Bat recommendations are a "bomb to the green transition"

New recommendations call for halting wind turbines at lower wind speeds out of consideration for bats. Green Power Denmark fears this could stop renewable energy projects

DCE - National Center for Environment and Energy has updated their recommendations on how to reduce bat fatalities at wind turbines.

Since most bat fatalities, according to DCE, occur at low speeds, the center suggests that wind turbines should have a cut-in speed of 8-10 m/s in areas with bats.

And since the average wind speed in Denmark is around 7 m/s, this could lead to a significant drop in production from Danish wind turbines, and affect the willingness to invest in future renewable energy projects.

- It is critical if the wording of the report becomes applicable for the authorisation process. It hits wind and solar on land, but also risks affecting the upcoming offshore wind tenders. This is not a situation we can live with if we want to achieve the green transition, says Thomas Aarestrup Jepsen, director of Renewable Energy production and Public Affairs at Green Power Denmark.

I can understand that some find our recommendations annoying, but it has simply not been our job to consider the business aspect of the issue. Morten Elmeros, senior advisor at the Institute for Ecoscience at Aarhus University and lead author of the Handbook on Animal Species on Annex IV of the Habitats Directive.

On a collision course

Morten Elmeros is a senior advisor at the Institute for Ecoscience at Aarhus University and the lead author of the new recommendations from DCE. He addresses the criticism calmly, referring to the necessity of the update to incorporate new knowledge about bats:

- The previous recommendations were based on old American studies. At that time, the recommendation for the cut-in speed was 5-6 meters per second. Since then, a lot of research has been conducted in our neighboring countries, and there has been an increased awareness that wind turbines and bat populations are on a collision course, says Morten Elmeros to Energy Supply.

Thus, he is not surprised by the criticism from Green Power Denmark:

- They have a political agenda to follow. So, I can understand that some find our recommendations annoying, but it has simply not been our job to consider the business aspect of the issue, says Morten Elmeros.

Excerpt from "Handbook on Animal Species in Annex IV of the Habitats Directive"

Mitigation measures for bats at wind turbines

Most bat fatalities at wind turbines occur at low wind speeds (Rydell et al. 2011, Voigt & Kingston 2016). The only documented effective mitigation measures to reduce bat mortality from wind turbines are to stop the turbines or feather the blades so that they rotate very slowly (Arnett et al. 2011, Voigt & Kingston 2016, Adams et al. 2021).

A very low rotation speed will increase the bats' chances to detect and avoid the rotating blades (Long et al. 2010). The wind turbines should be feathered or stopped entirely during periods when bats can be expected to be present in the area around the wind turbines.

Generally, the cut-in speed, at which the turbine blades are stopped or feathered, should be at least 8-10 m/s, especially for wind turbines located in or near forests and other important habitats for bats. The lower the cut-in speed, the better the protection of bats and biodiversity, and the greener the energy production from the wind turbines.

The operational stop should apply from sunset to sunrise throughout the summer and autumn. In areas where bats are only present during the migration periods in spring and in the late summer and autumn periods, for example, sea wind turbines and coastal wind turbines on land and offshore in wooded areas.

For sea wind turbines in the inner Danish waters, where foraging bats may occur over the sea, the operational stop should also cover the summer period.

No methods have been developed that can detect bats at a sufficient distance from wind turbines to allow for the turbines to be stopped in time, partly because ultrasound is quickly attenuated in the air and the turbines do not tolerate hard braking.

Source: Handbook on animal species in annex IV of the habitats directive, DCE - Danish centre for environment and energy, 2024

For Thomas Aarestrup Jepsen, it is essential to harmonize commercial interests and biodiversity conservation into a unified approach.

- The report employs a pronounced precautionary principle, leading to the installation of wind turbines and solar panels needing to yield to the slightest consideration for the protection of bats. We, of course, must take care of nature and wildlife because we are facing both a biodiversity crisis and a climate crisis, but there is a need for political prioritization so that addressing one crisis does not come at the expense of the other, says Thomas Aarestrup Jepsen.

According to Morten Elmeros, the environmental agency has not challenged the expert conclusions in the updated handbook.

Energy Supply is working on getting a comment from the Environmental Agency.

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