Solar cells are regarded as one of the key technologies towards a sustainable energy supply.
Mankind's traditional uses of wind, water, and solar power are widespread in developed and developing countries; but the mass production of electricity using renewable energy sources has become more commonplace only recently, reflecting the major threats of climate change due to pollution, exhaustion of fossil fuels, and the environmental, social and political risks of fossil fuels and nuclear power. Many countries and organizations promote renewable energies through taxes and subsidies. Varying definitions of the term renewable energy have been adopted to define eligibility under these policies.
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