Caldeira Lab Research:Energy, Global Carbon Cycle, and Climate

Harnessing high-altitude wind power

Bryan W. Roberts, David H. Shepard, Ken Caldeira, M. Elizabeth Cannon, David G. Eccles, Albert K. Grenier & Jonathan F. Freidlin

Jet streams, winds located around 15,000 ft aboveground, are both powerful and reliable. As of yet, the kinetic energy they harbor has not been used. This is an investigation of the possible implementation of tethered rotorcraft in high altitude winds to use their natural energy as a way to begin supplying the world with clean power.

Roberts, B.W., S.H. Shepard, K. Caldeira, M.E. Cannon, D.G. Eccles, A.J. Grenier and J.F. Freidlin, Harnessing high-altitude wind power, IEEE Transactions on Energy Conversion 22 (1): 136-144, 2007

Advanced rotorcarft: A rendered photograph of a rotorcraft being developed by the Sky WindPower corporation.


Flying electric generators (FEGs) are proposed to harness kinetic energy in the powerful, persistent high-altitude winds. Average power density can be as high as 20 kW/m2 in an approximately 1000-km-wide band around latitude 30◦ in both the hemispheres of the Earth. At 15,000 ft (4,600 m) and above, tethered rotorcraft, with four or more rotors mounted on each unit, could give individual rated outputs of up to 40MW. These aircrafts would be highly controllable and could be flown in arrays, making them a large-scale source of reliable wind power. The aerodynamics, electrics, and control of these craft are described in detail, along with a description of the tether mechanics. A 240 kW craft has been designed to demonstrate the concept at altitude. It is anticipated that large-scale units would make low-cost electricity available for grid supply, for hydrogen production, or for hydro-storage from large-scale generating facilities.