“By delaying the turbines’ rotation until highest possible wind speeds and feathering the blades we can maximize our energy production and not injure bats.”
Wind power has been one of the big success stories of the move to more environmentally sustainable power generation, but it turns out it’s not so sustainable for bats.
In recent years, large numbers of bats have been found dead underneath wind turbines, especially at some wind farms including Summerview, east of Pincher Creek.
Transalta, one of Alberta’s largest wind power generators, was concerned and joined forces with University of Calgary bat researcher, Robert Barclay. The bats don’t appear to have died from being hit by the turbine blades. They appeared to have just fallen out of the sky.
Barclay, along with PhD student Erin Baerwald, discovered the bats were not dying from being hit by the turning blades but from “baro-trauma.” In other words, their lungs had exploded.
Bats’ lungs aren’t able to compensate for changes in air pressure and if they suddenly move into an area of low pressure, the increase in air volume in their lungs causes catastrophic injuries to their lungs. It seems the bats fall into pockets of low pressure that develop off the ends of the turbine blades. It’s a phenomenon called wingtip vortices, which has also caused airplane accidents.
Transalta reasoned that since each bat weighs less than 30 grams, the weight of four loonies, they would fly only in relatively light winds, less than about 12 km/h. and the company modified their wind turbines to cut the risk of injury to bats.
Jason Edworthy, director of community relations for Transalta, explains that each wind turbine has its own computerized running instructions that control the blades based on information from its weather station on top of the nacelle – the pod behind the centre of the turbine hub. You can actually see the weather station if you look at the top of a nacelle with binoculars. Some have traditional wind meters with three spinning cups, other newer types have electronic instruments.
When the weather station indicates wind speed is adequate to generate enough energy to justify the wear and tear on the equipment the computer in the nacelle directs a computer in the base of the stand to activate motors that turn the turbine into the wind, and the nacelle computer allows the blades to turn and feathers the blades (alters their pitch) to optimize power generation.
“Because each wind turbine is controlled by its own computer based on the winds at that exact spot, you can see exactly where the wind is,” says Edworthy. “Winds vary from place to place, even across a wind farm. We could never visualize this before, but now you can see it from the wind turbines turning at different speeds or stopped.”
Transalta engineers raised the windspeeds at which the turbines start to turn and increased the pitch of the blades so that for each turn they generate more electricity. This seems to have cut fatalities to bats by about 60 per cent.
“The energy we can get from wind is almost nothing in winds less than about 10 km/h,” says Edworthy. “But we can produce energy above 12 to 14 km/h. And above about 14 km/h, the energy increases very steeply. By delaying the turbines’ rotation until highest possible wind speeds and feathering the blades we can maximize our energy production and not injure bats.”
Protecting bats is important because each bat eats up to three times its weight in insects each night. Some U.S. studies have found bats save farmers millions of dollars a year by destroying crop pests. Some of these elusive creatures are endangered or considered species of concern.
Transalta used ultrasonic recorders to monitor bats’ flying and identify each species by their acoustic signals. The bats that have died at wind turbines are mainly hoary and silver-haired bats, both tree-roosting species with a few of the less-common red bat. All three species migrate to the southern U.S. or Mexico and are most often killed during their migration.
The researchers are working on learning more about bat migration. Fewer bats are killed at turbines further from the mountains, so they may migrate down the foothills where there are more trees for roosting than on the Prairies.
Farmers and other landowners can help tree-roosting bats by leaving trees standing, especially those with holes where bats can roost. Few people are aware of these creatures, which are less common than those that live in buildings or caves or bat houses.