Flying Fan

People have been using wind energy ever since the beginning of history. Can you imagine Holland without windmills? Modern windmills change the landscape, they are still expensive, but they generate a considerable amount of power.

Assuming that the density of air is r=1,3 g/dm₃ = 1,3 kg/m₃, *) and the velocity of wind is v = 10 m/s (quite strong, but 'acceptable') the mass of the air blowing within 1 second over the base of a cylinder of a radius of R = 10 m is equal to M = pR²vr=4000 kg, and its kinetic energy amounts to ca. 200 kJ. Supposing the efficiency of transforming the energy of the air flow into power is 15% (due to the fact that after passing the windmill the air still flows with some velocity) we can establish that a single windmill generates a power of 30 kW. An average household has a contract with electricity board which guarantees the maximum power consumption of 3 kW, but even if a washing machine, and a refrigerator and TV set are on, power consumption amounts to ca. 2 kW.

In other words, one modern windmill provides power for a small block of flats.