How Much is Too Much Heat for Birds?

In testimony submitted in advance of California Energy Commission (CEC) evidentiary hearings scheduled for the end of this month, the CEC staff estimates that the impact of heated air above BrightSource's proposed Palen hybrid solar and natural gas project may result in as much as 2.5 times more bird deaths than at the BrightSource's Ivanpah hybrid project (I use the term "hybrid" because Ivanpah will burn nearly 525 million standard cubic feet  of natural gas, annually.  Palen will burn at least 728 million standard cubic feet of gas, annually.  Unlike photovoltaic solar projects, BrightSource's power tower design needs fossil fuels to warm up the boilers that also convert the sun's energy into electricity).

This peregrine falcon was found emaciated at BrightSource Energy's Ivanpah solar project and later died. Note the clear singing of the feathers likely caused by the intense heat generated by BrightSource's mirrors. Photo from the National Fish and Wildlife Forensics Laboratory report submitted to the California Energy Commission.

BrightSource has argued that birds are only at risk of death from solar flux (air heated by the concentration of the solar mirror field) in the air space close to the power tower where the heat is most intense.  CEC staff, however, assesses that birds are at risk from injury or death as soon as they enter the flux field, and that they do not need to reach the area close to the tower to be at risk of death.  At issue is the examination of dead birds found at BrightSource's Ivanpah project; some dead birds' feathers were singed by the heat, while others were found with no singing at all.  Early analysis suggested that the birds with singed feathers died of solar flux exposure, and dead birds with non-singed feathers may have died from collision with mirrors.  However,  CEC staff argues that dead birds with non-singed feathers found further from the power towers are also dying from exposure to heat from the solar flux based on the distribution of dead birds throughout the solar field.   This would mean that thermal stress alone, not just the singing and impairment of feathers, is leading to bird deaths.  The reason this is significant is because this would further underscore the increased threat BrightSource's technology poses to wildlife compared to other types of solar facilities, where collision is the primary threat.

The graphic above submitted by CEC staff compares the size of the Palen and Ivanpah solar towers and solar flux fields (Palen is the larger tower and field).  The color coding represents the relative thermal intensity at the Palen project; the intensity of the heat increases closer to the power tower.  CEC staff assesses that birds are at risk upon entering anywhere in the solar field and that the risk increases closer to the power tower, whereas BrightSource maintains that birds are only at risk of death or injury in the cone close to the tower (the darker red shading).

Shawn Smallwood, an expert on bird mortality at renewable energy projects, submitted testimony that the Palen hybrid project could incur as many as 10,787 birds per year (at an 80% confidence interval) based on preliminary data from Ivanpah and a study of bird mortality at the smaller Solar One in Dagget during the 1980s.  Mr. Smallwood also critiques BrightSource's proposal to use various technologies in an attempt to deter birds from coming close to the Palen project, such as the use of lasers, balloons and an untested means of disorienting the magnetic field of birds.  As Mr. Smallwood notes, "[a]nother approach with just as much sense would be to cut off one or both wings of birds so that they cannot fly at all."  Discussion at the evidentiary hearings this month may also examine whether or not BrightSource can curtail operations of the Palen project during peak bird migration months or when migratory birds are nearby, but BrightSource itself has pointed out that this would be infeasible because financially and because the project takes too long to power down.