Sunday, May 27, 2007

Wind Turbines and Air Pollution

(Sorry for backing up here: this is something that deserves lengthy treatment, and the long holiday weekend in the U.S. finally provides the time I needed.)

Christopher Mitchell at the blog Energista does a good job of commenting on a Matt Wald story in the May 4 New York Times entitled "Wind Farms May Not Lower Air Pollution, Study Suggests." You can view the entire Wald story here.

Some additional comments:

Wind Farms May Not Lower Air Pollution, Study Suggests

WASHINGTON, May 3 - Building thousands of wind turbines would probably not reduce the pollutants that cause smog and acid rain, but it would slow the growth in emissions of heat-trapping gases, according to a study released Thursday by the National Academy of Sciences.

This headline and lead are very strange, because neither of these findings appears to be news. The reason wind power, in theory, won't reduce emissions of sulfur dioxide and nitrogen oxides is that nationwide emissions of these pollutants is limited by law--no matter how many wind turbines are installed, the limit doesn't change. As Christopher Mitchell points out, though, since wind generators emit no pollutants, more wind should mean that the cost of complying with the limits is reduced. The limits on sulfur dioxide were part of the Clean Air Act of 1990, so this is a 17-year-old story.

With respect to carbon dioxide, the primary "heat-trapping gas," there are no limits, and so more wind generation does indeed reduce CO2 emissions.

So why the peculiar lead and headline?

Even the scale of local damage from wind farms is unclear. Bats and raptors are thought to be the animals most threatened by wind turbines because they reproduce more slowly. But scientists base estimates on fairly primitive methods, like counting animal carcasses nearby and hoping that few have been carried off by animals, said Paul G. Risser, chairman of the academy's study.

I'm not sure I'd call this "primitive." It's the standard method that is used by wildlife biologists to study and report on bird (or bat) mortality caused by collisions with structures of all types, such as communications towers, buildings, and even automobiles. Typically, estimates of "predation" (carcasses being carried off by animals) are developed at each site by leaving carcasses on the ground and seeing how swiftly they are removed. These estimates (for example, 25% removed within a week) are then included when the scientists conducting the study extrapolate a range of total mortality from the dead bodies that are found.

"If 100 bats are killed, we don't know whether that's 100 out of 10 million or 100 out of 100 million," Dr. Risser said.

Excellent point. More federal research dollars invested in getting a handle on bird and bat (especially bat) populations would be a very good thing. At present, almost nothing is known about bat populations. Also, though, it is quite interesting that neither the New York Times nor the National Academy of Sciences study mentions a currently ongoing bat research program that is jointly funded by Bat Conservation International, several wind power companies, the U.S. Fish and Wildlife Service, and the U.S. Department of Energy's National Renewable Energy Laboratory. More info about this here.

At the moment, the research is focused on testing a sonic deterrent that would warn bats away from wind farms. Much more testing and engineering work needed before it can be declared a solution.

And researchers do not know whether newer windmills, which have huge blades that rotate slowly, are any safer for birds and bats than older models, which spin more like airplane propellers.


1) Some studies of raptor vision suggest that slower-rotating blades should be easier to see. But it's almost impossible to test this in the field. The only way to do it would be to install one type of machine, then remove it and install the other, measuring mortality at each for the same period of time. You'd also have to hope that nothing else changed in the meantime.

2) The numbers of birds that are killed at most wind sites are so low that studies of this question are unlikely to be fruitful.

Wind power could also reduce coal-plant carbon dioxide, which is thought to cause climate change, but the impact may be small, the report said. By 2025, wind turbines could cut carbon dioxide output by 4.5 percent compared with what it would otherwise have been, but this "would only slow the increase," said Dr. Risser. "It wouldn't result in a decrease in the amount of CO2."

The study relied on an Energy Department projection that in the next 15 years, onshore wind capacity would range from 19 to 72 gigawatts, or 2 percent to 7 percent of the nation's generating capacity. The actual impact would be smaller, however, because wind machines run fewer hours than coal or nuclear plants.

As a matter of fact, they run about the same number of hours (65% to 80% of the time), but unlike coal or nuclear plants, wind turbines usually generate at well below their peak capacity. As I've indicated elsewhere in this blog, this is one way of looking through the telescope. Looking through the other end, we find that using essentially the same data and statistics, wind turbines would cut new CO2 emissions between now and 2020 by 30%.

Wind output quadrupled from 2000 to 2006, but wind turbines still produce less than 1 percent of the electricity used in the United States. And the amount of wind energy that can be integrated into the electricity grid is limited, the researchers said. The maximum that could be accommodated, Dr. Policansky said, is probably 20 percent of the nation's electricity use.

These last two sentences that I have bolded are probably the clearest example of minimizing wind's contribution, otherwise known as damning with faint praise. First, we know little about what the upper limit on wind is, and it will be many years before we have solid knowledge. But second and more important, 20% is huge. It's as much as nuclear power generates today, and more than any other source except coal. The fact that we could get that much electricity from a new clean alternative energy source is the real news contained in this story. It would be great to see a story in the Times someday with the headline, "Wind Farms Could Provide 20% of U.S. Electricity, Study Says."


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