Threading the Solar-pollinator Needle
Susan Opperman, associate scientist, Environmental
May 10, 2021
Aerial photos of utility-scale solar energy projects often depict arrays of dark, glossy panels standing over sand or gravel. But the antiseptic landscapes long associated with solar installations are increasingly giving way to vibrant canvases of wildflowers, grasses, and other plants.
This developing approach to solar vegetation management can complement and amplify the environmental benefits of solar energy. A vegetative landscape combats soil erosion, conserves moisture, sequesters carbon, and sharply reduces applications of fertilizer and pesticide. In addition, diverse plant communities support pollinators – bees, butterflies, and other critical species – that are in widespread decline. Adding pollinator habitat to solar sites works particularly well in the central United States, where prairie vegetation once dominated the landscape before being substantially eliminated by row crop agricultural development.
Establishing habitat that benefits both pollinators and solar projects, however, requires more than turning soil and broadcasting seed. It necessitates introducing the right plant species and management regimes while simultaneously controlling the costs tied to habitat development and maintenance. In fact, an examination of scientific literature reveals that some seed mixes specifically marketed for pollinators carry the highest price tags while yielding few overall benefits.
For a recent solar project, we proposed a solution that aims to thread the solar-pollinator needle more perfectly.
The problem: One of our clients requested that vegetation beneath the solar panels grow no taller than 18 inches, the height of the lowest edge of the panels, to avoid shading – an obvious issue when converting sunlight into electricity.
Our review of commercially available mixes marketed for solar projects failed to locate a product that would meet this height requirement while still providing the plant species shown to most benefit pollinators. We found no commercial mix with native or naturalized plant species that grow shorter than 30 inches, let alone 18 inches. Also of concern, some mixes marketed to solar facilities were found to contain invasive species.
Many mixes that simply combine the most readily available grass and wildflower species do not meet the height prescription because many such species evolved to grow tall on open prairie landscapes. In addition, a solar array results in a non-homogenous light environment. Some areas are sun-splashed, while others fall in shadows, which means the ideal seed mix should include shade-tolerant species.
The solution: We designed a custom mix of seed that strikes a balance. It aims to satisfy our client’s maximum height requirement while also providing vegetation beneficial to pollinators.
Within the footprint of the arrays, the planting regime calls for a mix of cultivars that have been bred to grow shorter. The mix includes naturalized species, which, though non-native, have been present for many decades and are well-adapted to regional soil and climatic conditions. White clover is a prime example of a naturalized species that grows short while being readily utilized by pollinators.
Conversely, the perimeter buffer areas surrounding the solar arrays are perfectly suited for taller-growing grasses and wildflowers. The seed mix we created includes such native species.
All species selected for the mix will establish quickly and put down long, strong root systems. This helps further reduce maintenance costs by crowding out weeds, controlling erosion, and holding more moisture and nutrients in the soil. In addition, the custom mix includes species that produce abundant pollen and nectar for pollinators, helping to address an ecological problem with potential implications for food security and biodiversity.
A groundbreaking assessment in 2016 estimated that between $235 billion and $577 billion in global food production relies directly on pollinators – roughly one-third of the global food supply.
Maintaining pollinator habitat on the land surrounding solar projects produces more than good public relations, it produces myriad benefits that are strongly supported by research. For my master’s thesis, I researched the correlation between habitat restoration and pollinator populations, which showed that even micro-plantings of habitat in urban settings – just a few square feet – quickly helped improve the abundance, diversity, and long-term persistence of pollinator species.
Establishing pollinator habitat on solar project sites produces tangible ecological benefits. And doing so does not have to result in dramatically higher maintenance costs for project owners – as long as they start with the right seed mix.
Susan holds a master’s degree in sustainable natural resource management from Unity College. In her role at Olsson, she produces biological studies, environmental surveys, and permitting for energy, transportation, land and facilities, and government markets. She can be reached at 402.938.2414 or email@example.com.