Solar panels might be good for cities — but what about the plants living underneath?

Nestled between the Great Basin and the Sierra Nevada mountains, the Mojave Desert is a harsh environment and the plants that thrive there work hard to survive. For many, the key to success lies in microhabitats, or tiny spaces where they can get more of the resources they need — especially water.  The difference between population booms and busts, may be as simple as germinating in the shade of a solar panel.  

In the wake of solar expansion across the desert, a group of researchers from UC Santa Cruz and UC Davis set out to understand how solar infrastructure impacts the populations of two desert annuals: the common Eriophyllum wallacei and the rare Eriophyllum mohavense, which is only found in a small range in the central Mojave Desert on gravel soils in the central Mojave Desert on gravel soils. They represent a small fraction of the floral diversity in the Mojave that may be impacted by solar development. Their study was published last April in the journal Ecological Applications.  

These plants are minute and tend to go unnoticed unless one takes observation to a whole different level — something solar developers rarely do. “They are belly-plants,” said lead researcher and plant ecologist Karen Tanner. “You have to lay on your belly on the dirt to see them.” Their small stature poses difficulties for those assessing the ecological impacts of potential solar infrastructure.  

Population responses to solar panels were mixed  

To test how this pair of woolly daisies respond to solar infrastructure, the team of researchers constructed experimental solar arrays which create two different microhabitats: a shaded habitat under the panel and a small area next to it where rain flows off.  

The experiment ran from 2011–2018 and included the extreme drought event of 2012. This was such a dry year that, according to Tanner, no annual plants grew — not even exotic invaders. It also included a super bloom in 2017 where the sites received nearly 90% of the average water — a blessing after the years-long drought.  

In the drought years, the shade from the solar panels provided some relief for the rare E. mohavense. Tucked away under the protective covering of the panel, more seeds germinated and plants flowered. But 55 km away, where E. wallacei lives, researchers found fewer plants under the panel than in the unmodified, adjacent control plots. E. wallacei seems to prefer sunbathing since researchers found less plants under the protective structure. 

During times of high rainfall, the shade of the solar panels did not benefit either species. According to Tanner, this may be due to increased competition in the shade where other plants create a carpet of plants and escape from the desert heat. However, both species thrived in the run-off zone below the sloped panel, benefiting from the extra moisture.  

“The findings are very nuanced,” explained Tanner. The effect of solar infrastructure is dependent on the species, site, and the year, making these findings difficult to generalize. “We won’t know the impact unless we do studies like this,” she said.   

The desert may not be the right place for solar panels  

The desert is a deceiving environment for solar facilities that hope to minimize ecological damage. At a first glance, arid lands like those the researchers studied might be ideal for this type of infrastructure because of the apparent lack of life, but the ecosystem, and its inhabitants, can change dramatically. Depending on the weather conditions, some species may not be visible when the development begins.  

“In an environment like the Mojave, just because you may not see [a plant] doesn’t mean it isn’t there,” said Tanner. Even when the desert looks barren, tiny belly plants might be hiding in the microhabitats.  

Now the question is, how do energy companies balance the need for green energy without harming delicate ecosystems? According to Tanner, one solution is to build solar plants in areas of the desert that are already degraded to minimize the impact; or move towards rooftop solar near large populations.  

Shawn McCoshum, a biological consultant for energy companies who wasn’t involved in this study, believes the Mojave isn’t the ideal environment for solar facilities, despite the open land and abundant sun. He argues that, because urban areas are growing faster than we can produce solar energy, we should focus on developing solar technology, like rooftop solar panels, within the urban environment. “If we simply put solar panels for urban expansion on new businesses, we would be able to completely step aside from solar farms,” he said.   

Still, the effect of solar panels on plants like the woolly daisies deserves further research. According to McCoshum, despite the existence of plants under solar panels, few solar farms emphasize conserving the existing plant communities, so at this point, understanding the effect of solar panels on plants is theoretical. “When you look at the solar facilities from Google Earth or drive up to the panels, you can see nothing is under those solar panels except for dirt,” he said.  

As the world hastens to move away from fossil fuels, we need to consider the impacts of where we are placing new energy infrastructure. The tiny plants living near the panels may adjust to new microclimates or they might not. Tanner said that the main takeaway from their study is that we don’t know enough about how solar infrastructure impacts desert plants. Having insufficient information makes it difficult for land managers to devise conservation strategies that protect sensitive species from solar development. For the time being, both researchers and practitioners agree it is best to continue to developing solar infrastructure on disturbed land and urban environments. 

Brianne Palmer is a Ph.D. student in the joint ecology program at San Diego State University and University of California, Davis. Her research focuses on how soil microbes recover from disturbance and the role of microbial communities in restoration. She is passionate about science communication and about raising awareness for plants and soil. You can find her on twitter @briecology.