Using Clean Energy to Generate Electricity
Understanding Sustainable Energy Alternatives to Coal
Oct 14, 2009
The United States currently runs on fossil fuels, with just 7% of the country's energy coming from renewable sources such as wind, geothermal, hydroelectric, and solar power as of 2009. The remaining 93% of America's energy comes from nonrenewable sources; specifically, fossils fuels – coal, oil, and natural gas – and nuclear power (Energy Information Administration, web page viewed on October 13, 2009).
What is all of this energy used for? America uses oil primarily for transportation (refined to form gasoline and diesel fuel), while natural gas is used for heating, cooking, and industrial applications (Energy Information Administration). Nuclear reactors help generate electricity, but the bulk of electricity in the United States comes from power plants that burn coal. Coal is, by far, the dirtiest fossil fuel in terms of damage to the Earth and to public health (Environmental Protection Agency web page, viewed on October 14, 2009).
Burning coal causes global warming, acid rain, and dangerous particulates that cause illness. Coal-fired power plants are also the nation's number-one source of mercury contamination, causing neurological damage and birth defects in humans (United States Geological Survey web page, viewed on October 14, 2009). Furthermore, Jeff Goodell writes that, in the three years he spent completing his book Big Coal: The Dirty Secret Behind America's Energy Future (Mariner Books, 2006), "...the American Lung Association calculates [that] about 72,000 people in the United States died prematurely from the effects of coal-fired power plant pollution -- more than from AIDS, murder, or drug overdose".
Clearly, clean and renewable energy sources will be a vital part of a greener, healthier America. But, renewable energy sources can be bewildering. Just how can wind, heat from the Earth, energy from the sun, and moving water be used to generate electricity? Can these sources of energy really replace coal in powering America?
Why Does the United States Depend On Coal?
How did America come to rely on coal for its electricity? There are three major reasons:
- Fossil fuels, including coal, are excellent "energy reservoirs". Combusting coal, oil, or natural gas releases large amounts of heat, which is harnessed to generate electricity by boiling water to produce steam. The steam rises and turns a turbine, rotating a wire coil within a magnetic field, which induces a charge in the wire (electricity).
- Coal been used almost exclusively to provide energy for generating electricity for 100 years; therefore, using coal as a power source is technologically well understood.
- Coal is, by far, the most abundant fossil fuel in the United States, and is relatively cheap to obtain (compared to oil and natural gas). In fact, the United States has been dubbed "The Saudi Arabia of coal" (Goodell, 2006).
In spite of these reasons for using coal, the drawbacks of using coal – such as global warming, acid rain, mercury contamination, and particulate emissions – are now clear. But, how can wind, geothermal, solar, and hydroelectric energy be used to generate electricity, and replace coal in the future?
Using Wind to Generate Electricity
A windmill, or wind turbine, is built in regions of high wind speed, such as mountain passes, flat plains, or ridges. Each wind turbine contains a small generator. When the wind blows, the turbine blades rotate, which operates the generator to produce electricity (specifically, the turbine directly spins a wire coil within a magnetic field, inducing charge to flow within the wire). No heat is produced to boil water and make steam. No carbon dioxide emissions or other greenhouse gases are associated with wind power.
Using Geothermal Energy to Make Electricity
Naturally hot water or steam can be extracted from underground reservoirs and used to make electricity. The steam pushes a turbine, turning a wire in a magnetic field, causing a flow of electrons (electricity). High temperature reservoirs (such as those found in Iceland and Alaska) can be used in this fashion. Lower-temperature reservoirs are less well suited for power plants; instead, these can be used to heat homes or industrial buildings. Geothermal power produces no air pollution or greenhouse gases.
Making Electricity Using the Sun's Rays
Two very different methods are used to make electricity from the sun's rays:
- Solar thermal electricity generation The sun's rays are focused by parabolic mirrors on a tube of fluid (often, a synthetic oil), which in turn heats water to make steam to push a turbine to make electricity. Solel, Inc., a major developer of solar thermal power plants, states that one such plant operating at Kramer Junction in the Mojave Desert in California has produced as much energy as 1 million barrels of oil over its 25-year lifetime (www.solel.com, viewed on October 14, 2009).
- Photovoltaics Solar cells, which generate electricity without any moving parts when the sun's rays shine on them, are composed of thin silicon layers impregnated with special metals (often cadmium telluride or copper indium diselenide). The interaction between these metals, silicon, and the sun's rays produces electricity (Jefferson W. Tester in Sustainable Energy: Choosing Among Options, MIT Press, 2005).
Both solar thermal electricity generation and photovoltaics do not release harmful emissions into the atmosphere.
How Hydroelectric Power Works
Moving water can generate electricity when the flow of water pushes a turbine which is hooked up to a generator. The rotating turbine then turns a coil of wire in a magnetic field, producing electricity. According to the U.S. Department of the Interior Reclamation Department (web site viewed on October 14, 2009), hydroelectric systems can be almost 90% efficient.
Hydroelectric power does not release air pollutants or emissions of any kind. However, dams must be built to house the turbines and channel the water.
America's Energy Future Depends on Harnessing Multiple Renewable Energy Sources
Alternative energy sources for electricity generation in the United States have huge growth potential, and will eventually replace coal to prevent further global warming and environmental harm. However, wind, solar, geothermal, and hydroelectric power will need to be used in combination to make enough electricity to displace coal as a fuel source.
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