The Los Angeles Community College System in California (US) was all set to go with a huge solar installation, but the designs were scrapped because the arrays were going to be built above seismic faults. The problem may not have been that installing solar equipment in seismic areas is inherently life threatening, but rather that engineers and code enforcing agencies had nothing to go by in ensuring the safety of such systems. Fortunately this is changing. The Solar Photovoltaic (PV) Committee of the Structural Engineers Association of California (SEAOC) is a group of PV specialists who have been working on the development of standards for solar arrays in earthquake-prone regions, the results of which will likely have broad impact throughout the industry.
Previously PV was designed based on general building codes that had nothing to do with solar PV.
The group’s document called “Structural Seismic Requirements for Rooftop Solar Photovoltaic Arrays“ or SEAOC PV1, offers guidelines that are suitable approaches for both attached and unattached solar arrays. Having this document offers guidelines for project engineers that helps design projects that will comply with local or state code. Steve Bauer, Technical Director at Unirac, said that previously PV was designed based on general building codes that had nothing to do with solar PV. He said that the SEAOC group, of which he was a part, drew from their broad, collective experience in PV and came to the consensus presented in PV1. Unirac has referenced the PV1 document several times on projects in front of code enforcement bodies (or AHJs) in several states. “The early response from AHJs has been very positive both in California and elsewhere,” Bauer noted.
Cutting soft costs
The permitting process has, in the past, been blamed for holding up solar projects as well as driving up the soft costs of solar. Having the SEAOC document is helping to cut time and paperwork on projects, as the AHJs previously had no PV guidelines and now they know better what they’re looking for.
These guidelines provide a more commonsense path...
According to Mark Gies, Vice President of Reliability and Compliance at PanelClaw, the SEAOC guidelines are providing building departments with information dedicated to PV. “These guidelines provide a more commonsense path,” Gies said. He added that “it helps standardize installations, reduce soft costs while helping manufacturers streamline systems and reduce their backlog.”
In unattached arrays the primary risk is movement of the array, and the document describes the appropriate setback distances from roof edges and obstacles in order to predict and mitigate risk from system movement. Martin Lashgari of GameChange Racking pointed out that unattached arrays are ballasted against wind loads and, “if designed properly,” he said, “they are safe against such phenomena.”
Guidelines and testing requirements are included in the SEAOC PV document to help determine the coefficients of friction, as it is friction that enables unattached systems to resist movement. This is one of the areas where the SEAOC document is having the greatest impact. Gies said prior to the publication of PV1, the California building code had a rule that friction could not be used to resist seismic forces. “The SEAOC paper dictates to consider a percentage of friction and offers a way of going down that path,” Geis said. Bauer noted that the SEAOC group agreed that “if these things move a little on the roof, that’s not the primary concern,” adding that “it’s all about life safety—if you look at life safety as a driver, then there is room to let things move a bit under seismic load as long as the system can accommodate it and it stays on the roof.”
The PV1 guidelines also provide for shake table testing or nonlinear time history analysis for systems that do not qualify for evaluation using the prescriptive method.
In terms of securing an attached structure, Lashgari pointed out that seismic forces act on the horizontal and vertical directions. “Horizontal force needs to be transferred from rooftop system to building roof structure via seismic attachments in an attached system.” There are many different designs for attaching panels to the roof, but they should be designed to resist the lateral seismic force (Fp) specified in ASCE 7-10.
The national standard followed by solar installers in the US is the International Building Code and the reference standard ASCE 7 has a few chapters on seismic considerations, according to Ronald LaPlante, Past Chair of the SEAOC PV Committee. He said that while provisions for non-structural components attached to buildings have been around for years, it is in the area of unattached PV arrays that the most advancements have been made in the past two or three years.
The SEAOC PV committee focused on unrestrained solar arrays. LaPlante said that in order to do unrestrained solar arrays, “it’s important that the array slide around as a unit and not break apart.” He added that it takes a “fairly robust racking system or way that the array is connected together so it doesn’t tear itself apart.” In the SEAOC standards there are provisions for what the load should be so that it slides together on the roof in the event of seismic activity. The elements of the SEAOC guidelines have been simplified into code language and submitted to be adopted into the 2016 edition of ASCE 7. The recently published 2015 edition of the International Building Code contains provisions that permit unrestrained solar arrays with proper analysis or testing, such as that indicated in the SEAOC PV1 report.
...The industry could make progress if it created a standard that all manufacturers will follow.
The industry is still in the early stages of standards development for solar panels and racking systems, but as Gies said, “there’s already getting to be widespread adoption of the paper.” LaPlante concluded that if you asked many manufacturers and structural engineers out there, you’d find a consensus that the industry could make progress if it created a standard that all manufacturers will follow. SEAOC PV1 is currently underway and is moving the industry in that direction.
Overall the PV1 document “levels the playing field,” according to Bauer. “This is all about enabling solar in a safe way and it provides a good baseline that engineers can use,” Bauer said, adding that “the biggest challenge is getting the word out.”
Written by Anne Fischer, Managing Editor, Solar Novus Today