Any of various renewable power sources to use in place of fossil fuels and uranium .
Fusion devices (see nuclear fusion ) are believed by some to be the best long-term option, because their primary energy source would be deuterium , abundant in ordinary water. Other technologies include solar energy , wind power , tidal power, wave power, hydroelectric power , and geothermal energy . The amount of energy in such renewable and virtually pollution-free sources is large in relation to world energy needs, yet at present only a small portion of it can be converted to electric power at reasonable cost.