While it might be easy to dismiss this issue as a “glaring” oversight on the part of its planners (Ivanpah is owned by BrightSource Energy and NRG Energy) further investigation reveals that issues of glint and glare from the plant’s reflective arrays were addressed during the Application for Certification submitted to the California Energy Commission in 2007. The first detailed analysis was included in a 2008 response from CH2M HILL to the CEC’s review of the application.
In their response, CH2M HILL stated that beam safe intensity calculations had been performed and that “the likelihood of random heliostat beam hazard to aircrafts flying in the area is infinitesimally remote.” CH2M HILL is a Colorado-based engineering company contracted by state and federal agencies for design and construction consultation.  CH2M HILL has offices in Bellingham and Bellevue, WA.
Subsequently, the Heliostat Positioning Plan and Tower Luminance Plan, which described even greater analyses of potential glare hazards, was submitted in 2013.
Frank “Tex” Wilkins, executive director of the Concentrating Solar Power Alliance and formerly of the Department of Energy, said the conversation about glare and CSP plants is not a new one. Wilkins took part in discussions in 2009 that looked into the issue. “The FAA convened a panel,” Wilkins said, “where extensive studies were performed on the topic. The final determination was made that glare from CSP plants, in particular glare from power towers, would not create an issue for pilots.”
Cause and Effect
Although it has been reported elsewhere that the incidents may have occurred as a result of pre-launch testing and repositioning of heliostats that took place in August of 2013 — which coincides with the same time frame during which two complaints were filed with the Federal Aviation Administration's Aviation Safety Reporting System — Clifford Ho of Sandia National Laboratories’ Concentrating Solar Technologies Department thinks otherwise.
“I believe some of the glare that’s being viewed is taking place when the heliostats are in a standby mode,” Ho said.
During peak daylight hours, it is common for a number of heliostat mirrors to be taken offline to prevent heliostats from directing more thermal energy to the turbine than it is capable of receiving. Ho said that during standby, these heliostats are focused on aim points next to the receiver, forming a ring of glare above the tower.
According to Ho, the sunlight reflected from heliostats that are in standby mode could be having an exacerbating effect on the amount of reflection being emitted.
In examining photos of the glare taken by passengers flying over the Ivanpah plant, Ho said it’s apparent to him the intense light is emanating from the heliostats not in use. “You can clearly see the difference between what’s just the diffuse reflection from the towers versus one or more heliostats that are in standby mode and reflecting light toward the observer.”
Ho has performed helicopter surveys of heliostats in standby mode at Sandia National Laboratories’ National Solar Thermal Test Facility. “It’s bright,” he said, emphasizing that the Sandia CSP array is much smaller than that of Ivanpah. “When you’re close, it can be like looking into the sun.”
Requests for Remedy and Possible Solutions
On March 10, the Clark County Department of Aviation (CCDOA) sent an official notification of complaint to BrightSource Energy, the California Bureau of Land Management, and the California Energy Commission. In the docket, the CCDOA requested that BrightSource take a number of actions to “respond to and address any complaints about adverse visual impacts to pilots.”
Included in the docket are requests for BrightSource Energy to take measurements of any observed glare and to determine if that glare is within the “maximum permissible exposure.” Ho indicated plans are already in motion to respond quickly.
“We will be doing some additional monitoring of the glare at the site,” Ho said. In addition to helicopter surveys of the area surrounding the Ivanpah plant, ground-based evaluations will also be performed.
One possible solution, as suggested by Ho, is to reposition heliostats that are in standby mode so that they stand vertically — thus reflecting the glare toward the ground instead of upward. Regardless of whether that’s done, Ho believes it is imperative that pilots are briefed on the location of the plant so that they will be aware of potential glare issues.
Ian Gregor, Public Affairs Manager for the Pacific Division of the FAA, concurs. “The FAA is aware of potential glare from concentrating solar plants and is exploring how to best alert pilots to the issue,” Gregor said. “The final Environmental Impact Statement for the Ivanpah project includes mitigation measures that address the issue of glare, which the aviation community raised during the EIS process.”
Sandia National Laboratories currently offers a Solar Glare Hazard Analysis Tool that Ho helped to create, which he says is fundamental to preventing similar issues from arising in future solar development projects. “The solution is to be aware of the potential issues of glare during the planning stage, to ensure it doesn’t become a hazard.”