Image thanks to Joby Energy
"We might extend the application of [wind] power to the heights of the clouds, by means of kites." ~utopian technologist John Etzler, 1833
High Altitude Wind Power
Wind increases in velocity, predictability and consistency at higher altitudes. The graph at right compares the power density (available power per unit volume) at 400 ft with that at 2000 ft. Warm colors (red/orange) indicate more power than cooler colors (blue/green). Also notable is the global prevalence of these power dense winds.
Cristina Archer and Ken Caldeira analyzed 27 years of data to assess the available wind power resource worldwide in their paper, "Global Assessment of High-Altitude Wind Power" (2009).
They conclude that the jet streams can produce 1700 TW of power with negligible effect to global climate.
Closer to the surface and more ideal for early AWES, another type of jet occurs, low-level jets (LLJs). LLJs are narrow, nocturnal wind speed maxima. According to a recent study by Archer, Monache, and Rife,* these LLJs are more prevalent and frequent than previously thought, especially during summer months, and can have "extraordinarily high wind power densities (up to 15,000 W / m^2)."
Occuring below 3 km (and often below 500m), the LLJs blow at between 30-60 MPH. By analyzing 21 years of hourly wind speed data, they conclude:
Preliminary calculations show that, even with intermediate densities of AWE systems per unit land, potential from WSM exceeds 7.5 TW, which is ~3 times higher than the 2012 global electricity demand of 2.4 TW.
LLJs form over almost a quarter of the globe. Sweet spots include the American Great Plains, offshore of the Horn of Africa, and above large stretches of tropical oceans near descending branches of the Hadley cells.
The Jet Stream: "Straalstroom" by Ellywa at nl.wikipedia
Low Level Jet acting on smoke rising from a wild fire
Showing potential locations for LLJ formations in the US. Image from University Coorporation for Atmospheric Research
NASA’s Goddard Earth Observing System Model - Global Winds: surface winds shown in white; upper level winds shown by intensity with red indicating higher speeds