You’d think that painting a single turbine blade black is a pretty inexpensive fix for accidental bird deaths. It sounds almost too good to be true, which perhaps it is.
At the Smøla wind farm in Norway, every wind turbine had one of its blade painted black for an extended science experiment back in August 2013. Over the next three years, the number of bird carcasses found fell by 70%.
However, similar experiments in the Netherlands did not yield positive results, because apparently this fix depends heavily on the local bird species and population size.
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Too many dead birds
There are a total of 68 turbines at the Smøla wind power plant, an archipelago off the coast of Central Norway. Researchers from the Norwegian Institute for Nature Research compared four regular turbines with four neighboring ones that had one blade painted black for this experiment.
They regularly counted the number of bird carcasses within 100 meters of the wind farm. This continued over a period of more than ten years, combining 7.5 years of baseline data from before painting any turbine blades to 3.5 years of data from after. In 2020, they published their findings in a paper called Ecology and Evolution.
Turns out that this small change in visual cues reduced the number of bird deaths by over 70%, proving especially effective on the somewhat rare white-tailed sea eagle population of the region. While the researchers noted that this anecdotal data may not hold up to different bird populations, this was still independent real-world confirmation of a separate laboratory experiment that found similar results in 2003.
How a black blade is supposed to help
What difference does one black blade make? According to researchers, it has to do with how birds process visual cues.
Animation designers call it motion smearing, where images that move too fast for the human eye to follow are inferred in the brain as one continuous motion. When turbine blades are in motion, birds find it difficult to notice the threat because the unicolor rotating blades look like one giant circle.
When you paint one of these blades black, it breaks up the pattern so the moving blades are more easily distinguishable to the eye. But as Audubon reported, these are preliminary findings that won’t translate to all bird species equally — especially ones that don’t have the visual acuity to notice the difference. There’s also a significant amount of effort involved, since painting turbines in operation requires both lifts and specialist crews who can navigate the height.
When the trick stops working
Most of the land experiments so far have stuck with black, but at sea, a new trial is experimenting with a different color.
Dutch consortium Ecowende is fitting seven Vestas V236-15.0 MW turbines with one red 115.5-meter blade each. Red was chosen after weighing options against criteria such as durability and heat management, apart from the obvious benefit of being more easily discernible from a distance.
That said, seabirds may generally need less help than expected. A Vattenfall and Spoor study at its Aberdeen offshore wind farm tracked 2,007 flight paths over 19 months. It found no confirmed collisions, with birds typically keeping 100 to 200 meters away.
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ritoban@nutgraf.agency (Ritoban Mukherjee)
