Renewable energy is a term used to describe energy that is derived from resources, like the sun and the wind -- resources that are continually available to some degree or other all over the world. We never run out of them. And their use or capture does not inflict any material damage on the environment.
Sunlight is the source of most renewable energy power, either directly or indirectly. The sun can be harnessed to produce solar energy -- electricity for heating, cooling, and lighting homes, offices, entertainment complexes, airports, and a variety of other industrial structures.
Heat from the sun also produces wind, whose energy is captured by wind turbines and turned into electricity capable of powering entire towns.
Hydroelectric power is produced from streams, rivers, and waterfalls that flow downhill, their tremendous power turning large turbines that convert the flow to electricity. Industrialized nations have already developed most of the world's large hydroelectric resources, but small-scale technologies are being developed that will provide additional localized power in the future.
Organic plant matter, known as biomass, can be burned, gasified, fermented, or otherwise processed to produce electricity, heat and biofuels for transportation. Biomass combined heat and power (CHP) facilities simultaneously produce both heat and electricity (Click to view the Pew Trust’s CHP video: Turn Heat Into Power With Industrial Efficiency). Bioenergy is another term for energy that is produced from biomass for any of these purposes.
Geothermal energy taps the Earth's internal heat in the form of steam for a variety of uses, including electric power production, and the heating and cooling of buildings. Some new systems are in development for harvesting even more power by injecting water back into underground heat sources to produce more steam.
Ocean energy can also be used to produce electricity. In addition to tidal energy, energy can be produced by the action of ocean waves, which are driven by both the tides and the winds. Because of their link to winds and surface heating processes, ocean currents are considered as indirect sources of solar energy.
Waste Heat to Power (WHP) is the process of using recovered waste heat to generate power with no combustion and no emissions, using the same technologies deployed for the geothermal and other industries. Anywhere there is an industrial process that involves transforming raw materials into useful products – steel mills, paper plants, refineries, chemical plants, oil and gas pipelines, and general manufacturing -- heat is wasted as a byproduct. This waste heat is produced whenever the operation is running, often 24 hours a day, seven days a week, 365 days a year. If not recovered for reuse as lower temperature process heat or to produce emission-free power, the heat will dissipate into the atmosphere, a wasted opportunity.