If commercial wind farms in the open ocean become technically and economically feasible, they could potentially provide humanity’s present electric power needs – “civilisation-scale” at 18TW, a new US study suggests.

To achieve this on “an annual mean basis” would require turbines installed over more than a 3 million sq km (1.16 million sq mile) area in the North Atlantic, larger than Greenland and the UK combined, estimate researchers at the Carnegie Institution for Science in Stanford, California.

While facilities even a fraction of that size are hard to imagine given construction, energy transport and maintenance costs, as well as design, access-use and other challenges, the study highlights the geophysical potential for wind energy over the open oceans.

It was published Monday in the Proceedings of the National Academy of Sciences.

The study uses modeling tools to compare the energy generation of a theoretical nearly 2 million sq km onshore wind farm whose epicentre is in Kansas with one of similar size over the open Atlantic.

Focusing on the North Atlantic region, the study provides evidence that recovery of energy over some ocean areas is potentially “at least three times as high” as from wind farms on land.

The study suggests there are several reasons for this. First, “surface drag” on land created by man-made and natural obstacles and structures places a ceiling on energy generation.

Second, the amount of electricity produced per individual turbine decreases as the turbine density and geographical area of the wind farm increases. As each turbine extracts kinetic energy (KE) from the mean flow, wind speed is reduced.

“As KE is continuously removed from the atmosphere, the maintained rate of power generation in the wind farm is constrained by the extent to which KE can be restored to its free flow value over the wind farm area,” study co-authors Ken Caldeira and Anna Possner write.

These wake effects are less pronounced over the open oceans in midlatitude wind belts in each hemisphere given that the greater sustainable downward transport of KE from the “free troposphere may be sustained at levels several times greater than may be sustain over land,” they note. Storms are the conduit for drawing down this energy.

“Over land the turbines are just sort of scraping the kinetic energy out of the lowest part of the atmosphere, whereas over the ocean, it’s depleting the kinetic energy out of most of the troposphere, or the lower part of the atmosphere,” Caldeira told the Washington Post.

The study found mean surface wind speeds are, on average, 70% higher over the oceans than on land.

For all the wind resource over the oceans, trying to generate the massive amount of electric power humankind needs would be unwise, he adds, since such a move could affect the entire planet.

Examples include up to a 13-degree Celsius cooling of surface temperatures in regions of the Arctic and sizable changes wind resource available to onshore installations in the UK, France and Western Europe.

He told the Post that the climate effect would be reduced if open ocean installations were considerably smaller in number and area in the North Atlantic, and also spread out among other regions of the world.

The bottom line is that while open-ocean offshore wind is a valuable renewable resource whose scalability is almost limitless, humanity would be wiser to look at developing a balanced clean portfolio that includes onshore wind, solar and emerging technologies such as tidal and wave energy.

Wind

Deep-ocean wind could 'power all humanity': US study