In a remarkable document, the head of the U.S. Fish and Wildlife Service’s division office in Palm Springs, Calif., is asking that regulators put off approval of proposed power tower solar projects in order to get data on the impact they could have on birds and bats.

The request to the California Energy Commission and other regulators – first reported by Chris Clarke on the ReWire blog – comes as BrightSource Energy, which is more than halfway done with the Ivanpah plant in the Mojave Desert, is pursuing permits to build the Rio Mesa and Hidden Hills power tower projects in the Southern California desert. This type of concentrating solar power technology uses heliostats — large mirrors — to direct light onto a receiving tower, where water or other fluids can be heated and then used to produce energy.

ivanpah birds power tower
The three-tower Ivanpah project, under construction (image via BrightSource Energy)

“It would be beneficial to the permitting process for pending and future projects, including Hidden Hills and Rio Mesa, to gather monitoring data that answer some of the questions about avian physiological tolerance and behavioral response to power towers, from already approved projects, before approving more projects,” wrote Pete Sorensen, division chief of the Palm Springs Fish and Wildlife office, in a letter to the state energy commission.

Sorensen went on to call for “a couple of years of scientifically robust monitoring,” a move that would seemingly delay any new approvals for several years, were it embraced.

When we originally posted this story, we included a link to Sorensen’s letter, which had been posted to the California Energy Commission website. But apparently the letter and its implications raised a ruckus over at Fish and Wildlife. The letter has been removed from the energy commission’s website. And, as noted in a comment posted to this story from BrightSource Energy (see below), Fish and Wildlife contacted ReWire to say the disappeared Sorensen letter “merely urges … fellow agencies to proceed with caution in approving such projects until more research is done.”

In any case, according to the National Renewable Energy Laboratory, there is currently only one power tower plant operating in the United States: the Sierra SunTower (previously known as the Gaskell Sun Tower) in Lancaster, Calif. At 5 megawatts and with 24,000 heliostats, it’s tiny compared to Ivanpah, rated at 392 MW using 173,000 of the giant mirrors to reflect light onto three towers. Ivanpah is expected to be completed in 2013, as is SolarReserve’s 110-MW Crescent Dunes Solar Energy Plant near Tonopah, Nev.

Utility-scale solar power plants have run into well-publicized environmental challenges, but usually the issue is water use or the impact on terrestrial critters. At Ivanpah, BrightSource has been mired in issues over the desert tortoise. When it comes to birds and clean energy, it’s typically been big wind that has had issues.

In an attachment to the Sorensen letter, the Fish and Wildlife Service outlined its concerns about how the power tower plants could harm birds and bats:

Incident solar rays reflect off the heliostats towards the top of the tower, where the concentrated radiant solar power, also known as flux, heats a working fluid to a temperature to power a steam-powered electrical generator. Impacts to avian and bat species from the increased flux levels that result from the concentration of solar energy remain uncertain in the absence of engineering and biological data. A more thorough understanding of the power tower technology is needed to identify whether there are injurious/lethal thresholds to species and additional studies are warranted to evaluate behavior within and around operating facilities.

A June 21 story in the Los Angeles Times recounted apparent problems for birds at a pilot power tower plant in the desert, called Solar One, which operated from 1982 to 1986. The Times said ornithologists “found that some birds flying through the solar field were incinerated outright. Others perished after their feathers were singed or burned off, or when they collided with the mirror structures or the central tower.”

solar one power tower birds
Early California power tower project (image via Wikimedia Commons)

Responding to the suggestion that Ivanpah would pose a danger to avian wildlife, BrightSource wrote on its website: “Our technology has been specifically designed to avoid harming birds. Unlike older technology, when our mirrors are not focused at the top of the tower, the light is focused in a diffuse ring around the top of the tower, at concentration levels too low to have any detrimental effect on birds.  We have also reduced the size of the heliostats and placed them lower to the ground to avoid collisions, and we avoid siting projects adjacent to actively farmed and irrigated agricultural land or standing water that might attract insects and birds.

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