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3.1 Ocean energy: New life for an old idea

Almost a century after the French physicist D’Arsonval first proposed the idea, the extraction of heat energy from the ocean to generate useful power is moving closer to practical application. A working model of such a generator was built in the 1930-s and recent experiments indicate that the operations could profitably be combined with mariculture to help provide power and food for countries near tropical seas.

Electrical power from oceanic generators could potentially have the lowest cost of any solar-generated electricity. There is a concept of a partly submerged ocean-thermal power plant, making use of temperature differences between warm surface water and cold deep water. Some 45% of the total incoming solar energy falls on tropical seas, which form a heat reservoir whose stored energy is 10,000 times greater than present human demand. The problem that has delayed exploitation of

this vast resource is its lack of concentration – temperature differences between the sea surface and the coldest depths are only about 400 F.

Conventional power plants depend on heating various materials (steam or jet fuel) by hundreds or thousands of degrees. As these expand they drive turbines or pistons and thus convert heat into work. The greater the temperature differential, the more easily heat can be transformed.

Now designers believe they can efficiently convert the small oceanic temperature differences into useful energy by using them to boil and then recondense ammonia. Sea surface temperatures are above the boiling point of ammonia; temperatures at great depths, below. The expanding ammonia gas could then drive a turbine in much the same way boiling water is used to drive a steam turbine. But unlike steam engines, which must be constructed from heavy, cast metal to keep them from bursting, sea-thermal plants could be built from light-weight materials

because of the surrounding inward pressure from the sea. A neutrally buoyant, lightly constructed apparatus could be made from aluminum and suspended at 200 feet depth (where the external pressure is equal to the vapor pressure of ammonia) and the total energy cost of refining the aluminum would be recovered in the first few hours of the plant’s operation.

But several problems must be resolved before sea-thermal energy can be considered economically feasible. Because the operating temperature differential is so small to begin with, heat transfer through the thin walls of an apparatus might be cut to inoperable levels by even a thin veneer of algae growth – a constant problem in ocean-borne equipment.

Corrosion must be a major consideration in the design of any seaworthy machines. Also, several of the technical advances upon which supporters base their optimism have not been proven yet outside the laboratory.

(Science news, Washigton, D.C)

Примечания

1. mariculture – морская культура (все, что связано с жизнедеятельностью моря, океана и т.д.)

2. submerge – затоплять; погружать(ся)

3. ammonia – аммиак

4. because of – из-за, вследствие

5. buoyant – плавучий, способный держаться на поверхности