Wind farms in the U.S. have decided to voluntarily reduce the turning speed of the blades to 1-3 revolutions per-minute during the fall migration season of bats. This is important because:

  1. They are doing so voluntarily. Rarely does an industry self-regulate its environmental impacts, especially when they have no direct benefit from doing so.
  2. It is estimated the around 888,000 bats die each year at wind farms in the U.S.
  3. Lowering the the speed at which turbines turn is estimated to reduce the impact that wind farms have on bats by 30%.

Wind farms are a very deadly threat to bats. It is sufficient that bats get close enough to the blades to experience the pressure reduction of 5-10 kPa which leads to death by BarotraumaWhile possibly not a substantive source as initially hypothesized, autopsies of bat carcasses  found around the bases of  turbines reveal ruptured lungs and internal hemorrhage.


With wind energy growing fast (8% in 2014, projected to grow by 13% in 2016) the deaths of bats at wind farms are a cause of concern to the well being of bat species. Contrary to what people might think, bats do not appear to develop an avoidance behavior towards wind turbines like birds have developed. A recent paper argues that this is a result of the similarity of wind currents around the blades to those around trees; which triggers a dive and forage response from the bats. Meaning bats behave around wind turbines like they behave around trees – causing them to get dangerously close to the blades.


The wind energy will be leaving electrons lying in the wind but in the grand scheme of things that might be compensated by the pest control that bats provide. Insectivorous bats consume around two thirds of their body weight in insects every night. The ecological literature  suggests the value of pest control provided by bats is on the magnitude of billions of dollars a year. While we have empirical results that demonstrate that bats do prey on insects that damage crops, we have yet to validate the relationship between bats and the use of pesticides by farmers – which is the focus of one of my research projects.


This is a very important move towards reducing the stress on bats. We should know in a few months whether or not it was as effective as suggested.

2 Responses to “Reducing the Turning Speed of Wind Turbines to Save Bats”

  1. Yaron Israel

    Wow it’s nice to see that not everything revolves around money and that sometimes industries take responsibility and not just look the other way. I salute them.

    Are there any technologies that prevents the bats from being attracted to the wind turbines?

  2. Hebergement web

    Braking of a small wind turbine can be done by dumping energy from the generator into a resistor bank, converting the kinetic energy of the turbine rotation into heat. This method is useful if the kinetic load on the generator is suddenly reduced or is too small to keep the turbine speed within its allowed limit.

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