News and analysis about renewable energy in California.

Group Urges Delay on New Solar Power Towers

Solar Two, where a 1986 study reviewed solar injuries to wildlife | Photo: GoShows/Flickr/Creative Commons License

The Center for Biological Diversity (CBD) is urging the California Energy Commission (CEC) to hold off on approving new concentrating solar power tower projects until studies can be made of what effect highly concentrated sunlight may have on wildlife at similar projects now under construction. CBD made the request in a September 6 comment letter sent to the California Energy CEC in response to a workshop on solar injuries to birds and other wildlife. The letter reads, in part;

We strongly urge the CEC to consider delaying any additional project approvals until monitoring results from the project currently under construction are implemented and evaluated. This approach is entirely reasonable and would clearly support a better understanding of the impacts of this technology on avian species in general, and listed, special status and rare species in particular.
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"There's a serious lack of data on how these large projects, and their associated solar flux, will affect wildlife," Ileene Anderson, CBD's Public Lands Desert Director, told ReWire. "We think the prudent course would be to step back, study the effects that Ivanpah and Crescent Dunes have on avian species, and then proceed cautiously from there once we have more data."

The Ivanpah Solar Electric Generating System is now being built in the Mojave Desert a few miles from the Mojave National Preserve, and the Crescent Dunes Solar Energy Project is under construction near Tonopah, Nevada.

CBD's letter was sent as a formal comment on an August CEC workshop held to discuss impacts of that concentrated solar energy -- "solar flux" -- on wildlife in relation to the proposed Hidden Hills and Rio Mesa solar power projects.

Both the Hidden HIlls and Rio Mesa projects would surround two 750-foot towers with tens of thousands of mirrored heliostats, and each project would generate up to 500 megawatts of power. The Ivanpah project will at completion include three 450-foot towers surrounded by heliostats. Crescent Dunes, being built by Solar Reserve, will split the difference with a 640-foot tower.

Environmentalists and wildlife managers are concerned about the possibility that projects which concentrate the sun's rays into a relatively small area pose a risk to wildlife, in much the same manner as a magnifying glass on a sunny day poses a risk to an ant. Solar developer BrightSource Energy, which owns the Ivanpah project as well as the proposed Hidden Hills and Rio Mesa projects, holds that its design reduces the solar flux threat to wildlife:

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 avoid siting projects adjacent to actively farmed and irrigated agricultural land or standing water that might attract insects and birds.

But others point to a 1986 study of the now-dismantled Solar One power tower project near Daggett, California, which found a small but significant number of wildlife burn injuries the researchers believed were due to solar flux exposure.

In the letter, written by Anderson and CBD attorney Lisa Belenky, CBD points out that the Solar One facility was of a much smaller scale than BrightSource's current projects.

[T]he only published, peer-reviewed study of power tower technology (McCrary et al. 1986) documents impacts to avian species from a 10 MW [megawatt] project with a single 86m (280_ft) tower - while the first three power towers now under construction for a 370MW project are each 137m (450 ft) in height. The next set of proposed power tower projects, now under consideration by the CEC would each be 500 MW and have two towers each all over 230 m (750 ft) in height. As a result the proposed power tower projects in California are 50 to 75 times the size of the facility studied in the 1986 peer-reviewed paper.

Distressingly, the CBD letter says that the facilities' high levels of reflected light may cause significant damage to birds' vision, noting that discussion at the workshop had suggested that blinding light from the white-hot power towers could cause damage to birds' retinas, that this damage could become greater with repeated exposure, and that eagles and other sharp-eyed raptors might be more vulnerable to such injury than other birds.

As ReWire reported on August 30, the US Fish and Wildlife Service (FWS) made a public comment on the matter as well, in the form of a letter from FWS's Palm Springs Division Chief Pete Sorenson. That letter read, in part,

We are concerned about the increasing number of power tower projects that are proposed or undergoing permitting review, given the outstanding questions about the impacts of utility-scale application of this technology. As such, 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. Increasing our knowledge about potential impacts from this technology would further our ability to complete science-based analyses of direct, indirect, and cumulative effects to the avian community, as required by our joint public trust responsibilities. Therefore, we suggest that the Agencies limit the number of power tower projects that are considered for permitting and development until we obtain a more detailed understanding of this technology and its impacts, based on at least a couple years of scientifically robust monitoring.

ReWire characterized Sorenson's remarks on behalf of the FWS as a call for a moratorium. The next day, August 31, we were contacted by FWS Regional Director for External Affairs Paul McKim who clarified FWS's intent was merely to suggest the CEC proceed with caution in approving new power tower projects.

Sorenson's letter was removed from the CEC's website that same day, an unusual move for a document that had been formally docketed as part of a CEC siting case.

CBD's comments refer to Sorenson's letter, saying:

The letter simply reconfirms the paucity of scientifically rigorous, peer-reviewed data pertaining to avian impacts from power tower technology and the suggestion that more information be gathered before additional projects of this type are approved is entirely reasonable and in keeping with the precautionary principle. Only rigorous monitoring and additional data collection can help inform the agencies of the impacts of this technology.

The Center included a copy of Sorenson's letter as an attachment to their comments, ensuring that it would once again be available from the documents pages for the two solar project proposals. For its part, the CEC says the letter is available to the public on request despite not being mentioned on the relevant web pages.

The CBD comments also challenged some of the information offered at the August workshop, pointing out that a BrightSource study of potential solar flux effects on birds didn't study birds that weighed less than about an ounce and a half. The endangered southwestern willow flycatcher weighs only half an ounce, and smaller birds made up the bulk of the burn injuries in the 1986 study. CBD also pointed out that at typical flightspeed, a flycatcher might need 15-30 minutes to traverse the larger projects' heliostat field, adding that the figures provided during the workshop referred to a maximum exposure of about 30 seconds. BrightSource's reduced solar flux "halo" in times when the heliostats were not aimed directly at the tower also came under CBD scrutiny:

Instead of defined "standby points", the project proponent proposes to focus the mirrors in a "halo" if they are not focused on the "receiver". However this "halo" is calculated by the project proponent to be approximately 150 KW/m2 [kilowatts per square meter], well above the 50 KW/m2 that caused feather singeing and muscle tissue effects in the study birds. It is unclear how many hours per day this "halo" will be in place or if, for example, the "halo" could be dispersed to reduce the intensity of the radiation below levels that would physically damage avian species. These issues should be analyzed to minimize impacts.

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About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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