Electricity generated by wind power relies on air moving past a propeller to spin a turbine. Wind is created as a result of the differential heating of the earth's surface of the sun. Air masses move from areas of high atmospheric pressure to low atmosphere pressure. Wind energy creates very few greenhouse gases and will exist as long as the sun shines and winds blow. There are challenges to implementing wind energy, though. Wind energy, like other forms of renewable energy, operates effectively only in certain geographic areas and climates. Wind speeds and direction can vary hourly, daily, and seasonally. For example, winds are typically stronger during the day than at night. In temperate climates, the wind tends to be stronger during the winter than during the summer. Hence, a wind turbine only makes economic sense if, on average, the wind blows at a certain minimum average velocity, usually at least 10 to 12 mi. (16 to 10 km.) per hour for much of the calendar year. Winds lower than that cannot move the large propellers to spin the turbine.
A wind turbine also needs a relatively open space, so that trees or buildings do not affect wind speeds. Critics of wind farms also argue that wind turbines can harm migrating birds and bats, are an aesthetic blight on the landscape, and cause irritating "flicker" as sunlight reflects off of the rotating propeller blades.
Solar power can reduce greenhouse gases in several ways. First, passive solar energy can be used for heating. Dark surfaces absorb energy from the sun better than light surfaces. This principle can be used to heat water or warm a house. Water stored in a dark container or cistern on the roof of a house can become very hot. This water can be used for showers, laundry, or cleaning. Similarly, a dark exterior on the roof or walls of a house can help warm the house on a cold winter day. This helps reduce greenhouse gases, because like all renewable energies, its use offsets the use of fossil fuels.
Second, active solar energy can generate electricity through the use of photovoltaic cells. This technology relies on semiconductors to take direct light from the sun and convert it into electricity. This form of energy production is renewable.
However, it has several limitations, including the daily fluctuations in light, as well as regional variations in the amount of annual sunshine received. Solar energy is more economical in the American southwest, where sunshine is abundant. It is less viable in areas that have more cloud cover. However, solar energy is viable in most parts of tropical and mid-latitude regions.
Geothermal energy can be used to offset fossil fuels in several ways. First, the energy can be used to heat and cool buildings. Typically, a residential geothermal system relies on the fact that the Earth's temperate remains constant at about 55 degrees F (12.7 degrees C) at about 12 ft. (3.6 m.) below the surface. During the summer, the heat from the house is drawn down into the ground through a closed system, where it dissipates into the cool ground. During the winter, the relatively warm temperature of the ground is brought to the surface and used to help heat the house on a cold day.
hydrogen and biomass
Many researchers tout hydrogen as the ultimate renewable energy source, because it is the most common element in our universe. Hydrogen-based fuel cells operate by reacting pure hydrogen with oxygen to generate electricity. Energy is released that is then converted into electricity, with water as the only by-product. Unfortunately, pure hydrogen must be created through the hydrolysis of water. This is an expensive process that relies largely on conventional energy sources. Hence, there are significant technological barriers to the widespread adoption of hydrogen power.
Biomass, or plant material, can also be a significant source of energy for the production of electricity and for transportation. The DOE identifies three biomass sources: wood, waste, and biofuels. Wood can be cut and burned directly for home heating. The by-products of processing wood into paper products can also be co-fired with fossil fuels to make coal-fired electrical plants burn cleaner. Combustible biomass can also come from municipal solid waste, industrial waste, and landfill gas. Biomass can be used to create alcohol fuels such as ethanol, or diesel fuels, such as soy diesel. Advocates of these fuels, used largely for transportation, argue that their production and use creates fewer greenhouse gases than conventional fossil fuels.
Critics argue that biofuels must still be burned and therefore still generate greenhouse gases. They also argue that the increased production of corn and soybeans for ethanol or soy diesel will increase food prices, while degrading soil quality. This will require more use of petroleum-based fertilizers. Finally, skeptics suggest that biofuels are not a viable alternative because the energy it takes to produce ethanol is more than the energy contained in the fuel.
cost of alternatives
The high cost of production and related technological barriers affect all alternative energy sources. A comparison of production costs shows that fossil fuels are simply cheaper to produce than alternative fuels, which often need government subsidies to make them economically feasible. For example, it costs approximately 4.0 cents per kilowatt hour ($/
kWh) and around 5.0 C/kWh to produce electricity from natural gas and coal, respectively. Electricity from large-scale hydroelectric generators can cost between 5.0 and 12.0 C/kWh. Electricity from nuclear fission can cost between 11.0 and 15.0 C/kWh.
Great technological strides have been made in the advance of renewable fuels. Electricity from wind, which cost over 40.0 C/kWh in 1980, now costs in the range of 4.0 to 6.0 C/kWh. However, that makes it barely competitive with coal. Electricity from solar photovoltaics still costs almost 20.0 C/kWh, while that from hydrogen-powered fuel cells costs $4.00 per kWh. That is why some scientists suggest that while research is done over the long term to reduce the costs of producing energy from wind, solar, biomass, or hydrogen, the focus should be on increasing the efficiency of current systems. Environmentalist Amory Lovins argues that existing technologies can help reduce energy needs. Examples include more fuel-efficient vehicles, homes with better insulation to reduce heating and cooling costs, and more efficient appliances. The refrigerator exemplifies this progress in energy efficiency. In 1980, a 20 cu. ft. refrigerator used about 1,300 kWh of electricity per year. In 2001, a comparably sized unit used 500 kWh of electricity per year.
Alternative energy can be an important part of a strategy to reduce global warming if the commitment to energy efficiency can be increased in the short term, with continued research on alternative energy technologies in the long term. It may also mean combining energy types to maximize the amount of work that can be done. Increasing investments by the public and private sector in research and development can help make this happen.
sEE ALso: Alternative Energy, Ethanol; Alternative Energy, Solar; Alternative Energy, Wind; Biomass; Energy, Renewable; Nuclear Power; Sunlight.
BIBLIogRAPHY. Jared Diamond, Collapse: How Societies Choose to Fail or Succeed (Penguin Books, 2005); David Green, ed., Scientific American: Oil and the Future of Energy (Lyons Press, 2007); Intergovernmental Panel on Climate Change, www.ipcc.ch (cited August 2007); Intergovernmental Panel on Climate Change, Climate Change 2001: Working Group III: Mitigation (Cambridge University Press, 2001); Bj0rn Lomborg, The Skeptical Environ mentalist: Measuring the Real State of the World (Cambridge University Press, 1998); National Aeronautics and Space Administration, www.nasa.gov (cited August 2007); Arundhati Roy, Power Politics (South End Press, 2002); Nicholas Stern, The Economics of Climate Change (Cambridge University Press, 2007); U.S. Department of Energy, www.eia.doe.gov (cited August 2007); U.S. Environmental Protection Agency, www.epa.gov (cited August 2007); World Bank, www.worldbank.org (cited August 2007).
Christopher D. Merrett Western Illinois University
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