How to simplify module-level rapid shutdown on huge commercial roofs
Adding module-level power electronics (MLPE) to rooftop solar projects to meet the latest rapid shutdown requirements will typically not add too much time or labor to installations. But that rooftop safety requirement isn’t just for residential homes — commercial roofs require the same treatment.
C&I installers today install rooftop projects in dimensions comparable to their on-ground counterparts – PowerFlex, for example, recently completed the current largest community rooftop solar project in the country, clocking in at 9.2 MW. Each of the 22,320 solar panels on the roof required a quick shutdown device (RSD) underneath.
But PowerFlex was not deterred when NEC 2017 created that requirement. By then, the company had already started installing SolarEdge power electronics on its commercial rooftop projects. The string-inverter-plus-optimizer solution gave designers more flexibility to maximize PV coverage on irregular roof surfaces, so the rest of the array is unaffected if a module is shaded or experiencing limited performance from dust and debris.
“As a designer, if you have the freedom to have multiple string lengths because of… that inherent flexibility in that technology, that’s a big advantage,” said Pete Vash, PowerFlex technical director. “Therefore, when optimizers became available to the market, people who were making commercial roofs were very interested in that for that design, even before there were any requirements for quick shutdown, just because of the improved manufacturing and the design flexibility.”
After NEC 2017 was adopted by many jurisdictions, SolarEdge optimizers meet the requirements to reduce voltage to 80V or less within 30 seconds. PowerFlex is technology agnostic, but today the company uses SolarEdge for most systems.
“We actually had something that worked and we could just continue with the same kind of design that we had,” said Vash. “They’ve been a good partner to PowerFlex and supported projects during the commissioning process, so there’s a good synergy there.”
In addition to optimization, SolarEdge touts the safety benefits of its inverter solution. If installation errors are made, SolarEdge says the temperature-sensitive software will catch them.
“Our technology has that module-level visibility that we can see. We can even see a blown bypass diode on the module. We can see that there is an error. We have sensors that detect it, they report it, and that means people can fix it,” said Carolyn Humphreys, C&I sales manager for Eastern North America at SolarEdge.
SolarEdge also stands for its fundamental architecture offerings. Instead of separate entities set up to work together afterwards, the technology is part of one cohesive system.
“We believe having everything integrated as a system from one vendor is a huge advantage,” said Jason Bobruk, director of code compliance at SolarEdge. “And we also maintain the reliability and robustness of that system through our quality control programs, and all of this philosophy translates into our certification approach as well. When we certify a quick shutdown system, we certify as a whole, complete system— [that] including the optimizers, including the inverters, including the small DC disconnect enclosure with the switch on it.
Struggle to Streamline Closure
Whatever an installer’s quick shutdown equipment may be, installing hundreds or thousands of additional components on a project has its inherent drawbacks. It takes more time to prepare all equipment, install and commission each unit. Perhaps the bigger headache, though, is the added O&M stress of adding many extra potential points of failure into a project.
“While there is a bit of a cost to install, I think you may be underestimating the backend cost of using an asset,” said Matt Cote, senior purchasing manager at PowerFlex. “Even if you have a 0.1% failure rate, if you implement thousands of these things, it adds up over time and creates a lot of different challenges.”
Tigo Energy is another major MLPE manufacturer that is UL certified as a quick shutdown system with: numerous inverter brands. The company also recently announced its own inverter. Tigo offers three variants of fast-closing MLPE: standalone RSD, RSD plus monitoring, and RSD plus monitoring and optimization. Since pricing in C&I projects is highly competitive, James Dillon, Tigo’s Chief Marketing Officer, said most installers currently choose RSD only to save the extra $10 or so per unit.
“That’s a shame, because that’s a trade-off between [operating expenses] and cost – how much work do you want to do upfront compared to long-term use and maintenance? I think we need to better explain the value and have a great software solution that installers will get the most out of,” he said.
Illinois-based GRNE Solar is installing commercial projects in the Midwest, where some licensing offices still use the 2014 NEC. The company-wide view is that security is paramount, so GRNE believes that a module-level rapid shutdown should be implemented regardless of the code’s application in the area. The company has run into that philosophy by developers.
“The cost increase for material and installation can make a significant contribution to the overall budget of a project. When considering a competitive quote, it’s not always an apples to apples comparison when a quick shutdown is not included in every contractor’s quote,” said Jeremy Hoerauf, commercial project manager for GRNE Solar, in an email.
Another common problem is that it is sometimes unclear who is responsible for O&M over the lifetime of these commercial projects, Tigo’s Dillon said. If it is not the installer, they are even less likely to opt for the more expensive monitoring solution. But he expects the present-oriented nature of the market to change as rapid shutdown systems begin to age.
“The bill won’t come in for a few years, so if anyone has problems with installations that they did three, four, five, eight years ago, they’ll learn from that and build it in the future,” Dillon said.
Another stressor that comes with adding hundreds of extra components between the module and inverter is the hundreds of extra PV connectors required to install them. At the moment there is no universal standard for PV connectors, but the latest code requires all connectors used on a product to be the same: either made by the same manufacturer or UL tested to be compatible. This means that companies often struggle to buy enough connectors from one manufacturer, with mixed results.
“It may sound like a trivial matter, but can you imagine not all USBs were created equal and every laptop had a slightly different sized connector?” said Vas.
GRNE made the same complaint after encountering connectors that are not compatible with the selected modules or quick trip units.
“What we’d like to see from quick disconnect manufacturers is a standard connector that will work for any module manufacturer,” Hoerauf said. “As the industry moves more and more towards each module manufacturer having its own connector, quick shutdown suppliers need to standardize the connector and have it approved for all modules.”
The installer has also noticed that the module industry is moving towards shorter wire cables, so the RSD makers have to start making longer cables to connect them. These logistical issues may seem minor, but can lead to cumbersome delays that hurt business.
Simplifying the MLPE offering
Because the fast shutdown requirement is relatively new, new products and improvements are being rolled out quickly to meet the need. Cote said the main pain point he hopes manufacturers will address is the complexity of businesses having to buy and install different components from multiple manufacturers. Package deals with pre-assembled components and integrated RSDs can save installation teams time on site.
“If vendors innovate and collaborate to create something that’s just a full-featured package for a company like us, that would be super beneficial and take a lot of the guesswork and design headaches away,” he said. .
But that kind of collaboration isn’t easy in an industry where technology is changing rapidly.
“The challenge with that is that there are so many different options,” said Tigo’s Dillon. “We’re actually compatible with hundreds of inverter options – you have to do it with every size from every manufacturer. It’s an endless upgrade battle.”
So Tigo is taking a different route to simplify their devices for installers. Engineers are working to condense their MLPE into one device and use hardware to enable the various functions instead of offering the features of RSD, monitoring and optimization in three different devices. That hardware-enabled device would eventually, ideally, also receive other updates digitally.
“That would make it even easier — if you could put one piece of hardware in there and say, ‘I want optimization on this half of the building, and on this half I just need to shut down quickly because there’s no chance of shade,'” said dillon .
As a relatively new requirement, module-level rapid shutdown wrinkles are still being smoothed out, especially on large-scale commercial roofing projects. In the meantime, installers will need to continue learning best practices to make both installation and ongoing maintenance as simple as possible.