The semi-circular power kite of the KiteGen device curls in the wind, rotating a vertical shaft to generate electricity in Italian inventor Massimo Ippolito's system.
Like the Makani founders, Ippolito says he was inspired by kite-surfing. Active computer controls help keep the kite, with its airfoil shape, optimally oriented into the winds, Ippolito said in an interview for Build Your Own Small Wind Power System. Each airfoil is controlled by two lines, much like a stunt kite, as the shaft rotates in a circular pattern.
Ippolito said he hopes to get his airfoil 2,625 to 3,281 feet (800 to 1,000 meters) above ground—about six to eight times the height of today's popular ground-based 1.5 megawatt (MW) wind turbine. By leaving all the expensive generating equipment on the ground, Ippolito said he hopes to reduce costs, risks, and maintenance time. He said he is trying to develop KiteGen power plants with a capacity of 1,000 MW (about the same as a big coal plant).
In their new paper, Caldeira and his colleagues considered whether there are any significant geophysical limitations to considering wind energy as a major primary energy source (as coal is today). Would the increased surface drag of large-scale wind energy deployment have harmful impacts on the Earth's climate? Several studies in recent years have looked at large-scale wind farms and their potential to impact temperature or precipitation.
(Related Story: "Planting Wind Energy on Farms May Help Crops, Say Researchers")
Through climate modeling, Caldeira's team concluded that indeed, if wind power were deployed at a level about 100 times higher than civilization's current energy use, profound climate changes would occur. The drag created by the turbines would alter Earth's circulation pattern and impede heat transfer into polar regions. But at one percent of that level—if wind turbines were deployed to satisfy all of the energy civilization is currently consuming, from car-fueling to electricity—the resulting wind drag would alter the global climate by only a tenth of a degree Celsius and change precipitation rates only by one percent. In other words, says Caldeira, "Environmental consequences would be small and manageable."
Wind turbines, of course, are not alone among human developments that can cause wind patterns to shift. "This is also the case with converting forests to croplands, building cities, and many other changes," said Caldeira. "Any time you toy with drag in the atmosphere you will change circulation somewhat."
For next steps, Caldeira said his team is modeling airborne wind turbines on a theoretical planet that is entirely covered by water, to simplify the calculations and try to better understand the complex physics, "which are more complicated than we thought." Because airborne wind also seems to have a cooling effect, the team is also looking into how aloft turbines could be purposefully used, as a form of geoengineering, to cool down the over-heating planet. (See video of Caldeira discussing his research.)