Hydroenergy

The first recorded uses of hydroenergy, or water power, occurred during the first century B.C.E. Water eventually drove mills for grinding grain, powered machine tools in factories, and, finally, in the twentieth century, became an important source of energy for generating electricity.

Background

Although devices for moving water have existed since prehistoric times, apparently no one realized that water could be used to power mills or other equipment until approximately two thousand years ago. Farmers throughout the ancient Middle East used primitive waterwheels, known as noria, to transfer water from one level to another, as from a flowing river to an irrigation canal. Similar devices, which consist of jars or buckets attached to a wheel that is turned by the pressure of water flowing against it, can still be seen in use in Egypt and Iraq. Sometime around 100 B.C.E. an unknown inventor harnessed the power of the moving water to a mill for grinding grain.

The Roman Empire Through the Nineteenth Century

Following the invention of the waterwheel, its use for moving millstones spread throughout the Roman Empire. The water-powered mill made possible a dramatic increase in the production of flour. Sixteen to twenty man-hours were required to grind sixty kilograms of grain. Even a primitive waterwheel, one with the equivalent of perhaps three horsepower in motive power, could produce two and one half times that amount in only one hour.

Waterwheels and milling techniques remained relatively unchanged until the Middle Ages. Between the years 800 C.E. and 1200 C.E., innovations in waterwheel technology exploded across Europe. Millwrights refined waterwheels for greater efficiency and adapted wheels for use in a wide variety of applications. In addition to milling grain, waterwheels drove fulling hammers for processing wool in manufacturing felt and softened hides at tanneries. Towns grew up around milling complexes in European cities. Millers constructed dams to regulate the flow of water, while landowners became wealthy through the lease fees collected for choice mill sites on rivers and streams. A narrow stream might be dammed to provide water for one wheel, while wider rivers, such as the Seine in France, were spanned by a series of waterwheels and mills all constructed side by side. Artisans devised varied types of waterwheels and gearing to use with different levels of available water, such as undershot, overshot, and breast wheels, and they built ingenious systems of dams and timber crib weirs to exploit every conceivable source of moving water, from tidal flows to the smallest freshwater streams.

Waterwheels were also built in the Middle East, India, and China, but these never reached the level of complexity common in Europe even before the Renaissance. In the 1600s, European colonists brought waterwheel technologies with them to the New World, and, not surprising, patterns of settlement followed streams and rivers inland from the ocean. Although the eighteenth century invention of the steam engine and its contribution to the Industrial Revolution changed patterns of industrial development in Europe and elsewhere, the steam engine did not eliminate the importance of water power to manufacturing. While steam engines quickly found applications in the mining industry, it took many years for steam power to displace water power elsewhere. Steam engines eventually allowed industry to develop factory sites located away from sources of moving water, but did not reduce the importance of water power to many factories already in place. In fact, the rapid expansion of the textile industry in the United States relied far more on water power than it did on steam, even though steam engines were commonplace by the 1820s.

Textile factories, such as those located in Lowell, Massachusetts, used water power by developing elaborate systems of drive belts that extended through factories that were several stories high and hundreds of meters long. Dams on the river above the town diverted water into multiple canals, allowing factory construction well back from the original banks of the river. The development of the water-powered Lowell sites began in the early years of the nineteenth century and continued for almost one hundred years. It was not until the twentieth century, following the invention of the electric motor and the widespread distribution of electrical power, that factories began to abandon water power as a motive source. Even then, only the presence of other factors, such as the buildup of silt in mill ponds and the movement of industry from the New England states to the South, may have pushed factory owners to implement changes in sources of motive power.

Twentieth Century Developments

At the beginning of the twentieth century, industry moved away from direct exploitation of hydroenergy through the use of waterwheels and began instead to use electricity generated from hydroelectric power plants. plants generate electricity by converting the motive power of the water into electrical current. The water enters the plant through a power tunnel or penstock that directs the water into a casing. The casing, which looks like a gigantic snail, narrows as it spirals in and directs the water toward the blades of a turbine that turns the shaft an electric generator. Early hydroelectric plants utilized designs that converted the force of the water striking the waterwheel directly into electrical energy, but engineers and scientists quickly developed more efficient turbines to take advantage of available water resources.

The amount of energy potential in a water power site depends on two factors. First is the effective head, or the height difference between the level of the water standing behind the dam (before the water enters the power tunnel) and where it will exit at the tailrace on the downstream side of the turbine. Second is the volume of water. A large volume of water can compensate for a low effective head, just as an extremely high head can compensate for a low volume of water. High-head, low-volume hydroelectric plants generally rely on impulse wheels. Water enters the casing around the wheel under tremendous pressure and strikes the wheel buckets with incredible force. As the wheel spins in response to the force of the water striking it, it turns the shaft of a generator to convert kinetic energy to electricity. Impulse wheels have a fairly low efficiency rating, but they are often the only practical turbines for use in situations where water is in short supply. These impulse wheels, also known as Pelton wheels, are vertical water wheels that to the observer share an obvious ancestry with the old-fashioned waterwheels seen in bucolic illustrations of gristmills and ponds. Impulse wheels were once widely used throughout the western United States, where effective heads of several hundred meters are common.

Most large modern hydroelectric plants use a different type of turbine, a reaction turbine, that exploits the pressure differential between the water entering the turbine casing and the tailrace below. Engineers such as James B. Francis turned the vertical waterwheel on its side. In the process, Francis designed a turbine that creates a partial vacuum in the space between the turbine and the tailrace. The Francis turbine and other reaction turbines work, in effect, by sucking the water through the turbine casing, causing the water to flow faster and to increase the overall efficiency of the system. Reaction turbines can be used in settings that have extremely low heads if a sufficient volume of water exists to create an effective pressure differential. Reaction turbines are especially well suited for applications in run-of-the-river power plants in which the dam diverting the water into the turbine may be only a couple of meters high.

The Early Promise of Hydroenergy

Noted conservationists of the early twentieth century, such as Gifford Pinchot, unabashedly pushed for the widespread exploitation of hydroelectric sites. Pinchot and others in the movement encouraged the U.S. government to take a more active role in the development of hydroelectricity. The alternative to hydroelectricity was electricity generated by steam turbines, and steam required a fuel source such as coal or oil. Even before World War I first created shortages of fossil fuels, conservationists advocated greater use of renewable resources, such as hydroelectricity. Because hydroelectricity does not permanently remove water from a watershed—it merely diverts the flow to pass it through a powerhouse and then returns the water to the system—conservationists argued that hydroelectric sites should be exploited in order to conserve nonrenewable energy sources, such as coal. Conservationists devoted almost twenty years to lobbying for a water power bill, finally succeeding in 1920 with the passage of the Federal Water Power Act, which created the Federal Power Commission.

Not surprisingly, the following decades witnessed an explosion of hydropower development. The size of early hydro development had been limited by the available technology, but engineers quickly solved problems that had restricted turbine and generator size. Construction journals and the popular press alike regularly reported on new dams and power plants that would be the largest in the world, with each gigantic project quickly supplanted by a newer, bigger project. In the United States, this fascination with ever bigger hydroelectric projects became a physical reality with the construction of Hoover Dam on the Colorado River and the Bonneville Power Project along the Columbia. The arrival of the Great Depression in 1929 did not slow the construction boom. If anything, it may have accelerated it. In a time when millions of Americans were unemployed, massive construction projects such as Bonneville in the Pacific Northwest or the Tennessee Valley Authority dams in the South provided meaningful work.

Reassessing Hydro

By the 1950s, the enthusiasm for large hydroelectric projects had abated. Conservationists who had once advocated hydroelectricity because it was clean and renewable began to realize that it nonetheless posed significant environmental problems. Construction of a high dam such as Ross Dam on Washington’s Skagit River or Glen Canyon on the Colorado inevitably required that hundreds of square kilometers of land be permanently covered with water. Deserts, forests, farmland, and entire towns were all lost forever as reservoirs filled.

Nor were hydroelectric plants neutral in affecting aquatic life. The percentage of dissolved oxygen present in water changes as it passes through turbines, as does the water temperature. Water downstream from a hydroelectric plant may flow faster than before, vary widely in volume depending on power demands, and be warmer than it would be naturally. Some species of fish may disappear or be displaced by other species that find the changed conditions more favorable than the original native fish do. Upstream from the dam, the water on the surface of the will be both calmer and warmer than prior to construction, while the water at the bottom will be colder. Again, these changed conditions affect which fish will thrive and which fish will gradually disappear. Construction of a hydroelectric plant can change a stretch of a river from a trout stream into a bass lake.

The dam and power plant themselves present a physical barrier to spawning fish, a barrier that technical solutions such as fish ladders only partially solve. Fish may make it past the dam going upstream via a fish ladder, for example, but then be killed by pressure changes as they inadvertently pass through the turbines as they swim downstream.

In addition, twentieth century dam builders had to relearn what the mill owners of the Middle Ages and the early Industrial Revolution knew: Dams stop sediment as well as water. Mill owners in past centuries had learned to drain mill ponds periodically to remove accumulated silt, but such a procedure is impractical for a mammoth hydroelectric power plant. The effective life of dams has also begun to be examined: If a 90-meter dam was designed and built in 1920 to last for fifty years, what happens when it is time to replace it? About six hundred dams have been decommissioned in the United States.

The Promise of Hydroenergy

Despite the problems inherent in hydroelectricity, many environmentalists and advocates for sustainable development believe that the creation of small-scale hydroelectric power plants could significantly reduce reliance on nonrenewable fossil fuels. A typical small-scale hydroelectric plant might have a turbine rated at only 3,000 horsepower, as opposed to the 60,000 horsepower capacity of a large plant. On the other hand, where a large hydroelectric development, such as Glen Canyon, may cost millions of dollars, take many years to complete, and have a devastating environmental impact, small-scale hydro can be easily and cheaply implemented. Diversion dams for small-scale hydro need not even block the entire flow of a stream. That is, if a stream or river has a steady flow of water, a diversion dam to steer water into the power tunnel or penstock can be constructed that extends only partway across the streambed, allowing the water and aquatic life to continue their normal passage almost free from restriction. Such small dams can utilize indigenous materials, such as timber or rocks available on the site, making construction in underdeveloped regions easy and affordable.

In the United States, development of small-scale hydroelectric power plants has been explored by independent power producers. Changes in federal energy regulations require public utilities to purchase electricity produced by independent power producers, which can be companies that generate excess electricity as part of their normal manufacturing process as well as firms that have chosen to develop alternative energy sources rather than using fossil fuels. Small hydroelectric plants once existed in many small towns throughout the nation but were abandoned as economies of scale pushed public utilities to invest in larger plants or steam turbines. Exploiting these sites suited for small-scale run-of-the-river hydroelectric power is both possible and desirable. Hydroenergy harnessed by a 200-meter-high dam can be an environmental disaster, but hydroenergy behind a 2-meter dam has few negative side effects.

In 2021, hydroelectric power made up roughly 31.5 percent of the total renewable energy generated in the United States. That same year, it made up roughly 6.3 percent of the total energy generated by the nation.

Bibliography

Alternative Energy Institute, and Kimberly K. Smith. “Hydropower.” In Powering Our Future: An Energy Sourcebook for Sustainable Living. New York: iUniverse, 2005.

Boyle, Godfrey, ed. Renewable Energy. 2d ed. New York: Oxford University Press in association with the Open University, 2004.

Craddock, David. Renewable Energy Made Easy: Free Energy from Solar, Wind, Hydropower, and Other Alternative Energy Sources. Ocala, Fla.: Atlantic, 2008.

Gimpel, Jean. The Medieval Machine: The Industrial Revolution of the Middle Ages. 2d ed. London: Pimlico, 1993.

Gordon, Robert B., and Patrick M. Malone. The Texture of Industry: An Archaeological View of the Industrialization of North America. New York: Oxford University Press, 1994.

"Hydropower Explained." EIA, 2022, www.eia.gov/energyexplained/hydropower/. Accessed 27 Dec. 2024.

Raphals, Philip. Restructured Rivers: Hydropower in the Era of Competitive Markets, a Report. Montreal: Helios Centre, 2001.

Reynolds, Terry S. Stronger than a Hundred Men: A History of the Vertical Water Wheel. Baltimore: Johns Hopkins University Press, 1983.

Twidell, John, and Tony Weir. “Hydro-Power.” In Renewable Energy Resources. 2d ed. New York: Taylor & Francis, 2006.

U.S. Bureau of Reclamation. Hydropower 2002: Reclamation’s Energy Initiative. Denver, Colo.: U.S. Dept. of the Interior, Bureau of Reclamation, 1991.