The invention: Plant that converts the natural ocean tidal forces into electrical power.
The people behind the invention:
Mariano di Jacopo detto Taccola (Mariano of Siena, 1381-1453),
an Italian notary, artist, and engineer Bernard Forest de Belidor (1697 or 1698-1761), a French engineer Franklin D. Roosevelt (1882-1945), president of the United States
Tidal Energy
Ocean tides have long been harnessed to perform useful work. Ancient Greeks, Romans, and medieval Europeans all left records and ruins of tidal mills, and Mariano di Jacopo included tidal power in his treatise De Ingeneis (1433; on engines). Some mills consisted of water wheels suspended in tidal currents, others lifted weights that powered machinery as they fell, and still others trapped the high tide to run a mill.
Bernard Forest de Belidor’s Architecture hydraulique (1737; hydraulic architecture) is often cited as initiating the modern era of tidal power exploitation. Belidor was an instructor in the French Ecole d’Artillerie et du Genie (School of Artillery and Engineering).
Industrial expansion between 1700 and 1800 led to the construction of many tidal mills. In these mills, waterwheels or simple turbines rotated shafts that drove machinery by means of gears or belts. They powered small enterprises located on the seashore. Steam engines, however, soon began to replace tidal mills. Steam could be generated wherever it was needed, and steam mills were not dependent upon the tides or limited in their production capacity by the amount of tidal flow. Thus, tidal mills gradually were abandoned, although a few still operate in New England, Great Britain, France, and elsewhere.
Electric Power from Tides
Modern society requires tremendous amounts of electric energy generated by large power stations. This need was first met by using coal and by damming rivers. Later, oil and nuclear power became important. Although small mechanical tidal mills are inadequate for modern needs, tidal power itself remains an attractive source of energy. Periodic alarms about coal or oil supplies and concern about the negative effects on the environment of using coal, oil, or nuclear energy continue to stimulate efforts to develop renewable energy sources with fewer negative effects. Every crisis—for example, the perceived European coal shortages in the early 1900′s, oil shortages in the 1920′s and 1970′s, and growing anxiety about nuclear power—revives interest in tidal power.
In 1912, a tidal power plant was proposed at Busum, Germany The English, in 1918 and more recently, promoted elaborate schemes for the Severn Estuary. In 1928, the French planned a plant at Aber-Wrach in Brittany. In 1935, under the leadership of Franklin Delano Roosevelt, the United States began construction of a tidal power plant at Passamaquoddy, Maine. These plants, however, were never built. All of them had to be located at sites where tides were extremely high, and such sites are often far from power users. So much electricity was lost in transmission that profitable quantities of power could not be sent where they were needed. Also, large tidal power stations were too expensive to compete with existing steam plants and river dams. In addition, turbines and generators capable of using the large volumes of slow-moving tidal water that reversed flow had not been invented. Finally, large tidal plants inevitably hampered navigation, fisheries, recreation, and other uses of the sea and shore.
French engineers, especially Robert Gibrat, the father of the La Rance project, have made the most progress in solving the problems of tidal power plants. France, a highly industrialized country, is short of coal and petroleum, which has brought about an intense search by the French for alternative energy supplies.
La Rance, which was completed in December, 1967, is the first full-scale tidal electric power plant in the world. The Chinese, however, have built more than a hundred small tidal electric stations about the size of the old mechanical tidal mills, and the Canadians and the Russians have both operated plants of pilot-plant size.
La Rance, which was selected from more than twenty competing localities in France, is one of a few places in the world where the tides are extremely high. It also has a large reservoir that is located above a narrow constriction in the estuary. Finally, interference with navigation, fisheries, and recreational activities is minimal at La Rance.
Submersible “bulbs” containing generators and mounting propeller turbines were specially designed for the La Rance project. These turbines operate using both incoming and outgoing tides, and they can pump water either into or out of the reservoir. These features allow daily and seasonal changes in power generation to be “smoothed out.” These turbines also deliver electricity most economically. Many engineering problems had to be solved, however, before the dam could be built in the tidal estuary.
The La Rance plant produces 240 megawatts of electricity. Its twenty-four highly reliable turbine generator sets operate about 95 percent of the time. Output is coordinated with twenty-four other hydroelectric plants by means of a computer program. In this system, pump-storage stations use excess La Rance power during periods of low demand to pump water into elevated reservoirs. Later, during peak demand, this water is fed through a power plant, thus “saving” the excess generated at La Rance when it was not immediately needed. In this way, tidal energy, which must be used or lost as the tides continue to flow, can be saved.
Consequences
The operation of La Rance proved the practicality of tide-generated electricity. The equipment, engineering practices, and operating procedures invented for La Rance have been widely applied. Submersible, low-head, high-flow reversible generators of the La Rance type are now used in Austria, Switzerland, Sweden, Russia, Canada, the United States, and elsewhere.
Economic problems have prevented the building of more large tidal power plants. With technological advances, the inexorable depletion of oil and coal resources, and the increasing cost of nuclear power, tidal power may be used more widely in the future. Construction costs may be significantly lowered by using pre constructed power units and dam segments that are floated into place and submerged, thus making unnecessary expensive dams and reducing pumping costs.
See also Compressed-air-accumulating power plant; Geother-mal power; Nuclear power plant; Nuclear reactor; Solar thermal engine; Thermal cracking process.
