Wind energy is one of the fastest growing energy sources in the world. The number of wind turbines in the United States now generates over 61 gigawatts, equivalent to powering 15.3 million American homes, according to the Wind Energy Foundation. While this holds promise to lower greenhouse gas emissions, there’s another environmental impact to be considered if more turbine are built: bats. One reason the bat population is suffering these days is because large numbers are killed by wind turbines. But the solution isn’t to shut down the turbines, scientists are studying ways to help turbines and bats coexist. Delaware Public Media’s science reporter Eli Chen spoke to some bat researchers at Delaware State University who are doing just that.
[audio:http://www.wdde.org/wp-content/uploads/2014/12/BATFEATURE_FULLVERS.mp3|titles= Delaware Public Media science reporter Eli Chen examines efforts to protect bats from wind turbines.]
Nearly every day last summer, before sunrise, Kimmi Swift drove an hour from Dover to the University of Delaware’s wind turbine in Lewes to search for one thing: dead bats. She’d put on her gloves and her hardhat and scavenge for carcasses along a clearing of trees, flagged at 10-feet intervals with yellow ribbons.
Searching for dead animals in the dark under a large looming wind turbine, needless to say, was unsettling.
“It turned off once and started spinning and so I was right under it, and it’s just kind of eerie, you know, and it echoes funny," said Swift. "And I was here by myself and still kind of dark in the mornings, so and I was like oh god, is there a creepy person in the bushes kind of thing?”
Swift is a master’s degree candidate in biology at Delaware State University studying bat fatalities caused by wind turbines. In the winter, Swift only heads to Lewes once a week since most bats have migrated away by now. One weekend in December, I hopped into her car and accompanied her and her husband, Mike, down to the turbine.
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Today, Swift isn’t picking up bats. She’s checking the detectors they built at the turbine. They’re bendy, fishing pole-like structures arranged in a triangular formation, with a microphone dangling at the top to capture the sounds from bats flying overhead. There are four different detectors, placed at 15, 20, 250 and 300 meters from the site.
“We have two detectors set up under the turbine. So these are going to measure bat activity around the turbine itself and then we have two other detectors set up further away,” said Swift.
Swift isn’t counting bat carcasses and recording bat sounds just to monitor wind turbine-caused deaths. Inside UD’s turbine is a software program called “the bat shield” that turns the turbine on at a specific minimum speed called the “cut-in speed,” at which the propellers start spinning and generating power.
Bats are small and have difficulty flying in high winds, so they tend to fly when the winds are low. And it’s when the turbine is operating during low wind speeds that bats are more likely to get killed. In the late 2000s, studies in peer-reviewed journals began to indicate that raising the turbine’s cut-in speed could reduce bat mortality.
“So if the wind is over 6 meters per second, you don’t get as many bats flying," said Kevina Vulinec, the biologist that Kimmi Swift works for and who runs the bat lab at Delaware State University. "So what we did was have this gadget, controlled by whoever’s programming it, to stop the turbine if the wind gets lower than 6 meters per second.”
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Vulinec says there are two ways that bats can die by wind turbine - one being blunt force trauma from the blade and the other, a phenomena called barotrauma.
“As the blade is going around, it’s creating a vacuum behind it, and if the bat gets into that air space the air is less dense, the air in the bat’s lungs is denser, so it’s going to make the lungs explode,” said Vulinec.
Many bats migrate to the northeastern U.S in the summer, and in the summers of 2011 and 2012, Swift picked up 33 and 35 dead bats around the site, respectively. That established a baseline to test the effectiveness of the bat shield, which was installed in 2013. To test the shield, they alternated the weeks that the bat shield was activated during peak bat activity -- which takes place two hours after dusk.
“So it would be operational, not operational, operational and we did that throughout the summer," said Vulinec. "And then we compared the mortality between the bat was engaged to the time it was not.”
Under normal control conditions, they allowed the surrounding winds to spin the blades. But when the bat shield was engaged, the turbine would start up when winds blew at 5 meters per second. The researchers found a 90 percent reduction in fatalities when they compared the normal weeks to weeks when the bat shield was on-- other research on this method have, in the past, shown 30 to 50 percent reduction.
In the summer of 2013, Swift collected a total 23 bats on the turbine grounds. The results of the 2014 are currently under review, but will be released in early 2015.
Gamesa Technology Corporation, the developer of the wind turbine and the bat shield, has programmed the bat shield in wind farms all over Europe. However, Golanzo Palacio, Gamesa’s director of engineering, says they wanted measure how effective the device was. So they turned to the DSU researchers.
"The good thing is that they were already doing studies in 2012, 2013, previously before we had this software, said Palacio. "It gave us a very good feel to see a before and after, to see the effects of the software."
The only place Gamesa’s bat shield exists in the U.S. is in UD’s research turbine in Lewes.
There are a few species of bats that are affected by the Lewes wind turbine. In Dr. Vulinec’s laboratory, Swift put on gloves and took a few caracasses out of a minifridge to show me.
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The species most affected by the turbine is the eastern red bat, which Swift takes out first from its ziploc bag.
“So this is an eastern red bat and its the bat that Vulinec was teling you about was getting most killed by the turbines," said Swift. "So they’re red, quite eponymously named, right?”
In her hand, they’re small, like an acorn, and surprisingly adorable up close.
“The tail is furred, as you can see, you can actually kind of see here in its little death pose, it kind of curled up around itself but whenever they roost they actually curl up around themselves like a little blanket to keep themselves warm in in the tree whenever they’re roosting,” said Swift.
[audio:http://www.wdde.org/wp-content/uploads/2014/12/batapproachingturbine_sound1.mp3|titles= Listen to sound of bats approaching wind turbine recorded by DSU researchers.]
Vulinec’s other batwoman in training, Brittany Ellsaessar, goes through each file recorded from the detectors at the turbine site. These contain possible clues for why the turbine might be attracted to the turbine.
“At the beginning, when you heard the calls really close together, it’s what they call it an approach. The bat saw something it was interested in, so it was sending out more frequent sonar blasts to try and get closer to see what it was finding," said Ellsaessar. "As you get out here, they start to get further apart, because it lost whatever it was finding or it decided it wasn’t all that interested to begin with so it’s now it’s searching for food again.”
Recent research suggests bats perceive the wind turbine as a giant tree, a place to roost and hang up for the night. But Vulinec says the sound recordings, combined with the thermal imaging data showing the bats flying around the turbines, could indicate something else
[audio:http://www.wdde.org/wp-content/uploads/2014/12/twobatschatting_sound2.mp3|titles= Listen to sound of bats communicating recorded by DSU researchers near wind turbine.]
"Bats are just curious. It looked as though they were investigating what the turbine is," said Vulinec. "Because of that, they're getting killed by these turbines because they can't outfly the blades."
There are many reasons for concern over declining bat populations in North America. Bats are a major predator of crop pests, allowing farmers to save on buying pesticides, and they pollinate plants that produce products we enjoy, including mangoes, bananas and even tequila.
A 2011 study in the journal Science, estimated declining bat populations could lead to a loss of $3.7 billion annually in agricultural costs. And unlike other small flying animals, bats produce relatively few young and live long lives. So their populations are vulnerable, and with wind turbines and the rapid spread of white nose syndrome that’s suffocating bats--
“It’s a bad time to be a bat today in North America,” said Robert Barclay, head of the department of biological sciences at the University of Calgary in Canada. Back in 2008, he and other researchers published their experiments on the method of raising a turbine’s cut-in speed to reduce bat deaths.
While that seems simple enough, Barclay says that in practice, sophistication is required. The turbine has to be programmed to shut off not only during the critical two hours after sunset, but also at specific climate conditions. This is difficult to implement, especially across large scale wind farms.
“What’s often the problem is that the software that runs the turbine doesn’t have the ability to change how they operate on an hour or hour to daily basis," said Barclay. "One of the benefits of the Delaware study is that they’re working with software that allows turbines to operate differently under different conditions.”
In other words, flexibility in these programs is key, turning it on at night, turning it on during migratory season. Palacio from Gamesa says they’re able to program the turbine to work during specific weather conditions bats favor.
“Specific day, specific time of day, wind speeds, even wind direction of that day, based on all of those parameters. If all of those are met, then the wind turbine is going to stop,” said Palacio.
And while raising the cut in speed would slightly curtail the amount of electricity generated by the turbine, the loss in power production would be minimal since the turbine is being shut off in low wind conditions. Most energy would be produced when the winds are high, when the bats aren’t outside anyway.
“There is going to be revenue loss. But there's not going to be revenue loss when there's high winds," said Palacio. "We know that under those winds, there isn't going to be bat activity."
Vulinec’s bat lab will continue to examine the bat shield and how it should be programmed. For example, they want to find out whether or not setting the cut-in speed at 4 versus 5 meters per second matters. And they might eventually test other factors that influence when the bats are out, like barometric pressure and wind direction.
As scientists continue to fine tune the turbine’s schedules so that they’re off when the bats are lively, it’s definitely possible that bats and wind turbines might get along after all.