Solar for dryland soil health

Soil is a lot more than just dirt; healthy soil contains many nutrients and microorganisms that maintain the foundation of an ecosystem. In arid and semi-arid climes, soils are loaded with biocrusts, which are communities of living organisms that perform important functions in ecosystem management.

Biocrusts are made up of cyanobacteria, green algae, fungi, lichens, and mosses, forming a thin layer on the surface of soils in deserts and other dry biomes. Drylands cover roughly 40% of the continental Earth.

Human activity, including agriculture, urbanization and off-road vehicle use are degrading dryland biocrusts, harming these fragile environments. Biocrusts are increasingly being pressured by climate change, as well, as increased heat is making it difficult for the microorganisms to survive.

Arizona State University (ASU) professor Ferran Garcia-Pichel and his research team have proposed to use solar arrays as a solution to the problem of excess heat and light, creating a shaded nursery to promote biocrust growth. A report on the subject was published in Nature Sustainability.

Beneath the panels, biocrust development can be encouraged, and these organic materials can be moved to areas where damage has occurred, said Garcia-Pichel. The ASU team has dubbed the practice “crustivoltaics.”

“This technology can be a game changer for arid soil restoration,” said Garcia-Pichel. “Crustivoltaics represents a win-win approach for conservation of arid lands and for the energy industry alike.”

The researchers performed a proof-of-concept experiment in the Sonoran Desert, studying biocrust growth for three years. During the study, the PV array promoted biocrust formation, doubling biocrust total biomass and tripling its coverage area when compared to open areas with similar soil characteristics. Natural recovery of harvested biocrusts can take six to eight years to recuperate without intervention, but re-inoculated areas under the solar panels were able to nearly fully recover within one year.

The study estimated that adding crustivoltiacs to the three largest solar facilities in Maricopa County, Arizona could aid the rejuvenation of all idle agricultural lands within the county, spanning more than 70,000 hectares. The research group said a small enterprise could accomplish this in the span of five years.

Among the many ecosystem and agricultural benefits, the restoration project could potentially significantly decrease airborne dust that impacts the Phoenix Metropolitain area. The practice could also benefit solar asset owner and operators by reducing soiling on panels and increasing the value of carbon mitigation credits generated by the site.

Garcia-Pichel is a Regents’ Professor in the School of Life Science and the founding director of the Biodesign Center for Fundamental & Applied Microbiomics. The Center brings together researchers that study of microbiomes acting in unison in various settings, from humans to animals and plants, to oceans and deserts.

Biocrusts offer many ecosystems services. For one, they stabilize soil by binding particles together, mitigating topsoil loss from wind and water, and they increase the soil’s water retention, reducing runoff, which can be a problem for some PV plants in arid climates.

Biocrusts also aid nutrient cycling by converting atmospheric nitrogen into ammonia for use by plants. And they perform photosynthetic activities, removing carbon dioxide from the atmosphere. They also contribute to overall ecosystem biodiversity and resilience.

While biocrust development can be done more rapidly in a greenhouse, the technique requires fewer resources, minimal management, and requires no upfront investment. The team modeled that the crustivoltiacs method is less expensive by four orders of magnitude when compared to conventional greenhouse methods.

The next step for Garcia-Pichel and his team is to implement the practice at regional scales through the coordination of scientists, collaborative agencies, land users and managers.

“For the first time reaching regional scales at our fingertips, and we could not be more excited,” said Garica-Pichel.