The rapid expansion of utility-scale solar facilities has raised questions about their environmental impact, particularly concerning avian wildlife. The risk to bird populations depends heavily on the specific solar technology used. Understanding the evidence requires a clear distinction between photovoltaic (PV) panels and concentrated solar power (CSP) systems, as each presents unique threats.
Distinction Between Solar Farm Technologies
The impact of a solar facility on birds hinges entirely on whether it uses photovoltaic panels or concentrated solar power technology. PV solar farms are the most common type, using dark, flat panels to convert sunlight directly into electricity without generating intense heat. CSP facilities, however, use thousands of sun-tracking mirrors (heliostats) to focus solar energy onto a central receiver tower. This concentrated energy heats a fluid to extremely high temperatures, creating a unique thermal danger that PV farms do not.
Mortality Associated with Concentrated Solar Power
The primary threat from CSP facilities is “solar flux” or “avian flash,” which occurs when birds fly into the superheated air and concentrated light beams surrounding the central receiver tower. The intense thermal energy instantly singes feathers, leading to a catastrophic loss of flight ability and subsequent death. Studies at major CSP plants, such as Ivanpah in California, confirm this hazard. Fatalities are attributed to thermal injury or collision with the highly reflective heliostat mirrors, resulting in a higher avian mortality rate compared to PV farms.
Mortality Associated with Photovoltaic Panels
In contrast to CSP, PV solar farms primarily pose risks involving physical trauma. The leading cause of death is collision with the panels, perimeter fencing, and transmission lines. Because PV panels are non-reflective and low to the ground, they do not create the thermal danger seen at CSP sites. A hypothesized mechanism unique to PV arrays is the “lake effect,” where large, uniform expanses of panels are mistaken for bodies of water by migrating waterfowl. These birds may attempt to land on the perceived water surface, resulting in fatal collisions.
Contextualizing the Overall Risk to Bird Populations
To accurately gauge the environmental impact, avian fatalities at solar farms must be contextualized against other human-related causes. Solar energy production in the United States causes an estimated 37,800 to 138,600 bird deaths annually, a figure significantly lower than the 14.5 million deaths attributed to fossil fuel power plants. The largest sources of human-caused avian mortality dwarf these numbers, including collisions with buildings (up to one billion annually) and predation by domestic cats (1.3 to 4 billion annually). While solar-related deaths require mitigation, the technology is not a leading driver of overall avian population decline.
Ongoing Mitigation and Conservation Strategies
The industry and conservation groups are actively implementing strategies to reduce avian mortality at both PV and CSP facilities. For CSP towers, operational changes include adjusting heliostat aiming strategies to minimize solar flux during periods of high bird migration. Facilities also deploy nonlethal deterrents, such as acoustic and visual devices. PV farms reduce collision risk through design solutions like anti-perching devices on infrastructure and strategic placement away from known waterbird flight paths. There is also a focus on site selection, favoring disturbed land over pristine habitat, and integrating native vegetation to create wildlife-friendly buffer zones.