Two days ago, we posted a short note about a truly strange article in New Scientist magazine (see “New Scientist 'scoop': Wind power is not renewable”).
A reading of the article and the scientific journal submissions on which it is based reveals some additional grounds for criticism beside those enumerated by Dr. Joe Romm and others.
First, the study's wind resource estimate is based on a series of very questionable calculations. The authors take the Earth's raw wind production, 45,000 TW, and then whittle away 99.9% of that resource based on very questionable assumptions to get 18-68 TW of available energy.
To begin with, they use a very weakly supported and obsolete 1979 estimate to assume 98% of that energy is lost to friction. Even if that number were correct, in a world with a lot more wind turbines, a lot more of that energy could be captured before it was lost to friction.
Next, they throw away another 50% of the remaining energy due to assumed friction that seems to be redundant with what was thrown away in the previous step.
Finally, they throw away 75% of the remainder on the assumption that wind produced over the ocean and over glaciated land cannot be used. Even without offshore wind deployment that assumption would be flawed, as wind energy over the ocean interacts with air masses over land and generates wind there. They even note that that is a flaw in their paper. So even if just one of those exclusions is slightly too high, and several appear to be, the wind resource estimate would be orders of magnitude higher. That would put it in line with many of the other existing wind resource estimates, in particular Mark Jacobson’s work at Stanford.
Second, the paper's contention that using large amounts of wind energy would cause changes comparable to a doubling of atmospheric carbon dioxide is very misleading: the only metric on which they found wind-induced climate change that was “comparable” to doubling CO2 is changes in precipitation, not temperature.
All of their model runs indicate that a 100-fold increase in wind energy production would cause zero change in surface temperatures. A 1000-fold increase wind energy output does cause a small, 1 degree C increase in surface temperature, but that is not a real climate forcing, but rather just a localized movement of energy from the upper atmosphere down to the surface as the turbine catches less dense higher level air and it releases heat as it adiabatically expands. Again, no energy is being produced from that, and the earth’s energy balance is not being changed nor the climate forced; this is just a localized phenomenon downwind of a turbine that should normalize as the atmosphere mixes. More importantly, it only occurs at wind penetrations 1,000 times higher than we have today.
Back to precipitation: While their model does show a few mm/day change in precipitation as one gets to wind penetrations several hundred times higher than today, this appears to be a sum of absolute value amounts and thus ignores that these effects are going to be both positive and negative in different places and at different times, meaning they will mostly cancel each other out. In addition, most climate models are very poor at predicting changes in precipitation, and in fact, the two models they used disagree strongly on the impact. So the precipitation impact is not credible in any event.
In sum, the findings of the paper and the New Scientist article cannot be regarded as identifying a problem with the continued expansion of wind power as a clean, renewable energy source.
Concerning the wind resource estimate:
– It is a very conservative estimate.
– If more realistic assumptions had been used in several places, the estimated wind resource would have been dozens of times higher, which would put it in line with other estimates produced by researchers at Stanford University and at the U.S. Department of Energy, which calculated that there is enough wind energy to meet humanity’s energy needs dozens or even hundreds of times over.
– Even if the very conservative assumptions are correct, there would be more than enough wind energy to entirely displace humanity’s current use of fossil fuels.
– Wind energy is renewable, and always will be for as long as the sun continues to shine.
On the wind-climate issue:
– The study found humanity’s use of wind energy could increase hundreds of times over without having any impact at all on temperatures.
– Even at unrealistically high wind penetrations 1,000 times greater than we have today, which would produce dozens of times more energy than is used by humans today in total, the only impact on temperature would be to move some energy around in the atmosphere so that temperatures at the earth’s surface appeared slightly higher than they are today, but that impact would dissipate immediately as the earth’s atmosphere mixes.
– The study found that increasing our use of wind energy a hundred or more times over would also have no impact on precipitation or other aspects of the climate. Only at extremely high penetrations approaching 1000 times more wind energy than we have today were the authors able to estimate that there would be small, localized, and likely temporary changes in precipitation, and even then their models were uncertain about that conclusion.