- Wind power is a renewable source of energy.eolienne image by berdoulat jerome from Fotolia.com
Over the past few decades, concern about the possible impacts of pollution and the limited supply of fossil fuels has prompted many environmentalists and public policy advocates to call for a shift towards increased use of renewable energy for generating electricity. Renewable energy, unlike nonrenewable energy, is derived from sources that are naturally replenished rather than being depleted over time. - Most of the energy we use is ultimately derived from the sun; coal and oil, for example, are essentially solar energy stored by plants in the form of carbon compounds that were buried millions of years ago and altered by heat and pressure. In this context, however, solar energy refers specifically to devices that convert energy from sunlight into heat or electricity for human use. The potential for solar energy is tremendous; according to "Essential Environment", each square meter of Earth's surface receives an average of a kilowatt of energy from the sun, 17 times the amount of power needed to power a lightbulb. Yet harnessing this energy can be trickier than it seems, especially since some areas receive more sunlight than others; furthermore, solar energy is much less efficient on cloudy days. Thermal solar power plants focus sunlight onto a receiver, then use the heat to turn water into steam that turns a turbine. Photovoltaic cells or solar panels, on the other hand, are made of special materials that release electrons when struck by rays of sunlight and thereby generate electric current. Many scientists are working on improving these techniques to make them cheaper and more efficient for common use.
- Hot air rises while cool air sinks; this simple exchange is what causes wind. Wind is thus an indirect form of solar energy. Humans have used wind power for centuries, largely to drive windmills for pumping water and grinding corn. Modern wind turbines, however, use wind energy to turn a generator and thereby generate electricity. According to the American Wind Energy Association, most manufacturers sell turbines with capacity between 700 kilowatts and 2.5 megawatts a unit -- the smallest nuclear power plants have a 476 megawatt capacity by way of comparison. Like solar, wind is emission-free, but some parts of the country receive much more wind than others, so electricity generated by wind must often be transported across large distances to reach consumers.
- As the sun shines on the ocean, it heats water near the surface; some of this water evaporates and is carried by wind across the land, where clouds deposit it as precipitation. Snow and rain that falls at high elevations accumulates and, driven by gravity, heads downhill in rivers and streams. Humans can trap this water on its way and use it to spin turbines that drive generators and thereby generate electricity. According to "Essential Environment", hydroelectric power currently accounts for 16.2 percent of the world's electricity production but is inherently limited since there are only so many rivers and streams that can be dammed; moreover, building dams has major environmental impact by altering the natural habitat.
- Radioactive decay of elements in the Earth's interior heats the molten rock that lies beneath the Earth's crust; this heat creates convection currents. Hot magma rises and sometimes comes close to the Earth's surface, close enough on occasion to heat water trapped underground in aquifers. Humans can tap this hot water or steam and use it to drive turbines and generators; this is called geothermal energy. Like wind, solar and hydroelectric, geothermal energy is emission-free once the plant has been built; if the water in the aquifer is extracted too quickly, however, the aquifer may be depleted, in which case it will no longer be able to supply energy. According to "Essential Environment", geothermal in the US currently supplies enough electricity to power roughly 1.4 million homes.
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