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Susan Kraemer explores the CEC’s investigation of BrightSource Energy

At its latest permitting workshop in California, BrightSource Energy was tasked with providing evidence that CSP power tower solar technology will not kill birds and bats passing through the sunlight reflected by the mirrors.

The workshop was held by the California Energy Commission (CEC) so that the company could respond to CEC data request No. 159, part of the permitting process for their two 500 MW CSP power tower projects in Southern California, Rio Mesa and Hidden Hills. These two plants could be pumping 1 GW of clean power onto the Californian grid by 2016.

In February, the conservation advocacy group Basin & Range Watch,brought up a 1986 study that examined avian mortality at the first pilot power tower, the DOE’s Solar One. They suggested that solar flux could damage or blind animals, burn or singe feathers and skin, and possibly result in death. The CEC feels that potential impacts of solar flux are not well understood, and requested the data be presented at the workshop.

So just what is solar flux?

“Solar flux is simply sunlight,” Kristin Hunter of BrightSource pointed out. “Solar Flux is not microwave radiation, laser beams or heat.  The solar flux at any point is the amount of sunlight crossing a given area. Flux, in and of itself, does not raise ambient air temperatures by any appreciable amount, even close to the boiler.”

Variations in solar flux, due to the Earth's varying distance from the Sun, were too small to even detect until the satellite era. Solar flux - the measure of the amount of light hitting a square metre - at a solar thermal power tower project increases as reflected sunlight from solar field mirrors converge, so solar flux can increase as one gets closer to the receiver.  

BrightSource supplied evidence at the workshop from the real-world experiences of smaller solar power towers in operation, including the Department of Energy’s 10 MW Solar One pilot, their own demonstration facility in Israel; a 6 MW Solar Energy Development Center, and Torresol’s 20 MW Gemasolar power tower operating commercially since last summer in Andalusia, Spain.  None of these operating plants have experienced significant issues with avian species, BrightSource says. Its Ivanpah project has broken ground, and will track bird deaths.  

A recent study carried out at their demonstration plant in Israel’s Negev Desert found that “avian species would have to be exposed to significant concentrations of solar flux for a sustained period of time before they experience negative effects.” No dead birds were found in a year-long affadavited study at Gemasolar by the ornithologist Juan Pleguezuelos, PhD.

Their studies have been replicated by the experience of other power tower developers.  

“The numbers have been insignificant,” SolarReserve told CSP Today. “The impact of these structures have been shown to be very small in comparison with predation by cats and other animals, impacts with cars and trucks on highways and other causes not covered by permit application studies.”

“Our Colorado project had a small local group focused on bird issues and had some specific questions, so we spent additional time addressing the questions raised,” said SolarReserve CEO Kevin Smith, who has several other permitted CSP power towers in the Southwest, including one in California. SolarReserve does extensive avian and bat studies before even beginning the development process of any project.

BrightSource had already reduced risks to birds since the days of the Solar One prototype referenced in the 30-year-old study, Hunter said. To minimise solar flux, smart technology - not available in the ‘80s - controls the heliostats, eliminating concentration points outside the receiver, creating a halo effect. 

“We are already seeing evidence of improvements in the permitting process,” Hunter pointed out.  “Our Ivanpah project was the first utility-scale solar project permitted in over two decades in California.  Since Ivanpah, over eight others have been approved in California alone.  As the regulatory agencies become more accustomed to evaluating and permitting large-scale solar projects, the process becomes increasingly more efficient.”

Last month Pete Sorensen, division chief of the Office of the U.S. Fish and Wildlife Service in wealthy Palm Springs had raised an alarm in the solar world when he said that he would like to see "at least a couple years of scientifically robust monitoring" for solar flux impact. But that has since been backtracked by FWS officials, who pulled the email, noting it is not the agency’s official position. Sandy Louey at CEC wanted to make it clear to CSP Today thathis email should not be seen as a moratorium and that it has been removed from the CEC website.

Asked if he thinks permitting will eventually become easier for solar once it's a few decades in, Roger Johnson, the CEC’s deputy director for siting said, “Sure hope so. That is the near-term plan for projects that propose to locate in the Desert Renewable Energy Conservation Plan preferred development focus areas.”

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Or contact the editor, Jennifer Muirhead