Build for a sustainable match

by Sally Colby

Solar power is one of the fastest-growing segments of renewable energy – it’s hard to find an area that hasn’t had some degree of solar development. While interest in solar is growing, there’s limited space for roof-mounted solar systems. Such systems provide ample kW production for one farm, but there is a growing need for large-scale ground-mounted solar systems. Preparation for ground-mounted systems is a costly segment of the overall project, and usually results in some level of disturbance to the existing ecosystem.

“The Department of Energy anticipates that by the year 2020, one-fifth of all installed solar costs will be just for site preparation to remove vegetation,” said Jordan Macknick, energy and environmental analyst at the National Renewable Energy Lab (NREL).

The installation and construction phase for ground-mounted solar typically involve disturbance of topsoil and vegetation removal using heavy equipment, followed by the ongoing need to maintain the ground under the panels. Proposals by solar companies to farmers are often met with strong resistance from the non-ag community who cite negatives including the loss of agricultural production, topsoil disturbance, runoff and disturbance of native species.

“What we’re exploring is how we can remove the need for heavy machinery and getting rid of vegetation to reduce site preparation costs and find a way to promote solar development that encourages vegetation and co-location with agriculture operations,” said Macknick.

Macknick discusses the concept of low-impact site preparation. Rather than clearing the growth, existing vegetation is left intact or replaced with low-growing native vegetation species or crops. Existing topsoil is left in place to allow native vegetation and to promote soil health after decommissioning. When possible, natural land contours are worked into the design to minimize or eliminate grading. The NREL has been working on a variety of projects to determine whether the ground under solar panels can be used for livestock grazing or crop production.

“With low-impact site preparation, we want to leave the existing vegetation and encourage low-height native vegetation and preserve the soil,” said Macknick, “and, if we can, also improve the soil quality of the land by use of different vegetation such as legumes for nitrogen content. We think we can also reduce the total land footprint and other land impacts as well as improve stormwater management of those sites.”

Macknick described three categories of low-impact solar development: solar-centric, vegetation-centric and co-location/co-optimization. “The solar-centric approaches require minimal changes to the solar configuration,” he said. “We find ways to include vegetation without affecting the solar operation. In the vegetation-centric approach, it’s the opposite – there are no changes to the vegetation or agricultural operation, and we find ways to incorporate solar without affecting vegetation or ag operation.”

The co-location approach optimizes both solar configuration and vegetation management. Macknick said this approach requires unique and innovative science and solar technology as well as vegetation or ag practices to result in a project that works for both the solar company and the landowner. Projects that incorporate livestock grazing or vegetable crops grown under the panels benefit the landowner by providing additional revenue.

Macknick said co-location can potentially eliminate the need for heavy machinery required for vegetation removal and site preparation. This can also significantly reduce site preparation costs.

While farmers often look solely at the income they’ll receive from the solar company, the benefits of co-location go far beyond the check. With appropriately sited structures, landowners can graze livestock on acreage where solar panels are installed. Panels afford ample shade and cover for livestock, and the fencing provided by the solar company is suitable for nearly every livestock species. Sheep are often used for managing vegetation under solar arrays, and cattle are also suitable grazing partners. Farmers can also choose to establish native species under solar panels to encourage pollinator species for crop pollination.

In a project at UMass, agronomist Dr. Stephen Herbert grew vegetable crops under solar panels. The solar array was established as a series of elevated panels with varying space between the panels. The project included research on how agricultural crops performed under the panels, especially in regard to various levels of shade throughout the day related to height and panel spacing. Herbert planted vegetable crops including broccoli, kale, beans, Swiss chard and peppers under solar panels, and found that crops performed and yielded well.

Macknick is optimistic about the prospect of incorporating solar and agriculture to benefit both farmers and solar companies. “It’s very encouraging for the co-location of agriculture and solar on a practical basis,” he said.

“We would like to see more solar projects to incorporate vegetation, to co-locate with agricultural operations in such a way that it benefits soils and ground cover as well as meeting all the needs of the solar industry,” Macknick said.

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