A University of Hawaii researcher says the ocean on the leeward side of the Hawaiian Islands may be a better location for generating continuous energy using ocean temperatures than on the windward side.

UH associate professor Gerard Nihous says the results of his study could improve the power output of future projects that use ocean thermal energy conversion, or OTEC, by 15 percent, improving the cost-effectiveness of future facilities. His paper was published online last month in the Journal of Renewable and Sustainable Energy.

"The article … simply sends a modest message to those interested in OTEC that we now have the tools to be a smarter about picking these locations," said Nihous, who is with the Department of Ocean and Resources Engineering. "It’s essentially a fine-tuning thing."

According to Nihous, an OTEC project would be more cost-effective on the leeward side of the islands because the surface water stays warmer there compared with the windward side — by a single degree Celsius. That difference can improve the output of a thermal conversion engine by 15 percent, which could make a multibillion-dollar project more affordable.

Nihous, who has been studying OTEC since the 1980s, said cost has been a factor in the lack of new facilities, but that an investment must be made for future generations before resources run out. He believes Hawaii is the best place for the technology in the U.S.

"We have all the ingredients here. We have the temperature, we have the steep submarine slopes, we also have an isolated power grid," he said.

OTEC technology dates back more than a half-century.

In 1974, Hawaii lawmakers created the Natural Energy Laboratory of Hawaii to support research on OTEC technologies. In 1979, NELH ran the world’s first energy-producing OTEC system, based at the Big Island’s Keahole Point.

Despite its cost, OTEC remains an attractive renewable energy source because it can be sustained continuously, unlike other renewable energy sources that are limited by the availability of sun, wind, or waves. Lockheed Martin is working on a pilot OTEC project that could be running in a few years in Hawaii, Nihous said.

OTEC captures energy through a floating engine turbine that is turned by a fluid changing from a liquid to a vapor and back to a liquid, like most power plants.

Inside the system, the fluid is changed to a vapor by the warm upper layers of the ocean and returns to a liquid when it is cooled by the deep-ocean waters.