Installing solar energy on a large scale requires increasingly larger plots to accommodate hectares and even kilometers of PV arrays on one piece of land. With that growing project size comes the responsibility to implement proper stormwater drainage measures to protect the environments and communities in which the projects are built.
On any construction project requiring civil work, excavated land that has not been seeded or lacks topsoil is at greater risk of erosion. Stormwater runoff, such as rain or snowmelt, can carry substances such as pollutants and debris that harm local waterways into adjacent areas and municipal sewers.
When sorting is necessary, the topsoil can be saved for later replacement. McCarthy Construction Companies
The National system for the elimination of pollutant discharges (NPDES) is a federally mandated permit program that includes measures for stormwater remediation on construction sites. This permit is issued directly by the Environmental Protection Agency or through an authorized state, where most are qualified as. From there, states can set their own requirements for stormwater remediation in workplaces.
Any construction project with a land disturbance of more than one acre generally requires an NPDES permit. It describes design parameters for establishing proper stormwater runoff management on a construction site and how to close the permit once a project is completed.
“The biggest challenge is managing stormwater to prevent any off-site impacts that could impact sensitive habitats,” said Christina Hebb, stormwater pollution prevention plan and senior manager of vegetation at McCarthy Building Companies. “The permit language states that during planning designs we must do everything in our power to truly minimize off-site sediment emissions.”
There are many preventative measures that can be taken to combat rainwater runoff from solar energy projects. Hebb oversees site preparation of solar projects for McCarthy, a national construction company with a utility-scale solar installations division. She said the most important part of preparing solar sites is establishing vegetation on the land before construction begins.
“Until you really get the vegetation established, you’re not going to have a completely stabilized site,” Hebb said. “Any seeding we can do before installing the piles will significantly reduce your costs, reduce risk and increase production during construction because you won’t be working on muddy ground.”
Rooted plants stabilize topsoil – the first few inches of dirt from the soil surface. As precipitation and runoff seep through the soil and flow over the ground, plant roots prevent it from washing away. It is rich in nutrients and the ideal place to sow native seed crops.
Although ground-mounted racks and solar tracking systems have become more adaptable to undulating topographies, there is still the possibility that some grading will be required at a solar project site to install the array. If the land needs to be graded, Hebb implores contractors to save the topsoil they remove because it can be replaced later.
Failure to establish the initially seeded topsoil may require additional soil amendments, soil compaction, and possibly multiple reseedings after establishment to allow vegetation to grow.
Once a site has the right vegetation, other methods can ensure stormwater runoff is properly managed, such as:
- Sediment basins are excavated at construction sites to collect and collect water so that the sediments within them can remain in place and settle in the ground.
- Check dams are temporary structures made of stone that are placed along water channels at construction sites to prevent sediment from flowing through them. They are used in combination with other drain retention systems.
- Swans are dug channels with grass cover that act as topsoil and guide water flow. Water flowing through a wadi is exposed to grass, which traps sediment and encourages the water to infiltrate the ground along its route.
- Sludge fences are installed on construction sites during construction and until vegetation has grown. They are made of fabric that acts as a barrier to keep soil and sediment in the workplace.
“The idea is that we allow water to flow down through the arrays and then capture any sediment that is moving, but in reality the perimeter and the basins are there to form that line of defense so that when water leaves the site it is clear . ” said Hebb.
Any tamped or graded land should be decompacted and loosened to promote future plant growth in that soil. Contractors must follow the natural drainage patterns of the land they are working on and maintain these water routes during and after construction. It may seem like a lot of work upfront, but it pays off in total.
“We really only work on a project from start to finish for two years, including pre-construction planning and design through operations,” Hebb said. “Solar energy projects are designed for a lifespan of approximately thirty years. Given the size of the project, and what we do during that period, you have such a big influence on the success of the project.”
Conflict over solar-powered rainwater
Stormwater drainage controls are required on construction projects throughout the United States. But that doesn’t mean every state will issue the same rules for every type of structure being built. Such is the case with stormwater controls on solar projects built in Virginia.
In the spring of 2022, the Virginia Department of Environmental Quality (DEQ) released an update to the Virginia Stormwater Management Program, which changed the fact that solar panels are considered impervious surfaces. An impermeable surface is a surface that does not allow water to penetrate into the ground. DEQ considers sidewalks, streets, industrial buildings, lawns and now solar panels to be impervious surfaces.
Reseeding solar sites is a crucial step to prevent long-term stormwater runoff. McCarthy Construction Companies
“There are no additional required stormwater controls specific to solar development versus other land-disturbing activities,” Virginia DEQ Director Mike Rolband said in an email. “DEQ does have that, though accompaniment which requires any solar project that has not obtained interconnection approval from a regional transmission organization or electric utility by December 31, 2024, to consider all ground-mounted solar panels as non-connected, impervious cover.
DEQ states that impermeable cover is typically attached to stormwater controls. Solar projects are considered “unconnected, impermeable cover” because precipitation falling from the modules must travel along the ground before reaching a stormwater channel. This change in post-construction stormwater management could require developers to use more land for stormwater controls on their solar panels.
Opponents of this change for stormwater controls on solar projects believe so unfair and a disadvantage for the industry in the state. Still, Virginia has a history of stormwater drainage problems, and so does the state efforts increased to comply with minimum erosion controls on construction projects.
“Without proper stormwater management and erosion control equipment, erosion and sedimentation of natural receiving channels and waterways can occur,” Rolband said. “Additionally, increased runoff resulting from the change in land cover conditions may result in increased flooding of downstream properties and resources.”
Not every state will regulate stormwater controls on solar projects like Virginia does. Each region has individual environmental and regulatory features that solar installers must adhere to to keep the land they build on as green as the PV modules they install. Starting with a baseline of good topsoil and vegetation management and adding proper stormwater channels can help developers keep surrounding waterways clean during construction and the entire life of the project.