Are global wind power resource estimates overstated?

Update: I have bumped this 2013 post to emphasize the significance of this work on limits to wind extraction. The answer to the captioned question is “Yes”, probably overstated by a factor of 5x to 10x. This isn’t an issue for small, dispersed collections of turbines – but it is absolutely a big problem at the scale Germany is planning for offshore wind.

Harvard’s Amanda S Adams and David W Keith recently published their modeling and analysis of the impact of scale on available wind resources in Environmental Research Letters. Update: Dr. Keith’s video abstract is compelling – not to be missed.

(…) Each wind turbine creates behind it a “wind shadow” in which the air has been slowed down by drag on the turbine’s blades. The ideal wind farm strikes a balance, packing as many turbines onto the land as possible, while also spacing them enough to reduce the impact of these wind shadows. But as wind farms grow larger, they start to interact, and the regional-scale wind patterns matter more.

Keith’s research has shown that the generating capacity of very large wind power installations (larger than 100 square kilometers) may peak at between 0.5 and 1 watts per square meter. Previous estimates, which ignored the turbines’ slowing effect on the wind, had put that figure at between 2 and 7 watts per square meter.

In short, we may not have access to as much wind power as scientists thought.

(…) “One of the inherent challenges of wind energy is that as soon as you start to develop wind farms and harvest the resource, you change the resource, making it difficult to assess what’s really available,” says Adams.

(…) “If wind power’s going to make a contribution to global energy requirements that’s serious, 10 or 20 percent or more, then it really has to contribute on the scale of terawatts in the next half-century or less,” says Keith.

If we were to cover the entire Earth with wind farms, he notes, “the system could potentially generate enormous amounts of power, well in excess of 100 terawatts, but at that point my guess, based on our climate modeling, is that the effect of that on global winds, and therefore on climate, would be severe—perhaps bigger than the impact of doubling CO2.”

Environmental Research Letters Volume 8 Number 1; Amanda S Adams and David W Keith 2013 Environ. Res. Lett. 8 015021 doi:10.1088/1748-9326/8/1/015021

Besides scalability and intermittency there is the minor issue of “how much does it cost“.