Renewable Energy

All naturally occurring products, substances, or sources of energy that are useful to human beings are termed resources. Any resource, including any energy resource, is either renewable or non-renewable. The major non-renewable energy resources are fossil fuels such as coal, petroleum, and natural gas or elemental fuels such as uranium (U). Although these materials might be renewed or replaced by natural processes over millions of years, they are not renewed on the time-scale of human history. For all realistic purposes, once they are used, they are gone forever.

Some renewables, like solar energy, tidal and wave energy, hydropower (electricity produced by rivers running downhill through dams), and wind energy, are perpetual. That is, no matter how many windmills are raised...