New “research” has shown that if wind turbines operate for less time – then the number of bat deaths at wind turbines would be reduced!
Paradoxically, it is the bats’ sophisticated sonar -based flying ability which enables them to avoid the spinning blades of a wind turbine, but which kills them.
Many large birds are killed by impact with the whirling blades of wind turbines but the large number of bats that are killed die because the blood vessels in their lungs explode as their sonar helps them to avoid the blades themselves but which lands them in the low pressure zone behind the blades.
The latest independent reports estimate the number of birds killed by wind turbines at about 100,000 per year. That’s according to a 2007 report from the National Research Council called “Environmental Impacts of Wind-Energy Projects. The American Bird Conservancy estimated in 2003 that between 10,000 and 40,000 birds were killed each year at wind farms across the country, about 80 percent of which were songbirds and 10 percent birds of prey. “With the increased capacity over the last seven years, we now estimate that 100,000 – 300,000 birds are killed by wind turbines each year,” said Conservancy spokesman Robert Johns.
BAT KILLER: The zone of low pressure behind wind turbine blades seems to be responsible for killing migrating bats:Image via Wikipedia
Wind Turbine blades are airfoils and there is an air pressure drop across the blade width of 5 – 10 kiloPascals. The low pressure zone behind the blades does not persist for very long and the air pressure quickly equalises a few metres behind the blades. The greater the power output of a turbine, the greater its height, the greater the pressure drop and the larger the low-pressure zone. But it is this low pressure zone which is a death trap for bats.
Scientific American: Scientists have known since 2004 that wind farms kill bats, just as they kill birds, even though the flying mammals should be able to avoid them. Many biologists thought that the bats, like their avian counterparts, might be falling victim to the fast-spinning turbine blades. But an examination of 188 hoary and silver-haired bats killed at a wind farm in southwestern Alberta in Canada between July and September in 2007 showed that nearly half showed no external injuries—as would be expected if the giant blades had smashed the flying mammals to the ground.
Instead, 90 percent of the 75 bats the researchers ultimately dissected had been killed by burst blood vessels in their lungs, according to results presented in Current Biology—suggesting that the air pressure difference created by the spinning windmills had terminated them, not contact with the blades. “As turbine height increases, bat deaths increase exponentially,” says ecologist Erin Baerwald of the University of Calgary in Alberta, who led research into the deaths as part of her master’s project. “What we found is a lot of internal hemorrhaging.”
Pressure drops of as low as 4.4 kilopascals kill common lab rats and all the bats autopsied showed internal damage and bleeding consistent with this type of death, known as barotrauma. “If bats have a lungful of air as they fly through the air-pressure change, there’s nowhere for the air to go,” Baerwald explains. “The small blood vessels around the lungs burst and fill the lungs with fluid and blood.”
This may also explain why, although some birds are killed by wind farms, the majority of casualties are bats.
Recently research has suggested that the colour of a turbine can affect the attraction exercised on insects which seem to like congregating at wind turbines. The gathering of insects is thought to be the reason why so many bats make their way to these locations. The research suggested that insects do not like the colour purple and it has been proposed that painting all wind turbines purple could save some bats.
Now new research published online November 1, 2010 in Frontiers in Ecology and the Environment has come to the not very unsurprising conclusion that if wind turbines operate for less of the time less bats will be killed!!
Via EurekAlert we learn that:
In a study to be published online November 1, 2010 in Frontiers in Ecology and the Environment (e-View), a journal of the Ecological Society of America, Edward Arnett from Bat Conservation International in Austin, Texas and colleagues examined the effects of changes in wind turbine speed on bat mortality during the low-wind months of late summer and early fall.
Currently, most wind turbines in the U.S. are programmed to begin rotating and producing power once wind speed has reached approximately 8 to 9 miles per hour (mph)—the wind speed at which turbines begin generating electricity to the power grid is known as the cut-in speed. Wind turbines with a low cut-in speed run more frequently than those set at higher cut-in speeds since they begin rotating at lower wind speeds.
The researchers found that, by raising the cut-in speed to roughly 11 mph, bat fatalities were reduced by at least 44 percent, and by as much as 93 percent, with an annual power loss of less than one percent. That is, programming the turbines to rotate only when the wind reached approximately 11 mph or higher caused the turbines to rotate less frequently and, therefore, killed significantly fewer bats. Because this was performed during months with seasonably low wind speeds already, the overall energy loss was marginal when the researchers calculated the annual power output.
“This is the only proven mitigation option to reduce bat kills at this time,” said Arnett. “If we want to pursue the benefits associated with wind energy, we need to consider the local ecological impacts that the turbines could cause. We have already seen a rise in bat mortality associated with wind energy development, but our study shows that, by marginally limiting the turbines during the summer and fall months, we can save bats as well as promote advances in alternative energy.”
Of course it does not need a great deal of research to conclude that if the wind turbine did not rotate at all no bats would be killed, and if the contraption did not even exist then all bird collisions with the stationary towers could be eliminated.
