News and analysis about energy in California with an eye toward renewables.

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:

Staff believes that it's a near certainty that golden eagles and other special status bird species will be killed or injured over the 30-year life of this project.

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:

This is all [a] surprise to me. You know, no advance notice of this even five minutes ago. What staff is attempting to do is to present evidence that goes beyond what they previously filed in realtime and I strenuously object....

If staff's concern is that our rebuttal testimony was somehow improper, that rebuttal testimony was filed a long time ago. They could have filed a motion to strike ahead of these hearings, let alone walking in and not even given us any oral notice on the day of the hearing. So I am objecting to this in the strongest possible terms.

Celli responded a bit wryly:

We have live expert testimony. We're going to put limitations on their expression. We want to hear everything they have to say. All parties -- this is very important. The Committee is very interested in avian flux and we are doing to hear whatever they have to say and if it's relevant, it comes in. If it's not, make an objection, but apparently I have earned a reputation for overruling objections.

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:

I looked over the staff's analysis and have three sort of fundamental conclusions. One is that this is really almost an impossible problem to model. There are some biological problems that can be modeled very well; there are others that can be modeled very poorly or not at all. A flapping bird in flight is an exceedingly complicated thermodynamics problem. We've talked before about convection, and convection depends very strongly on fluid flow in the actual fluid dynamics. And, because the fluid flow in birds is so complicated, this makes this almost impossible to address in a theoretical fashion.

My second conclusion is that what the staff has modeled is not a bird in flight. What they've really modeled is -- imagine the blackest asphalt surface that you've ever seen, something practically like midnight, and it is flying through the air as smoothly as possible at a ninety degree angle to all the radiation that hits it. This is not remotely what a bird in flight would be like.

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:

So, to begin with, we should probably put this 4 kilowatts per meter squared threshold -- or let's say 5 kilowatts per meter squared threshold into some kind of real context, because most of us don't deal with kilowatts in our regular life. So the way to think of it is a kilowatt per square meters is one sun. So, when you're talking about 4 kilowatts per meter squared you're talking about aiming three mirrors at your body, with the fourth sun being provided by the sun in the sky. This is something that people did in the fifties with regularity.

They had those mirrors that they would sit, you know, at the beach; they would have a tripartite mirror which they would hold very carefully to aim three suns from the mirrors at their face, and then the fourth sun was provided by the actual sun. And these people were experiencing fluxes on the order of 3 kilowatts per meter squared to 4 kilowatts per meter squared, depending on how far to the tropics they got and how high the sun got in the sky and so on.

These people, you know, were using their actual skin, not feathers. This skin had nerves; they could feel pain, and so you could pretty much guarantee that they were not experiencing 160 degrees centigrade temperatures. So, for me, this threshold just did not pass the common sense test. But, by being someone who likes to combine theoretical understanding with empiricism, I got out a hand lens in my office, and, if you take a hand lens and you focus the sun to a size that is half the size of the original hand lens, you are now focusing four suns on whatever strikes it. I aimed this at my palm, and I left it there for about thirty seconds.

My palm got warmer -- and remember there's no convection to help this cool, remember the sun is hitting me directly straight on -- and my hand got warmer, but I did not feel pain, I did not char, and my skin was good afterwards, and so on, and so on.

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:

If you're standing in front of a fireplace and you turn sideways, you'll get less heat, because you aren't getting the direct exposure to the radiation.

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

So, we basically believe that the staff, although the fundamental equations were certainly correct and we would get the same results if we used their data, but their data and their assumptions are incorrect and do not lead to reasonable results for a flying bird.

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:

Dr. Johnsen's affidavit does not cure the unfairness of Staff's tactics. however, it addresses certain technical evidence Dr. Johnsen would have presented if Staff's exhibits and testimony had been timely pre-filed, and had Dr. Johnsen been afforded a reasonable opportunity to review these documents before they were received into evidence. Dr. Johnsen identifies several errors and issues contained in the new testimony presented by Staff on March 14th, but which was not fully addressed within the time constraints of the evidentiary hearing.

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

Staff has made a good faith but highly flawed attempt to apply simple engineering to an extraordinarily complex problem....The difficulty is not in doing the calculations. The difficulty is in applying them to flying birds and getting a meaningful result. At the moment, this cannot be done; merely presenting the equations does not make them accurate. All I did in my analysis was correct several fundamental mistakes in Staff's implementation of these equations and show that the zone of uncertainty conservatively starts at a much higher flux level. Staff's simplified analysis (including, fundamental errors such as confusing emissivity with absorptivity, air temperature with sky temperature, and absorptivity with the inverse of reflectance) is not "more conservative" than those proposed by Dr. Caretto and myself; it is simply wrong. More importantly, the very concept of attempting to calculate with simple equations the complex interaction of solar flux and living, flying birds is, as I testified, "a fool's errand." Even correcting for Staff's errors, all the calculation tells you is a threshold of where solar flux might begin to impact birds. Above that threshold (including mine), however, the calculation tells you nothing about whether living, flying birds will, in fact, be harmed and, if so, at what flux levels. In my expert opinion, that question is best answered by studying real birds at real operating projects or by field tests such as those conducted by [CH2M Hill's] Mr. Santolo.

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:

[W]e 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.

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.


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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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