Letting the sunshine in and monitoring stormwater runoff
As the buzz around renewable energy grows louder, a research endeavor led by the Water Center at Penn exemplifies of how addressing energy demands goes hand-in-hand with tackling water challenges.
By Xime Trujillo
On both traditional and solar farms, sunlight gets converted into usable energy. Utility-scale solar arrays, however, can impact the local water cycle in ways that are quite different from a traditional agricultural field. Imagine rain falling on the impermeable surface of photovoltaic (PV) cells dotted across a field: One can easily grasp that the rain will converge and drain differently in that landscape compared to a field of wheat or corn, with potential impacts on soil moisture, stormwater runoff, and groundwater recharge.
However, thoughtfully designed solar arrays that incorporate sustainable stormwater management practices can mitigate the potential impacts of PV development. Given that transforming sunlight into electricity is an important strategy for addressing the climate crisis and enhancing energy security, investigating solar farms’ stormwater runoff and identifying monitoring strategies is crucial for a sustainable future.
In answer to this need, the Water Center at Penn, in partnership with Keith VanDerSys, senior lecturer at the Weitzman School of Design, Alain Plante, professor in the Department of Earth and Environmental Sciences, and Nuo Chen, a second-year student of the Master’s in Environmental Studies program, are using support from the Environmental Innovations Initiative’s PPA Renewable Energy Research Program to assess stormwater runoff at central Pennsylvania solar energy facilities operated by AES that supplies the equivalent of approximately 70% of Penn's campus electricity.
From farm to solar farm and back
Stretching over 2,000 acres of land, AES’ Great Cove Solar facility produces approximately 420,000 MWh. “The scale of the PPA solar farm is striking,” says Emma Denison, communications and student manager at the Water Center. “It was hard to picture in my mind until I stood there.” Before becoming a large-scale solar array, the site was farmland, she says, so one of the goals of “a long-term stormwater monitoring protocol is to ensure that after harvesting solar power for over two decades, the site can return to its previous land use.”
In 2023, Great Cove went operational “following county stormwater management standards,” says Brenton McCloskey, the Water Center’s director of strategic development and communications. The site incorporates intentional design choices to help manage stormwater, including a fully vegetated landscape beneath the panels, rain basins to protect power substations critical for transforming and transporting electricity, and trackers that adjust the panels’ direction following the sunlight throughout the day rather than having them at a fixed tilt. Furthermore, AES installed soil amendments that enhance rainwater infiltration and prevent flooding. “Layers of different materials constitute these amendments; they have a crispy texture when you step on them, and precautions are in place to avoid compaction,” notes Chen.
In addition, AES also put in place plants that attract pollinators and facilitate infiltration, including creeping red fescue (Festuca rubra), hard fescue (Festuca ovina), Kentucky bluegrass (Poa pratensis), white clover (Trifolium repens), and oats (Avena sativa). To maintain the vegetative cover, the site also hosts sheep that graze the project area, creating new revenue streams for local farmers.
Background knowledge and next steps
As part of designing a monitoring framework, the Penn team, with input from AES, will survey the performance of stormwater management infrastructure. For this purpose, Penn researchers are leveraging different types of data, including meteorological measurements and rain gauge observations. “Each parcel has two meteorological stations, and there are 17 parcels in one of the two solar farms,” says Chen. “Currently, we are also doing an inventory of rain gauges and setting a weekly and monthly data collection protocol.”
Chen had studied urban stormwater runoff quality as an undergraduate student, equipping her with relevant skills to take on the PPA project. Still, there is a unique aspect of conducting field studies in a solar farm catchment. “Beyond complying with extensive safety protocols, once you are on site, seeing the PV panels track the sunshine is impressive;” Chen says.
In this first phase of the project, Chen is gaining background knowledge about the development and construction of the solar array, as well as learning about the permitting process and stormwater controls in place. For instance, as a starting point, the AES permitting team shared the findings from Photovoltaic Stormwater Management Research and Testing (PV-SMaRT), a project aiming to understand the impacts of utility scale solar arrays and identify best practices for stormwater management considering the characteristics of PV panels mounted on the ground.
The project's next steps include creating a hydrological model of Great Cove, which will simulate the local system to uncover how the water moves and is stored both on the surface and underground. Field observations will support the simulations and inform the stormwater assessment. “Using a hydrological model will allow us to map and predict runoff and infiltration rates for various rainfall scenarios,” says Chen, information that will, in turn, inform what data is most important to collect through future monitoring efforts.
As the buzz around renewable energy grows louder, assessing stormwater management of a solar farm is an example of how addressing energy demands goes hand-in-hand with tackling water challenges. “This focus on future solutions, without leaving behind ubiquitous natural resources, like water, motivates me the most about this project,” says Chen.