The Soviet Union began to generate electricity from a tidal power plant constructed using revolutionary techniques, pointing to the possibility of tidal power as a major energy source.
During the closing days of 1968, the Soviet Union began operating the Kislaya Guba Experimental Tidal Plant, its first facility to generate electrical energy from tidal energy. This plant differed in capacity and construction from the first large-scale tidal power plant, which went on line in 1966 at the Rance estuary in Brittany, the westernmost region of France. The Soviet plant had a rated capacity of less than 2 percent that of the French facility: 400 kilowatts compared to 240 megawatts. More important, the Soviet approach required a far shorter construction period and vastly curtailed costs.
Construction at La Rance utilized cofferdams, or caissons, which are temporary dams built to enclose an underwater area that was pumped dry to allow workers to build the foundations of the 910-meter-long dam. The cofferdams constituted almost one-third of the cost at La Rance. In contrast, the inlet to Kislaya Bay is a channel only fifty meters across set between forty-meter-high cliffs. Soviet engineers precast concrete cellular units elsewhere, towed them to the site, and sank them by partially filling them with sand.
Throughout history, humanity has attempted in various ways to extract energy from moving water. Waterfalls provide one opportunity. Likewise, the seemingly eternal energy of the tides has long fascinated ingenious people; in one sense, the rhythmic tidal variation of water levels produces small waterfalls. The earliest English written record of a tidal mill occurs in The Domesday Book (1086). Tidal mills, water mills based on small tidal basins or ponds, sprang up on the North Atlantic coasts of Europe around the eleventh century, and tidal mills persisted well into the twentieth century.
These mills have had several rudimentary forms. The incoming (flooding) and outgoing (ebbing) tides might simply run beneath and turn a waterwheel; water entering a basin at high tide might be impounded, its subsequent release turning a waterwheel; or the incoming tide might lift a float, its subsequent fall doing work in some manner. Each of these methods provided mechanical energy to grind grain, pump water, or saw wood, work previously done by animal or human muscle. The concept of tidal mills, however, has adapted much less readily to generating electricity than have facilities at waterfalls.
Tides result from differences in gravitational pull on different parts of the earth. Sir Isaac Newton’s law of universal gravitation enabled scientists to quantify the tidal effects of the sun and the moon. The moon pulls more strongly on a kilogram of water on the nearer side of the earth than on a kilogram of the earth’s core, creating a bulge toward the moon. Similarly, a second tidal bulge results on the far side of the earth; in this case, the moon, in effect, pulls the earth from under the water on that side. Solar gravity causes another pair of tidal bulges on the earth. When solar and lunar tidal effects combine, spring tides, the highest tidal ranges between successive high tide and low tide, result. This occurs at full moon and new moon, when earth, moon, and sun lie along a line. Neap tides are just the opposite: The lowest high tides and highest low tides combine for the minimum tidal range, occurring at quarter phases of the moon.
Local geography greatly alters the particular circumstances of the tides at any given location. For example, a funnel-shaped bay increases the local tidal range compared to a straighter coastline; this is especially obvious at the Bay of Fundy, a gigantic projection of the Atlantic Ocean between Nova Scotia and the New Brunswick-Maine border. This bay displays the world’s largest consistent tidal ranges, around fifteen meters.
In general, consecutive high tides and low tides are separated by about six hours and twelve minutes. This pattern of semidiurnal tides predominates along much of the North Atlantic Coast and in the White Sea, an arm of the Arctic Ocean that reaches into northern Russia. Yet at some places on earth, as in the Gulf of Mexico, consecutive high tides called diurnal tides occur twenty-four hours and fifty minutes apart.
Strictly, the word “tide” applies to a vertical movement of the water; “current” applies to a horizontal movement. Whereas the tide falls and rises, tidal currents ebb and flood. Several oceanographic and geographic factors affect how much electrical energy a system of turbines might extract from tidal currents at a given location. Clearly, a large tidal range is desirable, as this means a large volume of water will pass through the turbines. The average tidal range at La Rance is about twelve meters. Semidiurnal tides yield twice the energy-production possibilities of diurnal tides. The size of the basin being filled and drained by the tides is another consideration; again, increased water flow means increased available energy. Local weather conditions are also a factor, but a variable one.
Any scheme to use tidal energy must take into account various technological and economic considerations. An extreme illustration of these economic constraints is seen in Australia’s Kimberleys, a remote, sparsely populated region with vast tidal power potential in northwestern Australia. Its remoteness increases construction costs of any tidal power station and means that the generated power would be far from large numbers of consumers.
The use of turbines that can generate electricity when the tide is moving both in toward and out from shore results in a sizable gain in daily energy production. The Rance facility illustrates this, generating power during both flood tide and ebb tide with a single basin. Although electricity may thus be generated for four periods per day, each period is shorter than those available with one-way generation because of the time necessary to build up a sufficient head of water, or difference in level between the two sides of the dam, to turn the turbines. Turbines require a head of about three meters. The major technological constraint in efficient two-way generation is the requirement that the turbine blades must have variable shape.
Another economic advantage results from the integration of a tidal power plant with a national power grid. For example, nuclear power plants operate most efficiently at a certain level, regardless of power demand. When tidal power installations can also act as pumps, they can utilize excess electrical energy from other plants, putting energy into the grid to store it for subsequent peak demand.
The Russian engineer Lev Borisovich Bernshtein, widely recognized as a pioneer in tidal energy development, suggested as early as 1947 that tidal power plants should use reversible turbines. His monograph “Tidal Power in Modern Power Engineering,”
Bernshtein’s concepts culminated in the Kislaya Bay tidal plant on the Kola Peninsula, in Russia near Finland. Although the average tidal range is not spectacular, only five meters, the narrow connection between site and ocean makes this a superb location for a pilot tidal power station. The nearest major city is Murmansk, the world’s largest city north of the Arctic Circle; the warm Gulf Stream keeps Murmansk’s harbor ice-free year-round. Kislaya Bay has an area of about 1.1 square kilometers.
As with La Rance, the Kislaya Guba facility utilizes turbines designed for two-way generation as tidal currents enter and leave the single impoundment. Its great contribution has been in the novelty of the techniques used in its construction, primarily the floating in of precast concrete boxes.
As Bernshtein once pointed out, the Kislaya Guba Experimental Tidal Plant is a small plant generating great expectations. Tidal energy plants, virtually pollution-free yet having no fuel cost, are extremely attractive to a world with a continuously increasing demand for electrical energy. For example, Japanese consumption of electrical energy rose 270 percent in the years between 1970 and 1975. The disproportionately high capital investment required has repeatedly stymied development of tidal energy; not surprisingly, the Kislaya Guba plant is one of very few tidal power plants operating in the world.
La Rance, by far the largest plant, has steadily produced 540 gigawatt-hours of energy per year. The People’s Republic of China has four experimental tidal power stations. The largest, at Jianxia, was constructed on a rockfill dam originally built to reclaim land. Its six turbines, which were placed in service between 1980 and 1986 and have a capacity of 3 megawatts, operate in a two-way mode.
The first tidal power station in North America was completed in 1984 at Annapolis Royal, a part of the Bay of Fundy in Nova Scotia. The 18 megawatt facility benefited from lower construction costs in two ways: Construction of a dam was not necessary because a rockfill causeway and a dam with sluices to control flooding had previously been constructed across the estuary mouth; also, the powerhouse was placed on Hog’s Island, an island in the estuary crossed by the causeway.
The Kislaya Guba plant utilized a single float-in structure that completely closed the opening to the basin in one step. In this way, the bulk of the construction was executed at a site already prepared for heavy construction. The success of this technique indicates that site selection should consider how easily the ocean bottom material could be prepared to receive a float-in structure. Since Bernshtein demonstrated its practicality, the float-in method of construction has become widely accepted as the most cost-effective. The plant also overcame ice problems, verifying that tidal power can be utilized in inclement sites; new materials that resisted freezing were developed to coat the concrete hydroelectric station where ice would otherwise form.
The successes of Kislaya Guba and La Rance have encouraged evaluation of a considerable number of potential sites for tidal power development. Two of the most prominent are the Severn River in Great Britain and the Bay of Fundy. The Severn River, one of Great Britain’s major waterways, rises in Wales and meanders 338 kilometers to the Bristol Channel. Schemes for damming the Severn date back to the late nineteenth century. Its estuary, the broad mouth of a river into which the tide flows, sees a tidal range of eleven meters, and it is the British site most studied for tidal power utilization. Estimates suggest that one dozen of the most promising tidal sites around Great Britain could provide about one-sixth of the country’s electrical needs. The Severn project alone might yield some 6 percent of Great Britain’s electrical needs.
Twice daily, more than one hundred billion cubic meters of water enter and leave the mouth of the Bay of Fundy; this is more than five hundred times the volume of water that fills La Rance basin. At some places, the water enters faster than an unwary beachcomber can run toward shore. In 1919, Dexter P. Cooper first proposed converting this huge amount of energy into electricity. It has been estimated that some 150 gigawatts, an amount of power equivalent to the production of 250 large nuclear plants, could be generated from the Bay of Fundy tides. The Annapolis River plant is successfully prototyping larger projects in the bay. Public interest in Fundy projects ebbs and floods. For example, a 1983 hearing before the Committee on Environment and Public Works of the U.S. Senate explored the effects of a proposed tidal hydroelectric project in the Bay of Fundy.
One aspect of such debate is ecological. The presence of a tidal power plant in an estuary influences two major factors affecting estuarine ecology. The dam reduces the amount of oxygen the water absorbs in flowing, causing problems for many estuarine animals. On the other hand, the water picks up less suspended matter, decreasing the turbidity of the water and allowing light to penetrate more. This light will permit the mud flats exposed at low water to support life better. Overall, it is likely that a given estuary will support at least as many life-forms, although some shifting may well occur in the species already present.
Tidal power is not expected to provide a large portion of the world’s needs for electricity; economically suitable sites are simply too rare. Along the shores of several countries, however, are estuaries where tidal power stations may become cost-effective, pollution-free components of national power grids.
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Barr, David Ian Hunter. “Power from the Tides and Waves.” In The Marine Environment. Vol. 5 in Environment and Man, edited by John Lenihan and William W. Fletcher. New York: Academic Press, 1977. This chapter begins with a historical survey of tidal mills and tidal electrical power, discusses differences between oceanic and nearshore tides, analyzes various turbine designs and ancillary systems, and overviews existing installations and proposed sites for tidal power. Wave power is given relatively little treatment. Thorough index and fourteen suggestions for further reading. -
Bernshtein, L. B. “From Experimental to Large Tidal Power Stations (Twentieth Anniversary of the Kislogubsk Tidal Power Station).” Hydrological Construction 22 (September, 1989): 687-691. Bernshtein points with rather justifiable pride to the long service of the Kislaya Guba station and to the widespread acceptance of his ideas, such as a single basin with two-way generation and floated-in construction. He then considers two possible locations for further tidal power plants in the Soviet Union. -
_______, ed. Tidal Power Plants. Seoul, Korea: Korea Ocean Research and Development Institute, 1996. Lengthy study of the advantages, disadvantages, and logistical issues surrounding tidal power plants. Bibliographic references. -
Charlier, Roger Henri. Tidal Energy. New York: Van Nostrand Reinhold, 1982. An indispensable source for any student interested in further study, this 351-page volume is generally supportive of tidal power. The first chapter discusses in some detail seven schemes besides tidal energy to extract energy from the oceans. The Kislaya Guba project has its own chapter, along with chapters on La Rance, U.S. sites, Canadian sites, and the Severn. Glossary and bibliography. -
Duff, G. F. D. Tidal Energy: Or, Time and Tide Wait for No Man. College Park, Md.: American Association of Physics Teachers, 1986. A fascinating miniature textbook designed to acquaint students with the physics of the nature of tides, resonance effects in tidal power, and tidal power plants. Assumes some prerequisite knowledge of gravitational potential energy, Newton’s law of gravitation, standing waves, resonance, trigonometry, and algebra. Fifteen exercises. -
Gray, T. J., and O. K. Gashus. Tidal Power. New York: Plenum Press, 1972. Proceedings of an international conference on utilizing tidal power held in 1970 at the Atlantic Industrial Research Institute, Nova Scotia Technical College in Halifax. Includes work by thirty-one contributors, among them Bernshtein, from a half-dozen countries. Bernshtein’s report on the Kislaya Guba project is included in this massive book. Two other contributors discuss Bernshtein’s concept of precast floated-in construction material in tidal power installations. -
Greenberg, David A. “Modeling Tidal Power.” Scientific American 257 (November, 1987): 128-128C, 128F, 128H, 130-131. Fascinating account of simulating by computer the effect of a tidal power dam in the Bay of Fundy: The tidal range would be raised by fifteen centimeters as far away as Boston, with potentially serious effects on floodplains and structures near the water. These models can be used to help assess the environmental and economic cost of tidal power. -
Hammons, Thomas James. “Tidal Power.” Proceedings of the IEEE 81 (March, 1993): 419-433. An exceedingly thorough and even-handed treatment of all aspects of tidal energy. Hammons covers the physics of tidal power, the resource itself, factors affecting and components of the plants, mathematical modeling, present and prospective sites worldwide, and economic and environmental considerations. References.
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