Well I was shocked–shocked I tell you–when I saw this sensational headline on Google News, courtesy of Fox News: Wind farms are warming the earth, researchers say. Actually, the study the article cites isn’t some quackery cooked up by the oil lobby. As far as I can tell, this is legitimate science, to be published in the journal Nature: Climate Change. But you give a study like this to the likes of Fox News and they love to run amok.
Here are the findings: satellite data of large wind farms show localized warming effects of 0.72˚C caused by the turbulence generated by the turbines. The media (and not just Fox, mind you, even Christian Science Monitor jumped on this one with somewhat sensational headlines) has basically translated these findings as follows: haha, wind isn’t so green after all, and if we count on it as a carbon-free source of energy, we’ll just create more warming! Or as CSM put it, “Irony Alert!”
The following will probably fall on deaf ears for a lot of people because it looks like a green energy booster backtracking to defend his once benign and infallible wind power, but I’m really just going to point out some basic physics that the news media has conveniently left out of this story. (Caveat: I’m not a climatologist, merely an engineer.)
First off, wind energy is basically solar energy. The kinetic energy in the wind ultimately derives from the sun’s rays that are the main energy input in our climate system. That energy is often dissipated over long periods of time and over large distances, but in the case of wind farms, humans have erected machines to pull that energy out of thin air, as it were. The large turbine blades are shaped to produce lift forces, turning the rotors and generators and producing all that relatively cheap, green energy that we love.
But the wind conversion process isn’t perfect, and only part of the kinetic energy in a gust of wind can be harvested for electricity production. A portion of the energy simply gets converted into vibrations and noise (if you’ve ever seen a wind farm up close, you’d know what I’m talking about). Actually, the vibrations and sound waves can mostly be traced back to the generation of turbulence, mentioned in the above articles. The presence of all that equipment in the otherwise free-flowing wind creates swirls and eddies just like those seen around rocks in a stream. Those vortices dissipate some distance behind the turbine which is why wind turbines need to be spaced out about 1km apart: you need to provide space for vortices to die down so that each turbine has access to high quality wind. Anyway, the dissipation of turbulence represents another energy conversion process. In this case, kinetic energy in the turbulent swirls is being dissipated by frictional forces between the air particles. The end result is that the average energy of the surrounding air increases, and voila, we have a slight temperature increase. Phew.
In the end–I’m sorry to say Rupert Murdoch–wind turbines do not contribute any net energy to the climate system. They redirect small amounts of the energy already in the system (originally from the sun), converting some of it to heat which warms the air around the farm, but they are by no means slow-cooking the planet. If they were, we would really have something magical on our hands. Christian Science Monitor and Fox News and all the other papers would have to rerun the story with the following, equally sensational pseudo-science headline: “Wind Energy Found to Be Mysterious Source of Free Energy!”