Fuel cells are electrochemical devices that combine hydrogen and oxygen to produce electricity, with by products of water and heat. The fuel cell generates electricity (and the by products) as long as fuel is supplied. The process is cleaner, quieter, and more efficient than fuel-burning methods of generating power. In addition, fuel cells are highly reliable and durable, with nearly zero emissions and low maintenance cost.
Interest in fuel cells is mounting as more facilities realize the benefits of using fuel cells in stationary applications such as back-up power and peak shaving. Fuel cells are viable alternatives to generators to provide facility backup power when grid power is interrupted by increasingly common weather-related outages. The Energy Policy Act of 2005 (EPAct05) includes incentives for facilities with surplus capacity to sell excess power to their electric utility by paralleling the grid.
Today, fuel cell power plants are easily expandable, using stackable modules to obtain the required power output. Waste heat is often used to heat water to supplement building heating systems.
Fuel cells run on hydrogen; however, hydrogen fuel has a low energy density compared to liquid fuels, and there are serious safety concerns for storing hydrogen on-site. Instead, devices called fuel processors can be used to efficiently provide relatively pure hydrogen with a minimum of pollution. For example, reformers are used in vehicular applications to turn hydrocarbon or alcohol fuels into hydrogen. Stationary fuel cells can use natural gas, propane, or hydrogen that has been separated from water. Some fuel cell power plants can be supplied with integral fuel processors.
Membrane systems can extract clean hydrogen from a wide variety of fuels, such as ammonia, methanol, ethanol, gasoline, and diesel fuels, natural gas, and propane. Before membrane systems were available, fuel cells could only rarely be used as backup power units when replacing or complementing diesel generators. Commercially available diesel fuel can be used with palladium-alloy type membranes that can tolerate and remove sulfur. Some membranes can also be used with various renewable and alternative fuels, further extending their use.
Phosphoric acid fuel cells (PAFC) can be found in hotels, office buildings, schools, military bases, hospitals, nursing homes, utility power plants, landfills and waste water treatment plants. They generate electricity at 40% efficiency and higher and approximately 85% of the steam produced is available for cogeneration.
PAFCs are more efficient than the utility grid. These cells use liquid phosphoric acid as the electrolyte and operate at high temperatures – about 450_ F. In addition to the nearly 85% cogeneration efficiency, these fuel cells have a wide tolerance for impure hydrogen. PAFCs can tolerate a CO concentration of about 1.5%, which broadens the choice of fuels. When gasoline is used, the sulfur must be removed.
PAFCs that use hydrogen have been installed at the Los Angeles Zoo to produce 200 kilowatts (kW) of power. The Zoo system is connected to the Los Angeles Department of Water and Power (LADWP) grid. A railcar maintenance facility in New York uses natural gas to provide 250 kW of backup and grid-connected power using PAFCs. The heat generated is used to heat water for the facility.
Proton exchange membrane (PEM) fuel cells operate at relatively low temperatures (about 175_F) and have high power density. Outputs range from 50 watts to 75 kW. Output varies quickly to meet shifts in demand, and PEM fuel cells are suited for applications such as vehicles, that need fast startup. According to the U.S. Department of Energy (DOE), “they (PEM fuel cells) are the primary candidates for vehicles and buildings, and potentially for much smaller applications such as replacements for rechargeable batteries.”
A small (6 kW) unit is operating at a fire station in Oregon using hydrogen fuel. This unit is capable of providing up to 25,000 hours of reliable backup power. A PEM fuel cell is providing a NYSERDA (New York State Energy Research and Development Authority) office facility with 1 megawatt (MW) of backup power that is also grid connected. The fuel cell array consists of four 250-kW units that use hydrogen as the fuel source. Holding PEM cells back from even more applications is their sensitivity to fuel impurities.
PEM fuel cells are starting to be used in telecommunications applications, such as backup power for telephone central offices and cell towers. Fuel cells designed for telecom applications are usually provided in 24- or 48-Vdc versions and are equipped with modular electronics cards that provide both expandability and redundancy for higher reliability. These communications applications have stringent requirements, and the fuel cells must be NEBS certified.
Network equipment-building systems (NEBS) certification requires products – including fuel cells – to be tested for operational continuity under extreme climate conditions, structural integrity and resistance to earthquakes, firearms, drops, and other impacts (such as shipping) and exposure to fire. The testing also ensures EMC/EMI safety and compliance. Level 3 certification is a requirement for North American telecommunications carriers and meets strict industry recognized standards.
Molten carbonate fuel cells (MCFC) use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert matrix, and operate at high temperatures – about 1,200_ F. They require carbon dioxide and oxygen to be delivered to the cathode. MCFCs have been operated on hydrogen, carbon monoxide, natural gas, propane, landfill gas, marine diesel, and simulated coal gasification products. Ten kW to 2 MW MCFC units have been tested on a variety of fuels and are primarily targeted to electric utility applications.
A jail facility in California uses MCFCs to provide 1 MW (four 250-kW modules) for 90% of the base load to complement a 1.18-MW solar (PV) power system. At the USMC Camp Pendelton facilty in California a 500-kW MCFC (two 250-kW modules) supplies the base electric load for the Bachelors Enlisted Quarters. The waste heat provides hot water for the facility.
Advances in fuel cell technology continue to improve performance and moves them closer to becoming the power source of choice for more applications. As the fuel cell industry expands to fill these power needs, prices are expected to become more attractive.
To stay informed about the fuel cell industry and technology advances, go to: www.fuelcells.org. There are lists of fuel cell products and manufacturers, an electronic newsletter, and a searchable database of state programs, policy, incentives, initiatives, and stationary fuel cell installations. In addition, transportation applications, including vehicle demonstrations and hydrogen fueling station locations are also available.
