The staff of the California Energy Commission has released their assessment of BrightSource Energy's proposed Hidden Hills Solar Electric Generating System, and the verdict is that the project would, in the words of the CEC, "have significant environmental impacts in the areas of biological resources, cultural resources, land use, and visual resources even with the implementation of staff's recommended mitigation measures."
In other words, the project in Inyo County will have a big enough impact on the environment that it can't be approved unless the Energy Commission itself decides to override state rules requiring those resources be protected.
Hidden Hills, proposed for the California portion of the Pahrump Valley, would surround two 750-foot towers with about 16,000 mirrored heliostats, which would focus solar energy on boilers atop the towers. The project would occupy 3,277 acres of private land, some of which is still home to intact Mojave Desert vegetation. BrightSource's heliostat design limits the amount of grading the contractors would perform, especially compared to PV installations elsewhere in the desert, but the CEC staff concluded that the project would nonetheless harm desert vegetation on site:
The proposed project, which is located on private land, features minimal grading onsite; however, mowing of vegetation and fencing of the site would result in the functional loss of Mojave Desert scrub, shadscale scrub, ephemeral desert washes, and habitat for a variety of special-status species that occur within the approximately 3,277- acre site. Without mitigation the project would contribute to cumulatively significant impacts to biological resources within Pahrump Valley, a broader area encompassed by the Northern and Eastern Mojave Desert Planning Area, and extending into the Pahrump, Nevada environs.
Among those special status species, of course, is the desert tortoise:
The project site is expected to support an estimated six to 33 adult/subadult tortoises, three to 34 juvenile tortoises, and 46 to 158 desert tortoise eggs. The estimated numbers of desert tortoise that may occur on the project site were calculated using applicant survey data, formulas recommended by the USFWS, and published scientific literature. These numbers represent a conservative approach and the actual number of desert tortoise detected on the project site may vary.
Biologists also found a piece of horn and possible scat from Nelson's bighorn sheep on site: the mountain ranges surrounding the Pahrump Valley host a significant population of bighorns. Badgers and desert kit foxes have been directly observed on the site, and the area is prime habitat for burrowing owls and golden eagles.
One of the biggest controversies surrounding Hidden Hills and its twin project, Rio Mesa, is the effect of large solar power tower-heliostat installations on birds, especially birds of prey. Wildlife biologists and others have expressed concern that the concentrated solar "flux" poses a serious threat to birds flying near the power towers, and that mirrored heliostats, which may resemble open sky or standing water, create a collision hazard for birds. Earlier studies at the much smaller Solar One power tower unit near Daggett suggested that burns and collisions with mirrors may pose a significant risk to birds. BrightSource maintains that its design reduces or elminates both those risks, and cites the experience of a similar facility in Israel, at which the company says they've seen no mortality. But the CEC staff isn't buying it:
The applicant has indicated that heliostat mirrors at the proposed project would be shorter than those at the Solar One site, and that this design difference would reduce collision hazard for birds. However staff has been unable to find documentation of relative collision hazards of taller or shorter mirrors. Staff believes that collision hazard is more likely to be a function of the total area of mirror surface than the height of the individual mirrors, and how birds appear to interact with reflective surfaces. The HHSEGS project would have 37 times more surface area of mirrors. Based on those factors, the Solar One collision mortality rates extrapolate linearly as 56 to 67 (rounded) bird mortalities per week at the larger HHSEGGS project site.... Annually, this results in a range of mortalities from 2,912 to 3,484 birds. These estimates do not account for morbidity that occurs as a result of collision and exposure to concentrated solar flux.
As for the Israel site data, the CEC staff says:
staff concluded survey methodology was inadequate to detect carcasses presence
The risk from solar flux isn't limited to burns. Glare blinding to predators than hunt by sight is an obvious potential problem. And even if exposure to solar flux isn't enough to cause serious burns, singed feathers can seriously impair a bird's ability to travel, avoid collisisons, or carry captured prey back to a nest to feed young.
The upshot of the admittedly vague data, according to the CEC staff: far from being safer than the old Solar One in Daggett;
Hidden Hills and Rio Mesa facilities could each result in avian mortality in excess of 22 times that of the Solar One facility previously studied based on linear extrapolation from total relative mirror surface area of the two facilities.