Could airborne wind turbines power the world?

Source: Elizabeth Harball, E&E reporter • Posted: Tuesday, April 15, 2014

Some prototypes look like parachutes. Others, like one developed by the Google-owned startup Makani Power, look more like gliders. Another, called a buoyant airborne turbine, or “the BAT,” resembles a blimp, but it’s hollow, with a spinning turbine suspended in its center.While renewable energy developers dream of harnessing the stronger, more consistent breezes that blow thousands of feet above our heads, it’s hard to say when airborne wind energy technology will become commercially viable.But a recent study roughly estimates that if these high-flying devices are deployed at strategic locations around the globe, they have the potential to provide between 7.5 and 9 terawatts of energy — “more than enough to provide electricity to all of humanity,” it states.Lead author Cristina Archer of the University of Delaware’s College of Earth, Ocean and Environment cautioned that this finding, published in the April issue of the journal Renewable Energy, is only a “ballpark” estimate.

Data on the technology are currently limited because while several prototypes have been deployed, no airborne wind energy arrays have been installed. However, Archer said, the potential is undeniably enormous.

“That estimate I think is actually low, but it’s a very crude first estimate,” Archer said.

A ‘complement’ to land-based wind farms

Global electricity demand in 2012 was about 2.4 terawatts, so harnessing even a fraction of the 7.5 terawatts of high-altitude winds found in her analysis could transform the world’s energy portfolio.

Archer and her co-authors analyzed a data set of 21 years of global meteorological data, searching for optimum wind power densities at heights to which today’s airborne wind technologies can easily rise.

They found that there were several regions that were particularly rich in high-but-not-too-high-altitude wind potential, like the Somali jet stream that blows along the Horn of Africa, as well as the American Midwest, where traditional land-based wind turbines are already proliferating at a record pace (ClimateWire, April 11).

“What we found in this paper that there are a lot of sweet spots,” Archer said. “You have these very high winds much lower than you would have imagined.”

These widespread “sweet spots” are located at about altitudes of about 1,600 feet, about 400 feet higher than the top of the Empire State Building and about 1,000 feet taller than today’s tallest wind turbines.

While certainly in the nosebleed zone, this is low enough that cables tethering airborne wind devices to the ground don’t weigh them down or cause excessive drag, which can sap their efficiency.

Fort Felker, director of the National Wind Technology Center in Golden, Colo., said the study also took the “admirable second step” of identifying locations that had not just promising average wind speeds, but a steady wind resource, as well.

One of these areas is the U.S. Midwest, Archer noted, where wind speed maxima called “low-level jets” are currently a nuisance for wind farms. When they blow above the arrays, they stress the turbines’ blades, often forcing them to shut down.

But if airborne devices were deployed in the same place, low-level jets would become a help rather than a hindrance because these are exactly the winds that work best for this technology.

“If you have both, they kind of complement each other,” Archer said.

100 patents, but more work to be done

Airborne wind energy proponents celebrate the technology’s potential benefits, such as its ability to capture powerful high-altitude winds and its potential for reduced environmental impact, as no foundations or towers need to be constructed.

But for many years, it’s been considered a “fringe” technology, forever relegated to research and development limbo. Archer, however, is optimistic about its near-term potential, noting that more than 100 patents related to airborne wind have been filed in the United States.

While Felker was not comfortable providing any time frame for utility-scale deployment of airborne wind, he did say that the technology “shows sufficient promise that it continues to be worth additional pursuit.”

But there’s still a lot of work to be done if the massive energy source hinted at Archer’s paper is tapped.

While the authors excluded polar regions and oceans as potential sites in their analysis, they also didn’t consider how airborne wind energy arrays would fit into the current power grid, or how large of an impact seasonal changes in wind speed might have on their estimate (the authors only mapped wind densities for the months of January and July).

The study also doesn’t consider the potential environmental impacts of countless airborne wind energy devices filling the skies, not to mention safety issues like how widespread deployment might affect air travel. Wading through the mire of government regulations and insurance will also prove to be a significant hurdle for the technology to overcome.

However, Felker added that the study represents a key early step for airborne wind developers.

“For renewable energy systems, understanding the magnitude of the resources is really important,” he said.