Renewable energy sources, or RES, are those energy sources which are not destroyed when their energy is harnessed. Renewable energy sources are distinct from fossil fuels which must be combusted to release energy. Human use of renewable energy requires technologies that harness natural phenomena, such as sunlight, wind, waves, water flow, biological processes such as anaerobic digestion, and geothermal heat. Traditional use of wind, water, and solar power is already widespread; but renewable energy sources are becoming more attractive in the light of new technologies and the twin threats of energy crisis and climate change.
Renewable energies are all sustainable energys. Nuclear fission is not a renewable energy.

Renewable energy resources may be harnessed directly, such as in solar ovens, geothermal heating, and water and windmills. They may require energy harvesting through appropriate technologies such as: electricity generation through wind turbines or photovoltaic cells (PV cells), production of biofuels such as biogas from anaerobic digestion, or ethanol from biomass (see alcohol as a fuel). The development of renewable energy technologies is linked to concerns about the exhaustion of fossil fuels and the environmental, social and political risks of extensive use of fossil fuels and nuclear energy.

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