How to protect birds from CSP towers

The solar industry is by no means the first to need to deter birds from danger. The aviation industr

CSP towers create areas of solar flux near the tower that have singed the feathers of some birds flying within proximity of the towers at Ivanpah during its recent commissioning and startup. BrightSource Energy, the initial developer, has hired biologists


By Susan Kraemer

Dangerous interactions between birds and human technologies have been around a long time.

Like industries before it, the solar industry will also need to find ways to keep birds from encounters with solar panels, mirrors, and power towers.

In Concentrated Solar Power (CSP) tower technology, a tower receiver converts sunlight into thermal energy.

This thermal process - using the sun’s heat to ultimately drive turbines - makes CSP the only solar resource able to ship power at night, because it makes thermal storage possible.

But power towers also create areas of solar flux (basically concentrated sunlight) near the tower that have singed the feathers of some birds flying within proximity of the towers at Ivanpah during its recent commissioning and startup.

At the 392 MW CSP tower project, the three major causes of avian mortalities have been solar flux, collisions with mirrors and predator kills.

The death rate is higher during spring and fall migrations. In January, there were fewer than 10 deaths, but in April, there were 97, with almost half showing some signs of singed feathers.

Developed initially by BrightSource Energy, Ivanpah has become the big test that could determine the future of the CSP tower industry, by how successfully and humanely it can reduce this avian mortality.

In fact, the project is being closely watched as a preview for likely environmental impacts at Palen CSP plant, which BrightSource is developing with Abengoa as the EPC, and which has been amended to use parabolic trough instead of CSP tower technology.

Big picture

In a recent memo sent to the solar industry, U.S. Fish and Wildlife Service (USFWS) made it clear that it wants to encourage efforts to identify and implement “all reasonable, prudent and effective measures” to avoid harm.

“Ideally, a high quality, scientifically valid, and robust avian plan that is implemented in a timely and effective manner, and regularly reviewed and revised as needed, will maximise avoidance of species protected under our various laws while allowing for project development in the most environmentally conscientious ways practicable,” it explains.

As Executive Director of the Loan Guarantee Program under the Obama administration, Jonathan Silver helped fund the five big CSP projects in the U.S. that are now coming online, including Ivanpah.

“While no bird loss is desirable,” he says; “it is important to remember that less than a thousandth of one percent of the annual bird loss in the US is attributable to solar plants of all kinds.”

It is possible to mitigate or entirely eliminate damage to wildlife, he adds. “CSP projects and protection of critical ecosystems can easily co-exist. This does not need to be a win-lose situation. There are win-win solutions available here.”

Also, some perspective is needed. The USFWS finds the toxic waste pits of the oil and gas industry cause a million deaths annually.

Ivanpah has over $25 million invested in protecting tortoise habitat, and is fully mitigated, with 7,000 acres of private lands purchased and preserved in perpetuity. The plant is majority-owned and operated by NRG Energy, while BrightSource was the initial developer and Google is an equity investor. The three “Solar Partners" have hired biologists to understand the bird issue that arose during commissioning.

Now that majority owner NRG Energy has operational responsibility, it continues the avian mortality monitoring and has begun reporting begun during construction.

Humane solutions offered

The region within 50 meters of the tower is the main area of concern. The solution entails deterring birds here, as well as preventing them from colliding with the heliostats.

The California Energy Commission (CEC) is reopening consideration of the 500MW Palen power tower project developed by BrightSource Energy and Abengoa, with new evidentiary hearings on avian mortality and other issues, in June and July.

Although unable to comment during the ongoing CEC process of reviewing Ivanpah’s avian mortality for Palen permitting, BrightSource Energy spokesman Joe Desmond shared with CSP Today their research submitted to the record, identifying a range of humane visual and audio deterrent systems.

Next, a regulatory Technical Advisory Committee (TAC) will recommend its preferred deterrent method.

One of the humane options considered involves digital recordings of predator cries and alarm calls. According to the U.S. General Services Administration, while birds can distinguish an old-fashioned tape recording from the real thing, digital recordings work well.

The key is to randomly play these bird calls at irregular intervals and at varying locations, for each species you need to deter, according to CEO Jack Wagner, who considers his company BirdBusters the granddaddy of firms supplying distress call-based bird deterrents to a wide range of industrial sites, including multi-acre tailings ponds that seem like water to birds.

“Birds respond to species-specific distress calls,” he explains. “And we have probably the largest commercial sound library in the world. It's taken years to acquire.”

Natural sounding distress calls

In the wild, birds warn other birds of danger. Digital deterrents warn birds away with the calls their species makes when alarmed or in distress, by recording the sound they make under duress. “To get the alarm call, you can just scare them,” says Wagner. “The distress call is a bit different.”

To get that, a biologist lures the bird into a net so it can be held upside-down for several seconds.

The immediate cry of distress is recorded and then the bird is freed again, unharmed, and the sound added to a library of distress calls. These are combined into a customised combination of digital recordings for all species that frequent a particular site, along with the calls of their predators.

Bird species requiring deterrence from Ivanpah include various kinds of blackbirds, humming birds, sparrows, swallows, kestrels, finches and larks.

Just as in nature, these sounds must be played realistically: from various places around the site at various times.

“Birds habituate to what we call ‘same sound, same speaker syndrome’, so we mix this up,” says Warmer. “We put these sounds into a program so it's intermittent, so multiple sounds come out of multiple speakers at variable times.”

The sound must be no louder than nature, and directed up into the airspace. “If it's louder than nature, it sounds foreign to avian years, so all is lost.”

Occasional mechanical sounds help too; even a few minutes a week of helicopter blades or muffled shotgun blasts. These are played louder, delivered on a separate chip.

“You need a combination of state-of-the-art digital recordings managed by one person who understands birds’ behaviour and the existing conditions,” Wagner cautions. With a staff of biologists already on site, Ivanpah has that expertise.

Win-win solutions

Promising areas for future study include subsonic sound. Birds can hear low frequency sound that humans can’t.

Electromagnetics is another. Apparently, birds tend to fly toward the acute angle made between the earth's magnetic field and the surface of the earth, suggesting electro-magnetic signals could guide them away.

Encouragingly, it seems that avoidance becomes instinct over the long term. Newfoundland’s airport in Canada has deployed varied digital distress calls for a decade.

These days, even young gulls won’t cross that airspace. Apparently successive generations of local seagulls have passed on their knowledge to their children.

Humans have much to learn too. One firm’s digital deterrent recording was sent to the Beijing airport to deter crows with the terrifying call of their predator, a hawk. But the birds didn’t react. There was a language barrier: these were American hawks – new recordings were hastily made!

On the whole there are good reasons to be optimistic that, just as birds have learned to stay away from danger at airports, they can also learn to coexist with solar, which – as one of our solutions for climate change – will help preserve far greater numbers of them (and us) in the long run.

To comment on this article, please contact the author, Susan Kraemer.