"There is enough energy in high-altitude winds to power civilization 100 times over; and sooner or later, we're going to learn to tap into the power of winds and use it to run civilization." Says Ken Caldeira, Professor of Global Ecology at the Carnegie Institution for Science. 
It doesn't matter how much you use it. It's still there every day and it's free! Wind energy is viable, clean, plentiful and can even be cost effective with today's recent wind turbines. Wind at higher altitudes are faster and more consistent than winds near the Earth’s surface. The total wind energy in the jet streams is roughly 100 times the global energy demand. 
Several technologies have been proposed that aim at harnessing wind power at high altitudes. Most of them are still at an early stage of development; however, Magenn Power plans to start manufacturing its Magenn Air Rotor System (MARS) in 2010-11. (Figure 1)
Magenn Power's high altitude wind turbine called MARS is a Wind Power Anywhere™ solution with distinct advantages over existing Conventional Wind Turbines and Diesel Generating Systems including: global deployment, lower costs, better operational performance, and greater environmental advantages. MARS is a lighter-than-air tethered wind turbine that rotates about a horizontal axis in response to wind, generating electrical energy. This electrical energy is transferred down the 1000-foot tether for immediate use, or to a set of batteries for later use, or to the power grid. Helium sustains MARS and allows it to ascend to a higher altitude than traditional wind turbines. MARS captures the energy available in the 600 to 1000-foot low level and nocturnal jet streams that exist almost everywhere. MARS rotation also generates the "Magnus effect" which provides additional lift, keeps the MARS stabilized, and positions it within a very controlled and restricted location to adhere to FAA (Federal Aviation Administration) & Transport Canada guidelines. 
While Magenn Power has made what looks like a spinning, helium-filled blimp, Joby Energy's turbines fly by the same principle as kites. Lifted by the winds, they give the appearance of a flying frame ( Figure 2). Helicopter-like rotors keep Sky WindPower's device afloat while also being the turbine's rotors ( Figure 3).
Last but not least Magenn wind turbine is very light and safe and can be located in many more places than ground-based wind power, such as urban areas, off-shore or any other place which is in emergency need of energy. ”It's difficult in many countries to build transmission lines and generating capacity.” said Anthony Pizarro, director of corporate development at Magenn company. ”It makes more sense to have some autonomous source of power right there at that one spot.”
1. Discovery Channel, Project Earth, Infinite Winds episode
2. Roberts, B.W.; Shepard, D.H.; Caldeira, K.; Cannon, M.E.; Eccles, D.G.; Grenier, A.J.; Freidin, J.F. Harnessing high-altitude wind power. IEEE Trans. Energy Convers. 2007, 22, 136-144