What are the environmental issues surrounding solar power plants?

Solar power plants have been associated with a number of environmental issues. In particular, they require large amounts of land (Figure 1), between 5-15 acres per MW (see OWOE: How much land does a solar power plant require?). Coupled with the need for steady sunlight, the ideal locations for a large solar plant are dry, arid regions, such as the deserts of the US Southwest. One of the most promising of these is the Mojave Desert, which stretches from Palm Springs, California to Las Vegas, Nevada. However, there is a tension among environmentalists between those who are concerned with climate change and the need to expand solar power to reduce our dependence on fossil fuels and those who are concerned with biodiversity and see solar farms as a threat.

Arguments against solar plants in the Mojave Desert (see The New Lede article from February 2023) include:

1. Solar plants can disturb or destroy habitat for the desert tortoise (the state reptile, feared to be nearing extinction), the desert kit fox, and dozens of other threatened species.
2. Heat from the 40-story towers of the Ivanpah Solar Plant, on the California-Nevada border, incinerates thousands of migrating birds each year.
3. Solar plants are encroaching on Joshua Tree National Park and Native American sacred sites.
4. Bulldozing the desert degrades the soil's ability to sequester greenhouse gases and generates harmful air pollution.

Although focused on the Mojave Desert solar plants, the overall themes are relatively universal. With regard to #1, a 5-year study by the Argonne National Laboratory and the National Renewable Energy Laboratory (NREL) and published in December 2023 addressed the changes to biodiversity driven by solar farms in southern Minnesota. They found increases over time for all habitat and biodiversity metrics and concluded that "the expansion of utility-scale solar energy development in agricultural landscapes presents an opportunity for the dual use of the land for energy production and biodiversity conservation through the establishment of grasses and forbs [flowering plants] planted among and between the photovoltaic solar arrays." Although the study didn't focus on a desert environment, it helped provide momentum to the principles of "agrivoltaics", or agricultural production, such as crop or livestock production or pollinator habitats, underneath solar panels or adjacent to solar panels.

With regard to #2, concentrating solar power (CSP) plants (see OWOE: How do solar thermal power plants generate electricity?) developed a reputation as being harmful to birds when they were first operated. The sunlight that is reflected from the mirrors to the tower is so hot that it can burn the feathers of a bird that enters the beam. An Associated Press article in August 2014, when the Ivanpah Solar Electric Generating System was undergoing testing, was titled "Mojave solar plant scorching birds in mid-air" and syndicated across the country. Other articles built on this and even described California's BrightSource solar power plant as a "death ray" that was incinerating birds mid-flight. Various experts were quoted as saying that the plant was incinerating between 28,000 per year and one bird every two minutes, or hundreds of thousands of birds per year. BrightSource Energy, owner of the plant, claimed the numbers were less than 1,000. In reality, the numbers were even less than BrightSource Energy's estimate. Under rigorous oversight by the California Energy Commission (CEC), as part of the multiyear environmental permitting process and independently validated by environmental experts, Ivanpah reported 321 total avian fatalities between January and June 2014. Of these, only 133 were related to sunlight being reflected onto the boilers. Of course, by the time the real facts were known, public opinion had been turned against these types of CSP plants.

As an interesting follow-up story, in April 2015 CleanTechnica reported on a phenomenon identified during final commissioning, i.e., testing, of the Crescent Dunes Solar Energy Project in Nevada. One of the tests is for the standby position, which is where the heliostats aim away from the tower receiver prior to initiating the process to generate electricity. The original system design was based on the standby position creating a tight circle of solar flux that could be seen above the tower. Figure 2 shows this "halo" of solar flux from the heliostats. When the engineers initially focused 3,000 heliostats at this location on January 14th, 115 birds were killed as they flew through the concentrated solar flux. Testing was shut down, and the engineering team developed a new standby configuration which spread the solar flux over a several hundred meter 'pancake' shape with no more than 4 mirrors focused on any one point. Figure 3 reproduces the sketch made during a brainstorming session to address the issue. The plant reported zero birds killed during the 3 month period from the test to publication of the article.

There is clearly more progress to be made to ensure the needs for both clean power and biodiversity can be achieved with large solar farms. However, continued improvements in technology, awareness of issues on behalf of all stakeholders, and appropriate government regulations should enable such progress.

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