Reports have emerged about high numbers of birds burned to death at a solar energy facility in the southwestern US. What's behind this, is it happening elsewhere, and what can be done? DW takes a closer look.
It's a macabre ending for our feathered friends: Reports have emerged of birds catching fire midair over the Ivanpah Solar Plant in southern California. The objects that catch fire as they pass above the superheated air - which includes birds - have been dubbed "streamers" due to the streams of smoke they leave behind.
A preliminary analysis by the US Fish and Wildlife Forensics Laboratory cited an average of one streamer every two minutes, with estimates for annual bird mortality ranging from 1,000 to as many as 28,000.
The solar park, located in the Mojave Desert near California's border with Nevada, started operating in February this year. It utilizes a relatively new technology: concentrated solar power. Also known as CSP, the technology employs thousands of mirrors across a broad swath of terrain to concentrate the energy of the sun to heat liquid flowing through tall towers to a very high temperature, which is then used to power turbines and generate electricity.
Bird advocates are urging systematic monitoring to establish the true extent of bird mortality at Ivanpah, including an investigation into potential causes. It's the first case of such extensive wildlife death by a solar facility. But experts point out that heeding early warning signs can help prevent it from happening again, especially given the technology is still emerging.
Burned in midair
Robert Pitz-Paal, co-director of the Institute of Solar Research at the German Aerospace Center (DLR), explained how streamers materialize: Tracked mirrors redirecting the sun to a focal point act "like a big lens."
"If the birds enter very close to the focal point of this heliostat field, they get hit by very intensified solar radiation, by a factor of 500 or so," Pitz-Paal told DW. "If they stay there for a couple of seconds, the heat is so immense that they are probably going to die," he said.
Mirrors concentrate light to power towers, making the area at the top "brighter than many suns," Anderson said
Ileene Anderson, a senior scientist with the US-based endangered species advocacy group called the Center for Biological Diversity, described what this looks like from the ground: "You see something catch on fire in the form of smoke, and that dissipates."
One of the companies that run the Ivanpah plant - BrightSource Energy - has denied that all the "streamers" witnessed by the wildlife agency are actually birds. They could be insects, other flying objects, or even trash, facility officials have claimed.
Anderson said an expert hired by the Center for Biological Diversity extrapolated data from an Ivanpah report to calculate an estimate of bird deaths at the plant. Based on this data and bird fatalities at wind power generation sites across the US, he put the Ivanpah figure at up to 28,000 bird fatalities per year.
Ivanpah site developers, on the other hand, reported 519 bird deaths - but that was over a six-month period, and only from a small part of the CSP project, environmentalists pointed out.
"Some of [the birds] get burned up in midair," Anderson stated, adding that the remains of many other animals are likely eaten by scavenging species on the desert floor. Birds may also be singed and fly away, to later die as a result of their injuries.
There have also been reports of waterbirds crashing into CSP mirrors, possibly because they perceive them as water
Why so many streamers?
Experts agree that research should be immediately done to establish the causes of the high number of bird deaths. "Careful investigation is required, because that's not acceptable for a technology killing thousands of birds a year," Pitz-Paal said.
The DLR has co-developed the new CSP technology, and runs a CSP research plant in western Germany. The agency is also linked in with CSP application, in sunbelt regions including Spain.
"This is very surprising for us - we never heard about this massive number of birds [dying]," Pitz-Paal said. At one plant in Spain, about a dozen bird deaths were reported over a year, he added.
Garry George, renewable energy director for bird advocacy organization Audubon California, told DW the bird deaths are the result of "either the technology, or the location." Numerous birds fly through the region, he said: "There are a lot of avian stopovers on the migratory pathway through the desert; it is on the Pacific flyway."
Ariel Brunner, head of EU policy for BirdLife Europe, underlined George's point. Problems typically emerge due to unsuitable locations, Brunner said.
Proper planning for prevention
Brunner cited several incidents of poorly situated wind power generation sites in Europe in its 30-year history that resulted in large numbers of bird deaths, as the wind turbines' blades cut across the animals' flight path - and their bodies.
Raptors seek high perches to get a view of potential prey - and get hit by wind turbine blades as a result
But once flight patterns are understood, choosing the right locations to erect wind power turbines "can reduce bird mortality by more than 90 percent," Brunner told DW.
George as well emphasized how past mistakes can become lessons. His group Audubon opposed a wind power project in Altamont, California, that was built on a mountain pass and killed many raptors (or birds of prey) that flew through the area.
"The wind is great, but so were the numbers of raptors. And they just hadn't discovered that in their initial studies," George said. He added that part of the problem could be how studies on proposed projects are carried out by consultants hired by the companies, and face time and budgetary pressures. Long datasets are expensive, George pointed out - so such studies often "make a lot of early conclusions."
It's speculated, for example, that the bright light generated at Ivanpah is attracting insects, which in turn attracts birds as a potential food source - a factor simply not considered in the project's development.
Managing the mess, framing the future
At this point for Ivanpah, experts are now turning to what can be done to mitigate the streamer problem - and prevent it from happening again.
In the case of Altamont, environmentalists sued and eventually negotiated a settlement to replace older, deadlier turbines with more efficient models. That reduced raptor deaths there by half.
Bird expert Brunner suggested audio or visual measures to scare birds away at Ivanpah, or possibly shutting down operation during migration times - as was effective in some cases with wind farms in Europe.
For now, US environmentalists - while emphasizing a continued need for renewable energy development - are demanding that no more CSP facilities be built in the California desert until the streamer mystery is resolved.
"We don't want to stop wind and solar - of course, we want more of it - but we want it in the right places, and we want it to be developed and operated to avoid or minimize the impact on birds," George said.
Anderson pointed to Germany's solar success story: "Distributed generation on the already-built environment really can reduce a lot of these impacts to wildlife."
Wildlife will also have to "make their way through a climate changing world," Anderson concluded.