- June 18, 2024
- Perspectives
How to Preserve Topsoil and Native Plants at Solar Sites
Anna Lundin
Energy Practice Lead
Amanda Miller
Environmental Scientist
Soil—and more specifically, topsoil—is an integral element of holistic solar site design. The importance of topsoil is threefold: soil is arguably the most important factor on a solar site in regard to carbon sequestration, revegetation success, and site stability. Read more about how to preserve topsoil and leverage its nutrients for native plant restoration.
Assessing Topsoil from the Start
A gram of topsoil can contain over 50,000 species and is the most important biological characteristic of a development site. Potentially encompassing nearly 2 million acres in the US by 2030, utility-scale solar installations have traditionally relied on topsoil and plant removal to prepare the land for energy infrastructure. As experts identify better ways to enhance the multi-use functions of sites, low-impact development of solar installations is gaining traction. With this type of installation, developers retain and even enhance the pre-existing topsoil and native plant communities post-construction.
While there are many exciting opportunities to develop energy installations while retaining topsoil, the quality of the soil will vary depending on the characteristics and past life of the site. For instance, abandoned and often contaminated sites called brownfields may host soil contamination that prohibits rehabilitation without additional efforts. Because of these considerations, topsoil assessments are essential to determine soil quality and its capacity to support future plant growth.
After the buildable area of a site is determined, site experts can conduct topsoil assessments and a vegetation survey in tandem with other site analyses. The topsoil assessment should pinpoint field texture and report metrics for soil qualities, including pH and the presence of organic matter, nutrients, and salts. Additionally, the vegetation survey captures maps of plant types, health, productivity, and root mass along with non-native (noxious or invasive) species that may be present. Native plant root distribution can provide information on soil moisture and other characteristics, allowing stakeholders to make decisions on the land’s multi-use potential to support agrivoltaics, habitat preservation and enhancement for native wildlife, or other functions. These two analyses together provide a vivid picture of topsoil health and the site’s multi-use potential.
Preserving Topsoil through Tailored Grading
After reviewing the results of the topsoil assessment, solar site designers should create a low-impact grading plan. Preserving the most high-quality topsoil through targeted site grading helps maintain a native seed bank and root mass—which is more effective for stormwater management and water conservation than using imported seed, turf grass, or gravel.
Site designers can develop a low-impact grading plan by identifying areas with high-quality topsoil that should be avoided and passing on this information to the construction team to be incorporated into construction design and planning. Additionally, to allow native plants to flourish in the topsoil, the team can strategize how to remove non-native, undesirable plants and maintain weed-free areas after construction for the reclamation of desirable, native plants.
Site designers understand that grading and compaction is necessary for many site areas and must acknowledge that topsoil cannot always be preserved in its natural state. Where this is the case, teams can recover topsoil by implementing best management practices, such as the following, into integrated construction plans for the site:
Coordinate topsoil stripping to minimize exposed territory and then ensure quick transfer of the recovered topsoil to a storage location.
Avoid recovering wet or dry topsoil; instead, recover moist topsoil to preserve its natural texture.
Maintain topsoil in shallow piles at a weed-free storage location.
Keep recovered topsoil for less than a year and check it regularly for stability, seed bank, and seed viability.
Within a few days of seeding, return the topsoil to the site and avoid using excessive mechanical interventions to make it even.
Planning for Native Species Restoration
Whether a brownfield is being converted to a brightfield, a solar site is being restored post-construction, or sites are being decommissioned after their lifecycle, restoration of native plant communities helps the soil and overall land to thrive. Because of this, restoration plans that include topsoil management and native plant revitalization should be included alongside every project.
Firstly, restoration plans should delineate seedbed preparation methods, along with a timeline for when each stage of the process should be completed. Some considerations for seedbed preparation include standards for soil compaction, low-impact procedures, and specifications for the types of equipment to use—like disks, tillers, or harrows.
Additionally, unmixed native and/or cultivar seed mixes are recommended for purchase from local or regional suppliers. In the end, both individual species seeds or seed mixes should ultimately be weed-free and have a high germination rate that has been recently tested. Some best practices for seed purchasing are as follows:
Where possible, work with local seed providers with experience providing seeds for the region.
Plan for seed orders about four months before planting is scheduled, and order seeds about three months before planting.
If possible, purchase Pure Live Seed (PLS) over bulk seed orders; PLS is expected to germinate, while bulk seed orders may contain both viable and inviable seeds.
Obtain seeds in the original bag with a Certified Seed Blue Tag to verify purity and adherence to seed standards when possible; reject seeds that state “variety not stated,” “seed from a certified field,” “no tags available yet,” or “just as good as certified.”
Affirm that the seed tags and bag labels are accurate and that there is a complete analysis label on the bag and a recent germination test completed by an accredited laboratory.
Based on grading, topsoil, and season, various seeding types can be used to reintroduce native plants to a site. After seeding, site designers can implement best management practices to encourage topsoil stability and support germination, such as utilizing certified weed-free hay, bonded fiber mats, or other mulch types.
In terms of benefits, the soil moisture redistribution that occurs when native plants are restored can limit erosion and improve stormwater management. Additionally, aiming to restore native plants within the active or decommissioned site increases pollinator presence and biodiversity.
Prioritizing topsoil preservation and native plant restoration may add additional planning and design layers to a solar plan up front, but the impacts to the environment and to site potential far outweigh the initial investment.
About the Authors
Anna Lundin
Anna is an Energy Practice Lead with more than 23 years of experience siting and permitting energy projects throughout the West. With a background in environmental engineering, she has supported the development of strategy, management, and preparation of large, complex environmental impact studies and permitting projects for a range of state, federal and international agencies. Anna previously supported the Council of Environmental Quality and assisted in environmental policy development in Washington DC, but she has been Colorado-based for the past 17 years. In addition to her current role at Kimley-Horn, she serves as a Colorado Director for the Women of Renewable Industries and Sustainable Energy nonprofit and is passionate about energy transition in the West.
Amanda Miller
Amanda has more than 16 years of experience as a project manager and subject matter expert supporting energy developments throughout the continental United States. As a biologist and permit specialist, she has extensive experience coordinating with local, state, and federal authorities to gain necessary environmental permits for regulatory compliance. With a history of technical consulting experience on complex renewable and power delivery projects, Amanda has a portfolio of creative solutions to offer clients.