Originally created 07/10/01

Bugs called big problem for windmills



With California's energy crisis in the headlines, advocates of wind power are hoping it will mean a major boost for this source of clean, alternative energy.

But they face a previously underappreciated problem: bugs.

Dead bugs can accumulate like dried marmalade on the wind-turbine blades, slowing them and significantly cutting energy output, European scientists report in the current issue of the journal Nature.

The discovery attempts to explain an old mystery at wind-power plants. In the past, power losses have occurred "for no apparent reason," threatening "potentially catastrophic power glitches," Gustave P. Corten and Herman F. Veldkamp wrote in Nature.

Bugs also are a problem for engineers at the famed Altamont, Calif., "wind farm," which has seen efficiency losses of up to 40 percent due to bugs.

Fortunately for alternative-energy buffs, the solution is almost embarrassingly simple: Keep the blades clean. "A clean blade is a happy blade, " joked John D. Opris, operations manager at EnXco Service Corp., which runs the Altamont facility.

Lay people may be surprised to learn that a thin layer of dead bugs can slow a whirling wind turbine that is many stories high.

But in physics, the rougher the surface, the less smoothly it moves through a medium, be it air or water. That's why scraping barnacles off ship bottoms is important.

In the past, wind-power operators have been baffled by unexplained power shortfalls between 25 percent and 50 percent, Corten and Veldkamp said in Nature.

"Unpredictable changes in power levels have been noted on wind farms in California, with power sometimes falling to half the output predicted from the turbine design," the two researchers wrote. They work, respectively, at the Energy Centre of The Netherlands and at a wind-turbine manufacturer, NEG Micon A/S, in Denmark.

They hypothesized that bugs might be responsible. The puzzle, though, was this: Few bugs enjoy flying during the high-wind periods when wind turbines generate the most power.

So why blame bugs? As it turned out, the bulk of the bug impacts occurred during low-wind conditions. Gradually, the insect corpses accumulated on the blade, just as they do on a car windshield.

The splattered bugs didn't noticeably affect turbine performance, though, until high-wind conditions, when the blades are whirling like mad, the investigators found.

Bugs are not the only problem giant wind turbines have. Studies found that more than 1,000 eagles, hawks and other birds have been mangled and chopped by Altamont Pass' fast-moving windmills since the early 1990s.

Operators of the Altamont facility installed larger and slower blades in part to reduce the number of bird deaths.

Opris said bug impacts "can be a problem and efficiency losses of 40 percent or greater have been seen ... due to bugs, and other contaminates like dust and environmental grime which builds up on the leading edge of the blade."

The ideal way to clean the blades "is the rain ... but (this is) a lot harder to schedule," Opris said jokingly. "The most effective way is to shut the turbine down and scrub the blades individually, behind the ears and that kind of stuff."