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 hemispheres. 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 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 Kite Gen power plant,
where the average wind speed is estimated by Kite Gen Research at 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 Wind speed Wind power
m m/s W/mē
800 7.2 205
80 4.6 58
10 3.3 22
Every point on the Earth surface, on average, 800 m above it, has enough wind power to be exploited