Non–fi nite energy sources such as hydro power, biofuel, wind, solar power, tidal power, wave power, geothermal power.

Unlike fossil fuels, which are exhaustible, renewable energy sources regenerate and can be sustained indefinitely. The five renewable sources used most often are:

Biomass — including wood and wood waste, municipal solid waste, landfill gas, and biogas, ethanol, and biodiesel

Water (hydropower)

Geothermal

Wind

Solar

The use of renewable energy is not new. More than 150 years ago, wood, which is one form of biomass, supplied up to 90% of our energy needs. As the use of coal, petroleum, and natural gas expanded, the United States became less reliant on wood as an energy source. Today, we are looking again at renewable sources to find new ways to use them to help meet our energy needs.

In 2009, consumption of renewable sources in the United States totaled 7.7 quadrillion Btu — 1 quadrillion is the number 1 followed by 15 zeros — or about 8% of all energy used nationally.