Engineering Evaluation of Solar Panel Brackets  for Use at Closed Landfills

Through various programs, the Commonwealth of Massachusetts has been paving the way for a greener energy future. In 2008, the state Legislature passed the Global Warming Solutions Act and the Green Communities Act. They have also established grant programs and, in January 2010, approved solar renewable energy certificates (SRECs). These actions have positioned Massachusetts as one of the leading promoters of renewable energy in the country. The Massachusetts Department of Energy Resources (DOER) and Department of Environmental Protection (MassDEP) have been promoting the re-use of closed landfills as prime areas for redevelopment as locations for renewable energy facilities. With this focus, the market has responded with the redevelopment of closed landfills for photovoltaic installations. A solar racking manufacturer was interested in understanding the emerging landfill market. They engaged Geosyntec to conduct an engineering evaluation of their ground mount system related to its use on sloping ground, with a focus on closed landfill sites, and to develop a preliminary screening tool.

As part of our evaluation process, Geosyntec obtained representative samples of the racking system and ballast materials (metals and concrete) and various substrate materials (crushed stone, granular fill, topsoil, and asphalt). With this material, we conducted an extensive laboratory testing program to evaluate the interface friction angles between the various materials. This testing program provided sufficient information to determine the resistance against sliding and ultimately the ballast load requirements for the units. We evaluated the impact of placing a racking system on typical landfill slopes by performing static and seismic slope stability computations using the computer program SLIDE® for various landfill slope configurations.

As a separate task, our practitioners provided an assessment of the properties of the metals used to construct the racking system with their potential to adversely impact the soils at installation sites due to corrosion of the metal materials.

Geosyntec performed an overview of potential ballast system enhancements by conducting a detailed literature review of various types of external shallow ground anchors (e.g., helical anchors, vertical pins, and duck-bill type anchors) and provided recommendations to the client regarding the most appropriate type of anchor for their system. We summarized the findings of our evaluations in a series of technical reports to the client that included a summary of our findings, recommendations related to the use of their product on sloping ground and landfills, subgrade preparation guidelines, and recommendations for possible product improvements.

Using the results from an extensive interface friction testing program, Geosyntec was able to provide a screening tool for a specific racking system and recommended various ground anchoring systems and subgrade preparation techniques to allow our Client to properly evaluate solar installation on slopes and specific closed landfills.