ABSTRACT
Fuel cells and electrolyzers are simply devices for converting between chemical and electrical energy. As such, they are not an essential part of renewable energy and can be used even when the primary energy source is a conventional fossil fuel, such as petroleum or coal. Fuel cells are often included with renewable energy technologies because they exhibit high ef—ciencies, having the potential to greatly reduce the amount of fuel that must be consumed in order to generate a given amount of electrical power. Their high ef—ciency relative to heat engines comes from the fact that they produce electricity directly, with no moving parts and no Carnot-cycle limitations. They are also intrinsically “clean” in that even high temperature fuel cells operate well below the conditions where NOx is generated. In addition, the exhaust stream can be scrubbed of CO2 easily because it is not diluted with large quantities of N2. Finally, fuel cells allow §exible conversion of chemicals to energy and back. The same device can operate as a fuel cell or an electrolyzer by simply reversing the direction of the current.
