Argonne demonstrates benefits of restoring native vegetation at solar facilities

Trying to find some common ground between biodiversity, food production and renewable energy, researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory are helping facilitate the development of agrivoltaic systems — the restoration of native plants on large solar facilities.

The results are encouraging.

Over the past few decades, government agencies, research facilities and private landowners have been working to restore native plant habitat, where practical, in an effort to positively impact ecosystem services — the benefits we get from different parts of the natural environment. Advantages include bolstering soil fertility, water retention and carbon storage, and attracting wildlife that play an important role in pollinating vital plants and crops.

“All indicators are that solar development will continue to accelerate over the next ten years and beyond, so the more environmentally friendly we can make the solar facilities, the better for the industry, agriculture and conservation.” — Heidi Hartmann, Argonne environmental scientist

A recent collaboration between Argonne, the University of Minnesota and DOE’s National Renewable Energy Laboratory assessed how these ecosystem services could be affected by reinstating regional native vegetation at solar facility sites throughout the Midwest.

In 1673, when French explorers Louis Joliet and Jacques Marquette navigated the Mississippi River and several of its primary arteries, including the Illinois River, much of the area was part of a 1,000-mile stretch of tallgrass prairie that ran from Indiana west to Oklahoma.

In his history of Chicago, The City of the Century, author Donald L. Miller noted that the prairie grass was so high that the travelers barely noticed the bison grazing nearby. Marquette wrote of the landscape, “We have seen nothing like this river (the Illinois) that we enter, as regards its fertility of soil, its prairies and woods; its cattle, elk, deer, wildcats, bustards, swans, ducks, parroquets, and even beaver.”

Since then, 99 percent of that prairie has disappeared, and many of the native animal species with it, replaced primarily by agriculture over the ensuing centuries. Today, 37 percent of the Midwest, which covers about 1.1 million square kilometers, remains agricultural land.

The collaboration’s study, published in a recent issue of Ecosystem Services, examined all of the existing solar facilities in the Midwest that were possible to map, based on land-cover data sets that go back to the early 2000s. Of the 276 operating sites identified, 70 percent were on former agricultural parcels, the majority of them — 163 — in Minnesota.

Siting utility-scale solar facilities on agricultural land has become a popular trend as the properties represent flat, open areas unimpeded by trees and urban development. But with steady growth in the solar energy market, there is some concern as to whether solar sites will compete for agricultural space.

“One of the reasons we did this study was because in the Midwest and other agricultural areas, there’s this pushback that solar is going to take away prime farmland,” says Argonne’s Lee Walston, an environmental scientist and lead author of the journal article. “If we can show that solar can be compatible with, or at least benefit, the remaining farmland in that area, we hope it will alleviate some of those concerns.”

The group also wanted to address whether solar facilities negatively affect soil. The general consensus among scientists, says Walston, is that they don’t. And, as it turns out, the addition of pollinator habitat is beneficial because the root systems of native vegetation stabilize soil and reduce erosion.

To better assess this and other potential benefits, the researchers employed the Integrated Valuation of Environmental Services and Tradeoffs (InVEST) modeling tool that compares different land-use designs and how they affect various ecosystem services.

“A primary utility of InVEST is that you can spatially visualize the effects of different land uses on the ecosystem services we were looking at, such as water retention, soil erosion, habitat quality for pollinators and carbon storage,” says Walston. “It’s a nice way to look at trade-offs in different land-use designs.”

For this study, researchers fed information on 30 solar developments into the model and changed the land-cover data to one of three scenarios: a pre-solar, agricultural site; a solar facility with just turf grass; and a solar facility with native grassland.

They also incorporated other parameters into the model, such as historically derived climate data and published scientific data, including comparisons between the carbon storage capacity of residential turf grass, forests and native grasslands.

“We found the scenario that incorporates pollinator-friendly vegetation, the native grassland scenario, performed the best in terms of the four ecosystem services we were evaluating,” says Heidi Hartmann, an Argonne environmental scientist and paper co-author.

The study also validated a number of earlier findings from across the Midwest that used similar InVEST models, each showing that the native grassland scenario improved benefits to the ecosystem.

A Minnesota study conducted in 2012 showed that native grasslands maintained nearly 60 percent more carbon than agricultural land use over a prescribed amount of land. This current study suggests a similar increase in carbon storage between the two land-use scenarios across the new study’s facility sites.

“If done across an entire site and the vegetation establishes well, this may be coming close to restoring the land’s natural carbon storage potential,” says Hartmann.

In addition, the researchers reported that native grassland habitat produced a three-fold increase in habitat for local pollinators, like bees and butterflies, over purely agricultural usage, as well as increases in soil and water retention of over 95 percent and 19 percent, respectively. Increasing the number of pollinator insects could prove beneficial to surrounding agriculture as they could help fertilize local crops.

The paper also projects “the potential benefits of adopting native grassland management practices in current and future solar energy buildout scenarios,” with similar results.

For example, the models predict that native grasslands at all future solar facilities in the Midwest could increase the total carbon storage capacity by over 1.5 million tons of carbon compared to agricultural baseline estimates. This is equivalent to offsetting the CO₂ emissions from over 5,000 gigawatt hours of electricity generated from coal-fired power plants — enough to power 500,000 homes, annually.

Planting native vegetation at solar facilities will never restore the biodiversity witnessed by Marquette and Joliet, but the team is starting a three-year project to determine whether other wildlife, such as birds and bats, are attracted to and utilize the habitat established at solar sites.

“All indicators are that solar development will continue to accelerate over the next ten years and beyond, so the more environmentally friendly we can make the solar facilities, the better for the industry, agriculture and conservation,” says Hartmann.

This project is funded by DOE’s Solar Energy Technologies Office.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.

The U.S. Department of Energy’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science.