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What Is Renewable Energy?

  What Is Green Power?   What Are the Benefits of Green Power?  
  What Is Renewable Energy?   Glossary of Green Power Terms  

To be considered renewable energy, a resource must rely on naturally existing energy flows such as sunshine, wind and water flowing.  The energy source, or “fuel”, must be replaced by natural processes at a rate that is equal to, or faster than, the rate at which the energy source is consumed.

Renewable resources can have inherent and varying technological, environmental, social, and economic benefits.  Currently, renewable energy accounts for roughly 2.3% of the United States energy supply (Graphic 1).  EPA’s Green Power Partnership recognizes solar, biomass, geothermal, wind and low-impact hydro as eligible green power resources due to their respective environmental benefits and expressed consumer preference in voluntary green power markets.


Graphic 1: Electric Power Generation by Fuel Type (2005)

Pie chart graphic showing current fuel mix for U.S. Electricity Generation: Other Renewablel 1%;  Biomass 7%:, Oil 2%; Hydro 7%; Natural Gas 14%; Nuclear 20%; Coal 49%.

Data from Energy Information Administration (EIA, 2004).

Below is a list of common renewable energy choices currently available in today’s marketplace. Not all renewable energy sources are viewed as green power. A green power resource must produce electricity with zero anthropogenic (caused by humans) emissions, have a superior environmental profile to conventional power generation, and must have been built after the beginning of the voluntary market (1/1/1997). Green power products must exhibit credible benefits that satisfy specific environmental consumer needs in a voluntary marketplace.

Photo of wind turbines

Wind energy takes advantage of naturally occurring wind flows. Wind turbines produce significant amounts of electricity when mounted in areas with enough wind. Wind energy has become increasingly competitive in comparison to other energy sources. Wind power currently supplies most of the capacity for the voluntary green power market.

photo of sun

Solar power is a technology that harnesses the sun’s energy to produce electricity. Also known as photovoltaics, solar can easily produce electricity at the point where it is used. Today, many states allow owners of on-site solar photovoltaics to “net-meter.” Net-metering allows the owner to gain credit for any electricity not used by feeding it back onto the utility grid. The owner earns an electricity credit that is available later when little or no electricity is being produced.

photo of geothermal steam rising

Geothermal energy is a technology that takes advantage of the naturally occurring heat that exists underneath the Earth’s surface. Geothermal energy can produce steam that spins generators to produce electricity. New studies show that geothermal energy is available almost anywhere in the United States.

photo of waterfall

Hydropower takes advantage of turbines placed downstream of a water flow, allowing the natural movement of the water to produce electricity. There are thousands of hydropower facilities found on many of our nation’s rivers and streams. Many of the larger dams create pollution-free energy, but they can also produce significant adverse impacts on the environment. As a result, hydropower must meet low-impact standards. Low-impact hydropower often operates in a “run of the river” mode where little or no water is stored behind a dam.

photo of agricultural crop

Biomass energy combusts naturally occurring organic materials to release energy when burned. Examples of biomass fuels include wood, wood waste, straw, manure, and agricultural crops. Most biomass power plants burn biomass fuels directly to produce steam. A turbine usually captures this steam, and a generator then converts it into electricity. Since organic materials comprise the biomass fuel, combustion of these fuels emits no net greenhouse gas emissions.

photo of methane (biogas) collection system

Biogas (or methane) is a fuel source produced when organic material (biomass) decays. Our nation’s landfills and wastewater treatment plants produce biogas as a natural by-product. Biogas is captured and burned to produce electricity. As with biomass energy, biogas emits no net greenhouse gas emissions because of its organic fuel composition.

photo of landfill compactor Municipal Solid Waste (MSW) can be combusted to produce electricity. Because no new fuel sources are used other than the waste that would otherwise be sent to landfills, MSW is often considered a renewable energy resource. The heat released from burning the MSW produces steam, which turns a steam turbine to produce electricity. Although MSW power plants do emit carbon dioxide, the primary greenhouse gas, the biomass-derived portion is considered to be part of the Earth's natural carbon cycle. In contrast, when fossil fuels (or products made with them, such as plastics) are burned, they release carbon dioxide that has not been part of the Earth's atmosphere.

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Washington, DC 20460

graphical bullet Partners in the Green Power Partnership commit to purchasing green power comprised of these eligible renewable resources. For more specifics, see the list of eligible renewable resources in the Green Power Partnership Program Requirements (PDF, 12 pp., 143 KB, About PDF).
graphical bullet The National Renewable Energy Laboratory’s Web site provides additional information on renewable energy resources.