From the site: Modellers have devised a map that could guide the positioning of wind turbines. It shows wind speeds 80 metres above the ground,which is the right height to turn most turbines’ blades and generate electricity.

Electricity generation becomes practical at locations with average wind speeds of about 25 kilometres per hour. The researchers say there are enough places with this kind of wind to produce 72 terawatts of electricity annually, in theory. Just 20% of this could satisfy the world’s energy needs, the researchers claim in the Journal of Geophysical Research.

This site Green Generation has some less ambitious wind turbines for home use.