U.C. Berkeleys PEER Center Hosts Shake Test for Alternative Solar Racking System
For the first time, a solar racking manufacturer tested its ballast-only roof-mounted racking system on U.C. Berkeley's Pacific Earthquake Engineering Research Center (PEER) shaking table in Richmond, Calif., and it appears to have passed with flying colors.
The March 5 test "provided us with information on how our roof mounting system acted [when] not connected to a roof," said Mike Williams, senior vice president-engineering for SunLink, San Rafael, Calif. The product "acted like we thought it would," he added.
SunLink has been teaming with engineering firm Rutherford and Chekene, San Francisco, on a series of seismic tests at PEER to calibrate and perfect proprietary seismic analysis models to improve the manufacturer's performance-based design. The team also tested wind-tunnel effects on rooftop solar arrays last year at the University of Western Ontario's Boundary Layer Wind Tunnel Laboratory.
Autodesk is also a partner in the program, which is being co-funded for nearly $1 million (with SunLink matching) by the California Solar Initiative Research, Development, Deployment and Demonstration program. The primary focus is on grid integration of solar energy, with a secondary focus on improved photovoltaic production technologies and business development and deployment. The California Public Utilities Commission is overseeing the $50-million, six-year state grant program.
The SunLink/Rutherford and Chekene project is called "Reducing California PV Balance of System Costs by Automating Array Design, Engineering and Component Delivery." Williams said the prevailing purpose is to lower roof installation costs, which grow dramatically when the systems are physically attached, and open up more installation work to general contractors and subcontrators, thus leading to a major expansion of solar use.
SunLink said building officials in California almost always require direct mechanical connection of PV systems to flat roof structures in order to prevent shifting during an earthquake, even though engineering analysis and design based on code criteria demonstrate that systems perform well without such anchoring. Building code officials also are influenced by the International Building Code's fastening requirements. Once the codes are adjusted, the permitting process should be easier.
The most recent test, which measured movement from the roof of a three-story office building, utilized seismic motion from the 1989 Loma Prieta Earthquake in three sequences: a 200-, 500- and 1,000-year event. Peak roof acceleration ranged from 0.65g to 1.95g. SunLink's CORE RMS model mounting system sits on rubber feet made from recycled tires (each foot eliminates two tires from landfills). The CORE model, according to SunLink, features a sturdy grid assembly that provides strength and load distribution for framed or laminate installations of 10 degrees or less. Projects can be installed with whatever custom row space is optimal given module size and energy production requirements.
The results will be distributed via reports to the California Solar Initiative and industry journals. Williams said the results will be used to validate and calibrate non-linear computer analysis models as well as influence the creation of new structural standards.
The so called 200, 500 and 1000 year event is misleading in the extreme. What is meant is that there<br/>is a probability that that in a given year there is a 1/2%, 1/5% or 1/10% that t...
is a probability that that in a given year there is a 1/2%, 1/5% or 1/10% that the mounting will far the
"200 year", "500 year" or "1000 year" "event" respectively.
Thus taking the so called "200" year event, in the first year there is 1/200 chance that the mounting will fail, before the first year is up given by multiplying the constant probability of failure in a year here 1/200 by the fraction of the period, here 200years (to failure)/200years = 1/2 of 1%
When 100 years has elapsed the chances that the mounting will fail will still be under this simplified analysis will still be 1/2 of 1% but there will just be an opportunity of 100 years for the mounting to fail thus the chances of failure in the 100th year is 1/2 of 1% X 100years/200years - 1/4 0f 1% so although the failure rate of the mounting per year may be considered acceptable, there are a sufficient number of years so that the chance of a mounting failure can be significant. Your chances of dodging a bullet may be good, but not your chances of dodging a barrage of machine gun fire.
For a "100 year event " there is a 26% probability that the mounting will fail at least once before 30 years, not repeat 100 years is up for example. Thus as noted by the Government, buying "100 year
flood insurace" still gives you a 26% probability of having at least 1 flood before your 30 year morgage is paid up.
The really interesting question is why such a grossly misleading statistic is used. Even using crude
statistics one can say using the deceitful verbiage if the mounting experiences an extreme event,failure, in 200 years, the on average the mounting will fail in 100 years.
The mounting may have merit. What is certain is that the advertising is deceitful.
