Governors' Wind Energy Coalition

A properly placed offshore wind farm could provide far more electricity than an identical land system and power the entire planet, according to a surprising new study.

There was a previous assumption that deep-sea turbines might produce about the same power per unit as their land counterparts. But the Carnegie Institution for Science team found an ocean system could produce at least three times as much electricity, because of unique atmospheric conditions created by heat released from the ocean.

The study suggests open ocean farms theoretically could be more economical per unit of energy than ones on land, and provide “civilization-scale” amounts of energy, at least from the studied region of the North Atlantic.

“What was surprising to us was the increase of the kinetic energy extraction over the ocean,” said Anna Possner, an atmospheric scientist at the Carnegie Institution and co-author of the research published yesterday in the Proceedings of the National Academy of Sciences.

The team found a hypothetical open-ocean wind system spread across about 3 million square kilometers — or about the size of Argentina — in the North Atlantic could meet 18 terawatts of annual demand, enough to power all human needs. By contrast, a land-based wind farm of the same size would produce less than half that electricity.

Earlier studies show land farms appear to be limited to about 1.5 watts per square meter of production. Open-ocean wind could average more than 6 watts per square meter, Possner said.

While the study focused on the Atlantic, there may well be other similar ocean areas situated in the Pacific and in midlatitudes of the Southern Hemisphere, she said.

There are challenges in building a small offshore farm, much less one the size of Argentina in deep water. The study was not designed to be a policy blueprint or to assess factors such as installation costs, according to researchers. New types of turbine technology would be needed to harness power at scale from high-speed winds in the deep ocean. Offshore farms now operate in relatively shallow waters.

There’s no “magic bullet,” but the study suggests deep-sea wind could have a role in the future, said Ken Caldeira, a senior scientist at Carnegie and study co-author. Nascent efforts to commercialize floating wind turbines “show great promise” when viewed from geophysical perspectives, he said.

Statoil ASA, for example, is planning to build the world’s first floating wind farm off the coast of Scotland, to power 20,000 homes.

“There is a huge resource out there that people are just starting to tap,” he said.

It’s long been known that wind speeds above the ocean are much faster than on land, but scientists didn’t know whether that could translate into more electricity.

It was unclear whether ocean winds were so fast “just because there was nothing out there to slow them down,” said Caldeira.

On land, individual turbines in a farm typically pull energy away from each other, helping cause a wind slowdown.

Deep-sea turbines slow down wind just as land turbines do — and as other obstruction like buildings do — but the study’s simulations show they also recover faster. They appear not to be held back by the drag they create.

Possner pointed to a temperature differential between land and water that helps drive air circulation in such a way to replenish high-speed winds and counter the drag. The temperature difference is particularly strong in the winter, as the ocean releases stored heat, while the land is colder.

The stormy low-pressure systems that span the Atlantic prove to be very efficient at drawing energy down from higher altitudes and creating a steady stream of power at the turbine level. “There’s a continual mixing of high-speed wind downward where the turbines sit,” said Possner.

That differs from land systems, which are limited by available wind at the surface.

A next step of research is determining how far offshore turbines would have to be placed to achieve the effect, Possner said.

Other barriers with the concept include less potential power in the summer and the possibility such a large wind farm would alter the atmosphere in places far away, including the Arctic. Caldeira said multiple smaller farms would address that issue.

“If open-ocean wind power really scales up, you would want to spread it out broadly so as to avoid hitting any one area too hard,” Caldeira said.

Lee Miller, an expert on large-scale wind at Harvard University who did not participate in the study, said it is a “nice example” of a next phase of research examining the effects of turbines on the atmosphere. While developing floating turbines for the big wind and waves of the North Atlantic would be quite different from coastal Europe, it “could be feasible sometime in the future,” he said.