InSPIRE/low impact/habitat/site design and construction
Low-Impact Development Strategies
Native Vegetation and Pollinator Habitat
Site Design and Construction
The upfront design of a solar facility can often impact the total installed cost along with needed O&M spending over the life of the project. Often the most important thing for reducing costs is minimizing grading before equipment installation. However, a less uniform slope can lead to changes in the racking design and may not allow for tracking systems. Cost savings from reduced grading can sometimes be partially offset by additional racking expenses as the length of many of the posts must increase to maintain a consistent height across varying topography. Steps can be taken during construction to minimize immediate impacts on the environment that could lead to costly issues later.
Even though a best practice of site design and construction is a reduction in grading, the solar developer may incur higher costs trying to install the racking system at the same height for module installation if the land is uneven. There are several different racking systems that solar installers can use, including concrete sleeper and rammed posts.
With concrete sleepers, developers can place concrete blocks that act as foundations for the solar equipment. This option can preserve local vegetation, be fast to install, and allow for easy site remediation after project life. However, this option requires very level ground and may lead to increased grading. Also, only fixed tilt systems can be employed for this option.
Rammed posts, however, are more conducive to uneven terrain and can help facilitate the avoidance or reduction of grading. Rammed posts involve using a machine whereby solar installers can drive posts into the ground that provide the foundations for installing PV systems. This option has become an industry standard as it is cheap, fast, and can accommodate different grades. Also, rammed posts can be used for both fixed tilt and tracking systems. Installing rammed posts may also allow developers to preserve native vegetation and habitat and reduce grading. Soil and rock conditions (sometimes not surveyed upfront during site selection) may impact rammed posts and unideal conditions can lead to project delays.
Installers can minimize soil compaction during construction by avoiding construction activities during wet and rainy conditions, establishing set pathways for construction equipment, and minimizing the duration of construction equipment on-site.
Minimal vegetation removal and some grading could still be required in order to provide a relatively level surface for the solar arrays and racking system. Vegetation removal might also be needed for access roads and construction laydown areas. Brush, trees, and some herbaceous vegetation might need to be cleared to facilitate access for workers and equipment, as well as to meet safety standards. Vegetation removal can be accomplished with the use of handheld non-motorized equipment as well as with chainsaws, mowers, and hydraulic tree-cutting equipment, if necessary. To minimize disturbance, vegetation can be cut at or slightly above the ground surface. Rootstock or stumps can be ground down to the soil surface. Rare and unique natural resources should be given prioritization to remain or be transplanted.
If necessary, the developer should obtain authorization under a National Pollutant Discharge Elimination System (NPDES) Permit. A Stormwater Pollution Prevention Plan (SWPPP) should be prepared in accordance with the NPDES prior to initiating any construction. During the construction phase, installers should implement appropriate measures to stabilize any recently graded and/or exposed soils. Soil replacement and/or soil amendments may be necessary in some areas.
Specific erosion control measures may include, but are not limited to:
- Minimizing vegetation removal, grading, and other ground disturbance
- Erosion control materials/mats/fabrics
- Weed-free mulching
- Protective berms
- Silt Fences
To prevent the introduction of noxious weeds and invasive species (NWIS) on lands disturbed by construction activities, the following practices can be beneficial:
- Minimize soil disturbance and grading to the extent possible
- Check construction equipment for weeds
- Clean equipment prior to arrival onsite to prevent the introduction and spread of NWIS into the facilities from offsite locations
- Re-vegetate with intended plant species (e.g., low-growing perennials) as soon as practicable to discourage noxious weed growth
- Encourage early detection and eradication of patches of weeds through appropriate measures
- Locate and use weed-free staging areas if there is an issue at the site
- Mulch and wood chips used for soil stabilization should consist of certified weed-free material
Based on discussions with industry members, the following best practices were identified:
- Use and development of solar racking technologies that can handle greater tolerances for topography, thus requiring less site grading work
- Avoid sensitive areas, like wetlands or drainage features, that require special design, this leading to permitting delays and cost increases
- Keep inverters and other electrical equipment out of flood plains if possible as this can cause increased racking and insurance costs
- Driven posts are advantageous to reduce cost and minimize environmental impact. Driven posts can reduce the loss impact for wetlands, thereby avoiding extensive permitting requirements
One industry representative was quoted saying, “Measurable environmental costs probably don’t exceed $0.10/watt. However, the most extreme environmental-related costs are associated with the significant delays in project completion resulting from problems obtaining environmental permits.”