General information about renewable energy

Most renewable forms of energy, other than geothermal and tidal, are in fact stored solar energy. Water power and wind power represent very short-term solar storage, while biomass represents slightly longer-term storage, but still on a very human time-scale, and so renewable within that human time-scale. Fossil fuels, on the other hand, while still stored solar energy, have taken millions of years to form, and so do not meet the definition of renewable. Renewable means not just for 10 years but for 100 or 1000.

Renewable energy resources may be used directly as energy sources, or used to create other forms of energy for use. Examples of direct use are solar ovens, geothermal heat pumps, and mechanical windmills. Examples of indirect use in creating other energy sources are electricity generation through wind generators or photovoltaic cells, or production of fuels such as ethanolfrom biomass (see alcohol as a fuel).