At present, most of our energy comes from fossil fuels (coal, oil and natural gas). However, reserves are limited. Because demand for electricity is rising rapidly, fossil fuels will be exhausted in a relatively short time. Therefore, people must develop and use alternative energy sources.With fast growth of civilization there is also an ever mounting need for energy. In tropical countries, due to having much sunshine, the sunshine is used to generate electricity. And a lot of countries in the world use different resources instead of using water to generate electricity.