On the German mainland, over 30,000 turbines have already been installed, and the industry is currently scrambling to find increasingly scarce suitable sites.
As a result, forests are becoming more prominent as potential sites.
A scientific team has now shown that wind turbines in forests harm endangered bat species: common noctules (Nyctalus noctula), a species that is at high risk of colliding with rotor blades, are drawn to forest wind turbines if they are near their roosts.
Collision risk and habitat loss
James Wainscoat/Unsplash
The findings show that wind turbines in forests harm common noctules in two ways: noctules face an increased risk of colliding with the turbines if they are built near roosts, and they lose foraging habitat because they avoid wind turbines far from roosts, as per ScienceDaily.
The team concludes in their paper that wind power development in forests should be avoided or, if necessary, undertaken with great care and caution.
The wind turbine should be located at least 500 meters away from bat roosting sites, and any loss of foraging habitat should be compensated for by diverting forests away from wind power (or other anthropogenic activities).
Wind energy production is an important pillar in Germany's energy transition to renewable energies, and it contributes significantly to reducing greenhouse gas emissions.
In Germany, approximately 8% of wind turbines have already been built in forests.
This figure is expected to rise significantly in the coming years as suitable open-space sites become increasingly scarce. "A large number of bat species occur in forests because there are many tree roosts and suitable foraging habitats with a high abundance of insects, their prey," explains Christian Voigt, head of the Leibniz-Department IZW's of Evolutionary Ecology.
Among these are species such as the common noctule, which is the most common victim of wind turbines in Germany.
Common noctule populations are declining across Germany, according to the German Federal Agency for Nature Conservation (BfN). It is therefore critical to investigate the interaction of bats with wind turbines in forests.
Voigt and his colleagues used miniaturized GPS loggers to study the space-use behavior of common noctules.
Over 1-2 nights, these loggers recorded the flight paths of 60 bats with high temporal and spatial resolution before automatically disconnecting from each animal.
Bats, as highly social mammals, use exposed structures as meeting places. If wind turbines are located near roosts, this could explain why they frequently approach wind turbines, which rise well above the canopy. The animals are at high risk of colliding with the rotor blades as a result of this.
The authors also discovered that common noctules avoided wind turbines further away from tree roosts.
They discovered this after performing data analysis in which all bat GPS locations near roosts were excluded from the analysis.
This demonstrated that wind turbines are avoided by bats if they are placed far enough away from roosts.
As a result, the scientists recommend that wind turbines be avoided in forests and that special precautions be taken if no other options are available.
During the approval process, a minimum distance of 500 meters between wind turbines and known bat roosts should be considered, and the loss of foraging habitat in the vicinity of wind turbines should be compensated for elsewhere.
According to Voigt and Reusch, the expansion of wind energy production into forests poses a significant conservation challenge due to the complex interaction of bats with wind turbines in forests.
The current and future numbers for wind power are astounding. To meet the wind power goals set by China, Europe, and the United States, capacity is expected to reach 600 GW in 2019 and grow to around 1,000 GW by 2030, as per Routledge.
The annual energy production and how the value of the energy produced compares to other sources of energy are critical factors in deciding where to locate a wind farm (also known as a wind park or wind plant). Using long-term data is thus critical.
A rigorous analysis should be performed to determine whether historical data from one site is adequate to describe long-term wind resources at another.
The annual hourly linear correlation coefficient between the reference site and off-site data should be at least 0.90.
Wind shear must also be considered if the heights at the two locations differ. If the two sites do not have similar wind speed and direction trends, as well as similar topographic exposures, they are unlikely to have a high correlation value.
Even after a wind farm is installed, these wind power stations should continue to collect data. The data improves wind farm siting and also provides reference sites for delineating wind resources in the region for single or distributed wind turbines.
The number of met stations and the time it takes to collect data to predict energy production for a wind farm varies depending on the terrain and the availability of long-term base data in the area.
In general, numerical wind flow models can predict wind speeds to within 5% for relatively flat terrain and 10% for complex terrain, resulting in an energy error of 15-30%.
A wind measurement program is thus required prior to the installation of a wind farm. However, if there are already a number of wind farms in the area, one year of data collection may be sufficient.
