BrightSource on Hidden Hills Bird Risk: 'It's Complicated'

Golden Eagle | Photo: Penn State/Flickr/Creative Commons License

In Parts One and Two of our series this week on potential risk to birds posed by the proposed Hidden Hills solar power plant in Inyo County, we went into some detail both about the potential mechanisms by which concentrated solar power from facilities such as Hidden HIlls might injure birds, as well as an assessment by the staff of the California Energy Commission about the level of risk the facility could pose.

But what's project proponent BrightSource's take on the issue? The firm and its consultants maintain that the risk to wildlife of its proposal isn't nearly what the CEC staff alleges, and that CEC staff has oversimplified the science.


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A refresher on the basic topic so far: The CEC is evaluating BrightSource's proposal to build a 500-megawatt solar generating facility on 3,100 acres of land east of Tecopa in the California desert. The Hidden Hills Solar Electric Generating System would surround two 750-foot power towers with thousands of mirrored heliostats, which would focus the sun's energy on boilers atop the towers. Both the CEC and BrightSource agree that there is some risk to birds who fly into the concentrated solar energy field -- "solar flux" -- surrounding each tower. The solar flux threatens the keratin that makes up birds' feathers; if that keratin suffers heat damage, then birds can be injured or killed outright.


But BrightSource is maintaining that CEC should assess the project using a safety threshold of 50 kilowatts of concentrated solar energy per square meter (kW/M2), approximately 50 times as powerful as ambient sunlight. The firm has based this assessment on the result of tests conducted by consulting firm CH2M Hill at a smaller BrightSource facility in Israel. In that test, CH2M Hill scientists hung euthanized birds in front of a similar power tower and focused solar flux on the carcasses for up to 30 seconds, then studied the results.

BroghtSource has refused to release photos of the post-study bird carcasses to the public. However, CEC staff who have viewed the photos and seen BrightSource's reported data claim that the study's methodology is flawed, that the assumption that birds will be exposed to solar flux for no longer than 30 seconds is invalid, and that even so CH2M Hill's test birds showed carbonization of feathers -- a level of damage well above the degradation of keratin the CEC's biologists want to avoid.

At first, the CEC staff countered with a suggested safe exposure threshold one fifth of the level that BrightSource is advocating: 10 kW/M2, or ten times normal sunlight. That would mean that each power tower at Hidden Hills would have a zone of solar flux field strength about 2,000 feet across in which birds would be well advised to avoid lingering.

But at a CEC evidentiary hearing held March 14 in Shoshone, not far from the Hidden Hills site, CEC staff scientist Rick Tyler and his colleagues dropped a bomb on BrightSource: The CEC staff would be recommending a safe exposure threshold of 5 kW/M2, half the staff's previous recommended level and a tenth BrightSource's suggested threshold. Tyler offered this bleak assessment of Hidden Hills' threat to wildlife:

That's the context.

BrightSource representatives reacted strongly at the March 14 hearing to the introduction of what they characterized as "surprise" evidence. BrightSource attorney Chris Ellison filed a formal objection to the introduction of that evidence at the outset. That objection was overruled by the CEC's hearing officer Kenneth Celli, but that didn't keep Ellison from getting his procedural objections on the record:


Celli responded a bit wryly:

Despite the "surprise," BrightSource's experts rose to the occasion. After CEC staff testified on the effects of solar flux, BrightSource's assumptions about bird flight speed and behavior, and a handful of other related topics, BrightSource brought its own team to the stand to advance a few objections to the CEC's own scientific assumptions.

Here's biologist and BrightSource consultant Sönke Johnsen, for instance, a biologist at Duke University and author of "The Optics of Life: A Biologist's Guide to Light in Nature," providing his initial take on the CEC's testimony:

Johnsen pointed out that birds' bodies move while in flight, reducing the time of exposure of each individual feather to solar flux. Air currents around and through the feathers will reduce the temperature in the keratin, mitigating the solar flux's effect, and that solar flux may well pass through the feathers or be reflected off them.

Having launched his testimony by saying the CEC staff's analysis was simplistic, Johnsen then suggested that CEC staff had utterly overthought its suggested 5kW/M2 solar flux safety threshold:

Johnsen was followed up by retired Cal State Northridge Engineering professor Larry Caretto, who pointed out that the angle at which the flux hits the bird is an important component of determining exposure which he maintained CEC staff overlooked:

After digging into some details, Caretto provided as concise a summation of BrightSource's rebuttal as can be found in the transcript:

The BrightSource objection to the new testimony wasn't limited to the evidentiary hearing. In a formal Motion to Supplement the Evidentiary Record filed by BrightSource on March 22, Ellison and his colleagues attached an affidavit by Johnsen, but noted:

For his part, in his affidavit, Johnsen may have subtly undermined BrightSource's position. In a rebuttal to CEC staff's assumptions, he says:

The notion of basing safety thresholds on real-world tests of live birds at operating solar facilities has been suggested before in the context of Hidden Hills' environmental impact. At least one frequent intervenor in CEC proceedings, Basin and Range Watch, has suggested that the CEC use the near-completed Ivanpah Solar Electric Generating System as a test site for solar flux bird mortality, then using data gathered from Ivanpah's operation to better forecast the risk at sites like Hidden Hills.

Even the U.S. Fish and Wildlife Service (FWS) has suggested that CEC back off on new solar power tower projects until we have more data on wildlife risk from existing plants. In a 2012 letter sent by FWS representative Pete Sorenson to the CEC in a discussion of Hidden Hills and the now-languishing Rio Mesa solar projects, Sorenson said:

It's doubtful that BrightSource would be comfortable with putting its projects on hold for a couple years while biologists scour Ivanpah for dead birds. Though Johnsen definitely brings a significant amount of gravitas to his consulting client, his throwaway line in his affidavit may serve to shoot BrightSource in the foot.

Any time you build a project that poses a potential risk to wild birds, especially eagles, you're talking about involving FWS. CEC staff highlighted Hidden Hills' potential risk to eagles at the March 14 hearing; the topic of FWS involvement in enforcing provisions of the Bald and Golden Eagle Protection Act by way of management plans and take permits is now on the table. We'll cover that in greater detail in Part 4 of this series, coming soon.

For ongoing environmental coverage in March 2017 and afterward, please visit our show Earth Focus, or browse Redefine for historic material.
KCET's award-winning environment news project Redefine ran from July 2012 through February 2017.

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