A fuel cell uses the chemical energy of hydrogen or other fuels to cleanly and efficiently produce electricity. Fuel cell systems are a clean, efficient, reliable, and quiet source of power. Fuel cells do not need to be periodically recharged like batteries, but instead continue to produce electricity as long as a fuel source is provided. Due to their chemistry, fuel cells are very clean. Fuel cells that use pure hydrogen fuel are completely carbon-free, with their only byproducts being electricity, heat, and water. Some types of fuel cell systems are capable of using hydrocarbon fuels like natural gas, biogas, methanol, and others. Fuel cells are also scalable. This means that individual fuel cells can be joined with one another to form stacks. In turn, these stacks can be combined into larger systems. Fuel cell systems vary greatly in size and power, from combustion engine replacements for electric vehicles to large-scale, multi-megawatt installations providing electricity directly to the utility grid. Below are a few of the most commonly used fuel cells: Molten Carbonate Fuel Cell (MCFC) operate at temperatures upwards of 1200 degree Fahrenheit and can also use natural gas directly as its fuel source, as its high temperatures allow internal reforming of the natural gas into hydrogen within the system itself. MCFCs can reach efficiencies of 50-60%, and 70% - 80% in CHP applications. These fuel cells are typically deployed in stationary applications, providing high-quality primary and back-up power to utilities and businesses. Phosphoric Acid Fuel Cell (PAFC) use a liquid phosphoric acid and ceramic electrolyte and a platinum catalyst. PAFCs are typically used in a cogeneration mode to not only produce electricity, but also heat to be captured to assist heating and cooling. PAFCs are often seen in high-energy demand applications, such as hospitals, schools and manufacturing and processing centers. Proton Exchange Membrane Fuel Cells (PEMFCs) use a polymer membrane for its electrolyte and a precious metal, typically platinum, for its catalyst. Pure hydrogen gas is the typical fuel for PEMFCs. PEMFCs are well-suited for cars and other specialty vehicles such as forklifts that need to quickly start up or accelerate. Additionally, PEMFC’s can be scaled in stationary applications for use in telecommunications, data centers, and residential markets. Direct Methanol Fuel Cell (DMFC) use a polymer membrane as an electrolyte and commonly a platinum catalyst. DMFCs draw hydrogen from liquid methanol, rather than use direct hydrogen fuel. Applications of DMFCs range from small electronics, such as battery chargers and laptops, to larger applications like stationary power for telecommunications backup. Solid Oxide Fuel Cell (SOFC) are the highest temperature fuel cells, operating at about 1800 degrees Fahrenheit. SOFCs are being used in a range of applications, from small residential auxiliary power units supplying heat and power to homes, to large-scale stationary power generators for larger buildings and businesses. Alkaline Fuel Cell (AFC) are best known for their roles in the NASA Apollo mission to provide both water and electricity to the crew. The AFC is one of the most efficient types of fuel cells, with a potential of 60% electrical efficiency, and 80% to 90% in CHP applications. AFCs use hydrogen as a fuel source, though are highly sensitive and can fail when exposed to carbon dioxide, which is why they are primarily used in controlled aerospace and underwater applications.