Pennsylvania Department of Environmental Protection Stormwater Guidelines for Solar Farms

Categories : Uncategorized
June 18, 2021

In early 2019, the Pennsylvania Department of Environmental Protection released a Frequently Asked Questions (FAQ) article addressing National Pollution Discharge Elimination System (“NPDES”) permits and requirements for utility-scale solar and solar farm development. Our firm has analyzed this FAQ and addressed what we consider the most important points for utility-scale solar and solar farm developers. 

Why do I need NPDES permits for a solar panel farm?

Pursuant to 25 Pa. Code §102.5(a), if the earth disturbance associated with the construction of the proposed utility scale solar or solar farm is at least 1 acre, NPDES permit coverage is required. Since almost all utility scale solar or solar farms will affect more than 1 acre of land, it is wise to assume that NPDES permit coverage is always needed for these types of projects. 


What constitutes “earth disturbance” during development of a solar energy farm?

Each site is unique depending on its own topography, sloping and soil. But, any kind of grading, clearing and grubbing is considered earth disturbance. As well as any disturbance needed for the installation/mounting of the solar devices, including any necessary access roads and support buildings. 


How can such minimal earth disturbance affect the underlying land?

According to the Erosion and Sediment Pollution Control Program Manual, even small construction sites can yield the following serious potential hazards:

  1. Exposure of soil to erosive forces;
  2. Increased volumes of stormwater runoff, accelerated erosion and sediment yield;
  3. Alteration of the groundwater regime affecting drainage systems, slope stability and survival of vegetation;
  4. Exposing subsurface materials that are unfavorable to established vegetation; and
  5. Adverse alteration of surface runoff patterns.

Erosion and Sediment Pollution Control Program Manual, PADEP, Pub. No. 363-213-008. 


How do I avoid these potential hazards?

Developers proposing utility scale solar or solar farms should locate sites where earth disturbance will be as minimal as possible (flat, cleared and accessible). When earth disturbance is necessary, developers should maximize protection of the existing drainage features and vegetation, avoid soil compaction, and prevent increased stormwater runoff. For more information, see Best Management Practices (BMPs) located in the Erosion and Sediment Pollution Control Program Manual


What BMPs can I utilize for my construction site to be considered pervious cover? 

  1. Minimal earth disturbance and grading along with preserving natural vegetative cover via low-impact construction. See BMP 5.6.1-5.6.3. PA Stormwater Best Management Practices Manual, PADEP, Pub. No. 363-0300-002; 
  2. The vegetative cover should have a minimum uniform 90% perennial vegetative cover with a density capable of resisting accelerated erosion and sedimentation. 
  3. The individual photovoltaic panels are organized in a way that:
    1. Allows the passage of runoff between each module.
    2. Allows for vegetative growth beneath the panel and between the arrays.
  4. Solar panels should be situated on a slope of 10% or less.
  5. Find a “sweet spot” for the solar array vertical clearance. A height that is high enough to promote vegetative growth underneath the array, but also low enough to minimize the potential for accelerated erosion between the arrays.

Note: For some solar farms not all of these conditions will be feasible. But, the more a developer is able to do, the more likely their site can maximize pervious coverage. 


Are there different requirements for tracked-panel units compared to fixed units?

There are a few noticeable differences. Tracked-panel units will require more land area because they need to be spaced out more due to shading overlap. They also require additional mechanisms to properly track the sun to maximize the direct radiation. The additional land will result in additional earth disturbance, but as long as the BMPs described above are implemented, earth disturbance can still be relatively low. 


Can I grow agricultural crops underneath my panels?

Yes, and it is a great way to maximize the use of the land, provided that:

  1. Proposed crops are shade tolerant.
  2. Proposed crops don’t require Moldboard Plowing.
  3. A written erosion and sediment control plan must be developed for agricultural plowing or tilling activities.
  4. The application of herbicides, pesticides, and chemical fertilization is limited to the agronomic needs of the crops.
  5.  Depending on the height of the crops, the height of the panels may need to be increased. As noted above, when panels are placed higher, more controls are needed to address erosion and scour between the panels. 


What can I do to better manage wider solar panel modules?

The wider solar panels become, the more difficult it is for adequate vegetative cover to be established and maintained. According to the DEP, additional BMPs can be done to offset this additional width. Infiltration trenches or infiltration berms can be installed down gradient between each row. For more information see PA Stormwater BMP Manual, BMP 6.4.4: Infiltration Trench and BMP 6.4.10: Infiltration Berm and Retentive Grading for additional guidance.



Are there additional requirements if my proposed construction site needs to be re-graded?


If the area needs to be re-graded, soil/landscape restoration and soil amendments should be implemented after the re-grading. For more information see PA Stormwater BMP Manual, BMP 6.7.1: Landscape Restoration and BMP 6.7.3: Soil Amendment and Restoration.


For more information please see the Pennsylvania Department of Environmental Protection’s Best Management Practices FAQs for solar farms here


NPDES permits and requirements are but one step to developing a comprehensive and successful site plan for a utility scale solar or solar farm project. For any other questions related (or unrelated) to solar development, please don’t hesitate to email Andy Miller (, Cory Dillinger ( or anyone in our office with questions or comments.

Learn More About Solar Farms


Leave a Reply

Your email address will not be published. Required fields are marked *