Ocean thermal energy conversion — the technology known better as OTEC that more than 30 years ago was viewed as the great hope for this oil-dependent state — gradually lost some of the cachet it had among funders of research. Now it’s beginning to make a comeback, and that ought to be applauded by anyone concerned about Hawaii’s energy future.

Although OTEC is a long way from becoming a commercial power source, last week a demonstration project using the technology was launched on a barge off Hawaii’s Kona Coast, at the Natural Energy Laboratory of Hawaii.

Its sponsors at Makai Ocean Engineering say the project’s roughly $6 million in federal funds underwrite a search for ways to make a commercial project more viable. The primary cost hurdles are the heat exchanger that enables electrical generation and the system of pipes that circulate the seawater.

Hawaii is suited to OTEC because it has both warm and cold seawater within fairly easy reach. The heat from the surface water is used to generate steam from a fluid with a low boiling point, ammonia in this case. The steam drives the turbine and the cold, deep water is used to chill and re-liquefy the ammonia for reuse.

Progress is being made already toward an improved model, one that resists corrosion and replaces costly titanium components with other metals. But with no other OTEC plants in operation, it could be years before investors are convinced the financial risks have been managed and are willing to underwrite development.

This is why the state must pursue the more mature technologies — primarily wind, solar and geothermal — that can deliver commercial power from a "green" source and help Hawaii meet its goals of reducing reliance on fossil fuels. The Clean Energy Initiative, which former Gov. Linda Lingle signed with the U.S. Department of Energy, aims to improve Hawaii’s clean-energy picture by 2030, reducing energy use by 30 percent and increasing to 40 percent the share of the portfolio coming from locally generated renewable sources. To reach those ambitious benchmarks, the state can’t afford to wait until OTEC comes up to speed.

But that doesn’t mean this alternative should be shelved. Everyone agrees that, despite the cyclical changes in the oil market, the long-range trend is not coming down. And that suggests that Hawaii will need a full menu of renewable options, each one shifting in relative importance as technological advances make one system or another more advantageous.

To preserve the OTEC option, the state should explore various ways of encouraging development once the economy stabilizes, including offering investment incentives and easing permitting burdens. For now, OTEC remains a distant prospect, but we shouldn’t repeat the mistake of the last three decades by letting it fade away altogether.