Runoff from solar arrays 2

[psmart]

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

http://www.hydrocad.net

 

[Twinkie]

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.

Link

 

[peter246]

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

http://www.dlhowell.com/news/241-are-solar-panels-impervious-or-pervious

 

[cvg]

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.

 

[beej67]

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

http://ascelibrary.org/doi/abs/10.1061/(ASCE)HE.1943-5584.0000530

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

 

[BUGGAR]

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.

 

[LincolnPE]

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.

 

[civilman72]

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

 

[LincolnPE]

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

 

[beej67]

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.1943-5584.0000530

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[cvg]

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.