One Weird Trick Prevents Bird Deaths At Solar Towers

April 16th, 2015 by Susan Kraemer

Sorry about the clickbaity title, but as it turns out, the solution to a serious problem discovered last year at Ivanpah — the first solar power tower in the US — actually has turned out to be “one weird trick.” Below is the exact problem, and how the problem was solved.

America’s second solar power tower, the 110 MW Crescent Dunes project, the first US power tower to include storage, has been undergoing final commissioning (testing) at Tonopah in Nevada, where it will supply power for Las Vegas till midnight.

So SolarReserve is putting the thousands of heliostats (mirrors) through their paces to make sure everything works.

One of the tests is of standby position. (Standby is when the heliostats are waiting to go to work making electricity by focusing on the tower receiver. During standby they are not aimed at the tower receiver, but somewhere in the air.)

Originally, the standby position was to create a tight circle of solar flux you can actually see above the tower.

But when the engineers focused 3,000 heliostats there on January 14th, 115 birds were killed as they flew through the concentrated solar flux at the focal point where all the reflections met.

According to the compliance report filed by Stantec with regulators as required by the BLM:

“Approximately 3,000 heliostats were staged in a position which reflected light and heat to a concentrated point above the central tower. A halo above the tower was visible from the ground (Figure 1). The heat was so intense that birds flying into the halo were immediately burned and smoke was clearly evident. Approximately 115 mortalities were noted between 11:15 AM and 3:30 PM. Appropriate agencies, including BLM, were notified of the situation around 12:27 PM when bird mortalities associated with the halo were confirmed.”

SolarReserve shut down the test and brainstormed how to solve the problem to reduce solar flux in standby position. The engineering team recalibrated the standby algorithm and the next day they put this into effect. Their new algorithm was designed so that no more than four ‘suns’ would hit any one focal point during standby.

“The difficulty is that that was a concentrated solar energy in that area above the tower,” SolarReserve CEO Kevin Smith told me this week.

“So what we did is we spread them over a several hundred meters of a sort of ‘pancake’ shape so any one point is safe for birds — it’s 4 suns or less.”

The one weird trick?

Focus no more than 4 mirrors on any one place in the air during standby. (When the focal point is the receiver – no dead birds. The potential danger is only during standby.)

“We have had zero bird fatalities since we implemented this solution in January, despite being in the standby position as well as flux on the receiver for most days since then,” he said. “This change appears to have fully corrected the problem.”

Since January’s mishap that delivered the Eureka moment for safe solar power tower development, no more dead birds at all. I did the math as of our conversation this week; a day or so short of 3 months with zero fatalities.

Solar flux — a feature or a bug?

Solar flux is how power towers work. Focusing thousands of mirrors on a receiver in a tower heats a fluid just with reflected sunshine.

Most people are familiar with solar PV, which makes electricity by science magic. But concentrated solar power (CSP) makes electricity by making steam that drives a turbine, like combustion of coal or natural gas does.

Except that instead of creating heat by removing mountains to dig up coal or fracking up groundwater to get at natural gas, CSP boils a heat transfer fluid using just reflected sunlight for clean energy.

In power tower CSP, thousands of mirrors concentrate multiple ‘suns’ on one spot; the receiver in the tower. The solar flux heats what’s in the receiver (water for Ivanpah; molten salt for Crescent Dunes) to ultimately make the steam.

The “bird-killing solar” story till now

The first power tower out of the gate in the US was Ivanpah, Google-funded and DOE-supported — in other words, just asking for trouble.

So when Ivanpah accidentally killed birds during standby heliostat positioning, the opposition jumped at the chance and exaggerated the numbers into the tens of thousands.

The actual tallied numbers got no media traction. For psychological reasons, truthiness beats truth.

But even frying 321 birds in the first 6 months on the huge desert site was upsetting enough to the Ivanpah developers, who had already fronted millions to build tortoise nurseries, and had committed to the purest form of CSP, using only sunlight and water, precisely because of its environmental friendliness. And now this.

Even though Ivanpah owners then implemented bird deterrents the same way that the aviation industry, landfills, golf courses, and sports stadiums have been doing since forever, and worked with Sandia National Laboratory and reduced its solar flux in standby, power tower solar was as good as dead — at least in the US — from what E&E News has since characterized as a PR Nightmare.

The brouhaha initially wound up derailing the Palen power tower project, which was to have been BrightSource Energy’s next project together with Abengoa (though Abengoa might try again alone.)

What is at stake?

Dispatchable power. If we are going to switch to a civilization powered by clean energy, we need dispatchable energy that is available whenever the the grid needs it, day or night — that is cheaper than batteries at grid scale and better for the environment than natural gas peaker plants.

Currently, natural gas supplies dispatchable power — mostly to even out the “duck curve,” the steep ramp-up in load in the evening, that gets steeper the more of us put solar on our roofs supplying daytime power — and that means fracking.

Power tower solar with storage can enable night time solar that could supplant the use of natural gas for smoothing out the duck curve (which is already a factor in California, and will only increase as the rest of the US goes solar).

That’s why this one weird trick that has not merely reduced but now appears to have ended solar power tower avian mortality altogether is such a big deal.









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