**An update to this article, “Solar Towers Don't Seem to Be the Bird Destroyers Once Thought,” reports on the latest findings showing that the avian death rate at Ivanpah is smaller than previously believed and still shrinking.**
Imagine you're a bird and you're flying in the Mohave Desert along the California side of the Nevada border and in the distance you see a massive reflective field, kind of like a lake, but more like thousands of puddles hovering together in a herd. You see insects swarming around it. You're hungry and thirsty. Or maybe you're just curious. So, you decide to fly over and see what's up.
Now, stop imagining, because the rest is not very pretty. What our bird has unwittingly stumbled upon is the Ivanpah solar thermal power plant, a circular array of over 300,000 mirrors aligned in such a way as to deliver a concentrated solar beam onto a central water tower. As the bird passes over the facility, its wing feathers begin to curl and singe. Its tail feathers, which it relies upon for aerial lift, ignite and burn. It rapidly loses altitude, trailing a plume of smoke behind it, and suddenly it's more of a comet than a bird.
This is the series of events that researchers at the U.S. Fish and Wildlife Service witnessed last fall at the 377-megawatt Ivanpah power plant and which they describe in an avian mortality report released last month by the California Energy Commission. (KCET, a public television station in California obtained a copy of the report months earlier.) The report, which calls the Ivanpah solar power plant a "megatrap," issues grave warnings about the threat that this relatively new technology poses to all species of birds. It also offers some basic recommendations for how to make solar thermal safer for birds, both at the Ivanpah plant and at future facilities—because, yes, newer, bigger ones are already on the way.
Photo Credit: Chris Carlson/AP Photo
The Ivanpah Solar Electric Generating System, which is currently the biggest facility of it's kind, generated its first kilowatts of power last September. The sum of the focused rays of light delivered by the Ivanpah heliostat mirror array is called solar flux. According to the USFWS report, if all the mirrors in the facility were being used simultaneously, they would produce a solar flux that was 5000 times as hot as unfocused sunlight. But in reality, only a fraction of the mirrors are used at a given time. BrightSource Energy Inc., the company that runs the Ivanpah plant (with help from Google and NRG Energy, Inc.), has not disclosed just how hot their solar flux gets. The USFWS took one measurement at a mirror on the outer right of the array and recorded a temperature of 93° C. The report estimates that the focal area at the tower reaches 500° C. The heat has to be at least sufficient to bring the water inside of a central tower to a raging boil and produce enough steam to turn an electricity generating turbine.
Environmentalists have long been worried about the threat that such temperatures pose to animals in the desert. Debate over the issue seems likely to determine the fate of future projects as well. BrightSource is now seeking approval for another, larger solar thermal plant near the Joshua Tree National Park. The proposal has gone through a protracted cycle of denials and resubmissions. According to AP, the California Energy Commission is considering the plan once again. (Expect a decision sometime this fall.) And once again, avian deaths are a big part of the conversation.
The accounts collected by the USFWS visits to the power plant last fall suggest that there is indeed cause for concern. During successive visits researchers found 141 bird carcasses. Most had died directly from exposure to solar flux. Others had lost their ability to fly and eventually starved or became prey.
At one point, the researchers describe watching a bird fly over the heliostat array, ignite, lose and regain altitude and alight on a perch on the other side. Because of such events—in which a bird might live for long enough to leave the monitored area, but die soon afterward, having lost it's ability to fly—the report makes its very clear that the numbers they collected are likely lower than than the number of actual deaths caused by the Ivanpah facility.
"The number of dead birds are likely underrepresented, perhaps vastly so," claim the authors.
The researchers report no trend in the type of birds they collected. They found swallows, owls, hawks, falcons, hummingbirds, among many other species. The service also reported high numbers of insects and bat carcasses, which was itself a troubling sign:
It appears that Ivanpah may act as a "megatrap," attracting insects which in turn attract insect-eating birds, which are incapacitated by solar flux injury, thus attracting predators and creating an entire food chain vulnerable to injury and death.
According to AP, the USFWS is urging the California Energy Commission to require BrightSource to conduct a more thorough, formal, year-long, observation of the Ivanpah power plant before deciding whether to give the green light to an even larger facility near Joshua Tree, which commission staff members say would be four times more lethal to birds and would sit smack dab in the middle of the main aerial highway that birds use to travel between the Colorado River and California's Salton Sea.
The report also issues a number of recommendations. All of them are relatively straightforward and easy to implement—covering ponds to discourage waterbirds from loitering, clearing additional land around the plant to make it less attractive and more visible to birds in flight, covering railings with perch guards.
One of the suggestions, however, would probably cost a lot of money. The report asks that the power plant be turned off during the migratory season.
Any power company that makes more money the longer it keeps the water boiling is not going to like this last one. But, then again, with great power comes great responsibility.