Five or six miles up in the atmosphere, near where airliners reach cruising altitude, very strong winds blow incessantly over many densely populated regions of the world.
Researchers at the Carnegie Institution and California State University believe that, if the technical challenges can be resolved, large metropolises like New York, Seoul, and Tokyo may be able to tap into the high-altitude winds for abundant energy.
One possible way to do this could be by using giant tethered kitelike wind turbines, like the one imagined in this illustration.
Illustration of four-rotor flying generator by Ben Shepard
“There is a huge amount of energy available in high-altitude winds,” said study coauthor Ken Caldeira. “These winds blow much more strongly and steadily than near-surface winds, but you need to go get up miles to get a big advantage. Ideally, you would like to be up near the jet streams, around 30,000 feet.”
The study identifies New York as a prime location for exploiting high-altitude winds, which globally contain enough energy to meet world demand 100 times over.
“The researchers found that the regions best suited for harvesting this energy match with population centers in the eastern U.S. and East Asia, but fluctuating wind strength still presents a challenge for exploiting this energy source on a large scale,” says a Carnegie Institution statement.
Using 28 years of data from the National Center for Environmental Prediction and the U.S. Department of Energy, Ken Caldeira, of the Carnegie Institution’s Department of Global Ecology, and Cristina Archer, of California State University, Chico, compiled the first-ever global survey of wind energy available at high altitudes in the atmosphere.
The researchers assessed potential for wind power in terms of “wind power density,” which takes into account both wind speed and air density at different altitudes.
“A potentially vast and dependable source of energy”
“Jet streams are meandering belts of fast winds at altitudes between 20,000 and 50,000 feet that shift seasonally, but otherwise are persistent features in the atmosphere,” the Carnegie Institution said. “Jet stream winds are generally steadier and 10 times faster than winds near the ground, making them a potentially vast and dependable source of energy.”
Several technological schemes have been proposed to harvest this energy, including tethered, kitelike wind turbines that would be lofted to the altitude of the jet streams. Up to 40 megawatts of electricity could be generated by current designs and transmitted to the ground via the tether, the researchers said.
Jet stream clouds picture courtesy NASA
“We found the highest wind power densities over Japan and eastern China, the eastern coast of the United States, southern Australia, and north-eastern Africa,” said lead author Cristina Archer. “The median values in these areas are greater than 10 kilowatts per square meter. This is unthinkable near the ground, where even the best locations have usually less than one kilowatt per square meter.”
Included in the analysis were assessments of high-altitude wind energy for the world’s five largest cities: Tokyo, New York, Sao Paulo, Seoul, and Mexico City. “For cities that are affected by polar jet streams such as Tokyo, Seoul, and New York, the high-altitude resource is phenomenal,” Archer said. “New York, which has the highest average high-altitude wind power density of any U.S. city, has an average wind power density of up to 16 kilowatts per square meter.”
Tokyo and Seoul also have high wind power density because they are both affected by the East Asian jet stream.
Mexico City and Sao Paulo are located at tropical latitudes, so they are rarely affected by the polar jet streams and just occasionally by the weaker sub-tropical jets. As a result they have lower wind power densities than the other three cities.
“While there is enough power in these high-altitude winds to power all of modern civilization, at any specific location there are still times when the winds do not blow,” Caldeira said. “Even over the best areas, the wind can be expected to fail about five percent of the time. This means that you either need back-up power, massive amounts of energy storage, or a continental or even global scale electricity grid to assure power availability.
“So, while high-altitude wind may ultimately prove to be a major energy source, it requires substantial infrastructure.”