Solar Thermal: Hazard for Pilots?

As discussed here last week, the Ivanpah Solar Electric Generating System, located about 40 miles southwest of Las Vegas in the Mojave Desert, kills butterflies, dragonflies, other insects, bats, and birds.

Tens of thousands of large mirrors (“heliostats”) focus sunlight on boilers (“receivers”) perched atop 459-foot towers. The “solar flux” field surrounding the boilers can reach temperatures of 800ºF — hot enough to melt, singe, and burn the feathers of birds that fly through it.

The intense luminosity of the boilers attracts insects, which attract insect-eating birds, which in turn attract raptors. Fish & Wildlife Service (FWS) officials investigating the site observed “streamers” — trails of smoke from birds transiting the flux fields — about once every two minutes.

Update: Environmental journalist Chris Clarke, who’s been reporting on avian mortality at Ivanpah since September 2013, reports that a federal study confirms that glare from Ivanpah’s heliostat arrays may create safety hazards for commercial and private aviation in the area.

In March, Ivanpah co-owner NRG Energy told Nevada aviation officials that potentially-hazardous glare was a temporary problem likely to abate once all heliostats were “calibrated” for commercial operation. But, reports Clarke, Sandia National Laboratories finds that the heliostats cause intense glare when they are in “standby position” — their default position when not aimed at the boilers. From the article:

According to the report, “Evaluation of Glare at the Ivanpah Solar Electric Generating System,” released by the Sandia Labs on July 17, heliostats in standby position generate glare bright enough that it can cause visual afterimages for observers as distant as six miles from the power plant. . . . [This is not a problem for motorists driving by the facility.] 

But for aerial observers, including pilots flying into and out of airports in the Las Vegas area, glare from heliostats in standby mode was bright enough at distances of six miles or less from the plant to cause persistent afterimages, a potential hazard for pilots in the busy airspace over Ivanpah Valley. . . .

Ivanpah came online in February, with all its heliostats presumably calibrated and the standby protocol fully developed. Three months later, in May, California Department of Transportation aeronautics chief Gary Cathey said in an email to the California Energy Commission’s Jim Adams that a May 8 overflight of the Ivanpah plant “generated the brightest, most extensive amount of glare that I’ve seen in my aviation career — and I have been flying since 1986.”

“As you may have noticed,” Cathey told Adams, “I had to shield my eyes with my hand as I was scanning for airport traffic while we flew eastbound . . . to [Ivanpah] from the nearest waypoint.”

How significant is this problem? That depends on how fixable it is. As Clarke notes, “around 120 commercial aircraft fly between McCarran and Los Angeles-area airports on a typical weekday, and that’s not including a large number of private aircraft plying the Mojave skies in the region.”