For centuries, people have harnessed the sun's energy in form of light and heat using technology that continues to evolve. The sun is a renewable source of energy because it does not diminish regardless of how much it is exploited. Photovoltaic systems harness solar energy and convert it to electricity to run industries, entire office buildings and schools; solar energy can even pump water in isolated areas.
People are able to generate power from wind and water as well. These two are also renewable sources of energy that produce power by driving electricity-generating turbines. A variety of wind turbines ranging in size can produce considerable quantities of power, as much as several megawatts. Water, on the other hand, including steam, can drive turbines as well to generate power. Running water and wave energy are used to produce electricity in hydroelectric plants, while steam is used in thermoelectric power plants.
Fossils fuels were formed through natural processes of decomposition of plants and animals buried under the earth's crust over a long period. They include coal and petroleum products such as oil, paraffin and natural gas. Fossil fuels are nonrenewable in the sense that they take a very long time to replenish; we burn fossil fuels for energy at a much faster rate than natural processes can restore them.
Nuclear energy is another arguably nonrenewable source of energy; it is sourced from chemical processes such as nuclear fission. Nuclear fission is the splitting of radioactive atoms such as uranium. This reaction produces heat that turns water into steam for driving electricity-generating turbines.