Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Runoff from solar arrays

Runoff from solar arrays

Runoff from solar arrays

Modeling runoff from solar arrays is an increasingly common challenge for H&H engineers. Solutions range from ignoring the panels, to special Curve Number weighting, to separate routing of the flow under each panel. I would be interested to know how the engineers on this forum are tackling the problem.

Peter Smart
HydroCAD Software

RE: Runoff from solar arrays

In my municipalities we had been completely ignoring the panels, with the underlying thought that the pre-development cover doesn't really change.

We have now been falling in line with the State of MD guidance, which specifies a disconnection of the panels.


RE: Runoff from solar arrays

In the one project that I've been involved with, the panels were ignored by the regulators - mainly because the total disturbance was less than the SPDES threshold, and overall runoff patterns weren't being changed.

I really appreciate seeing the MD guidance for future projects that will require in-depth analyses. I work in NY, which takes much of it's stormwater permitting from MD.

In speaking with a regulator on the topic, they sent me this interesting article

RE: Runoff from solar arrays

for the utility scale projects I have been involved with in California, the panels or collectors were ignored. however there was significant grading involved to level the site and construct O&M roads which does have an effect on the post development runoff by increasing the runoff coefficient and also changing some of the flow patterns.

RE: Runoff from solar arrays

I did a flood study for a solar installation recently, as chance would have it, and ran across this:


Short answer - the solar panels themselves don't really change your curve number, but changing the ground cover underneath them (like to gravel for instance) might.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: Runoff from solar arrays

I think there is a bigger hydrological impact from people replacing there lawns with "landscaping" over impervious sheeting weed block.
I've seen solar panels on vacant land spaced to permit vegetation growth below. Somewhere there are allowable "shadows" for different growing situations. When we build piers and docks, we have to allow for sunlight penetration for underwater life.

RE: Runoff from solar arrays

Looking at the attached image, it is clear to me that this needs to be addressed on a case by case basis.

Look at the different sizes, configurations...and angle of inclinations. Some are practically flat.

RE: Runoff from solar arrays

You would think large arrays of panels could induce erosion at the drip line and eventually develop concentrated flows.

RE: Runoff from solar arrays

I'm a backpacker..and lean-to's work. They block the ground that is underneath them from the rain...

RE: Runoff from solar arrays

This is the abstract of the academic paper I linked above:


Because of the benefits of solar energy, the number of solar farms is increasing; however, their hydrologic impacts have not been studied. The goal of this study was to determine the hydrologic effects of solar farms and examine whether or not storm-water management is needed to control runoff volumes and rates. A model of a solar farm was used to simulate runoff for two conditions: the pre- and postpaneled conditions. Using sensitivity analyses, modeling showed that the solar panels themselves did not have a significant effect on the runoff volumes, peaks, or times to peak. However, if the ground cover under the panels is gravel or bare ground, owing to design decisions or lack of maintenance, the peak discharge may increase significantly with storm-water management needed. In addition, the kinetic energy of the flow that drains from the panels was found to be greater than that of the rainfall, which could cause erosion at the base of the panels. Thus, it is recommended that the grass beneath the panels be well maintained or that a buffer strip be placed after the most downgradient row of panels. This study, along with design recommendations, can be used as a guide for the future design of solar farms.

Read More: http://ascelibrary.org/doi/abs/10.1061/(ASCE)HE.19...

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: Runoff from solar arrays

it depends on whether the panels are trackers or not. Most utility scale projects use tracking collectors to increase the efficiency. The "flat" ones shown in the photo are trackers, the angle of inclination tracks the sun throughout the day. the steep ones are also trackers because you would never set a fixed collector at a steep angle like that. they are in the night position or the "stowed" position. The stow position is usually vertical and is done when there is inclement weather in order to protect the panels. It would also limit the effect on rainfall runoff. If they are tracking, than very unlikely a drip line would be developed.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close