Investigating Avian Attraction to Solar Energy Facilities Through a Lake Effect

Assessing how reflected and polarized light from solar energy facilities may attract birds

U.S. Geological Survey

Recipient

Henderson, NV

Recipient Location

6th

Senate District

7th

Assembly District

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$499,785

Amount Spent

closed

Completed

Project Status

Project Result

The project has been completed, and a final report has been submitted to the CEC. This study was the first to determine whether there was evidence to support the lake effect hypothesis. The lake effect hypothesis implies a chain of events leading to bird fatalities, namely that birds in flight perceive large solar facilities as water bodies, reorient and descend toward those facilities, and in some cases succumb due to collision with the panels or become stranded on the ground. The study found that solar panels polarize visible and ultraviolet light in a manner similar to water, and that birds are more attracted to more highly polarized sources of visible light. Many birds approaching solar facilities from the north during daylight hours in the fall migration season were shown to descend toward solar facilities. Aquatic habitat birds, particularly birds that live on the water, were among the fatalities found at some of the solar facilities surveyed. The survey data on bird use and deaths at solar facilities and reference areas failed to support the alternative hypothesis that birds die randomly across the landscape, independent of the presence of solar panels. Taken together, these results are consistent with an operational lake effect hypothesis of avian mortality at solar facilities. However, they do not confirm it in its entirety. Attraction of aquatic habitat birds to photovoltaic solar facilities is likely a nuanced process, however, so such facilities are unlikely to provide the cues of a lake to all aquatic habitat birds at all times.

The Issue

PV utility-scale solar facilities in California (and possibly elsewhere) are sources of bird mortality. At the inception of the project, it was unknown what behavioral processes and mechanisms lead to bird mortality observed at solar facilities. The leading hypothesis suggested that large fields of photovoltaic panels reflect light in a manner similar to large bodies of water. Moreover, the presence of these water-like surfaces in arid landscapes may add to their attractiveness to passing birds. Left unaddressed, this problem will lead to increased costs to ratepayers as solar energy projects face greater environmental permitting and mitigation challenges associated with developing and operating these facilities.

Project Innovation

Researchers explored the behavior of attraction by birds to solar facilities, particularly in relation to the "lake effect" hypothesis. Specifically, they studied 1) the ability of birds to detect potentially attractive visual cues associated with solar facilities (e.g., polarized light, irradiance); 2) the corresponding change in flight behavior characteristic of movement toward solar facilities; and 3) the mortality and natural history of birds that actually occupy solar facilities. First, the recipient examined the sensory basis of attraction through field and lab experiments. Second, radar and thermal imaging were used to measure the degree to which birds alter their flight paths to settle at solar facilities. Data on behavior and mortality from multiple solar facilities were gathered to inform a statistical model to determine what characteristics of solar facilities and species' natural history together explain variations in mortality exhibited across sites.

Project Goals

Understand if birds are able to see polarized light and use it as a cue in locating water bodies.
Investigate the polarization properties of solar panels and determine whether they mimic natural water bodies.

Project Benefits

This project is the first systematic study to determine whether birds are attracted to solar energy facilities and if so, to develop an understanding of the sensory basis and proximal response of birds to solar facilities in relation to the "lake effect" attraction phenomenon. Following from that new understanding, the project identified potentially viable methods for deterring birds from approaching solar facilities and informing future siting decisions in ways that reduce the likelihood of birds fatally interacting with solar facilities.

Lower Costs

Affordability

This project will lower costs by streamlining the permitting process of renewable energy projects in California because information on the impacts on wildlife is insufficient or unavailable.

Environmental & Public Health

Environmental Sustainability

By combining mortality and natural history data with new data gathered during the project, solar energy companies, agencies, and the public have access to the best information for risk assessment and future siting decisions.

Key Project Members

Project Member

Robert Diehl

David Stoms

David Stoms

CEC Project Manager
California Energy Commission

Subrecipients

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Western EcoSystems Technology, Inc.

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Cal Poly Humboldt Sponsored Programs Foundation

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Bard College

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Match Partners

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United States Geological Survey

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Western EcoSystems Technology, Inc.

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Cal Poly Humboldt Sponsored Programs Foundation

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NRG Energy, Inc.

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NextEra Energy

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Bard College

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8minuteenergy Renewables, LLC

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First Solar

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Recurrent Energy

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