Forget Aeolians, We Need Airborne Wind Farms To Harness Maximum Wind Energy

The wind holds much promise for our energy worries, considering that it's a renewable resource. But not only has it yet to fulfil its portion of the renewable energy hype, optimistic projections of wind-generated energy are just that... optimistic. The US Department of Energy, for instance, estimates that by 2030, only a 20% share of the country's electricity production will be generated from wind energy (pdf report).

This uninspiring estimate though, does no justice to the amount of power scientists now believe can be harnessed from the wind. A new paper, published this weekend in Nature Climate Change, used a model which considered the theoretical limits of energy extraction from the wind to postulate some astonishing results. Low-altitude winds near Earth's surface hold at least 400 TW of power. But go higher up to altitudes between 200 m and 20 km and the winds confine a massive 1,800 TW, at least. Such an extraordinary amount of power can sustain an equivalent of 200 Earth habitations (Earth's global energy demand is 18 TW)!

Attempting to harness wind power at dizzying heights appears to be an attractive proposition. High-altitude winds are faster and as such, comprise more power. Power is proportional to the cube of velocity. This means that if wind velocity doubles, wind power grows by eight times. In addition, high-altitude winds are also steadier and more predictable.

A report published last year by GL Garrad Hassan, an independent renewable energy consultancy, shows that a number of companies are indeed focusing on harnessing high-altitude wind energy. Prototypes are varied and range from kites and kytoons (which are basically kites which are lifted and held in position by balloons) to aerostats and gliders with turbines attached.

To harness wind energy, the wind's kinetic energy (or energy of motion) must be turned to mechanical energy (the spinning turbines) which should in turn be converted into electrical energy (by the turbines). The kite mechanism follows this pathway in an uncomplicated manner. The kite, tethered to the ground, rises to the heavens to meet high-altitude winds. Once floating at high speeds, the turbines fixed to the kite convert the kinetic energy of high-altitude winds into mechanical and then electrical energy. This is transmitted via the attaching conducting material back to the ground and immediately off to power homes, etcetera.

While it is attractive from a theoretical and technological viewpoint to set up wind farms at kilometres of altitude, it may not actually be feasible. For one, as George Dvorsky at io9 points out, the paper only looked at the theoretical limits of energy-harnessing from the wind without considering any other practical factors:

"The focus of their research was to determine the geophysical limits of energy extraction from the Earth's wind, disregarding such things as economic, social or environmental factors."

The paper itself also comes with a clear note of caution which emphasizes the theoretical focus of the study:

"It is likely that wind power growth will be limited by economic or environmental factors, not global geophysical limits."

Irrespective of this, the paper should provide a major boost to backers of wind-generated energy. Because science has confirmed that the sky's the limit.

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Reference:

Marvel, K., Kravitz, B. & Caldeira, K. (2012) Geophysical limits to global wind power. Nature Climate Change. DOI: 10.1038/nclimate1683.

Image credits: Top: Adapted from Pierre Andrews (from Flickr), Bottom: ERC HIGHWIND.