Solar panel arrays are now ubiquitous for gathering sunlight and converting electromagnetic radiation into energy. But this is not a simple task. Basically, the sunlight must convert photon energy – photons – onto large plates which convert into bundles of electricity in a direct current mode. This must then be converted to alternating current through inverters. This is where conversion get tricky, and we’ll come back to this at the end of the story. To continue, NFPA requires that there be fused disconnect at each location. This is no different than air-conditioning starter motors, spas, and outdoor pumps. It makes complete sense. Stop the power where a short-circuit occurs or where the local live system needs shutdown.
Now comes the risk part of the story and, unfortunately, this is real and local to Philadelphia. A major corporate center had a large office building and decided to go green. It was part of their social promise. Unfortunately, keeping this social promise undermined business continuity directly due to improper fire and emergency response procedures that were never tested or acted upon within the emergency procedure response plan by first responders nor the owner.
So, here's the unfortunate outcome of the story. Let's start with a flat roof, membrane style, and the roof is completely covered with solar panels, fused disconnects, and the soon-to-be-famous inverters. Not to mention conduits running all over the place.
A fire breaks out in one of the electrical systems after the fused disconnect. The fire burns for over 15 minutes until fire service comes, at which point the roof is fully engaged around the area fire and is burning through the membrane roof and into the structure below, into the interstitial space, and into the protected areas. I think you know where this might be going.
The fire service, sensing imminent danger to first responders on the roof, decides to turn off all main power to the building. Yep. They got the electrical service disconnected from the entire building and site. The fire burns through the roof while fire service attempts to mount suppression proving not only inadequate, but insurmountable.
No power; no fire pump. No fire pump; no water. No water; no suppression. No suppression; yikes, a catastrophe.
Inverters are generally only 50% efficient because they have to cycle through the DC power and rectified by making the power a sinusoid. You can do this a number of ways. One way is to convert multiple square waves of DC and combine them into one clean sinusoidal wave, or have one massive rectifier, that blows out significant heat as a by-product. Whenever one of these two methods goes awry, the heat buildup is caused by DC flowing where AC should be. Heat, oxygen, and readily accessible fuel from plastics, silicon, circuit boards, and conductors make a great combination for combustion, which is exactly what happened.
This is a multi-million-dollar lawsuit with subrogation claims going to the fire alarm contractor, the solar system contractor, the engineer, the fire department, and yes, you got it, the deep pockets of the roof manufacturer.
And you know, it's the roof manufacturer with the deepest pockets who had nothing to do with the installation and who strenuously avoids any loads, penetrations, and especially solar systems on roofs.
So, the moral to this story? Think fire protection and fire service. The two are inseparable. Just like good engineering and property/life safety.
Jerry ‘Dutch’ Forstater, PE, PSP, CET, is CEO/Managing Principal of PSE, a planning, design, and project management firm with over 35 years in code studies, life safety analysis, annual fire door/gate inspections, conditions reports, wet-pipe/dry-pipe/pre-action sprinkler systems, clean agent suppression, fire detection and notification, etc. You can contact ‘Dutch’ at 800.839.5060 x107 or by email @