Most renewable energy comes either directly or indirectly from the sun. Sunlight, or solar energy, can be used directly for heating and lighting homes and other buildings, for generating electricity, and for hot water heating, solar cooling, and a variety of commercial and industrial uses.
The sun’s heat also drives the winds, whose energy is captured with wind turbines. Then, the winds and the sun’s heat cause water to evaporate. When this water vapor turns into rain or snow and flows downhill into rivers or streams, its energy can be captured using hydro-power.
Along with the rain and snow, sunlight causes plants to grow. The organic matter that makes up those plants is known as biomass. Biomass can be used to produce electricity, transportation fuels, or chemicals. The use of biomass for any of these purposes is called biomass energy.
Hydrogen also can be found in many organic compounds, as well as water. It’s the most abundant element on the Earth. But it doesn’t occur naturally as a gas. It’s always combined with other elements, such as with oxygen to make water. Once separated from another element, hydrogen can be burned as a fuel or converted into electricity.
Not all renewable energy resources come from the sun. Geothermal energy taps the Earth’s internal heat for a variety of uses, including electric power production, and the heating and cooling of buildings. And the energy of the ocean’s tides comes from the gravitational pull of the moon and the sun upon the Earth
The ocean can produce thermal energy from the sun’s heat and mechanical energy from the tides and waves. NREL does not conduct research in ocean thermal energy or ocean mechanical energy. See the U.S. Department of Energy’s Consumer Guide Web site for basic information ocean energy.
Flowing water creates energy that can be captured and turned into electricity. This is called hydroelectric power or hydropower. NREL doesn’t perform any research in hydroelectric power technologies. For more information on hydroelectric power, see the Hydro-power Basics from the U.S. Department of Energy’s Wind and Hydro-power Technologies Program.
What Is Renewable Energy?
Renewable energy sources including biomass, hydro-power, geothermal, wind, and solar provide 7% of the energy used in the United States. Most renewable energy goes to producing electricity.
Renewable energy sources can be replenished. The five renewable sources used most often are:
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- Biomass — including wood and wood waste, municipal solid waste, landfill gas, and bio-gas, ethanol, and bio-diesel
- Water (hydro-power)
What Role Does Renewable Energy Play in the United States?
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 7% of all energy used nationally.
The Role of Renewable Energy Consumption in the Nation’s Energy Supply, 2008
Over half of renewable energy goes to producing electricity. About 10% of U.S. electricity was generated from renewable sources in 2009. The next largest use of renewable energy is the production of heat and steam for industrial purposes. Renewable fuels, such as ethanol, are also used for transportation and to provide heat for homes and businesses.
Renewable energy plays an important role in the supply of energy. When renewable energy sources are used, the demand for fossil fuels is reduced. Unlike fossil fuels, non-biomass renewable sources of energy (hydropower, geothermal, wind, and solar) do not directly emit greenhouse gases.
Why Don’t We Use More Renewable Energy?
In the past, renewable energy has generally been more expensive to produce and use than fossil fuels. Renewable resources are often located in remote areas, and it is expensive to build power lines to the cities where the electricity they produce is needed. The use of renewable sources is also limited by the fact that they are not always available — cloudy days reduce solar power; calm days reduce wind power; and droughts reduce the water available for hydropower.
The production and use of renewable fuels has grown more quickly in recent years as a result of higher prices for oil and natural gas, and a number of State and Federal Government incentives, including the Energy Policy Acts of 2002 and 2005. The use of renewable fuels is expected to continue to grow over the next 30 years, although we will still rely on non-renewable fuels to meet most of our energy needs.