An American company, Altaeros Energies, recently launched a prototype helium-shelled wind turbine that can be used at high altitudes. While the test run took place at 350ft above ground, the ultimate goal is a height of 1,000ft. Tethers send the converted power back to the ground. Compared with traditional wind turbines, the prototype garners twice as much energy, as wind is stronger at higher altitudes.
Sources: Green Tech Media, Smart Planet