The U.S. Fish and Wildlife Service (FWS) has weighed in on the California Energy Commission's assessment of the proposed Rio Mesa Solar Electric Generating Station. The verdict? FWS says the Commission needs to provide more data on potential risks to wildlife, especially migratory birds, from the proposed 500 megawatt project along the Colorado River south of Blythe.
Rio Mesa would consist of two 250 megawatt generators using boilers atop "power towers," each tower surrounded by tens of thousands of mirrored heliostats that would focus solar energy on the boilers. Proposed by Oakland-based BrightSource Energy, Rio MEsa and its near-twin the Hidden Hills solar project near Pahrump have been scrutinized for the potential risk the projects' concentrated solar "flux" would pose to flying animals, especially birds.
And in response to the Energy Commission's Preliminary Staff Assessment (PSA) on the Rio Mesa project, FWS says there isn't nearly enough data made available in the PSA for FWS to properly gauge the amount of risk the plant would pose to wildlife in the Colorado River Basin.
The Colorado River is a crucial wildlife corridor used by migrating birds traveling from the Sea of Cortez to spots northward along the Pacific Coast and in interior lakes such as the Great Salt Lake. The 16,667-acre Cibola National Wildlife Refuge on the river is just a few miles away from the Rio Mesa site.
According to the FWS's response to the PSA, the project site is predictably of significant importance for migrating birds:
Avian surveys for the proposed project to date have detected 130 species, including raptors, passerines, waterfowl, and 13 species on the Service's list of Birds of Conservation Concern... 70 percent of the approximately 440 known migratory bird species in North America use the Lower Colorado River Valley. For instance, State-listed Swainson's hawks (Buteo swainsoni) have been observed in kettles exceeding 100 individuals during migration throughout the area and flocks of ducks and geese also have been observed migrating above the Palo Verde Mesa. Large numbers of mourning doves (Zenaida macroura) make daily flights between water sources along the river and nesting/foraging habitat in desert habitats, directly over the Palo Verde Mesa and the proposed project site.... Since turkey vultures (Cathartes aura) primarily rely on an acute sense of olfaction to find food sources, they are particularly vulnerable in being attracted to the project site and its associated hazards because of their enhanced ability to detect odorants emanating from avian carrion. In addition, their abundance in the area (nearly 6,300 observations during project point surveys) suggests a large number of vultures may be exposed to flux and collision hazards, and other project effects.
The risks to birds of a heliostat-power tower solar project stem from two sources: collisions with mirrors, which can look like standing water or open sky, and vision damage and heat injury from the concentrated solar flux.
BrightSource maintains that the solar flux poses little risk to wildlife. Wildlife biologists and federal agencies aren't so sure. As the FWS says in its response,
As recently as the December 5, 2012, workshop hosted by CEC, it was acknowledged that no agreement has been reached on the thresholds of flux that adversely affect avian species. Because these additional threats are potentially lethal to appreciable numbers of many bird species, it is important that the PSA describe the extent of potential impacts from building and operating the proposed project.
We are concerned that two potential effects to avian species, including eagles and other special status species, were not sufficiently addressed in the PSA. First, the PSA includes a limited discussion on the risk of birds being blinded or otherwise suffering ocular impairment from exposure to concentrated solar energy (flux). However, the PSA does not clearly explain potential risks to the eyes of different species of birds and the expected magnitude of those risks.
Secondly, the PSA does not consider the potential for exposed avian skin to be burned or singed when a bird flies through the flux airspace surrounding the power tower. The PSA identifies tolerance thresholds for human skin exposed to flux and states that avian tolerance levels likely are higher due to the insulating effect of feathers. However, the PSA does not address potential effects to birds' skin not fully or sufficiently covered in feathers including the exposed heads of vultures and around the eye. Given the short exposure time and low flux level required to burn human skin, we are concerned that exposed bird skin may be burned at lower flux levels than those considered safe for bird feathers. We recommend a more in depth analysis of these potential effects be included in the FSA. In addition, the effects of multiple exposures to individual birds should also be addressed.
Neither the CEC nor BrightSource has replied to the FWS' comments so far. More than likely, any such comments will be made in the larger context of cumulative effects from Rio Mesa and Hidden Hills, as well as neighboring power tower proposals like the Quartzsite project about 20 miles north of Rio Mesa, which would include a 660-foot power tower.