BioEd Online

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.

Coming up with speed measurements at this height was difficult, according to Cristina Archer, an environmental engineer at Stanford University, California, who co-authored the study with her Stanford colleague Mark Jacobson. Most windspeed recordings are made about 10 metres off the ground, but wind speed increases the higher you go.

So the pair had to extrapolate from the few places where wind is measured at 80 metres, deriving models of how quickly the wind speed increases with height in different parts of the world. They then applied these models to thousands of the lower-altitude wind measurements.

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 Research¹.

Shooting the breeze

"The map definitely would be of interest to the wind power industry," says Tom Gray, spokesman for the American Wind Energy Association, based in Washington DC. "From the early days, there has been an issue with where the resource is."

However, there are practical obstacles to producing that much wind energy. Turbines cannot be erected just anywhere; they are big, often noisy, and many worry about their effect on bird populations.

Although this limits the potential sites, the untapped reserves of wind power could be even greater than 72 terawatts. "All our numbers are low estimates," says Archer.

Some of the world's windiest sites include the North Sea, the tip of South America, Tasmania, and North America's great lakes. The overall champ is Mount Washington in New Hampshire, where winds clock in at 60 kilometres an hour. "The wind speed there is incredible," says Archer.