Renewable Energy - Hydropower

Hydropower is the energy that comes from the natural flow of water. Usually, the power is harnessed by taking advantage of gravity when water falls from one level to another. The energy of falling water is converted into mechanical energy. In the past, water's energy was harnessed by waterwheels to grind grain or turn saws. Modern technology uses water's energy to turn turbines that create electricity. Hydropower is a renewable, nonpolluting, and reliable energy source.

FIGURE 10.6
Ethanol production capacity, 2001

Hydropower is still the only means of storing large quantities of electrical energy for almost instant use. This is done by holding water in a large reservoir behind a dam with a hydroelectric power plant below. The dam creates a height from which water flows. The fast-moving flow of water from the dam pushes the turbine blades that turn the rotor part of the electric generator. When the coils of wire on the rotor sweep past the generator's stationary coil, electricity is produced. Whenever power is needed at peak times, water valves are opened and, in a short amount of time, turbine generators produce extra power. The Hoover Dam, located on the Colorado River at the Nevada-Arizona border, is the site of one of the largest U.S. hydroelectric plants.

According to the Energy Information Administration's March 2004 Monthly Energy Review, in 2003 hydroelectric power generated about 2.8 quadrillion Btu of energy in the United States, down substantially from when it peaked at 3.64 billion quadrillion Btu in 1997. (See Table 10.1.) Hydropower accounted for 44 percent of the nation's renewable energy consumption in 2003.

Advantages and Disadvantages of Hydropower

Small hydropower plants in the United States are costly to build but quickly become cost-efficient because of their low operating costs. One of the disadvantages of small hydropower generators is their reliance on rain and melting snow to fill reservoirs, a problem especially during FIGURE 10.7
The carbon cycle years with drought conditions. Other concerns include the difficult search for the proper terrain on which to build a hydroelectric power plant; the high cost of construction; and the ecological concern that dams could ruin streams, dry up waterfalls, and interfere with marine life habitats.

Large hydropower plants suffer from the same problems except that they rarely lack sufficient water since they can be built only on very large rivers. There is little potential to build new, large, hydropower plants in the United States because plants have already been built at all of the best sites.

New Directions in Hydropower Energy

Since almost all power sites have already been developed, hydropower's contribution to U.S. energy generation should remain relatively constant—although existing sites can become more efficient as new generators are added.

Most of the new development in hydropower is occurring in developing nations that see it as an effective method of supplying power to their growing populations. Major hydropower development programs are tremendous public works projects requiring huge amounts of money, most of it borrowed from the developed world. Leaders of developing countries believe that, in the long run, despite threats to the environment, the dams will pay for themselves by bringing cheap electric power to their people.

While developing nations have utilized only a small portion of their large-scale hydropower potential, the United States and Europe have developed a major proportion of their potential. In addition, dams are now less favored because of their harm to the environment. Largescale hydropower development has virtually stopped in the United States, with not one new dam being approved for federal funding since the late 1980s.

Dams in the United States were usually constructed entirely with federal monies. Since 1986, however, any new dam proposed in the United States must receive half its funding from local governments. Any new major supplies of hydroelectric power for the United States will most likely come from Canada.

Other Alternatives Using Water

The potential power locked in the world's oceans is unknown. However, since the ocean is not as easily controlled as a river or water that is directed through canals into turbines, unlocking that potential power is far more challenging. Three ideas being considered are tidal plants, wave power, and ocean thermal energy conversion.

TIDES AND WAVES.

A tidal plant uses the power generated by the tidal flow of water as it ebbs (flows back out to sea). A minimum tidal range of three to five yards is generally considered necessary for an economically feasible plant. Canada, for example, has built a 20-megawatt unit at the Bay of Fundy, where the tidal range—15 yards—is the largest in the world. The largest existing tidal facility is the 240-megawatt plant at the La Rance estuary in northern France.

In 2000 the world's first commercial wave power station became operational on the island of Islay in Scotland. The small system is called a Limpet, short for land-installed marine powered energy transformer. The Limpet supplies up to 500 kilowatts of electricity to the island's electrical power grid. Several projects are underway in Japan and the Pacific region to determine a way to use the potential of the huge waves of the Pacific.

OCEAN THERMAL ENERGY CONVERSION.

In 1881 Jacques Arsene d'Arsonval, a French physicist, was the first to propose tapping the thermal energy of the ocean. Not until 1974, however, was a laboratory and test facility for ocean thermal energy conversion (OTEC) technologies built at the National Energy Laboratory of Hawaii. In 1980 the DOE built OTEC-1, a test site on board a converted U.S. Navy tanker. In 1980 Congress enacted two laws to promote the commercial development of OTEC technology—the Ocean Thermal Energy Conversion Act (PL 96-320) later modified by PL 98-623, and the Ocean Thermal Energy Conversion, Research, and Development and Demonstration Act (PL 96-310).

OTEC uses the temperature difference between the ocean's warm surface water and the cooler water in its depths to produce heat energy that can power a heat engine to generate electricity. OTEC systems can be installed on ships, barges, or offshore platforms with underwater cables that transmit electricity to shore. In addition to providing power, OTEC systems can be used to desalinate water, provide air conditioning and refrigeration, and produce methanol, ammonia, hydrogen, aluminum, chlorine, and other chemicals.