Shutting down wind turbines at night can reduce bat mortality by five, reveals a study by scientists from the National Museum of Natural History

The temporary shutdown of wind turbines at night makes it possible to divide bat mortality by five, indicates France Inter on Sunday October 25, according to a study carried out by the National Museum of Natural History and financed by the Ecological Transition Agency (Ademe). Every year in France, up to 60,000 bats die when they hit wind turbine blades.

The study explains that bats are attracted by the silhouette of wind turbines which they can confuse with that of a tree, and also attracted by the large quantity of insects around the mast. To reduce this mortality, there is a measure called restraint. “It is a method which consists of stopping wind turbines in specific conditions. We know for example that bats are only active at night, and they are more active when the wind is very weak and the temperature is quite high,” explains Andréas Ravache, one of the authors of the study. The study specifies that regulation by restraint is already implemented in a little less than 50% of the 600 French wind farms.

With this technique, the loss of energy produced is estimated between 10% and 15%. The loss can be 3% to 5% if the restraint is optimized, with more parameters such as precipitation. France has more than 10,000 wind turbines which produce around 10% of electricity nationally. The researcher points out that bats are essential for biodiversity because they eat insects that are potentially harmful to crops. These mammals can consume up to 80% of their weight in insects each night in temperate zones.

Methodology: This is the first large-scale multi-site study. Of the 600 French wind farms, the researchers selected 38 for which they compared the mortality rate during a year without restrictions, and a year with the restriction measure put in place. They also took into account 16 other parks, as a “control” group, that is to say in which no restrictions were implemented during the two years studied.