CLASSIFICATIONS OF FUEL CELLS

CLASSIFICATIONS OF FUEL CELLS

MSE-5390-SPRING-2015FUNDAMENTALS OF SUSTAINABLE ENERGYUNIVERSITY OF TEXAS, ARLINGTON

ByMUSALI, DAKSHINIKOTA, SHANMUKA PRASAD GUPTAGROUP # 6

ABSTRACTFuel cells generate electricity and heat during electrochemical reaction which happens between the oxygen and hydrogen to form the water. Fuel cell technology is a promising way to provide energy for rural areas where there is no access to the public grid or where there is a huge cost of wiring and transferring electricity. In addition, applications with essential secure electrical energy requirement such as uninterruptable power supplies (UPS), power generation stations and distributed systems can employ fuel cells as their source of energy.The current paper includes comparative study of basic design, working principle, applications, advantages and disadvantages of various technologies available for fuel cells. In addition, techno-economic features of hydrogen fuel cell vehicle (FCV) and internal combustion engine vehicles (ICEV) are compared. The results indicate that fuel cell systems have simple design, high reliability, noiseless operation, high efficiency and less environmentally impact.INTRODUCTIONFuel cells are basically open thermodynamics systems. They operate on the basis of electrochemical reactions and consume reactant from an external source. They are favorable alternatives to conventional electricity generation methods for small scale applications. Hydrogen and hydrocarbon fuels contain significant chemical energy in comparison with conventional battery materials; hence they are now widely developed for numerous energy applications.Fuel cell technology is a promising substitute for fossil fuels to provide energy for rural areas where there is no access to the public grid or huge cost of wiring and transferring electricity is required. In addition, applications with essential secure electrical energy requirement such as uninterruptible power supplies (UPS), power generation stations and distributed systems can employ fuel cells as their source of energy. Fuel cell systems perform with the highest efficiency compared to conventional distributed energy systems. They have simple design and reliable operation as well. In addition, utilizing hydrogen as the reactant makes them the most environ-mentally clean and noiseless energy systems. Currently, fuel cell systems are employed widely in small scale as well as large scale applications such as combined heat and power (CHP) systems, mobile power systems, portable computers and military communication equipment. Despite all the advantages, there are some limitations for utilizing fuel cells. For example, life span of fuel cells shortens by pulse demands and impurities of gas stream. Low power density per volume, less accessibility and less durability are other challenges for fuel cell technology development. Though, great break through is yet to be seen, positive progress is witnessed throughout the recent years.

HISTORYThe first references to hydrogen fuel cells appeared in 1838. In a letter dated October 1838 but published in the December 1838 edition ofThe London and Edinburgh Philosophical Magazine and Journal of Science, Welsh physicist and barristerWilliam Grovewrote about the development of his first crude fuel cells. He used a combination of sheet iron, copper and porcelain plates, and a solution of sulphate of copper and dilute acid.In a letter to the same publication written in December 1838 but published in June 1839, German physicistChristian Friedrich Schnbeindiscussed the first crude fuel cell that he had invented. His letter discussed current generated from hydrogen and oxygen dissolved in water.Grove later sketched his design, in 1842, in the same journal. The fuel cell he made used similar materials to today'sphosphoric-acid fuel cell. In 1939, British engineerFrancis Thomas Baconsuccessfully developed a 5kW stationary fuel cell. In 1955, W. Thomas Grubb, a chemist working for the General Electric Company (GE), further modified the original fuel cell design by using a sulphonated polystyrene ion-exchange membrane as the electrolyte. Three years later another GE chemist, Leonard Niedrach, devised a way of depositing platinum onto the membrane, which served as catalyst for the necessary hydrogen oxidation and oxygen reduction reactions. This became known as the "Grubb-Niedrach fuel cell".GE went on to develop this technology with NASA and McDonnell Aircraft, leading to its use duringProject Gemini. This was the first commercial use of a fuel cell. In 1959, a team led by Harry Ihrig built a 15kW fuel cell tractor forAllis-Chalmers, which was demonstrated across the U.S. at state fairs. This system used potassium hydroxide as the electrolyte andcompressed hydrogenand oxygen as the reactants. Later in 1959, Bacon and his colleagues demonstrated a practical five-kilowatt unit capable of powering a welding machine. In the 1960s, Pratt and Whitney licensed Bacon's U.S. patents for use in the U.S. space program to supply electricity and drinking water (hydrogen and oxygen being readily available from the spacecraft tanks). In 1991, the first hydrogen fuel cell automobile was developed by Roger Billings. UTC Powerwas the first company to manufacture and commercialize a large, stationary fuel cell system for use as aco-generationpower plant in hospitals, universities and large office buildings.WORKING PRINCIPLE:Fuel cells generate electricity and heat via electro chemical reaction which is actually the reversed electrolysis reaction. It happens between the oxygen and hydrogen to form the water. There are a range of designs available for fuel cells; however, they all operate with the same basic principles. The main difference in various fuel cell designs is the chemical characteristics of the electrolyte. The electrochemical reaction depicts the operating principle of a fuel cell. 2H2 (g) +O2 (g) 2H2O + energyHydrogen + oxygen water + (electrical power + heat)A fuel cell has four main parts: anode, cathode, electrolyte and the external circuit. At the anode, hydrogen is oxidized in to protons and electrons, while at the cathode oxygen is reduced to oxide species and reacts to form water. Depending on the electrolyte, either protons or oxide ions are transported through an ion conductor electron insulating electrolyte while electrons travel through an external circuit to deliver electric power.

Nevertheless, fuel cells of ten produce only very small amount of current due to diminutive contact area between electrodes, electrolyte and the gas. Another problem to be considered is the distance between electrodes. To improve the efficiency of fuel cells and maximize the contact area, a thin layer of electrolyte with flat porous electrodes is considered for electrolyte and the gas penetration. The reaction between oxygen and hydrogen to generate electricity is different for various types of fuel cells. In an acid electrolyte fuel cell, electrons and protons (H+) are released from hydrogen gas ionizing at the anode electrode. The generated electrons pass though an electrical circuit and travel to the cathode while protons are delivered via electrolyte. This exchange releases electrical energy. Simultaneously at the cathode side, the water is forming as a result of the reaction between electrons from electrode and protons from electrolyte. The reactions happening at the anode and cathode areAnode: 2H24H++4eCathode: O2+4e+4H+2H2O Acid electrolytes and certain polymers that contain free H+ ions are often called proton exchange membranes. They serve more properly and effectively for proton delivering functions since they solely allow the H+ ions passing through it. The electrical current is lost in the case of delivering electrons through the electrolyte.

DESIGN FEATURESThe most important design features in a fuel cell are:The electrolyte substance. The electrolyte substance usually defines thetypeof fuel cell.The fuel that is used. The most common fuel is hydrogen.The anode catalyst breaks down the fuel into electrons and ions. The anode catalyst is usually made up of very fine platinum powder.The cathode catalyst turns the ions into the waste chemicals like water or carbon dioxide. The cathode catalyst is often made up of nickel but it can also be a nano material-based catalyst.A typical fuel cell produces a voltage from 0.6 V to 0.7 V at full rated load. Voltage decreases as current increases, due to several factors:Activation Loss, Ohmic loss (voltage dropdue to resistance of the cell components and interconnections), Mass transport loss (depletion of reactants at catalyst sites under high loads, causing rapid loss of voltage). To deliver the desired amount of energy, the fuel cells can be combined in seriesto yield higher voltage, and in parallel to allow a higher current to be supplied. Such a design is called afuel cell stack. The cell surface area can also be increased, to allow higher current from each cell. Within the stack, reactant gases must be distributed uniformly over each of the cells to maximize the power outputTYPES OF FUEL CELLSFuel cells are different according to their operating temperature, efficiency, applications and costs. They are classied based on the choice of fuel and electrolyte in to 6 major groups Alkalinefuelcell(AFC) Phosphoricacidfuelcell(PAFC) Solidoxidefuelcell(SOFC) Moltencarbonatefuelcell(MCFC) Protonexchangemembranefuelcell(PEMFC) Direct methanol fuel cell(DMFC)ALKALINE FUEL CELL (AFC)The AFC generate electric power by utilizing alkaline electrolyte potassium hydroxide (KOH) in water based solution.

The presence of the hydroxyl ions travelling across the electrolyte allows a circuit to be made and electrical energy could be extracted. At anode, 2 hydrogen gas molecules are combined with 4 hydroxyl ions with a negative charge to release 4 water molecules and 4 electrons. The redox reaction taking place is oxidation.Oxidation: 2H2 + 4OH 4H2O + 4eElectrons released in this reaction, reach the cathode through the external circuit and react with water to generate (OH) ions.At cathode, oxygen molecule and 2 water molecules combined and absorbed 4 electrons to form 4 negatively charged hydroxyl ions. The occurring redox reaction is reduction. Reduction: O2 + 2H2O + 4e 4OHAFCs generally perform in temperatures between 60 and 90. However, recent designs can operate at low temperatures between 23 and 70. AFCs are classied as low operating temperature fuel cells with low cost catalysts. The most common catalyst to speed up electro chemical reactions in cathode and anodes in this type of fuel cell is nickel. Electrical efficiency of AFCs is about 60% and CHP efficiency is more than 80%. They can generate electricity up to 20k. NASA has rst used AFCs to supply drinking water and electric power to the shuttle missions for space applications. Currently, they are employed in submarines, boats, fork lift trucks and nichetran sportation applications. AFCs are considered as the most cost efficient type of fuel cells since the electrolyte used is a standard chemical potassium hydroxide (KOH). The catalyst for the electrodes is nickel which is not expensive compared with other types of catalysts. AFCs have simple structures due to eliminating bi polar plates. They consume hydrogen and pure oxygen to produce portable water, heat and electricity sources. The by-product water produced by AFC is the drinking water which is very useful in space crafts and space shuttle eets. They have no green house gas emissions and operate with a high efficiency of about 70%. In spite of all the advantages of AFCs, they are defeated by getting easily poisoned with carbon dioxide. The water based alkaline solution (KOH) used in AFCs as electrolyte, absorbs CO2 through the conversion of KOH to potassium carbonate (K2CO3) and consequently poisons the fuel cell. Therefore, AFCs typically use puried air or pure oxygen which in turn increases the operating costs. Hence, one concern is to nd a substitute for KOH.PHOSPHORIC ACID FUEL CELL (PAFC)Phosphoric acid fuel cells (PAFC) use carbon paper electrodes and liquid phosphoric acid (H3PO4) electrolyte. H3PO4 (3.09%H, 31.6%P, 65.3%O) is a clear colorless liquid used in fertilizers, detergents, food avouring and pharmaceuticals. The ionic conductivity of phosphoric acid is low at low temperatures, so PAFC can operate at the range of 150220C temperature. The charge carrier in this type of fuel cell is the hydrogen ion (H+Or proton). They pass from the anode to the cathode through the electrolyte and the expelled electrons return to the cathode through the external circuit and generate the electrical current. At the cathode side, water is forming as the result of the reaction between electrons, protons and oxygen with presence of platinum catalyst to speed up there actions. Expelled water is usually used in heating applications. Continuous operation and system start up is a concern at 40C due to Phosphoric acid fuel cell (PAFC). Solidity of phosphoric acid at this temperature.

The hydrogen expelled at the anode splits in to its 4 protons and 4 electrons. The redox reaction taking place in anode is oxidation. While at cathode, the redox reaction is reduction where 4 protons and 4 electrons combine with the oxygen to form water.Oxidation: 2H2 4H+ + 4eReduction: O2 + 4H+ + 4e 2H2OThe electrons and protons pass through the external circuit and the electrolyte, respectively. The result is generation of electrical current and heat. The heat is usually exploited for water heating or steam generation at atmospheric pressure; however, steam reforming reactions produces one carbon monoxide (CO) around the electrodes which might poison the fuel cell and affect the PAFC performance. The solution to reduce the CO absorption is to increase the anode temperature tolerance. The higher tolerance for CO means higher temperature tolerance at anode. At high temperatures, the CO is desorbed in reversed electro-catalyst reaction at cathode. Contrary to other acid electrolytes that need water for conductivity, PAFC concentrated phosphoric acid electrolyte is capable of operating in temperatures higher than boiling point ofwater. PAFC does not require pure oxygen for its operation since CO2 does not affect the electrolyte or cell performance. They run on air and can be easily operated with reformed fossil fuels. Besides, H3PO4 has lower volatility and long term stability. The initial cost is high since PAFC uses air with 21% oxygen instead of pure oxygen resulting in 3 times reduction in the current density. Therefore, PAFC is designed in stack bipolar plate to increase electrode area for more energy production which implies high initial cost for this technology. Currently, PAFC systems are in commercial stage with capacity up to 200kW and systems with higher capacities (11MW) are already tested. The PAFCs are expensive to manufacture due to the need for nely dispersed platinum catalyst coating the electrodes. Unlike AFCs, hydrogen steam impurity (CO2) does not affect the PAFCs. Electrical efciency of this type of fuel cells is between 40 and 50% and CHP efficiency about 85%. They are typically used for onsite stationary applications.SOLID OXIDE FUEL CELL (SOFC)Solid oxide fuel cells (SOFCs) are high temperature fuel cells with metallic oxide solid ceramic electrolyte. SOFCs generally use a mixture of hydrogen and carbon monoxide formed by internally reforming hydro carbon fuel and air as the oxidant in the fuel cell. Yttria stabilized zirconia(YSZ) is the most commonly used electrolyte for SOFCs because of its high chemical and thermal stability and pure ionic conductivity.

Oxygen is oxidized in reduction reaction at the cathode (air electrode) at1000C, while, fuel oxidation happens at the anode. The anode should be porous to conduct fuel and transport the products of fuel oxidation away from the electrolyte and fuel electrode interfaces.Oxidation: (1/2) O2 (g) + 2e O2 (s)Reduction: O2 (S) + H2 (g) H2O (g) + 2eSOFCs are well adopted with large scale distributed power generation systems with capacity of hundreds of MWs.The byproduct heat is usually used to generate more electricity by turning gas turbines and hence increasing the CHP efciency between 70 and 80%. SOFC systems are reliable, modular and fuel adaptable with low harmful gas (NOx and SOx) emissions. They can be considered as local power generation systems for rural areas with no access to public grids. Furthermore, they have noise free operation and low maintenance costs. On the other hand, long start-up and cooling-down times as well as various mechanical and chemical compatibility issues limit the use of SOFCs. Possible solutions to reduce the operating temperature and claimed if successful and sustainable counter measures are builtup, SOFC may bring energy production to a new generation.MOLTEN CARBONATE FUEL CELL (MCFC)Molten carbonate fuel cells (MCFCs) are high temperature fuel cells. They use molten carbonate salt mixture as electrolyte suspended in a porous, chemically inert ceramic matrix of beta alumina solid electrolyte (BASE).

In MCFC, the reaction at the hydrogen electrode occurs between hydrogen fuel and carbonate ion, which react to form carbon dioxide, water and electrons. At the anode, the feed gas usuallyMethane CH4 and water H2O are converted to hydrogen (H2), carbon monoxide (CO) and carbon dioxide (CO2).Reform1: CH4 + H2O CO + 3H2Reform2: CO + H2O CO2 + H2Simultaneously, two electro chemical reactions consume hydrogen and carbon monoxide and generate electrons at anode. Both reactions use carbonate ions (CO32) available in the electrolyte.Oxidation1: H2 + CO32 H2O + CO2 + 2eOxidation2: CO + CO32 2CO2 + 2eThe reduction happens at cathode and expels new carbonate ions from oxygen (O2) and carbon dioxide (CO2). Here by, the carbonate ions produced at cathode are transferred through the electrolyte to the anode. Electric current and cell voltage can be collected at electrodes.Reduction: (1/2) O2 + CO2 + 2e CO32MCFCs are currently employed for natural gas and coal based power plants in electrical utility, industrial and military applications. The advantages and disadvantages of MCFCs are closely related to its high operating temperature. MCFC may be directly fuelled with hydrogen, carbon monoxide, natural gas and propane. They do not require noble metal catalysts for electro chemical oxidation and reduction. They also do not require any infrastructure development for installation; however, long time is needed to reach to the operating temperature and generating power.PROTON EXCHANGE MEMBRANE FUEL CELL (PEMFC)In PEMFCs, the hydrogen is activated by catalyst to form proton ion and eject electron at the anode. The proton passes through the membrane while electrons are forced to ow to the external circuit and generate electricity. The electron then ows back to the cathode and interact with oxygen and proton ion to form water. The chemical reactions occurring at each electrodeAnode: H2 (g) 2H+ + 2eCathode: (1/2) O2 (g) + 2H+ + 2e H2OOver all reaction: H2 (g) + (1/2) O2 (g) H2OBasically the PEMFC is comprised of bipolar plates and membrane electrode assembly (MEA). The MEA is composed of dispersed catalyst layer, carbon cloth or gas diffusion layer and the membrane. Membrane is to transport protons from anode to cathode and block the passage of electron and reactants. Gas diffusion layer is to access the fuel uniformly. Electrons at anode pass through the external circuit and generate electricity.

PEMFCs are low temperature fuel cells with operating temperature between 60 and 100C. They are light weight compact systems with rapid start-up process. The sealing of electrodes in PEMFCs is easier than other types of fuel cells because of solidity of the electrolyte. In addition, they have longer life time and cheaper to manufacture. The total cost of car with the FEMFC system is 500600$/kW which is 10 folded compare with cars using Internal Combustion Engine (IEC). Total cost of the PEMFCs includes the costs of assembly process, bipolar plate, platinum electrode, membrane and peripherals. From efciency point of view, the higher the working temperature the higher efficiency can be gained. This is due to the higher reaction rate. Nevertheless, working temperature above 100C will vaporize the water causing dehydration to the membrane which leads to the reduction in the proton conductivity of the membrane. Electrical efficiency of PEMFCs is between 40 and 50% and the output power can be as high as 250kW. PEMFC systems are usually used in portable and stationary applications. However, among applications of PEMFCs, transportation seems to be the most suitable since they provide continuous electrical energy supply at high level of efficiency and power density. They also require minimum maintenance because there are no moving parts in the power generating stacks of the fuel cells. Fuel cell vehicles are the most promising application of PEMFC systems. The reason is the observability of technology development by people which can signicantly improve the acceptability of such systems among communities. A report from McNicoletal states that a FCV can successfully contend against conventional ICE vehicles. However, the initial cost for FCV is higher than that for ICE vehicles.DIRECT METHANOL FUEL CELL (DMFC)Direct methanol fuel cell (DMFC) is promoted type of the PEMFCs. It is a suitable source of power for portable energy purposes due to low temperature operation, long life time and rapid refueling system characteristics. In addition, they do not need to be recharged and are addressed as clean renewable energy source. Energy source of the DMFC systems is methanol. At anode, methanol is reformed in to carbon dioxide (CO2) while at cathode steam or water is formed using oxygen available in the air. The reactions are Anode: CH3OH+H2OCO2+6H++6eCathode: (3/2) O2+6e+6H+3H2ODMFC systems are generally classied in to active and passive. Active DMFCs are high efficient and reliable systems consisting ofmethanol feed pump, CO2 separator, fuel cell stack, methanol sensor, circulation pump, pump drivers and controllers. Using pump for water circulation can signicantly increase the efficiency of such systems.

Active DMFCs are usually used in control applications for quantities such as ow rate, concentration and temperature. In the passive DMFC systems, the methanol pumping devices and external process for blowing air in to the cell are eliminated. Hence, oxygen of ambient air is defused in to the cathode via air breathing feature of the cell. Similarly, methanol is defused in to the anode from an integrated feed reservoir driven by a concentration gradient between the anode and the reservoir. Passive systems are cheap, simple and capable of substantial reduction in parasitic power loss and system volume. Methanol is utilized in DMFCs inform of vapor or liquid. Vapor feed is preferable to liquid feed in term of cell voltage and power density. Methanol does not perform perfectly for mass transfer and requires high localized cooling at anode. Furthermore, the extent ofmethanol cross over from anode to cathode and gas release at the electro catalyst surface leads to the lower performance of liquid feed cells. On the other hand, vapor feed cells have some draw backs as well, such as dehydrating the membrane, less life time and high temperature required for fuel vaporization. Consequently, more complex and costly reformer is needed. In addition, they are not suitable for portable applications. Proton Exchange Membrane (PEM) is considered as the main part in DMFCs to provide low penetrability and high proton conductivity. In addition, it provides high thermal and chemical stability for proper performing of DMFC. Flemion from Asahi Chemical and Naon from Dupont are the most common per uorinated ion-exchange polymers used for DMFC. They have both mechanical strength and high hydro phobicity of the sulphuric acids which is more prominent due to the presence of the water. As a consequence, water and methanol travel across per uorosulfonic acid membrane which is a form of methanol cross over that has negative impact on its performance. The PEM can be modied to overcome this problem in 2 ways: sulfonation and preparing composite membrane by the incorporation of in organic ceramic materials.Comparison of different fuel cell technologiesApplications of fuel cells depend on the type of fuel cell to be used. With various types of fuel cell technologies available, it is necessary to clarify which technology is best suited to a specic application. Fuel cells can produce a wide range of power from 1 to 10 MW; hence they can be employed in almost any application that needs power. They can be used in small range power devices and personal electronic equipment such as mobile phones and personal computers (PCs). Medium scale power applications include fuel cell vehicles, domestic appliances, military applications and public transportation. Finally, in the large range power applications (110MW),Fuel cells are used in distributed power systems and grid quality AC.

Operational Specifications of fuel cell technologies.Comparisons of technical characteristics of fuel cell technologies.

APPLICATIONS Fuel cells can be deployed in any setting where a reliable source of base load, on-site power is desired and, ideally, where by-product heat can be effectively utilized. They are also well-suited as alternatives to batteries or diesel generators for strictly back-up power applications, particularly in remote areas (such as cellular phone towers), and at critical facilities in urban areas with air quality issues. Current Fuel Cell Market There are currently several hundred large fuel cell installations in the United States. In 2010, the U.S. market grew by more than 50%. Globally, 30 to 50 megawatts (MW) of fuel cell capacity are being installed annually with a projected 213 MW of new installed capacity in 2013. Projects are getting larger, with the average stationary fuel cell installation growing to about 1 MW, up from 250 kW in 2005. Costs Costs for stationary fuel cell installations have dropped from about $600,000 per kW in the 1970s (when fuel cells were developed for NASA) to about $4,500 per kW today for the most widely deployed technologies. This is higher than the capital costs for fossil-fuel based distributed generation such as diesel generators and gas turbines. But it is lower than the capital costs of other distributed clean energy technologies such as solar photovoltaics. The U.S. Department of Energys goal is to reduce this cost to about $400 per installed kW by 2020 for solid oxide fuel cell technology. It has formed the Solid State Energy Conversion Alliance (SECA), a government-industry partnership to achieve that goal. Like renewable energy technologies, fuel cells are eligible for the 30% federal Investment Tax Credit and for direct financial subsidies, in some states, lowering their capital costs considerably. Because fuel cells can operate as a continuous, baseload source of power (unlike solar or wind which are intermittent), these capital costs can be spread out over far more kilowatt-hours (kWh) produced, especially when the byproduct heat is captured and re-used. UTC Power projects that its PureCell 400 kW unit will be able to produce power at 16/kWh (with 50% heat utilization), and at 14/kWh (with 100% heat utilization), before any federal or state subsidies. The capital costs of fuel cells can also be transferred through third-party ownership, in which a manufacturer or financial intermediary owns the system, realizes the tax benefits and sells energy to the host facility under a fixed price contract.BENEFITS OF FUEL CELLS Stationary fuel cells have considerable benefits both to the facility where they are installed and to the public at large. These benefits will multiply as the costs of fuel cells continue to decline relative to grid power and the number of installations increases. USER BENEFITS Reliability Fuel cells are well suited for primary power applications, providing both an extremely reliable and high-quality source of on-site power. This reliability makes them ideal for public safety facilities such as emergency dispatch centers, police and fire stations and hospitals. For private facilities such as computer server farms, data centers and laboratories where even momentary losses of power or voltage changes can disrupt computers and sensitive equipment, fuel cells deliver the sustained power quality needed, with grid power acting as a backup. Even noncritical facilities such as office buildings, retail stores and hotels can benefit from a grid-independent source of power that can also displace other fuels for heating, cooling and refrigeration. Siting While fuel cells have some local siting challenges, in general they are easy to site relative to other distributed generation technologies because they can operate emission-free, are quiet and compact. In some states such as California, they are completely exempt from permitting requirements. Fuel cell technologies that directly utilize natural gas (or biogas) avoid any local concerns over on-site hydrogen storage.Remote operation Fuel cells can be operated and monitored remotely. This is important for fuel cells installed as backup power in remote locations such as telecommunications towers. Base load Clean Energy Many businesses and public facilities are installing solar photo voltaics as a way of providing on-site clean energy. Fuel cells high efficiency and ability to produce constant power makes them a good complement to solar.

Energy Cost Hedge The installation of fuel cells can insulate businesses from unpredictable and rising electricity costs. While fuel cells still require hydrogen or natural gas as an input, these costs might rise less quickly than electricity, particularly in the event of state, regional, or federal carbon legislation. PUBLIC BENEFITS Environmental Stationary fuel cells result in dramatically reduced onsite air pollution relative to back-up diesel generators. They can also result in reduced emissions relative to grid power depending on the source of generation that is displaced. This is due to the use of natural gas or biogas as the source of hydrogen, the high conversion efficiency of fuel cells, and the absence of particulate emissions. Fuel cells are driven by electrochemistry, not combustion. As a result, fuel cells emit only trace amounts of NOx. Because fuel cells are intolerant of sulfur, the fuels used have to be desulfurized, and thus fuel cells emit no SOx. If the direct fuel input is hydrogen, then only water vapor is generated in the exhaust. Because of the high electrical efficiency of fuel cells, the amount of CO2 emitted per kWh of electricity generated is lower than from conventional fossil fuel generation. Avoided emissions are further increased when the facility is configured to utilize the waste heat from the fuel cell. Avoided Generation and Transmission Costs Like other distributed generation technologies, fuel cells displace utility purchases of wholesale electricity on the margin and during peak demand periods. The cumulative effect of fuel cells with other distributed generation resources can also defer the need to build both additional generation and distribution system upgrades. Public Safety and Security When power blackouts occur, the need to maintain critical public facilities and services ranging from police and fire dispatch to hospitals to water pumping and wastewater treatment is essential. Fuel cells provide a reliable way to ensure that these facilities stay up and running.CONCLUSIONS Fuel cells are coming into widespread commercial use for stationary applications, and their combination of reliability, efficiency, and low environmental impact make them an outstanding distributed generation technology for a range of applications. As the technology improves and costs decline, more businesses and public institutions should turn to fuel cells as a source of both primary and backup power. However, as with other clean energy technologies, states play an important role in accelerating their adoption through both public policy and financial support. Policies such as including fuel cells as eligible resources in state renewable portfolio standards, encouraging or requiring the use of fuel cells in critical public facilities, and adopting uniform siting guidelines are important steps. In addition, providing financial incentives through state clean energy funds can help businesses overcome the first cost hurdles of installing fuel cells. These policy recommendations are reviewed in greater depth in an accompanying briefing paper, Advancing Stationary Fuel Cells through State Policies.

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