Renewable Energy

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Renewable Energy


Renewable energy refers to energy from sources that can be replenished. Examples of renewable energy include sunlight, tides, wind, biofuels, and heat from Earth's subsurface (geothermal energy). If forests are replenished in a sustainable way, wood can be burned as a renewable energy source.

As long as there is weather, and the availability of plants for production of biofuel, renewable energy is infinitely obtainable. In contrast, oil and natural gas are derived from the decay of living creatures following their death. Nuclear power is based on the energy emitted by certain radioactive materials as they degrade. These fossil- and isotope-based fuels are non-renewable and their supply will eventually run out.

Renewable energy sources are advantageous from a climate standpoint because they produce fewer, if any, greenhouse gases, particularly carbon dioxide (CO2). Renewable energy can also be obtained with less degradation to the environment than non-renewable sources of energy.

Historical Background and Scientific Foundations

The capability of renewable energy has been around literally forever, in the form of solar power. Wind power has been used to power ships since at least 3200 BC, and

the windmill was invented in China around 200 BC. At the time of Christ, water power was being used to turn stone wheels to grind wheat into flour. Solar power dates to 1839, when French physicist Edmond Becquerel (1820-1891) discovered that certain materials could generate electricity when they absorb sunlight.

By 1920, hydroelectric power produced by the damming of rivers accounted for one quarter of the electricity generated in the United States. In the 1970s, the shortage of gasoline caused by lessened oil production in the Middle East spurred interest in renewable energy sources.

Interest in renewable sources lagged in the 1980s. Since then, however, the recognition of the political instability of areas of the world where oil is especially plentiful (such as Iraq and Iran) and the acceptance that greenhouse gases produced by human-related activities such as the use of gasoline-based vehicles is a major factor in the warming of Earth's atmosphere, spurred interest in renewable energy. Today, it has again become an important agenda of the U.S. government and others.

In solar power, the photons in sunlight are converted to electrical energy by a solar panel. Turbines incorporated into windmills, hydroelectric installations, and tidal power plants generate electricity from the conversion of the energy contained in the moving air or water.

These sources of energy are possible because one form of energy is easily converted to another form. Indeed, wind energy is essentially another form of solar energy; the heat energy of the sun causes air to warm and rise, which generates winds that power the wind turbines.


BIOFUEL: A fuel derived directly by human effort from living things, such as plants or bacteria. A biofuel can be burned or oxidized in a fuel cell to release useful energy.

GEOTHERMAL ENERGY: Energy obtained from Earth's internal heat, which is maintained by the breakdown of radioactive elements. Geothermal means, literally, Earth-heat. Geothermal energy may be used either directly as heat (e.g., to heat buildings or industrial processes) or to generate electricity.

GREENHOUSE GASES: Gases that cause Earth to retain more thermal energy by absorbing infrared light emitted by Earth's surface. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and various artificial chemicals such as chlorofluorocarbons. All but the latter are naturally occurring, but human activity over the last several centuries has significantly increased the amounts of carbon dioxide, methane, and nitrous oxide in Earth's atmosphere, causing global warming and global climate change.

PHOTON: Smallest individual unit of electromagnetic radiation (light energy). These light particles are emitted by an atom as excess energy when that atom returns from an excited state (high energy) to its normal state.

TIDAL POWER: Electrical power generated by harnessing the energy of rising and falling tides: a form of hydropower. Several countries have built or seek to build large tidal power facilities, but tidal power is not yet a major source of electricity.

WIND FARM: A cluster of wind turbines generating electricity. Wind farms are the most efficient way to generate large amounts of electricity from wind because they can share a single, high-capacity line to transmit their power output to the long-distance electric-power network (grid).


“Renewable energy generally has a positive effect on energy security, employment and on air quality. Given costs relative to other supply options, renewable electricity, which accounted for 18% of the electricity supply in 2005, can have a 30–35% share of the total electricity supply in 2030 at carbon prices up to 50 US$/tCO2-eq.”

As used in Intergovernmental Panel on Climate Change (IPCC) reports “a carbon dioxide equivalent (CO2–eq) is the amount of CO2 emission that would cause the same radiative forcing as an emitted amount of a well mixed greenhouse gas or a mixture of well mixed greenhouse gases, all multiplied with their respective GWPs [Global Warming Potential] to take into account the differing times they remain in the atmosphere [WGI AR4 Glossary].” tCO2 denotes tons carbon dioxide equivalents.

SOURCE: Metz, B., et al., eds. Climate Change 2007: Mitigation of Climate Change. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.

Impacts and Issues

Non-renewable energy sources are a major source of greenhouse gases such as CO2, whose accumulation in the atmosphere is driving the warming of Earth's atmosphere. In addition, the burning of fossil fuels to power gasoline-based vehicles is the major source of air pollution in urban areas.

Aside from climatic consequences, the use of nonrenewable energy also has documented healtheffects inhuman populations. For example, Health Canada reports that an estimated 16,000 people die every year in Canada from diseases related to air pollution, and thousands are disabled.

As of 2007, renewable energy has become an accepted alternative for major power projects. For example, in March 2007, leaders of the countries belonging to the European Union agreed in principle to have renewable energy supply 20% of the EU's energy needs by 2020. In another example, official approval was granted for construction of the London Array wind farm. When fully operational, the facility's 300+ wind turbines will generate enough electricity to power 30% of the homes in London. If generated conventionally, that much energy would produce almost 2.2 million tons (2 million metric tons) of CO2 emissions each year.

The benefits of renewable energy come with some disadvantages. For example, hydroelectric facilities alter watercourses and can cause destructive flooding of upstream dams. As of 2007, flooding caused by the Three Gorges Dam project in China has displaced over a million people. Elsewhere, the low-frequency drone produced by large wind turbines can be an irritant, disturbing the sleep of those living nearby.

The production of biofuels from crops such as corn may prove to be problematic, as the quantities of the crop needed to generate meaningful amounts of biofuel make less corn available for food, particularly for the raising of cattle. More importantly, the energy needed to generate the biofuel exceeds the energy that becomes available in the final product. For example, the conversion of corn to biofuel requires almost 30% more energy than the fuel produced, and conversion of sunflowers requires over 100% more energy than the fuel produced. This negative energy balance limits the use of biofuel as a major renewable energy source.

See Also Biofuel Impacts; Biomass; Ethanol; Geothermal Energy; Renewability; Solar Energy; Tides; Wind Power.



Boyle, Godfrey. Renewable Energy. New York: Oxford University Press USA, 2004.

Kruger, Paul. Alternative Energy Resources: The Quest for Sustainable Energy. New York: Wiley, 2006.

Pahl, Greg. Biodiesel: Growing a New Energy Economy. White River Junction, VT: Chelsea Green, 2005.

Web Sites

“Estimated Number of Excess Deaths in Canada Due to Air Pollution.” Health Canada,2005. <> (accessed December 2, 2007).

Brian D. Hoyle