Реферат: Wind Power Essay Research Paper The wind

relation to the ground or it is too

difficult to harness. 4) The gustiness of the wind field in both speed

and direction. Gusty winds greatly affect the power output of the

windmills and are usually harmful. 5) The wind direction distribution and

probability of sudden large shifts in di rection. The wind must be

unlikely to suddenly shift direction. It must blow in the same general

direction. 6) the seasonal density of the air, and variations of density

of the air with height. The denser the air, the worse it will be for

windmills. 7) Hazard conditions such as sandstorms, humidity, and

salt-spray, which are bad for windmills. The physics behind these will be

discussed later. 8) Trade winds in the subtropics, and the channeled

wind through mountain passes are especially beneficial to windmills. Once

a suitable location is found, the wind is analyzed extensively, and the

criteria is met, there are still more requisites. 1) The terrain upon

which the windmills are built must be relatively flat. The elevation

difference between the turbine site and the terrain is no larger than 60

meters over a 12-km radius. You may have seen windmills such as those in

California on little hills, but this is because the requirement is met.

The hill may be the only one around for miles. 2) All hills must have

small height to width ratios: h:l must be < 0.016. 3) The elevation

difference between the highest and lowest point must be 1/3 or less of the

height difference between the bottom of the rotor disk and the lowest

point in the terrain strip. The surface roughness of the terrain upon

which the windmill is to be built must be low. If it varies by more than

10%, this is no good. The terrain must be smooth, and consistently so. A

rough surface has more of a negative effect on the wind than a s mooth

surface. There is a value n, called, which is assigned to the terrain in

terms of its roughness. This value is used to calculate the height of the

windmill. For instance, over the sea, the index location, n is 0.14.