Wood, wind, water, and sun power have been used for cooking, heating, milling, and other tasks for millennia. During the Industrial Revolution of the eighteenth and early nineteenth centuries, these forms of renewable energy were replaced by fossil fuels such as coal and petroleum. At various times throughout the nineteenth and twentieth centuries, people believed that fossil fuel reserves would be exhausted and focused their attentions on sources of renewable energy. This led to experiments with solar steam for industry and solid wood, methanol gas, or liquid biofuels for engines. Attention has refocused on renewable energy sources since the 1960s and 1970s, not only because of concern over fossil fuel depletion, but also because of apprehension over acid rain and global warming from the accumulation of carbon dioxide in the atmosphere.
Acid rain is clearly the result of the use of fossil fuels, and most authoritative climatologists also believe that these fuels are contributing to global warming. Many scientists and environmentalists have, therefore, urged a global switch to renewable energy, which derives from the sun or from processes set in motion by the sun. These energy forms include direct use of solar power along with windmills, hydroelectric dams, ocean thermal energy systems, and biomass (solid wood, methane gas, or liquid fuels). Renewable energy thus differs not only from fossil energy sources such as petroleum, gas, and coal, but also from nuclear energy, which usually involves dividing uranium atoms.
In the early 1990s, one-fifth of worldwide energy use was renewable, with by far the largest portion of this coming from fuel wood and biomass. Hydroelectric dams made up most of the rest. More than half the world's population relied on wood for cooking and heating, and although wood is generally considered to be renewable, excessive reliance has long been recognized as a cause of deforestation. Forests disappear faster than they can be renewed by natural processes. Energy "crops" —for example, fast-growing acacia or eucalyptus trees planted for fuel wood in the Third World—and more efficient wood stoves may be useful to poor, wood-reliant nations.
Solar energy is a term for many techniques and systems. The sun's energy can be trapped under glass in a greenhouse or within solar panels that heat water. It can also be concentrated in a trough or parabolic collector. In arid climates a small version of a concentrator is sometimes used to substitute for wood. Although economical, it is unreliable, hard to transport, and difficult to operate. Larger concentrators can produce steam economically for industry or for electric utilities in some climates. Another form of solar energy comes from photovoltaic cells mounted on panels. These panels are economical for all kinds of remote power needs, from cheap hand calculators to mountaintop navigational beacons to orbiting satellites. Costs have dropped dramatically since the mid-1970s, from hundreds of thousands of dollars to several thousands per installed kilowatt, and are expected to drop to under a thousand dollars early in the twenty-first century. At some point they may become competitive with nuclear and fossil energy.
Water power has been well known since its use in the Egyptian and classical Greek civilizations, and at the outset of the Industrial Revolution, it was widely used in Europe and the Americas to grind grain and run looms and in other small-scale industrial processes. Today water power is by far the cheapest of all fossil, nuclear, and renewable forms of energy for producing electricity, but the ecological disruptions caused by hydroelectric dams have caused many environmental controversies. Ocean energy takes advantage of the movement of water in tides or waves or of the temperature difference between sun-heated surface water and cold deep water. A few tidal energy projects have been built, but this form of energy production is expensive and remains largely experimental. Like tidal energy, geothermal energy is produced by continuous natural processes not directly related to solar cycles. Geo-thermal energy takes advantage of hot water trapped deep inside the earth to produce electricity or heat for homes and industry.
Wind power has been used for grinding grain, pumping water, and powering sawmills since the Middle Ages, and thousands of windmills once dotted coastal areas of northern Europe. Water-pumping windmills were a fixture in the American Midwest well into the twentieth century. Windmills are returning in a high-tech form in places like Altamont Pass in California, where they produce electricity. They are widely used for pumping water in the Third World.
Biomass energy involves a wide range of low and high technologies, from wood burning to use of manure, sea kelp, and farm crops to make gas and liquid biofuels. Brazil leads the world in use of pure ethyl alcohol derived from sugarcane as a replacement for petroleum. A common fuel in the United States is corn-derived ethyl alcohol, which is used as a low-pollution octane booster in a 10-percent blend with gasoline called "gasohol." Another form of renewable energy used in the rural Third World is the gas-producing biogas digester. Human and animal wastes are mixed with straw and water in an airless underground tank made of brick or cement. Methane gas is siphoned from the tank to a cooking stove. Meanwhile, the tank gets hot enough to kill disease-causing bacteria, which is an important sanitary improvement in many countries. Over the past few decades, 5 million biogas tanks have been built in China and half a million in India.
Renewable energy resources are cleaner and far more abundant than fossil resources, but they tend to be dispersed and more expensive to collect. Many of them, such as wind and solar energy, are intermittent in nature, making energy storage or distributed production systems necessary. Therefore, the direct cost of renewable energy is generally higher than the direct cost of fossil fuels. At the same time, fossil fuels have significant indirect or external costs, such as pollution, acid rain, and global warming. How to account for these external costs and assign the savings to renewable energy is a matter of continued policy debate. Another policy issue is research and development support. Conventional forms of energy, such as fossil fuels and nuclear power, receive more financial support from the federal government than does renewable energy. U.S. government policy toward renewable energy has been a roller coaster of support and neglect. By the end of President Jimmy Carter's administration in 1981, federal contributions to research in solar photovoltaics, solar thermal energy, solar buildings, biofuels, and wind energy research had soared to almost $500 million, but by 1990 the figure was only $65 million. A global transition to renewable energy will have to include developing nations, where energy use in proportion to the world total grew from 20 percent in 1970 to 3l percent in 1990.
Bibliography
Berinstein, Paula. Alternative Energy: Facts, Statistics, and Issues. Westport, Conn.: Oryx Press, 2001.
Blackburn, John O. The Renewable Energy Alternative: How the United States and the World Can Prosper Without Nuclear Energy or Coal. Durham, N.C.: Duke University Press, 1987.
Butti, Ken, and John Perlin. A Golden Thread: 2,500 Years of Solar Architecture and Technology. New York: Van Nostrand Reinhold, 1980.
Flavin, Christopher. Beyond the Petroleum Age: Designing a Solar Economy. Washington, D.C.: Worldwatch Institute, 1990.
Kovarik, Bill. Fuel Alcohol: Energy and Environment in a Hungry World. London: International Institute for Environment and Development, 1982.
Sørensen, Bent. Renewable Energy: Its Physics, Engineering, Use, Environmental Impact, Economy and Planning Aspects. San Diego, Calif.: Academic Press, 2000.
—Bill Kovarik/H. S.
Encyclopedia of American History Copyright © 2006 by The Gale Group, Inc. All rights reserved.
