What is the definition of "alternative energy"?

Alternative energy is a substitute source of power that has equivalent or superior performance compared to existing technologies but do not exhaust fossil fuel or release carbon dioxide. These alternatives are renewable, readily available and ecological friendly.

Energy gathered from the sun, wind and water need to be utilized further to limit the use of fossil fuels, which emit the carbon dioxide responsible for some pollution and global warming. Alternative, clean and free energy sources also include biomass, geothermal and hydroelectric energy. Proof that alternative energy is vital includes the earth’s climate changes, continuous increase of population and fossil fuel reduction.