By Blake Jackson
As solar farms continue expanding across Pennsylvania and the United States, questions remain about how they affect stormwater runoff and local water systems. While many assume solar panels behave like rooftops or parking lots by increasing runoff, recent research from Penn State shows the reality is far more complex.
According to researchers Femeena Pandara Valappil and Lauren McPhillips, solar farms create unique water movement patterns that can be effectively managed through thoughtful design and land management.
Unlike traditional impervious surfaces, solar panels redistribute rainfall instead of simply preventing water from soaking into the ground.
Rainwater running off panel edges creates wetter areas along driplines, while the ground beneath the panels remains drier because it receives less direct rainfall. Vegetated spaces between panel rows play an important role by absorbing water, increasing infiltration, and reducing runoff.
Penn State field studies at two solar farms in Centre County found that soil moisture beneath panels was significantly lower than nearby reference areas, while moisture along panel driplines was noticeably higher.
Researchers also discovered that evapotranspiration was reduced beneath the panels, further influencing how water moves across the site. These findings demonstrate that solar farms function as diverse landscapes rather than uniformly impervious surfaces.
Additional research from the Photovoltaic Stormwater Management Research and Testing (PV-SMaRT) project supports these conclusions.
Studies found that healthy vegetation, suitable soil conditions, and site-specific planning are critical for minimizing erosion and improving infiltration.
The research also showed that runoff responses differ depending on factors such as rainfall intensity, slope, soil type, and vegetation cover.
Experts emphasize that well-designed solar farms generally do not produce significant runoff during smaller storms, although larger storms may require additional stormwater controls.
Practices such as preserving healthy soils, maintaining dense vegetation, and disconnecting runoff from panel edges help reduce environmental impacts.
To improve future solar development, Penn State researchers have also developed advanced hydrologic models and the Virtual Solar Array tool, which helps engineers, land managers, and the public evaluate sustainable site designs.
Together, these innovations support renewable energy expansion while protecting water resources, improving soil health, and promoting environmentally responsible land management.
Photo Credit: istock-shansekala
Categories: Pennsylvania, General