Very Clever Idea. Seems like a perfect compliment to Solar Thermal.
Main disadvantage appears to be that it requires a no fly zone but:
From their FAQ:To help visualizing the existing unexploited potential, just consider that the flight prohibited area over a nuclear power plant can easily get to contain 1 GW of wind power, equal to the power of the plant itself.
What is the cost of the energy produced by a Kite Gen power plant?
A 100 MW Carousel power plant is estimated to deliver energy for less than 0.03 Euro per kWh, which is cheaper than fossil fuel-based generation. Even lower costs are to be expected from bigger and more powerful plants. In the Stem configuration the foreseen cost is around 0.05 Ã¢â€šÂ¬ per kWh
How does wind power change with altitude?
As altitude increases, average wind speed increases (and remember that wind power grows with the cube of wind speed) and air density decreases. Wind power decreases linearly with air density, but even at 1000 m air density is reduced by only about 10%. Wind power therefore always tends to grow from ground up to approx. 10,000 m of altitude.
The following video shows how the Stem generator works: