U.S. support for new energy source

Press, 23 September 1980, Page 23

U.S. support for new energy source

Reprinted from the “Economist,” London President Carter has signed into law two bills giving" support for an almost untried source ot energy called ocean thermal energy conversion (Otec). Between them, the two bills require that 10,000 megawatts of Otec capacity should be built by the end of the century and also provide up to $2OOO million in loan guarantees for construction. .A. • The idea behind Otec is simple enough. It is to exploit the sharp difference in temperature that occurs in the tropics between warm, surface waters, oi the oceans (about 2a deg. C) and the cold water (about 5 deg. C) found at a depth of 1000 m. The warm." surface water is used to boil a liquid with very low boiling point, such as ammonia. The suiting ammonia “steam drives -a turbine which generates electricity just as any other steam-driven turbine does. The electricity is sent ■ ashore via submarine cable. Meanwhile, cold water extracted from the ■. ocean depths cools the ammonia, so that it returns to the liquid state, ready for the cycle to start again. Unlike electricity generated from the sun, wind and waves, Otec should provide a constant power output, unaffected bv the weather. A French scientist originated the concept back in the .1880 s. 1930, .a French engineer built tne world’s first Otec plant, which, after two weeks, was destroyed by a storm. Sqme development work continued but real interest ■ -.i- -

revived only after the 1973 oil crisis. Two American companies, Lockheed and T.R.W., are particularly keen on the : concept. If the basic idea sounds simple, consider some of the practical problems. To begin with, there is sheer size. To generate 400 megawatts of electricity (equivalent to the output of a coal-fired power station), an Otec plant weighing 200,000 tonnes would be needed. This is far bigger than any structure in the North Sea. The pipe needed to fetch cold water from the depths would have to be two or three times the height of the Eiffel tower, and carry as big a flow of water as the Nile river. The pipe would be subject to enormous stresses. Then there is the question of the heat exchangers needed to evaporate and condense the ammonia. Each of ■ these would be the equivalent of a. several-storey building, filled with masses of tiny tubes for (corrosive) salt water to flow through. The tiny tubes would be designed to achieve the maximum area of interchange for the transfer of heat between ■ ammonia and water. But what to make the tubes of Titanium is ideal, except for its high cost. Aluminium is a more likely material. But its behaviour in sea water over the 30-year life of an Otec plant is debatable. The heat exchangers must withstand not only salt corrosion but also fouling by marine organisms, large and small. A ’very small layer of slime in the tubes would sub-

stantially lower the efficiency of heat exchange. Optimism was fuelled by a three-month trial of a mini-Otec carried out last year in Hawaii. The s3m experimant was led by Lockneed with partners including Alfa-Laval of Sweden (a leader m the technology of heat exchange) and the state ot Hawaii. The plant operated successfully. No fouling occurred, either by barnacles or microbes.. A minute trace of • chlorine added to the sea water kept the tubes clean. ■ - But the Hawaiian plant was very small, and tne trial very short-lived. Only 50 kilowatts of electricity was generated, of- which 40 kilowatts was needed just to operate the plant. It all sounds a poor prospectus on which to pass the two bills President Carter has just signed. His office of manpower and budget had advised a veto on one of them. , However, among the bill’s advocates were m--fluential Democrats whom the president needs behind him during the campaign. . _ "3 The next stage m Otec development has already begun. A ship called Otec--1 is testing components in ocean conditions. If that is successful, a pilot plant to, generate 40 megawatts of electricity is planned. That would cost s2som. Even allowing for a generous learning cure and write-off of development costs, Otec power looks like being much more expensive than conventional ■ electricity. A capital cost of over $5OOO per kilowatt of capacity is being talked of,, three times the cost of •conventional power,