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Renewables: which way does the wind blow?

11 October 2012

Adapting a sophisticated climate model, researchers have shown that there is plenty of wind available to supply half to several times the world's total energy needs within the next two decades.

Onshore wind project, Goodnoe Hills, USA (photo courtesy of Dennis Schwartz/REpower)

If the world is to shift to clean energy, electricity generated by the wind will play a major role – and there is more than enough wind for that, according to new research from Stanford and the University of Delaware, writes Andrew Myers.

Researchers have developed a sophisticated weather model to show that not only is there plenty of wind over land and near to shore to provide half the world's power, but there is enough to exceed the total demand by several times, even after accounting for reductions in wind speed caused by turbines.

'The careful siting of wind farms will minimise costs and the overall impacts of a global wind infrastructure on the environment,' said Mark Jacobson, a professor of civil and environmental engineering at Stanford. 'But, as these results suggest, the saturation of wind power availability will not limit a clean-energy economy.'

High-resolution models
In their study, Jacobson and Cristina Archer, an associate professor of geography and physical ocean science and engineering at the University of Delaware, adapted the three-dimensional, atmosphere-ocean-land computer model known as GATOR-GCMOM to calculate the theoretical maximum wind power potential on the planet, taking into account wind reduction by turbines. Their model assumed wind turbines could be installed anywhere and everywhere, without regard to societal, environmental, climatic or economic considerations.

The new paper contradicts two earlier studies that said wind potential falls far short of the aggressive goal because each turbine steals too much wind energy from other turbines, and that turbines introduce harmful climate consequences that would negate some of the positive aspects of renewable wind energy.

The new computer model is more sophisticated in that it separates winds in the atmosphere into hypothetical ‘boxes’ stacked atop and beside one another. Each box has its own wind speed and weather. In their model, Jacobson and Archer exposed individual turbines to winds from several boxes at once, a degree of resolution earlier global models did not match.

The researchers were able to calculate the exposure of each wind turbine in the model to winds that vary in space and time. Additionally, the model accounts for the wind that gets claimed by the turbines. It then calculates the effect of these wind speed changes on global temperatures, moisture, clouds and climate.

Potential aplenty
Among the most promising things the researchers learned is that there is a lot of potential in the wind – hundreds of terawatts (TW), in fact. At some point, however, the return on building new turbines would plateau, reaching a level at which no additional energy can be extracted, even with the installation of more turbines.

"Each turbine reduces the amount of energy available for others," Archer said. The reduction, however, becomes significant only when large numbers of turbines are installed, many more than would ever be needed. And that's the point that was very important for us to find."

The researchers have dubbed this point the ‘saturation’ wind power potential - more than 250TW if we could place an army of 100m-tall wind turbines across the entire land and water of planet Earth. Alternatively, if we placed them only on land (minus Antarctica) and along the coastal ocean, there is still some 80TW available – about seven times the world’s current total power demand. Moreover, hypothetical turbines operating in the jet streams six miles up in the atmosphere could extract as much as 380TW.

So, how many?
Knowing that the potential exists, the researchers turned their attention to how many turbines would be needed to meet half the world's power demand (some 5.75TW) in a 2030 clean-energy economy. To get there, they explored various scenarios of what they call the ‘fixed’ wind power potential – the maximum power that can be extracted using a specific number of wind turbines.

Archer and Jacobson showed that 4 million turbines, each operating at a height of 100m and producing 5MW, could supply as much as 7.5TW of power – significantly more than half the world's all-purpose power demand – without significant negative affect on the climate. But as Jacobson points out, only one percent of the wind power needed is currently installed.

Jacobson and Archer propose siting half of the four million turbines over water, with the remaining two million requiring little more than one half of one percent of the Earth's land surface. However, virtually none of this area would be used solely for wind, but could serve dual purposes such as open space, farmland, ranchland or wildlife preserve.

"The careful siting of wind farms will minimize costs and the overall impacts of a global wind infrastructure on the environment," said Jacobson. "But, as these results suggest, the saturation of wind power availability will not limit a clean-energy economy."

Andrew Myers is associate director of communications for the Stanford University School of Engineering.





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