There must surely come a time when heat and power will be stored in unlimited quantities… all gathered by natural forces.
Thomas A. Edison, 1910
Energy storage will play a critical role in any future renewable energy system. There are two principal reasons why energy storage will be of increasing importance to renewable energy:
• Many of the most significant renewable energy sources like solar and wind are variable in nature
• The transportation system, including cars, buses, ships, and planes, requires energy to be carried by the vehicles. Whether as liquid fuels, hydrogen for fuel cells, or batteries for electric vehicles, some type of energy storage will be needed.