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In the gentle shade of solar panels, desert restoration gets an unexpected leg up

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In the gentle shade of solar panels, desert restoration gets an unexpected leg up

Delicate biocrusts are used to restore drylands; instead of cultivating them in high-tech greenhouses, researchers are growing them under solar farms.
April 25, 2023

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Sprawling solar farms could pull double duty as nurseries growing microscopic plants to help restore deserts and other dryland ecosystems, according to a new study. Researchers say the approach could benefit ecosystems, public health, and solar power’s bottom line alike.

Biocrusts are communities of cyanobacteria, algae, lichens, and mosses that form a thin layer at the surface of dryland soils, fertilizing the soil and protecting it from eroding or blowing away as dust. They’re easily trampled and can be damaged or destroyed by development, agriculture, and other human activities—and can take decades to recover on their own.

To restore degraded dryland ecosystems, people are looking to help regenerate biocrusts. But growing biocrusts in laboratories or high-tech greenhouses is costly and labor-intensive, enabling restoration of only small areas.

Enter solar farms: rows upon rows of solar panels that provide partial shade and more moderate temperatures—in other words, conditions similar to those in greenhouses for growing biocrusts, researchers from Arizona State University in Tempe argue in a paper published in Nature Sustainability. What’s more, solar farms are often located in drylands, conveniently right near areas where biocrust restoration is needed.

 

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To gauge the potential for solar farms to serve as biocrust nurseries, the researchers assessed natural biocrusts under at a solar installation in Mesa, Arizona. Solar panels double the biomass and triple the coverage of biocrusts compared to nearby patches of exposed soil, they found.

The researchers removed biocrust from some areas under the solar panels and monitored it as it grew back, to assess the potential for “harvesting” biocrusts to be transplanted to restoration sites. Without any other intervention, the harvested area can grow back its natural biocrust within 6 to 8 years, they found.

But a little head start from humans will speed things along. The researchers tested the ability of 5 different mixtures of local biocrust microorganisms to accelerate biocrust recovery. If just 10% of the harvested biocrust is used to inoculate the harvested area, the biocrust will recover within a year or two, they report.

This isn’t as fast as more intensive growing techniques, and the regrown crusts are less biodiverse than the originals, the researchers acknowledge. But the approach has the potential to scale biocrust restoration way, way up for relatively little effort. Humans only have to harvest the biocrust and re-inoculate the harvested areas; the solar panels do the rest.

“Our work suggests a continuous, low-tech, low-impact operation for solar farms as sustainable sources of biocrust inoculum, in which one can do away with work-intensive, specialized nurseries by simply re-investing part of the biocrust harvest as a boost to natural recovery processes in the areas harvested,” the researchers write.

For example, growing biocrust at the three largest solar farms in Maricopa County in central Arizona could provide enough biocrust to treat all of the county’s unused agricultural land within 4 to 5 years—in turn easing a major public health hazard that has emerged from blowing dust.

“Crustivoltaics,” as the researchers dub their method, by analogy with agrivoltaics or growing crops under solar panels, could also be a boon to solar farm operators. Stabilizing the surrounding soil would reduce dust deposition on solar panels and therefore increase their power output. Biocrusts are composed of photosynthetic organisms that fix carbon, so solar farms might also be able to claim carbon sequestration credits—perhaps on the order of US$300 per hectare, the researchers estimate.

Source: Heredia-Velásquez A.M. et al.  “Dual use of solar power plants as biocrust nurseries for large-scale arid soil restoration.” Nature Sustainability 2023.

Image: © Anthropocene Magazine

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