Solar farms are often bad for biodiversity — but they don’t have to be

Every several years — sometimes just once a decade — when the rains come in just the right amounts and at just the right times, rare flowers speckle the Mojave Desert in California. Some, like the Barstow woolly sunflower, emerge from plants no larger than a thumbnail. They spring forth from seeds that have persisted in the dry soil for years, waiting for just such a sporadic event.

In these brief “super-blooms,” the desert floor looks “like a carpet of wildflowers unfurled across the landscape,” said Karen Tanner, a researcher at University of California, Santa Cruz. The quick flash of flora helps replenish the seeds for future generations.

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At other times, large sections of this deceptively fragile ecosystem look “like the moon,” Tanner said. Which, under the punishing sun, makes it seem like an ideal place to build large solar installations. Swaths of the desert, which spans four states, have already been converted to solar facilities, and more are on the way — in the Mojave and across the US. More than 4,600 square miles of land is projected to be covered by solar installations by 2030.

A massive expansion of solar electricity is a crucial part of US plans to reach 80 percent renewable energy by the beginning of the next decade. This is essential to cutting carbon emissions and slowing catastrophic climate change — which poses a dire threat to plants and animals the world over, humans included.

But the race to erect large-scale, maximally efficient solar operations could hurt local ecosystems if operators aren’t careful. Based on her research, Tanner suspects many of these solar projects as they are traditionally executed are causing more local harm than some realize. She has spent nearly a decade closely studying — often on hands and knees with a magnifying glass — experimental solar plots in the Mojave, all located within six miles of four large solar installations. Her most recent findings, published earlier this year, have noted that solar panels changed the immediate microhabitat and had a detrimental impact on rarer plants, such as the Barstow woolly sunflower.

One thing is clear to her: “It’s just not enough to do one survey in one year and be like, ‘Oh yeah, there’s nothing here. Go ahead and install the infrastructure,’” she said.

Solar doesn’t have to be a zero-sum game that prioritizes either clean energy or biodiversity, scientists told Vox. Many projects and studies are currently looking for ways that solar installations can better protect — and potentially even improve — local ecosystems, along with the bottom lines of operators and even nearby landholders like farmers. These solutions can be as simple as prioritizing native plants or picking a location that’s already been disturbed by humans.

The darker side of solar

Solar installations, on the scale needed to supply power grids, are massive by necessity, transforming the lands where they’re located into a new kind of built environment. They can alter everything from sun exposure to moisture to surface temperatures. This can have unintended and unexpected impacts on local plants, animals, and even the area’s microbiome.

Photovoltaic panels shade the land while blocking some areas from rainfall and dousing others with heavy runoff. This changes the growing conditions for plants, with implications for other connected species. The other prominent form of solar, concentrating solar — in which mirrors focus the sun’s rays — generates so much heat that it “can incinerate insects and burn the feathers of birds that fly through,” Jeffrey Lovich, a research ecologist with the US Geological Survey who studies the environmental impacts of these installations, wrote to Vox.

In areas like the US Southwest, solar installations appear to contribute to bird mortality. Scientists aren’t entirely sure why this is, but one prevailing idea, known as the “lake-effect” hypothesis, is that migrating waterfowl making their way through the arid landscape mistake the installations for bodies of water and crash into them.

Large solar facilities in particular can also fragment important wildlife habitat or migration corridors via fences and landscape alteration, and can restrict gene flow for animal as well as plant populations.

Operators of these installations are generally keen to cut the costs of construction and maintenance, so most solar facilities replace the existing land cover with graded packed dirt, gravel, or mowed grass, further harming local biodiversity. “‘Blade-and-grade’ site prep that removes all vegetation clearly has a negative effect on biodiversity,” Lovich said. He expects mowed grass would “stress plant communities and the animals that use them.”

Many of the impacts remain unknown. It’s often difficult for researchers to gain access to solar facilities and the environmental data they collect — “even though the majority of facilities are situated on publicly owned lands,” Lovich and colleagues noted in a 2017 paper.

But it’s possible to dial down the potential harms of big solar farms. The type of solar infrastructure — whether concentrated solar or photovoltaic, and whether panels are fixed or rotating, high, or low — affects the potential downsides of large-scale installations. So does the nature of the landscape itself.

How solar can help native plants and crucial pollinators

Some solar operators are reimagining their facilities as prime protected habitats for native plants, bringing back key local species and potentially improving lands that humans have already disturbed. “Solar can be a net benefit in terms of restoring a native habitat and improving ecosystem services, like storm water control and carbon storage and sequestration,” said Leroy Walston, a landscape ecologist with Argonne National Laboratory who studies the relationship between renewable energy and the environment.

One in-vogue mitigation measure is pollinator-friendly foliage. At one experimental solar installation in Minnesota, pollinator-friendly plants helped boost energy yields a tad (by making the microclimate a touch cooler) and slightly reduced long-term maintenance costs (due to less-frequent mowing), according to a 2019 analysis from the Center for Business and the Environment at Yale University. The report also noted bigger wins: The plants helped reduce erosion, increasing groundwater stores and bolstering crop yields.

Experts have brought up concerns that solar operators will use a few flowers to green the image, but not the substance, of their operations. To help prevent this, some 15 states now have pollinator-friendly solar scorecards that aim to measure the actual impact of solar projects on the crucial creatures that carry pollen from plant to plant.

“They are voluntary, but they do help solar facilities to attain an objective certification that they’re pollinator-friendly, that’s been helpful to encourage some use of pollinator habitat at solar facilities,” said Heidi Hartmann, a colleague of Walston who works as a program manager for land resources and energy policy at Argonne. For example, the California renewable electricity provider MCE is now asking its facilities on arable land to use “reasonable efforts” to hit a certain score on these pollinator tallies.

Walston calls for an even broader approach to solar — one that focuses not only on bees and butterflies, but on native habitat restoration overall. Native plants are keenly tuned to the local environment, thriving in specific climate conditions, improving soil retention, and often benefiting the widest range of other area species, in ways non-native, flashy pollinator species might not.

Hartmann and Walston have modeled the impact of switching from maintained grass to native plantings. They found that in the US Midwest, native plants would bring in three times the number of pollinators. They’d also boost the carbon storage potential of the soil by 65 percent and would be more effective, once established, at keeping weeds at bay, which could reduce the need for harmful herbicide use.

“The equation is complex,” said Alyssa Edwards, vice president of environmental affairs at solar producer Lightsource BP, about the company’s impact on local habitats. Lightsource advertises itself as protecting ecosystems and boosting biodiversity. “Pollinator habitat, considerations of seed availability, vegetation height, insurance requirements, fire risk, and cost all come into play. Not to mention that pollinator habitat may not be the right choice for all sites, as other initiatives may be more valuable contributions to sustainability.” The company, a joint venture with the oil and gas giant BP, says it’s working on various solar projects that incorporate pollinator habitat, conservation of short-grass prairie land, and even animal grazing.

Wildlife corridors are another way solar installations could help support biodiversity. But for large sites to become a part of corridors, they may require substantial adjustments to fencing and other built infrastructure (and even then, they’d probably pose barriers to some larger species).

As more sites incorporate biodiversity as a benchmark, the devil is in the details. Tanner and others have found that solar panels can actually increase the number of plant species that grow beneath them, especially in harsh environments like the desert. However, some of these additional species are invasive or threaten to outcompete the smaller, rarer native ones that could tolerate such extreme desert conditions.

These kinds of wrinkles make it all the more important that scientists and operators actually measure their impact on ecosystems — that they’re “pausing for a moment and considering what sort of species we are considering that are making up the diversity,” Tanner said.

Build solar on lands that humans have already messed with, one expert says

Solar operators tend to look for new sites based on sun and climate conditions, but also proximity to the existing power grid — and a utility company in the market for their energy. Scientists told Vox that firms should also look for places that humans have disturbed, because the local ecosystem may have less to lose.

Lovich suggests siting more solar farms on “brown fields, roof tops, abandoned agricultural fields, dry lakes, and even airports — where wildlife are unwanted.” They’re also well-suited for canals and human-made reservoirs, where they’re sometimes called “floatovoltaics,” not least because they can slow water loss by evaporation. These less-conventional arrangements may have higher up-front costs, but the eventual environmental costs will be lower.

Building on an ecologically sensitive site can also be costly. Take for example BrightSource Energy, which spent at least $56 million relocating threatened desert tortoises from its Ivanpah solar development site in the Mojave Desert. Although these efforts allowed the project to go through, scientists are still learning about the consequences. An early study found that the relocated tortoises needed more time and effort to settle into normal movement patterns, potentially exposing them to additional threats. But as Lovich pointed out, “since tortoises are long-lived, results for the long term are not yet available.”

Such experiences have not deterred other desert sun-seeking operations. “Solar farms are operating or planned in excellent tortoise habitat affecting hundreds to thousands of tortoises,” Lovich said. Simply moving the tortoises — pricey as it may be — is not a sure cure. “Translocation has a checkered history of success,” he said.

Lovich is currently studying the impact of the Gemini Solar Project in Nevada, which would cover 11 square miles of publicly owned tortoise habitat and is home to hundreds of these long-lived, vanishing animals. For this project, the plan is to capture the animals, place them in a holding center for up to two years during construction, and then release them into the facility grounds “to see how they fare,” Lovich said.

“All energy sources will come with a cost to some wildlife,” Lovich and his colleagues noted in a 2020 paper. “The best mitigation strategy is to avoid developing sensitive and pristine areas.”

Other landscapes would not only tolerate solar farms, but could benefit from them. For example, a pollinator-friendly solar installation could add yield for farmers whose soy, citrus, almonds, cotton, or alfalfa needs some pollination help. More than 500 solar facilities already exist within easy buzzing-distance — less than a mile — from these crops in California, Massachusetts, and North Carolina, respectively, according to a 2018 study by Walston, Hartmann, and their colleagues. Nationally, more than 1,350 square miles of cropland would benefit if existing solar installations added pollinator-friendly plants, they concluded.

As solar has moved into lands that could otherwise be farmed, it has caused some tension with local residents. But solar farms and actual farms don’t necessarily need to be in opposition. It’s possible to co-locate solar and crops into “agrivoltaic systems,” which can feature grazing grass, corn grown for biogas, and even lettuce and tomatoes that may flourish under solar panels. Other crops could even be grown under semi-transparent solar panels.

Solar can protect plants and animals while it helps the planet

Redesigning solar developments — and steering them to the places where they won’t cause harm — isn’t easy. Maximizing energy output means finding locations with the right combinations of sun, temperature, wind, and humidity (one study pegged the best spots as croplands, grasslands, and wetlands) and packing solar-harvesting devices as densely as possible. All of these often work at cross-purposes with supporting a diverse range of plant and animal species.

Additionally, permits for these facilities are typically done at a very local level. (President Barack Obama had instructed these sorts of projects on federal lands to have a mitigation strategy — an order that President Donald Trump struck down his second month in office.) So it’s a patchwork of different levels of regulations and approval processes, some of which are more in tune with thoughtful evaluation of sites and long-term impacts. There is “more education that can be done at local government levels,” Hartmann said.

Without more thorough before-and-after research, we may remain in the dark about how these large facilities are changing the landscapes they cover. If site evaluations are performed over a relatively brief period of time — such as a single season in the run-up to the construction of a solar farm — operators could easily miss key aspects of biodiversity, like the Barstow woolly sunflower, which waits for just the right pattern of rare desert rain to emerge.

“We’re just starting to scratch the surface and determine how different organisms are likely to respond” to solar, said Tanner, the UC Santa Cruz researcher. For now, it behooves us to mess with their environment as little as possible, she noted, and to preserve as much as we can. “Especially in a context of climate change, we don’t know what species are going to be able to pass through that aperture in the future.”

As the world barrels toward climate catastrophe, scaling up carbon-neutral energy production as quickly as possible couldn’t be more urgent. “We need all the help we can get, and we need to move quickly,” Tanner said. On a planetary scale, clean electricity can help safeguard all species, and could arguably be worth the trade-off if it harms a few local species in the process.

But maybe there doesn’t need to be a trade-off, Tanner suggested. “I’m not sure it’s an either-or question,” she said.