At present, most of our energy comes from fossil fuels (oil, coal, and natural gas). However, such reserves are limited. Because power demand is increasing very rapidly, fossil fuels will be exhausted within a relatively short time. Therefore, people must develop and use alternative sources of energy.One alternative source is nuclear energy. Nuclear energy can provide enough electricity for the world’s needs for hundreds of years, but it can be very dangerous. Another alternative source of energy is geothermal heat, which comes from deep inside the earth. Scientists use this heat to make energy. However, this energy is available only in a few places in the world.The sun, water, and the wind are other alternative sources of energy. The wind turns windmills and moves sailboats. It is a clean source of energy, and there is lots of it. Unfortunately, if the wind does not blow, there is no wind energy. When water moves from a high place to a lower place, it makes energy. This energy is used to create electricity. Water power gives energy without pollution. However, people have to build dams to use this energy. And as dams cost a lot of money, water energy is expensive.The sun releases large amounts of energy every day. This energy can be changed into electricity. Many countries use solar energy for their daily life. Solar panels on the roofs of houses can create enough energy to heat or cool an entire house. Solar energy is not only plentiful and infinite but also clean and safe.Although there are some disadvantages, the potential of alternative sources of energy is great. However, how to make full use of these sources of energy is a question for researchers all over the world.