As a company headquartered in Northern California, we at SunLink are certainly used to feeling an earthquake every now and then, but we typically don’t look forward to them. That is until we had the chance to see how our roof-top systems would perform during simulated earthquakes, ranging from the sort of tremors we feel regularly to the “1000 year event.”
The tests were completed over the course of two weeks at UC Berkeley’s Pacific Earthquake Engineering Research Center Shake Table, the largest multidirectional shake table in the U.S. LinkUp took the trip to Berkeley to witness the tests for ourselves and to sit down over a cup of coffee with Kate, a structural engineer and the seismic testing project manager, to learn more about just how everything went down.
Kate let us know that the tests were made possible by a $1 million matching grant from the California Solar Initiative as part of a project called “Reducing California PV Balance of System Costs by Automating Array Design, Engineering and Component Delivery.” The goal of the tests was to help perfect proprietary seismic analysis models that SunLink has been developing with structural engineering firm Rutherford & Chekene to facilitate performance-based project design that will allow more ballasted systems to get permitted in every seismic zone in North America, including high risk seismic zone 4.”
There were a number of factors that made these tests very important to SunLink,” explained Kate. “First, we wanted to gather critical data to help us validate and calibrate the non-linear seismic analysis that we run on every individual project. Additionally, we intend to share the outcomes with building code officials and help inform new structural permitting standards for unattached PV mounting installations. And perhaps most significant, because ballasted systems are less expensive to install and maintain than connected systems, we want to use these test results to ultimately help lower costs for our customers.”So how did it work?
“SunLink engineers actually built two 18‘x25’ timber-framed roofs, one with a polyvinyl chloride (PVC) roof surface, the other with a mineral cap sheet (MCS) roof surface,” said Kate. “We then installed a steel frame on top of the 20‘x20’ PEER shake table in order to cantilever our roofs over the table. By increasing the test surface footprint, we were able to test two full-scale roof mount racking systems – our new Core RMS and the soon-to-be-unveiled Precision RMS ― on each roof. The testing not only assessed system performance when subjected to 200 seismic roof motions, but also assessed the role that various roof slopes, heavy and light ballast configurations, different roof surfaces, and wet and dry roof conditions would play.”
During each “earthquake,” sophisticated instrumentation collected approximately 1.4 million data points, which will be used by SunLink and Rutherford & Chekene to validate our seismic analysis modeling software.
“Analysis to determine the final results of the shake table tests is ongoing,” said Kate. “But preliminary results indicate that both Core RMS and Precision RMS were capable of withstanding the testing matrix of approximately 100 earthquakes each, and that the software tools we have developed are very accurate in predicting seismic-related system behavior.”
SunLink is proud to be the first solar racking manufacturer to perform extensive seismic testing of this nature on full-scale production systems, serving as yet another testament to SunLink’s forefront efforts to gain a better understanding of how various environmental forces impact solar technology. The company expects that, similar to its extensive wind tunnel testing program, the results of seismic shake table testing will provide critical insight that will benefit the solar industry as a whole.