Vast wind energy could be harnessed over oceans
The Washington Post
New research published Monday finds there is so much wind energy potential over oceans that it could theoretically be used to generate “civilization scale power” — assuming, that is, that we are willing to cover enormous stretches of the sea with turbines and can come up with ways to install and maintain them in often extreme ocean environments.
It’s very unlikely that we would ever build out open ocean turbines on anything like that scale — indeed, doing so could even alter the planet’s climate, the research finds. But the more modest message is that wind energy over the open oceans has large potential — reinforcing the idea that floating wind farms, over very deep waters, could be the next major step for wind energy technology.
“I would look at this as kind of a green light for that industry from a geophysical point of view,” said Ken Caldeira of the Carnegie Institution for Science in Stanford, Calif. The study, in the Proceedings of the National Academy of Sciences, was led by Carnegie researcher Anna Possner, who worked in collaboration with Mr. Caldeira.
The study takes, as its outset, prior research that has found that there’s probably an upper limit to the amount of energy that can be generated by a wind farm that’s located on land. The limit arises both because natural and human structures on land create friction that slows down the wind speed, but also because each individual wind turbine extracts some of the energy of the wind and transforms it into power that we can use — leaving less wind energy for other turbines to collect.
“If each turbine removes something like half the energy flowing through it, by the time you get to the second row, you’ve only got a quarter of the energy, and so on,” Mr. Caldeira explained.
The ocean is different. First, wind speeds can be as much as 70 percent higher than on land. But a bigger deal is what you might call wind replenishment. The new research found that over the mid-latitude oceans, storms regularly transfer powerful wind energy down to the surface from higher altitudes, meaning that the upper limit there for how much energy you can capture with turbines is considerably higher.
“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,”Mr. Caldeira said.
The study compares a theoretical wind farm of nearly 2 million square kilometers located either over the U.S. (centered on Kansas) or in the open Atlantic. And it finds that covering much of the central U.S. with wind farms would still be insufficient to power the U.S. and China, which would require a generating capacity of some 7 terawatts annually. A terawatt is equivalent to a trillion watts.
But the North Atlantic could theoretically power those two countries and then some. The potential energy that can be extracted over the ocean, given the same area, is “atleast three times as high.”
It would take an even larger, 3 million square kilometer, wind installation over the ocean to provide humanity’s current power needs, or 18 terawatts, the study found. That’s an area even larger than Greenland.
Hence, the study concludes that “on an annual mean basis, the wind power available in the North Atlantic could be sufficient to power the world.”
But it’s critical to emphasize that these are purely theoretical calculations. They are thwarted by many practical factors, including the fact that the winds aren’t equally strong in all seasons, and that the technologies to capture their energy at such a scale, much less transfer it to shore, do not currently exist.
Oh, and then there’s another large problem: Modeling simulations performed in the study suggest that extracting this much wind energy from nature would have planetary-scale effects, including cooling down parts of the Arctic by as much as 13 degrees Celsius.
“Trying to get civilization-scale power out of wind is a bit asking for trouble,” Mr. Caldeira said.