Solar racking manufacturers have had the seemingly unending task of keeping their systems compatible with the latest iteration of PV module. While large-format modules are already being used in ground-mount and some flat commercial rooftop projects, installers are inquiring about racking systems adapted to newer panel dimensions for residential applications, too.
The panel has always come before the racking, and it’s been up to manufacturers to play catch up. Previously, a typical 60- or 72-cell module would run between 65 and 74 in. long and 39 or 40 in. wide, respectively. Silicon wafer sizes have leaped from 125 mm to 210 mm in the last dozen years, with modules like Canadian Solar’s HiKu series now reaching more than 90 in. lengthwise.
“We’ve always tried to test with the biggest modules that we thought would be applicable to that market. These modules are bigger than any of those modules, so we’re having to go back to all of our certifications and also adjust those to take these larger-format modules into account,” said Ernest Gallegos, director of products with Unirac. “It’s really been disruptive for racking manufacturers, whether they want to admit it or not, whether they realize it or not yet.”
As panels integrate newer wafer sizes and layouts, the increased module sizes might not necessarily affect the number of penetrations in a rooftop project, but it will require greater consideration for panel clamps. Snow load and downward pressure aren’t as much of an issue as wind and uplift.
The number of modules on a rooftop project could remain the same, but an increase in square footage from large-format modules would create a bigger surface area and “the effect of the wind doesn’t change, but it’s applied over a bigger area, which means higher loads on your clamps,” Gallegos said.
“For the most part, if the total size above the rail says the same, then your attachment spans are going to stay the same,” he continued. “None of that is affected, but when you start talking about your clamps and if your clamps are designed to handle a certain module, then your clamps need to get more robust. Your rails, your T-slots, your hardware, whatever they’re designed for, will need to be more robust on the rail.”
Structural code ASCE 7-16 helps engineers calculate system loads on rooftop projects across many industries, but it also sets limits on structures that can be installed on a roof, including solar panels. The code limits PV module cord length to 6 ft. 7 in. (2.04 m) on flush, flat and pitched array designs, and larger-format panels are bucking against that limit.
“There’s no good, direct code-based way to establish loads on these right now,” Gallegos said. “We’re not sure exactly how other people are dealing with it, but we’re trying to figure it out ourselves.”
As solar panels increase wattage and size, there will need to be new structural codes to advise system design, and racking manufacturers will try to keep up.