Jim Dehlsen, a 79-year-old wind-energy pioneer who sold one turbine company to Enron and took another public, has spent his life thinking about the best way to make blades turn in the sky. For his latest effort, he’s flipping a turbine upside down and plunging it hundreds of metres deep in the ocean. There, marine currents rotate the 27-metre long blades to pull power from the sea.

Aquantis, Dehlsen’s Santa Barbara, California, company, will start deploying turbines in 2018 in waters near Wales and the Isle of Wight. Its most ambitious project is a 200-megawatt field of marine turbines in the strong Gulf Stream off the coast of Florida, due to come online in 2019 or 2020. The world’s oceans remain relatively untapped as an energy source, compared with wind and solar. By 2030, Dehlsen says, marine energy could serve 8 per cent or 9 per cent of US power needs. “The oceans are the major remaining potential for renewable energy,” he says. “Getting on that now is really urgent.”

It took wind at least 15 years to become a viable, cost-effective resource. In the late 1970s, when scientists first started experimenting with wind turbines, “people laughed at you and said, ‘Wind will never work,’ ” says Robert Thresher, a research fellow at the National Renewable Energy Laboratory in Golden, Colorado. In the ’80s and ’90s, the industry settled on the three-blade turbine design considered the standard today. Many aspects of turbine design can be applied to the oceans, adjusted to handle the slower, heftier fluid dynamics of seawater.