Renewable energy can be utilized through a variety of sources, approaches, systems and technologies. Plants and algae require sunlight for photosynthesis before they can be converted to biofuels or biopower. Hydropower capitalizes on the rain and snowfall resulting from water evaporation and transpiration. Wind generates electricity directly by turning a turbine or indirectly in the form of ocean waves, but the wind itself is driven by the sun. Tides go up and down due to the gravitational attraction between the oceans and the moon. The heat trapped in the earth itself can be put to productive use through geothermal applications.

When the potential for these alternative energy sources is quantified, the numbers are startling. One recent assessment which collected actual data on wind speeds at 80 meters from 7,753 surface stations identified about 72 terawatts (TW) of potential. One-fifth of this potential could satisfy all of the world's energy demand and more than seven times its electricity needs. Excluding biomass, and looking at solar, wind, geothermal and hydroelectric energy resources, the world has roughly 3,439,685 terawatt-hours (TWh) of potential—about 201 times the amount of electricity humans consume each year.

So far, less than 0.09 percent of the potential for renewable energy to meet global energy needs has been harnessed. However, that percentage is starting to increase.