Scientists working in the field of wind power have been working on ways to reduce incidences of birds and bats killed by wind turbines due to a direct collision or the effect of the extreme difference in air pressure. They have tried mounting a warning device at the center of the turbine or on each blade. The device emits a noise to scare off the approaching birds. They have also redesigned the layout of the wind farm to lower the chance of birds hitting the rotating blades.
Recently, a research team composed of members from the Norwegian Institute of Nature Research and Lake Ånnsjön Bird Observatory in Sweden has proposed a simple, low-cost, and effective solution to this problem after studying the interaction between birds and a wind farm over several years. Specifically, the team earlier conducted an experiment that involved painting one of the blades of a turbine black. As a result, birds became more aware of the wind turbines that were in their flight paths. According to the study that the team has just published in the journal Ecology and Evolution, changing the color of one blade to increase the visibility of the whole working turbine can reduce bird deaths by as much as 70%.
The market growth of wind power has been rapid thanks to technological advances. The total installed generation capacity of wind turbines worldwide rose from just 6.1GW in 1996 to 591GW in 2018, and another 60GW was added in 2019. The expansion of installed generation capacity together with the maturation of related technologies have also contributed to a sharp decline in cost. In some cases, electricity produced by a wind farm is close to being cheaper than electricity produced by a thermal power plant that burns fossil fuel. However, wind farms, especially those that are built on land, still have some significant shortcomings. The threat that wind turbines pose to local populations of birds, bats, and insects has been a growing environmental concern as more wind farms are being built.
An article published in the journal Biological Conservation in 2013 stated that 140,000 to 328,000 birds are killed annually in the US due to collisions with wind turbines. In the case of bats, the rotating blades of wind turbines can kill these animals by hitting them or producing the pressure difference that cause their tiny lungs to explode. Although it can be argued that more birds die from getting electrocuted on power lines or choked out by smog, the number is not really the issue. Minimizing the fatalities of flying fauna resulting from contacts with wind turbines is critical because developers of wind farms must gain popular support and approvals from the local authorities in order to carry out their projects.
Some researchers contend that the trend of the increasing turbine size has led to a reduction in bird strikes because larger blades rotate slower and are thus less dangerous. There are also reports suggesting that the impact of wind farms on local bird and bat populations are exaggerated. Nevertheless, there are experiments that show birds are not good at spotting some obstacles in their flight paths. Manufacturers of wind turbines might want to consider measures that help birds recognize the danger at a safe distance.
The team of Norwegian and Swedish scientists began the research project in 2013 at an onshore wind farm located on the Norwegian archipelago of Smøla. This wind farm, which deploys 68 turbines and covers an area of 18 square kilometers, has been criticized by environmental groups for causing the deaths of six to nine white-tailed eagles annually. In particular, there are four turbines at the site with a very terrible record for bird strikes. Each of them is 70 meters tall and has three blades that are 40 meters long.
In the experiment conducted by the bi-national team, the above-mentioned four turbines had one of their blades painted black in order to serve as a visual cue to warn birds. Another four turbines at the wind farm were designated as the control group. The team regularly checked the turbines to track bird deaths. Roel May, senior researcher at the Norwegian Institute of Nature Research, said that the rotating blades of a wind turbine creates “motion smear” that makes them harder to detect for birds. May further pointed out that a single colored blade will reduce motion smear and raises the visibility of the whole sweep area of the turbine.
After three years, the team found that a total of six birds were killed from collisions with the turbines in the test group. In contrast, the number of bird deaths from collisions with the turbines in the control group during the same period came to 18. Hence, painting one of the blades black resulted in a 71.9% decrease in the annual fatality rate.
Although the study demonstrates that changing the color of a single blade can cut bird deaths at wind farms by a large percentage of around 70%, a closer look at the data of the experiment also reveal seasonal influences on the effectiveness of this measure. The team pointed out that painted turbines were very effective in mitigating bird strikes during spring and autumn but much less so during summer. To confirm the team’s findings, other research agencies will have to undertake long-term replication studies at wind farms elsewhere.