Federal Study Confirms Aviation Glare Hazard From Solar Project

Photos of glare from the Ivanpah Solar Electric Generating System, taken from an airliner approximately 40 miles away | Photo: Mike Pasqualetti, Arizona State University, via Sandia National Laboratories

A federal laboratory has released its report on hazards from glare at the Ivanpah Solar Electric Generating System in San Bernardino County and the risk that glare poses to aviation in the area. That report isn't good news for those flying between L.A. and Vegas.

ReWire reported in March on complaints from pilots flying near the 390-megawatt solar power tower plant that the facility's tens of thousands of mirrors created intense and potentially hazardous glare that interfered with the pilots' ability to scan the air for nearby aircraft. In that month, Ivanpah's owner Energy Services, a division of NRG Energy, replied to state regulators that the glare was likely caused by mirrored heliostats that had not yet been "calibrated," implying that the issue would be largely fixed once the plant went online.

But a study from the Sandia National Laboratories published on the California Energy Commission website Thursday found that significant and potentially hazardous amounts of glare are created when the facility's heliostats are in what the operators call "standby position," the default position for heliostats not aimed directly at the plant's boilers.

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Ivanpah's three units generate power by aiming the independently targetable heliostats at boilers atop three 460-foot power towers. There are times when the amount of radiation being concentrated on the boilers has to be reduced for one reason or another, at which point a number of heliostats will be moved to "standby position," in which they reflect sunlight at a point just slightly off the boilers. (If the plant's heliostats were all put in standby position, the concentrated energy would form a "halo" around each of the boilers.)

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.

The report noted that observers at the same elevation as the plant, including passersby on Interstate 15 through the Ivanpah Valley, are unlikely to experience glare from any single heliostat persistent enough to cause even temporary visual afterimages, though the power towers themselves are certainly bright enough to be a distraction.

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. (As we reported in March, 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.)

According to the report, glare from the heliostats can be many times brighter than that from the white-hot power tower boilers. Aerial photos taken by Sandia researchers and filtered to reduce relative light levels show the power towers, with boilers, as dark objects backlit by the brilliant heliostats.

"It should be noted," reads the report, "that two of the authors who were in the helicopter qualitatively confirmed these results after observing the glare. The pilot acknowledged that the glare was very bright, but he also stated that it did not impair his flying ability since he was aware of the glare and avoided looking in that direction when flying over ISEGS."

In March, Energy Services informed the California Energy Commission that previous pilot reports of distracting glare from the Ivanpah facility took place before the current standby mode had been developed:

The two reports... occurred in August 2013 prior to the facility's full commissioning. Testing, calibration and commissioning of the entire facility (Units 1, 2 & 3) was ongoing, and many of the heliostats at the facility were in the process of being brought into operation through a calibration process. A number of heliostats had not been through the calibration process at the time of the reports. The status of the solar field is different today from the status of the field at the time of the reports, with more heliostats through the calibration process. In addition, during operations, the ISEGS project implemented a revised stow strategy that places stored heliostats in random orientation when the solar filed [sic] is not in use.

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." Cathey pointed out that that particular route is one used by commercial and private aircraft flying into and out of Las Vegas airports, adding:

I sincerely hope that if similar facilities are proposed in the future, the CEC will consider the "lessons learned" from the construction of this facility at this location to alleviate problems of similar magnitude at other locations.

The CEC is in fact considering whether to approve a similar facility -- the Palen Solar Electric Generating System -- in the very near future, with hearings scheduled in Blythe from July 29-31. Palen would be significantly larger than Ivanpah, with 750-foot towers and heliostats packed more closely across the desert terrain, with likely consequent increases in glare problems. You can bet that's going to be mentioned in Blythe.

For the record: This piece was published with a typographical error that misstated the capacity of the Ivanpah plant. It's been corrected.

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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