But the technology is expensive and can work in only a limited number of places, like the tropics, where there is a large difference in temperature between the ocean’s layers. This excludes many major population centers, although proponents hope that Florida and the Gulf Coast could also be markets. (Other types of ocean energy being explored would harness the tides and waves.)

Meanwhile, Lockheed is developing a test cold-water pipe  to be 13 feet in diameter and 40 feet long  in a laboratory in Sunnyvale, Calif.

Last year, Gov. Linda Lingle of Hawaii announced a partnership between Lockheed and the Industrial Technology Research Institute in Taiwan to build a test plant in Hawaii.

Lockheed says it hopes to obtain financing for the project from the Defense and Energy Departments, as well as from the private sector; if enough is available, the company says it would like to have the platform working by 2013. A Japanese engineering company, Xenesys, is also exploring ocean thermal energy for Cuba and Tahiti, among other countries.

Lockheed and the federal government have worked on this type of energy before, after the 1970s oil crises. In 1979, a 50-kilowatt test project was briefly run off the coast of Hawaii’s Big Island. Financing for ocean-energy projects was slashed significantly by the Reagan administration, and Lockheed abandoned its pursuit of the technology in the mid-1980s.

Proponents say that since the last attempt to develop it, the technology has improved enormously. Offshore oil platforms similar to the platforms needed for the ocean energy system have become more sophisticated, for example in their ability to withstand hurricanes and to moor in deeper water.

In theory the technology could, among other uses, provide substantial amounts of power to Hawaii and other warm-water sites and also be used in floating power plants making industrial products like ammonia. However, such goals are distant.