Determining a Runoff Curve Number for Ground Mounted Solar Arrays

The attendees will understand how to determine a Runoff Curve Number for ground mounted solar arrays for post-development that takes all important factors into consideration to better determine the runoff will be generated by a ground mounted array.

Full Abstract: As ground mounted solar arrays are being built in many parts of the United States, there have been adverse environmental impacts associated with them with stormwater runoff being the largest issue. These systems significantly increase both the volume and rate of runoff for all storm events. There are several issues which create these problems. The first issue is the erroneous assumption that solar panels are pervious simply because there is grass under them. In other cases, it has been defined in state law or regulations that the panels are pervious and thus design professionals do not feel obligated to design stormwater management systems for these sites.
This presentation will focus on how to determine an appropriate Runoff Curve Number (RCN) for the post-development conditions of a ground mounted solar array. There are many factors that go into the determination of an RCN. Normal conditions which affect the RCN are soil types, and vegetative cover (both type and condition). For post-development conditions for ground mounted arrays, there are additional factors which come into play in determining the RCN. These include the following:
A. What is the alignment of the panels relative to the land slope?
B. What are the slopes on which the panels are being installed?
C. The separating distance between panel rows?
D. Was the soil compacted during the installation process?
E. Were there significant cuts/fills of the natural grade under the array?
F. If the soils were compacted, have the natural infiltrative capacities been reduced?
G. Has topsoil been placed in the area array for final stabilization?
H. What type of seed mixture will be used for final stabilization?
It will be discussed how to evaluate all these factors to come up with the most realistic RCN value to determine post-development runoff. Additionally, strategies will be presented on how to address grading and compacted issues and testing protocols which need to be implemented to prove the strategies will be effective.