It has three spokes with cups that spin on a revolving wheel when the wind blows. It is hooked up to a meter that tells the wind speed. As a rule, wind speed increases with altitude and over open areas with no wind breaks. Good sites for wind plants are the tops of smooth, rounded hills, open plains or shorelines, and mountain gaps that produce wind funneling. The three biggest wind plants in California are located at mountain gaps.
Wind speed varies throughout the country.
It also varies from season to season. In Tehachapi, California, the wind blows more from April through October than it does in the winter. This is because of the extreme heating of the Mojave desert during the summer months. The hot desert air rises, and the cooler, denser air from the Pacific Ocean rushes through the Tehachapi mountain pass to take its place. In a state like Montana, on the other hand, the wind blows more during the winter.