How large or small can a fuel cell be?
Fuel cells can be manufactured as large or small as necessary for the particular power application. Presently, there are micro fuel cells that are the size of a pencil eraser and generate only a few milliwatts of power while there are others large enough to provide the electrical needs of hundreds of homes. Since an individual fuel cell may theoretically produce an open circuit voltage of approximately 1 V, their power output is fully scalable by varying the cross-sectional area of each cell to obtain the desired current and by stacking multiple cells in series to obtain the desired voltage.
