zero
emissions power plant of the 21st century.
Applications of SFOCs
Combined with low noise and ability to utilize readily-available fuel such as methane and natural
gas, SOFC generators are best suited for the provision of power inutility applications, due to the
significant time required to reach operating temperatures, and can have broad applications
ranging from large-scale power plants to smaller home-scale power plants and
portable/emergency power generators. SOFCs could be used in many applications. Some of them
are:
High power reliability: computer facilities, call centers, communication facilities, data
processing centers high technology manufacturing facilities.
Emission minimization or elimination: urban areas, industrial facilities, airports, zones
with strict emissions standards.
Limited access to utility grid: rural or remote areas, maximum grid capacity.
Biological waste gases are available: waste treatment plants, SOFC can convert waste
gases (methanol from biomass) to electricity and heat with minimal environment
intrusion.
Future of SFOCs
Focusing their efforts on SOFCs, which have been on the verge of commercial viability for
years, researchers around the world are making a concerted effort in the development of suitable
materials and the fabrication of ceramic structures which are presently the key technical
challenges facing SOFCs. Programs are underway in Japan and in the US that use a relatively
simple ceramic process to develop a thin film electrolyte that decreases the cell resistance, and
both double the power output and significantly reduce the cost of SOFCs. There is also a current
effort in integrating the SOFCs and developing a novel stacking geometry. The demonstration of
low-temperature SOFC operation directly on methane, signals an important new opportunity for
making simple, cost-effective power plants . The global SOFC making company continues to
realize very significant improvements in basic fuel cell design. A measure of their success is the
realization of a 48.6% improvement in single cell power densities which represents the highest
published power densities for commercial-sized SOFCs in the world. Changes in cell
composition and design have resulted in these improved power densities. Higher power densities
contribute to lower weight, size and cost of fuel cell systems. SOFCs could someday be suitable
for small-scale residential market applications if ultimate cost goals of $1000/kW are reached.
Energy exploitation of fossil fuels is reaching its limits. Future alternatives must therefore be
developed for long-term and environmental-friendly energy supply needed by a constantly
growing world population. SOFCs provide highly efficient, pollution free power generation.
Their performance has been confirmed by successful operation power generation systems
throughout the world. Electrical-generation efficiencies of 70% are possible nowadays, along
with a heat recovery possibility. SOFCs appear to be an important technology for the future as
they operate at high efficiencies and can run on a variety of fuels, from solar hydrogen to
methanol, from biomass to gasified coal. As the technology develops, and if the cost of fossil
fuels continues to rise, this clean, efficient alternative will stimulate the thermo mechanical
engineers, despite their Carnot and Ranking limitations, to even greater efforts for the SOFCs to
find more and more practical uses. The United Nations agency GEF (Global Environment
Facility), which operates through the UN Development and Environment Programs and the
World Bank, is launching fuel cell projects of more than $130 million between 2002 and 2003
for major cities and capitals with some of the world’s worst air pollution levels in Brazil,
Mexico, Egypt, India and China.
Conclusion
Fuel cell is valuable energy saving technology in today’s era. Fuel cells have the potential for
development to a sufficient size for applications for commercial electricity generation. It
converts chemical energy of a fuel gas directly into electrical work, and is efficient and
environmentally clean, since no combustion is required. It appears as to be one of the most
efficient and effective solution for the environmental problems being created today.
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a
chemical reaction with oxygen or another oxidizing agent. The first fuel cells were invented in
1838. The first commercial use of fuel cells came more than a century later in NASA space
programs to generate power for probes, satellites and space capsules. Since then, fuel cells have
been used in many other applications. Fuel cells are used for primary and backup power for
commercial, industrial and residential buildings and in remote or inaccessible areas. They are
also used to power fuel-cell vehicles, including forklifts, automobiles, buses, boats, motorcycles
and submarines. Fuel cells are different from batteries in that they require a continuous source of
fuel and oxygen/air to sustain the chemical reaction whereas in a battery the chemicals present in
the battery react with each other to generate an electromotive force. Fuel cells can produce
electricity continuously for as long as these inputs are supplied.
Every fuel cell also has an electrolyte, which carries electrically charged particles from one
electrode to the other, and a catalyst, which speeds the reactions at the electrodes. Hydrogen is
the basic fuel, but fuel cells also require oxygen. One great appeal of fuel cells is that they
generate electricity with very little pollution–much of the hydrogen and oxygen used in
generating electricity ultimately combines to form a harmless byproduct, namely water. Fuel
cells are a promising technology for use as a source of heat and electricity for buildings, and as
an electrical power source for electric motors propelling vehicles. Fuel cells operate best on pure
hydrogen. But fuels like natural gas, methanol, or even gasoline can be reformed to produce the
hydrogen required for fuel cells. Some fuel cells even can be fueled directly with methanol,
without using a reformer.
The purpose of a fuel cell is to produce an electrical current that can be directed outside the cell
to do work, such as powering an electric motor or illuminating a light bulb or a city. There are
several kinds of fuel cells, and each operates a bit differently. But in general terms, hydrogen
atoms enter a fuel cell at the anode where a chemical reaction strips them of their electrons. The
hydrogen atoms are now "ionized," and carry a positive electrical charge. The negatively charged
electrons provide the current through wires to do work. If alternating current (AC) is needed, the
DC output of the fuel cell must be routed through a conversion device called an inverter.
Types of fuel cells
1. Alkali fuel cells
Alkali fuel cells operate on compressed hydrogen and oxygen. They generally use a solution of
potassium hydroxide (chemically, KOH) in water as their electrolyte. Efficiency is about 70
percent, and operating temperature is 150 to 200 degrees C, (about 300 to 400 degrees F). Cell
output ranges from 300 watts (W) to 5 kilowatts (kW). Alkali cells were used in Apollo
spacecraft to provide both electricity and drinking water. They require pure hydrogen fuel,
however, and their platinum electrode catalysts are expensive. And like any container filled with
liquid, they can leak.
2. Molten carbonate fuel cells
Molten Carbonate fuel cells (MCFC) use high-temperature compounds of salt (like sodium or
magnesium) carbonates (chemically, CO3) as the electrolyte. Efficiency ranges from 60 to 80
percent, and operating temperature is about 650 degrees C (1,200 degrees F). Units with
output up to 2 megawatts (MW) have been constructed, and designs exist for units up to 100
MW. The high temperature limits damage from carbon monoxide "poisoning" of the cell and
waste heat can be recycled to make additional electricity. Their nickel electrode-catalysts are
inexpensive compared to the platinum used in other cells. But the high temperature also
limits the materials and safe uses of MCFCs–they would probably be too hot for home use.
Also, carbonate ions from the electrolyte are used up in the reactions, making it necessary to
inject carbon dioxide to compensate.
3. Phosphoric acid fuel cells
Phosphoric Acid fuel cells (PAFC) use phosphoric acid as the electrolyte. Efficiency ranges
from 40 to 80 percent, and operating temperature is between 150 to 200 degrees C (about 300
to 400 degrees F). Existing phosphoric acid cells have outputs up to 200 kW, and 11 MW
units have been tested. PAFCs tolerate a carbon monoxide concentration of about 1.5 percent,
which broadens the choice of fuels they can use. If gasoline is used, the sulfur must be
removed. Platinum electrode-catalysts are needed, and internal parts must be able to
withstand the corrosive acid.
4. Proton exchange membrane fuel cells
Proton Exchange Membrane (PEM) fuel cells work with a polymer electrolyte in the form of
a thin, permeable sheet. Efficiency is about 40 to 50 percent, and operating temperature is
about 80 degrees C (about 175 degrees F). Cell outputs generally range from 50 to 250 kW.
The solid, flexible electrolyte will not leak or crack and these cells operate at a low enough
temperature to make them suitable for homes and cars. But their fuels must be purified, and a
platinum catalyst is used on both sides of the membrane, raising costs.
5. Solid oxide fuel cells
Solid Oxide fuel cells (SOFC) use a hard, ceramic compound of metal (like calcium or
zirconium) oxides (chemically, O2) as electrolyte. Efficiency is about 60 percent, and
operating temperatures are about 1,000 degrees C (about 1,800 degrees F). Cells output is up
to 100 kW. At such high temperatures a reformer is not required to extract hydrogen from the
fuel, and waste heat can be recycled to make additional electricity.
Fuel cells today
The concept of a fuel cell was demonstrated in the early nineteenth century by a number of
scientists including Humphry Davy and Christian Friedrich Schönbein. William Grove, a
chemist, physicist and lawyer, is generally credited with inventing the fuel cell in 1839. Fuel
cell technology offers clean, efficient, reliable power generation to almost any device
requiring electrical power. Fuel cells are used in a wide range of portable, stationary and
transport applications, from battery chargers to home heating and power to cars. Arguably,
fuel cells represent the most versatile energy solution ever invented. Fuel cells are used in a
large number of different applications. It is mostly used for portable power generation,
stationary power generation, and power for transportation.
Fuel cells are applicable in following areas:
a. Residential heat and power
A wide variety of technologies are available to provide heating and electricity to our homes.
In countries with a stable electricity grid, lighting and heating are taken for granted; but the
desire for cleaner energy is highlighting how dirty grid electricity is around the world, and
concerns over the future of nuclear power are adding to the debate. Many countries also have
a network that distributes natural gas, and off-grid options such as heating oil or LPG are
available, but when burned in conventional boilers these fuels only produce heat.
Combined heat and power (CHP) is the term used for when electricity and heat are coproduced from a single source of fuel, such as natural gas, and when done on a residential
scale this is known as micro-CHP. Micro-CHP can replace or supplement grid electricity as a
form of distributed generation of power in customers’ homes, and producing energy at the
point of use avoids transmission losses.
b. Uninterruptible power supply
Events such as Hurricane Katrina in 2005 have focused attention on the availability and
reliability of telecommunications services worldwide. Both wireless and wireline
communications are expanding globally, so the provision of reliable, economical power is
vital. Terrestrial Trunked Radio (TETRA) networks in use by emergency services, military
personnel and government agencies require total system reliability during emergencies, when
loss of communication would exacerbate an already critical situation. The rapid expansion of
cellular networks in countries without more traditional land-based telephone systems is also
demanding the provision of reliable power supplies and this market is one of the fastest
growing worldwide. The choice of backup power technology for telecommunications
therefore has a direct impact on the everyday life of people around the world. Traditional
solutions have included generators and batteries, but issues of maintenance, noise, pollution,
size, insufficient runtime, remote monitoring difficulties and operation under extreme
conditions all pose problems for these technologies. This has led to interest in fuel cell
technology for this application, and fuel cell backup power units are now being installed in a
number of countries.
c. Converting waste to energy
Waste management is a necessity wherever people live, but traditionally waste is viewed as a
problem, something that pollutes and needs reducing or mitigating. What if this mindset
could be changed such that we value our waste as a source of bioenergy? Waste contains
significant quantities of energy and, if we could harness this close to where the waste is
generated and convert it to a useable form, it could provide both a distributed source of
electricity and contribute to solving the global problem of waste.
Biogas is widely produced from processed municipal waste using anaerobic digesters and
then is usually combusted. However, biogas can be fed to a fuel cell to produce electricity
and heat.
d. Renewable energy system
Generating renewable electricity is an important way to reduce carbon dioxide (CO2)
emissions and many countries are installing wind and solar power plants to help meet targets
for cutting CO2. One drawback of these energy sources is their variability: the wind tends to
blow intermittently and solar power is only available during the daytime. Hence renewable
power plants either have to be over-engineered to take account of this lower capacity factor,
or they must be supported by spinning reserve power stations, typically fast-response opencycle gas turbines – which goes against the environmental aims of the projects.
Ideally, excess renewable energy generated during times of plenty can be stored for use
during periods when sufficient electricity is not available. But storing this energy is a difficult
task: batteries and similar technologies perform well over short timescales, but over periods
of weeks or months a different approach is necessary. Energy storage in the form of hydrogen
is one such possibility: excess electricity is fed into an electrolyser to split water into its
constituent parts, oxygen and hydrogen. The hydrogen is then used in fuel cells to produce
electricity when needed, releasing the stored energy back to the grid.
e. Prime power generation
A national electricity grid must always be able to meet the needs of its users. This requires it
to be: stable, maintaining the required electrical frequency (50 Hz in the UK); balanced,
continuously matching supply to demand; and adequate, ensuring total generation capacity is
never outstripped by demand.
Grid supply is split into three tiers: base, intermediate, and peak load. Baseload is a
permanent minimum amount of electricity that is required at all times and is met by
predictable, long-running power sources, usually coal-fired plants. Intermediate power plants
are more flexible and can vary output to suit the needs of the grid, but at a cost to the system
operator. These include nuclear, hydroelectric and gas/diesel combined cycle turbine plants.
Finally, peak power generators are called upon to meet short-term spikes of requirement and
as such must be able to start up and provide power instantaneously.
f. Vaolrising By Product Hydrogen
Electrochemical processes, such as the industrial production of caustic soda and chlorine, use
large quantities of electricity which contribute significantly to production costs, up to 70% in
some cases. They also produce hydrogen as a waste product (see diagram), which is either
combusted or vented to the atmosphere. Fuel cells offer a highly efficient method of utilizing
this hydrogen to produce electricity, offsetting much of a plant’s electrical demand whilst at
the same time reducing emissions.
Applications
a. Transport
Fuel Cell today defines fuel cells for transport as any units that provide propulsive power to a
vehicle, directly or indirectly (i.e. as range extenders). This includes the following
applications for the technology:
Forklift trucks and other goods handling vehicles such as airport baggage trucks etc.
Two- and three-wheeler vehicles such as scooters
Light duty vehicles (LDVs), such as cars and vans
Buses and trucks
Trains and trams
Ferries and smaller boats
Manned light aircraft Unmanned aerial vehicles (UAVs) and unmanned undersea
vehicles (UUVs), for example, for reconnaissance.
The fuel cell bus sector is showing year-on-year growth, with more prototypes being
unveiled. Successful deployments have taken place in Europe, Japan, Canada and the USA but
the high capital cost is still a barrier to widespread adoption. However, it is hoped that soon after
2014 fuel cell bus prices will be comparable to diesel-hybrid bus prices.
b. Portable
Fuel Cell today defines portable fuel cells as those which are built into, or charge up, products
that are designed to be moved. These include military applications (portable soldier power, skid
mounted fuel cell generators etc.), Auxiliary Power Units (APU) (e.g. for the leisure and trucking
industries), portable products (torches, vine trimmers etc.), small personal electronics (mp3
players, cameras etc.), large personal electronics (laptops, printers, radios etc.), education kits
and toys.
Fuel cells are being sold commercially for these applications, APU, small personal electronics,
education kits and toys (these we classify as micro fuel cells). Fuel Cell today defines a micro
fuel cell as a unit with a power output of less than 5 W. The difference between small and large
personal electronics is that the smaller devices, such as cameras or mobile phones only draw
around 3 W of power, whereas a laptop can use up to 25 W, requiring a fuel cell of higher power
density. Portable fuel cells typically replace or augment battery technology and exploit either
PEM or DMFC technology. PEM fuel cells use direct hydrogen, with no point-of-use emissions,
whereas DMFCs emit small quantities of CO2. The main drivers for fuel cells in portable
applications are as follows:
c.
Off-grid operation
Longer run-times compared with batteries
Rapid recharging
Significant weight reduction potential (for soldier-borne military power)
Convenience, reliability, and lower operating costs also apply
Stationary
Fuel Cell today defines stationary fuel cells as units which provide electricity (and sometimes
heat) but are not designed to be moved. These include combined heat and power (CHP),
uninterruptible power systems (UPS) and primary power units.
CHP units are sized between 0.5 kW and 10 kW, use either PEM or SOFC technology and take
advantage of the fact fuel cells generate heat alongside electricity. By making use of this heat, for
example to make hot water, the overall efficiency of the system increases. Fuel cells are also
more efficient at generating electricity which gives CHP units overall efficiencies of 80-95%.
Residential CHP units have been deployed extensively in Japan with more than 10,000
cumulative units by the end of 2010 providing home power and heating. South Korea has also
deployed CHP units for residential use but, as in Japan, their purchase still relies upon
government subsidies.
UPS systems provide a guaranteed supply of power in the event of grid interruption; this market
can be divided into five sub-sectors:
Off-line short run-time systems for telecommunication base stations
Off-line extended run-time systems for critical communication base stations such as
Terrestrial Trunked Radio (Tetra) networks
Off-line extended run-time rack mountable systems for data centers
On-line rack mountable systems for data centers
Off-line systems for residential use.
Large stationary refers to multi-megawatt units providing primary power. These units are being
developed to replace the grid, for areas where there is little or no grid infrastructure, and can also
be used to provide grid expansion nodes.
Fuel cell development in China
Fuel cells are not a new technology to China, but in fact have been researched and developed
since the 1970s, when a prototype alkaline fuel cell was developed for use in its domestic space
program. This unit never left the confines of the laboratory, but the interest in fuel cells remained
with PEMFC technology emerging as the dominant technology. Through the 1990s research
focused on automotive applications, but attempts to gain interest from commercial partners
proved fruitless. Around 1999, the government extended the electric vehicle R&D investment to
include fuel cell technology, and since 2000, a number of demonstration programs have taken
place raising the profile of fuel cells in the eyes of both the government and the public. Current
academic and commercial interest in fuel cells ranges from very small portable units for
powering torches and consumer electronics, through larger stationary systems for backup power
and all the way up to fuel cell electric vehicles and fuel cell buses.
Opportunities for fuel cells in China Stationary Systems
The market for stationary power has huge potential in China and in the backup sector for
telecommunications power it is beginning to gather momentum. China is home to the world’s
most rapidly expanding mobile phone network, but at the same time does not have an integrated
national grid system. China’s disjointed, and in some areas unreliable, grid system is composed
of power clusters spread across eight regions and controlled by three main companies. Backup
power cannot therefore be guaranteed and so battery backup is widely used in the
telecommunications industry. There are 30 to 50 billion RMB ($4.7 to $7.9 billion) of battery
sales per year in China for the telecoms industry alone, and currently more than one million cell
sites in the country. Growth of new cell sites currently runs at ten to twenty thousand per year.
Fuel cells in electric power train
Fuel cell and battery electric vehicles both use electric drivetrains, but where battery
electric vehicles (BEV) power their motors solely with batteries, fuel cell electric vehicles
(FCEV) are hybrids, powered by a hydrogen fuel cell with a small battery. Both vehicle types
benefit from near-silent operation, excellent drivability and no tailpipe emissions, or indeed no
tailpipe at all.
BEV is best realized as smaller cars in applications that require a continuous range of less than
200 kilometers (125 miles): city run-arounds and second cars. Restricted range and long
recharging times have limited their uptake to date. Plug-in hybrid electric vehicles (PHEV)
provide a bridge between conventional cars and electric vehicles, offering an electric drivetrain
with the convenience of using conventional fuel; however they can never be truly zero-emission.
FCEV provide all of the benefits of electric vehicles combined with the utility of a combustionengine car: they can be refueled in minutes by the driver using a nozzle similar to a conventional
fuel pump and then driven for hundreds of kilometers before they need refueling again. A large
proportion of road fuel is used in large and high-mileage vehicles and only fuel cells are proven
as a zero-emission power source for these vehicles. The mix of conventional conveniences and
electric advantages that FCEV can offer is a compelling proposition for personal transportation.
Solid oxide fuel cells: Most widely used fuel cells
SOFCs have recently emerged as a serious high temperature fuel cell technology. They promise
to be extremely useful in large, high-power applications such as full scale industrial stations and
large-scale electricity-generating stations. Some fuel cell developers see SOFCs being used in
motor vehicles. A SOFC system usually utilizes solid ceramic as the electrolyte and operates at
extremely high temperatures (600–1000°C). This high operating temperature allows internal
reforming, promotes rapid electro catalysis with non-precious metals, and produces high quality
byproduct heat for co-generation. Efficiencies for this type of fuel cell can reach up to 70% with
an additional 20% as heat recovery. SOFCs are best suited for provision of powering utility
applications due to the significant time required to reach operating temperatures.
Solid oxide fuel cell history
Emil Baur, a Swiss scientist and his colleague H. Preis experimented with solid oxide
electrolytes in the late 1930s, using such materials as zirconium, yttrium, cerium, lanthanum, and
tungsten oxide. The operation of the first ceramic fuel cell at 1000°C, by Baur and Preis, was
achieved in 1937. In the 1940s, O. K. Davtyan of Russia added monazite sand to a mix of
sodium carbonate, tungsten trioxide, and soda glass, in order to increase the conductivity and
mechanical strength. Davtyan’s design, however, also experienced unwanted chemical reactions
and short life ratings. By the late 1950s, research into solid oxide technology began to accelerate
at the Central Technical Institute in The Hague, Netherlands, Consolidation Coal Company, in
Pennsylvania, and General Electric, in Schenectady, New York. A 1959discussion of fuel cells
noted that problems with solid electrolytes included relatively high internal electrical resistance,
melting, and short-circuiting, due to semi conductivity. Not everybody gave up on solid oxides,
however. The promise of a high temperature cell that would be tolerant of carbon monoxide and
use a stable solid electrolyte continued to draw modest attention. Researchers at Westinghouse,
for example, experimented with a cell using zirconium oxide and calcium oxide in 1962.More
recently, climbing energy prices and advances in materials technology have reinvigorated work
on SOFCs, and a recent report noted about 40 companies working on these fuel cells that include
Global Thermo electric’s Fuel Cell Division, which is developing cells designed at the Julich
Research Institute in Germany. Cermatec Advanced Ionic Technologies is working on units up to
10 kW in capacity, running on diesel fuel, which would be used for mobile power generation.
The US Department of Energy announced that a SOFC-micro turbine co-generation unit has
been evaluated, since April 2000, by the National Fuel Cell Research Center and Southern
California Edison. The fuel cell was built by Siemens Westinghouse and the micro turbine by
Northern Research and Engineering Corporation. In a year of actual operating conditions, the
220 kW SOFC, running on natural gas is achieving an efficiency of 60%. Also, a world record
for SOFC operation, roughly eight years, still stands, and the prototype cells have demonstrated
two critical successes: the ability to withstand more than 100 thermal cycles, and voltage
degradation of less than 0.1% per thousand h. Moreover, a 140 kW peak power SOFC
cogeneration system, supplied by Siemens Westinghouse, is presently operating in the
Netherlands. This system has operated for over 16,600 h, becoming the longest running fuel cell
in the world. The first demonstration of the commercial prototype cells in a full scale SOFC
module is equally significant.
Design and operation of SOFCs
SOFCs differ in many respects from other fuel cell technologies. First, they are composed of allsolid-state materials. Second, the cells can operate at temperatures as high as 1000°C,
significantly hotter than any other major category of fuel cell. Third, the solid state character of
all SOFC components means that there is no fundamental restriction on the cell configuration.
Cells are being constructed in two main configurations, i.e., tubular cells or rolled tubes, such as
those being developed at Westinghouse Electric Corporation since the late 1950s, and a flatplates configuration adopted more recently by many other developers and employed today by the
electronics industry.
A SOFC consists of two electrodes sandwiched around a hard ceramic electrolyte such as the
remarkable ceramic material called zirconia.Hydrogen fuel is fed into the anode of the fuel cell
and oxygen, from the air, enters the cell through the cathode. By burning fuel containing
hydrogen on one side of the electrolyte, the concentration of oxygen is dramatically reduced. The
electrode on this surface will allow oxygen ions to leave the electrolyte and react with the fuel
which is oxidized, thereby releasing electrons (e). On the other side of the plate, which is
exposed to air, an oxygen concentration gradient is created across the electrolyte, which attracts
oxygen ions from the air side, or cathode, to the fuel side, or anode. If there is an electrical
connection between the cathode and the anode, this allows electrons to flow from the anode to
the cathode, where a continuous supply of oxygen ions (O2) for the electrolyte is maintained,
and oxygen ions from cathode to anode, maintaining overall electrical charge balance, thereby
generatinguseful electrical power from the combustion of the fuel.
Fuel for SFOCs
SOFCs require only a single partial oxidation reformer to pre-process their fuel, which can be
gasoline, diesel, natural gas, etc. The nature of the emissions from the fuel cell will vary
correspondingly with the fuel mix. Using hydrocarbons, for which a supply infrastructure is
currently available, offers a variety of advantages over446 A.B. Stambouli, E. Traversa /
Renewable and Sustainable Energy Reviews 6 (2002) 433–455using hydrogen. First of all,
hydrocarbons are much easier to transport and to store because they are in a stable state which
requires no processing before use. They are also more efficient at producing energy. Methane for
example yields eight electrons per molecule whereas hydrogen only yields two electrons energy.
This advantage could be magnified with the use of more complex hydrocarbons, such as pentane.
Benefits of SFOCs
Energy security: reduce oil consumption, cut oil imports, and increase the amount of the
country’s available electricity supply.
Reliability: achieves operating times in excess of 90% and power available99.99% of the
time.
Low operating and maintenance cost: the efficiency of the SOFC system will drastically
reduce the energy bill (mass production) and have lower maintenance costs than their
alternatives.
Constant power production: generates power continuously unlike backup generators,
diesel engines or Uninterrupted Power Supply (UPS).
Choice of fuel: allows fuel selection, hydrogen may be extracted from natural gas,
propane, butane, and methanol and diesel fuel.
SOFCs and their environmental impact
Recently, it created attention towards the utility industries especially for generation of heat and
power. The environmental impact of SOFC use depends upon the source of hydrogen-rich fuel
used. If pure hydrogen is used, fuel cells have virtually no emissions except water and heat. As
mentioned earlier, hydrogen is rarely used, due to problems with storage and transportation, but
in the future many people have predicted the growth of a solar hydrogen economy. In this
scenario, photovoltaic cells would convert sunlight into electricity. This electricity would be used
to split water (electrolysis) into hydrogen and oxygen, in order to store the sun’s energy as
hydrogen fuel. In this scenario, SOFCs generating stations would have no real emissions of
greenhouse or acid gases, or any other pollutants.
It is predominantly during the fuel processing stage that atmospheric emissions are released by a
fuel cell power plant. However, the high efficiency of SOFC results in less fuel being consumed
to produce a given amount of electricity, which corresponds to a lower emission of carbon
dioxide CO2, the main greenhouse gas responsible for global warming. When hydrogen from
natural gas is used as a fuel, SOFCs have no net emissions of CO2because any carbon released is
taken from the atmosphere by photosynthetic plants. A reduction of carbon dioxide emissions by
more than 2 million kg per year can be obtained. Moreover, emissions from SOFC systems will
be very low with near-zero levels of NOx, Sox and particulates, therefore eliminates 20,000 kg
of acid rain and smog-causing pollutants from the environment. In any case SOFCs generally
provide the lowest emissions of any non-renewable power generation method such as traditional
thermal power plants. This is very important with regard for energy related environment
concerns. When combined with a heat engine that uses any waste heat, SOFCs are the most clean
and efficient devices available for this purpose.
SOFC can also provide high-quality waste heat that can be used to warm the home or provide
refrigeration and air conditioning without harming the environment. If CO2 can be removed at
the source for disposal elsewhere, the SOFC really would become the ultra-high efficiency, zero
emissions power plant of the 21st century.
Applications of SFOCs
Combined with low noise and ability to utilize readily-available fuel such as methane and natural
gas, SOFC generators are best suited for the provision of power inutility applications, due to the
significant time required to reach operating temperatures, and can have broad applications
ranging from large-scale power plants to smaller home-scale power plants and
portable/emergency power generators. SOFCs could be used in many applications. Some of them
are:
High power reliability: computer facilities, call centers, communication facilities, data
processing centers high technology manufacturing facilities.
Emission minimization or elimination: urban areas, industrial facilities, airports, zones
with strict emissions standards.
Limited access to utility grid: rural or remote areas, maximum grid capacity.
Biological waste gases are available: waste treatment plants, SOFC can convert waste
gases (methanol from biomass) to electricity and heat with minimal environment
intrusion.
Future of SFOCs
Focusing their efforts on SOFCs, which have been on the verge of commercial viability for
years, researchers around the world are making a concerted effort in the development of suitable
materials and the fabrication of ceramic structures which are presently the key technical
challenges facing SOFCs. Programs are underway in Japan and in the US that use a relatively
simple ceramic process to develop a thin film electrolyte that decreases the cell resistance, and
both double the power output and significantly reduce the cost of SOFCs. There is also a current
effort in integrating the SOFCs and developing a novel stacking geometry. The demonstration of
low-temperature SOFC operation directly on methane, signals an important new opportunity for
making simple, cost-effective power plants . The global SOFC making company continues to
realize very significant improvements in basic fuel cell design. A measure of their success is the
realization of a 48.6% improvement in single cell power densities which represents the highest
published power densities for commercial-sized SOFCs in the world. Changes in cell
composition and design have resulted in these improved power densities. Higher power densities
contribute to lower weight, size and cost of fuel cell systems. SOFCs could someday be suitable
for small-scale residential market applications if ultimate cost goals of $1000/kW are reached.
Energy exploitation of fossil fuels is reaching its limits. Future alternatives must therefore be
developed for long-term and environmental-friendly energy supply needed by a constantly
growing world population. SOFCs provide highly efficient, pollution free power generation.
Their performance has been confirmed by successful operation power generation systems
throughout the world. Electrical-generation efficiencies of 70% are possible nowadays, along
with a heat recovery possibility. SOFCs appear to be an important technology for the future as
they operate at high efficiencies and can run on a variety of fuels, from solar hydrogen to
methanol, from biomass to gasified coal. As the technology develops, and if the cost of fossil
fuels continues to rise, this clean, efficient alternative will stimulate the thermo mechanical
engineers, despite their Carnot and Ranking limitations, to even greater efforts for the SOFCs to
find more and more practical uses. The United Nations agency GEF (Global Environment
Facility), which operates through the UN Development and Environment Programs and the
World Bank, is launching fuel cell projects of more than $130 million between 2002 and 2003
for major cities and capitals with some of the world’s worst air pollution levels in Brazil,
Mexico, Egypt, India and China.
Conclusion
Fuel cell is valuable energy saving technology in today’s era. Fuel cells have the potential for
development to a sufficient size for applications for commercial electricity generation. It
converts chemical energy of a fuel gas directly into electrical work, and is efficient and
environmentally clean, since no combustion is required. It appears as to be one of the most
efficient and effective solution for the environmental problems being created today.
