Wind is Sun’s heat transformed into kinetic energy through the greatest solar collector currently available, Earth’s atmosphere. Wind total power is estimated between 1,700 and 3,500 TeraWatt; by comparison, the whole mankind primary energy needs are estimated at approx. 14 TW.
Wind energy is not uniformely distributed, but mainly found in the higher layers of the troposphere at the mid latitudes of both North and South emispheres. The most favourable altitude in term of wind power is, quite difficult to exploit, at approx. 10,000 m (32,800 ft), where average wind speeds can exceed 45 m/s (equal to 162 km/h or 100 mph). The graphic below shows ten years of data at 250 hectoPascal (measure of atmospheric pressure, equal to millibar) equivalent to approx. 10,400 m of altitude (images provided by the NOAA/ESRL Physical Sciences Division, Boulder Colorado from their Web site at http://www.cdc.noaa.gov/).
From these heights, wind speed and energy decrease moving towards the ground, the layers of air giving back heat through friction between them and with the orography of the Earth’s surface. In the below graphic at 500 hPa (approx. 5,600 m of altitude) average wind speeds are already significantly reduced.
At 80 m above the ground, the hub height representative of the latest generation of wind turbines, the global average wind speed is estimated at 4.6 m/s, not enough for economical wind power generation; at 10 m above the ground is even lower, estimated at 3.3 m/s (see Evaluation of global wind power, Cristina L. Archer – Mark Z. Jacobson, Journal of Geophysical Research – Atmospheres, 2005).
But to break free from the ground and to reach altitude winds is already very beneficial at 800 m, the height representative of a KiteGen power plant, where the average wind speed is estimated to be 7.2 m/s. At this altitude wind power, as shown by the following table, is almost 4 times the amount available to wind turbines.
|Altitude [m]||Wind speed [m/s]||Wind power [W/m²]|
Every point on the Earth surface, on average, 800 m above it, has enough wind power to be exploited with a KiteGen power plant for energy generation.