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AN OVERVIEW
What is a Fuel Cell?
Types of Fuel Cells
From Cell to Stack
From Stack to System
Related Resources
What is a Fuel Cell?
A fuel cell is an electrochemical energy conversion device, similar to a battery in that it provides continuous DC power, which converts the chemical energy from a fuel directly into electricity and heat. When operated directly on hydrogen, the fuel cell produces this energy with clean water as the only by-product. Unlike a battery, which is limited to the stored energy within, a fuel cell is capable of generating power as long as fuel is supplied.
Although hydrogen is the primary fuel source for fuel cells, the process of fuel reforming allows for the extraction of hydrogen from more widely available fuels such as natural gas and propane or any other hydrogen containing fuel.
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Types of Fuel Cells
There are several types of fuel cells, with the predominant types being:
Proton Exchange Membrane (PEM) Fuel Cells
PEM fuel cells operate at relatively low temperatures (60-160°C) have high power density, can vary their output quickly to meet shifts in power demand, and are suited for applications where a quick startup is required.
Plug Power is focused on commercializing PEM fuel cells systems ranging in size from 1 kilowatt to 100 kilowatts.
Phosphoric Acid Fuel Cells (PAFC)
Phosphoric acid fuel cells have been field tested as early as the 1970s. These systems operate at temperatures between 150°C and 200°C. The principal use of these systems has been for mid-sized (200kW) stationary power generation applications.
Molten Carbonate Fuel Cells (MCFC)
Molten carbonate fuel cells operate at very high temperatures (600-700°C) that allow them to use fuel directly with a simplified fuel processor. They require significant time to reach operating temperature and to respond to changes in electricity demand, and therefore are best suited for the provision of constant power in large utility applications.
Solid Oxide Fuel Cells (SOFC)
Solid oxide fuel cells operate at extremely high temperatures (700-1000°C). As a result, they can tolerate relatively impure fuels. Their relatively simple design combined with the significant time required to reach operating temperature and to respond to changes in electricity demand make them suitable for large to very large stationary power applications.
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From Cell to Stack
To produce a usable amount of electricity, multiple fuel cells are combined into a fuel cell stack. The stack is essentially an assembly of individual fuel cells (each producing up to about one volt) designed to produce the desired electrical current and voltage for a specific application such as a residence or small commercial application. The direct current electricity produced can be varied over a wide range by altering the area and number of cells in the stack.
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From Stack to System
Producing electrical power for a working application requires more than just the fuel cell stack. A fuel cell system may include fuel processing, thermal management, power conditioning, electric grid connection and energy storage modules. The power conditioning system provides regulated DC or AC power appropriate for the application. The successful integration of an entire fuel cell system is critical to achieve optimal performance.
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