Renewable energy is energy derived from natural resources that replenish themselves over a period of time without depleting the Earth’s resources. These resources also have the benefit of being abundant, available in some capacity nearly everywhere, and they cause little, if any, environmental damage. Energy from the sun, wind, and thermal energy stored in the Earth’s crust are examples. For comparison, fossil fuels such as oil, coal, and natural gas are not renewable, since their quantity is finite—once we have extracted them they will cease to be available for use as an economically viable energy source. While they are produced through natural processes, these processes are too slow to replenish the fuels as quickly as humans use them, so sources will run out sooner or later.