Ocean thermal energy conversion (OTEC) as a means for generating electricity has been around for a long time. French physicist Jacques Arsene d’Arsonval proposed it in 1881. One of his students, Georges Claude, built a 22-kilowatt experimental system at Matanzas Bay, Cuba, in 1930. Five years later Claude built another plant aboard a 10,000-ton cargo ship moored off Brazil.

Both were destroyed by storms, and neither was able to produce more energy than required to run the open-cycle system.

In 1956 French engineers designed a 3-megawatt open-cycle plant off Africa’s west coast, but did not complete it due to competition with cheap hydroelectric power.

In 1979 the Natural Energy Laboratory of Hawaii, which was established in 1974 at Keahole Point on the Kona Coast of the island of Hawaii, began the first 50-kilowatt electric, closed-cycle OTEC on a converted U.S. Navy barge moored 1.2 miles off Keahole point. The plant produced 52 kilowatts of gross power and 15 kilowatts of net power.

In 1980, two laws were enacted to promote the commercial development of OTEC technology: the Ocean Thermal Energy Conversion Act and the Ocean Thermal Energy Conversion Research, Development and Demonstration Act.

Since then research has progressed at Keahole as well as on Nauru, where Japan built a shore-based 100- kilowatt closed-cycle plant that produced 31.5 kilowatts of continuous net power. In 1993 an open-cycle plant at Keahole produced a net 50 kilowatts.

Both open-cycle and closed-cycle systems use the difference between warm surface water and cooler water at depth to turn a turbine that generates electricity.

In the open-cycle system, warm surface water is evaporated in a vacuum chamber to produce steam that expands through a turbine. Cold water pumped from the ocean’s depth is used to condense the steam. The condensed steam can be used to provide a supply of desalinated water if it is kept separate from the cold sea water.

In the closed-cycle system, the warm water is used to vaporize a working fluid, such as ammonia, which turns the turbine. Cold sea water from depth condenses the working fluid, which is pumped back to the evaporator in a continuous closed cycle, functioning like a refrigeration unit running backward.

OTEC may provide Hawaii with a source of alternative energy if Lockheed Martin’s Alternative Energy Development team is successful. They have partnered with Makai Ocean Engineering on a 10-megawatt closed-cycle pilot system that is planned to become operational in 2012 or 2013 with a 100-megawatt commercial system.

Since 2008 Lockheed Martin has been awarded a total of $13.5 million to develop system components and designs for the plan. There are technical difficulties to be overcome, such as dissolved gases, biofouling, leakage and pipe material science.

Even the 100-megawatt plant is only a small fraction of the more than 1,300 megawatts required for the island of Oahu alone at today’s usage.

There are other benefits from OTEC that include desalinated water, refrigeration and air conditioning, mariculture and mineral extraction.

These are in early stages of development, and with the growth of OTEC technology it will become more prevalent in coming years.

Richard Brill is a professor of science at Honolulu Community College. Email questions and comments to rickb@hcc.hawaii.edu.