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Fire! Is Solar a Threat?


  09:24:00 am, by Jim Jenal - Founder & CEO   , 820 words  
Categories: All About Solar Power, Solar News, Commercial Solar, Safety

Fire! Is Solar a Threat?

We saw a piece today about a fire on a distribution warehouse in New Jersey that was gutted in part because the local fire department was afraid to interact with the solar power system on the warehouse roof.  As solar makes greater inroads on commercial buildings, what can we as an industry do to address this concern? (H/T SolarWakeup.com)

The distribution center, owned by Dietz & Watson, was a refrigerated warehouse that supported over 7,000 solar modules according to news reports.  From Google we get this image of the center in happier days:

Dietz & Watson distribution center, new jerseyThis is a very large commercial array by any measure - even if those are 200 Watt modules you are looking at a 1.4 MW install on the roof, to say nothing of the additional capacity installed in the carports to the west.

It is also a very nicely designed array with clear access paths throughout the roof and plenty of potential areas that could be broken open to allow for venting (although I’m sure from a fire fighter’s perspective, they would always want more).

Sadly, this is how it looked during the fire:

warehouse on fire

Here is the view of the blaze taken from the raw video recorded by local TV station NBC10:

Fire on warehouseThis image makes clear that the NE quadrant of the building has been extensively damaged - the black area is where the solar panels have been completely destroyed.

The image also makes clear that the fire department chose to fight this fire from the ground, spraying water and foam onto the roof as opposed to going on to the roof itself.  (There was no explanation given as to the cause of the fire.)

The local reporting indicated that the fire crews were concerned about possible collapse of the roof due to the amount of water being poured onto the fire.  But they also mentioned the concern over possible electrocution:

Firefighters had to pull back at some points because the fully-charged solar panels posed the risk of electrocution.

“With all that power and energy up there, I can’t jeopardize a guy’s life for that,” said [Delanco Fire Chief Ron] Holt.

So what to make of all of this?

There can be no doubt that solar installations have the potential to make the already dangerous business of fighting a fire more hazardous.  Strings of solar panels can produce as much as 600 Volts DC and as a general rule, there is no way to shut them off from the ground.  While a DC disconnect on the ground could isolate the array from a ground mounted inverter, there is still potential in the conductors leading from the roof to the inverter.  If those conductors are shorted together - due to either a fireman’s actions or the fire itself - there is the potential for significant arcing and possibly even electrocution.

Of course, one way to reduce that risk is through the use of microinverters or AC modules.  With a microinverter, the only conductor runs are AC which can be safely switched off from the ground meaning that any conductors coming from the roof to the ground will be safe.  The individual solar modules can still produce power, but there are no strings to slice into or suddenly short to create a dangerous condition on the roof.  While microinverter systems are not generally considered on systems of this size, Enphase recently announced the use of their products on a 2.3 MW commercial array - possibly larger than this one.

Which begs the question - would that have mattered here?  Maybe, maybe not.  The question really is a function of how well would the local fire department understand the difference?  When we talk with local fire inspectors, they are always appreciative of the added safety to be found with microinverter systems but how well does the inspector’s understanding extend to the fire crews reporting to that fire?  Would they have trusted that the claimed safety was real and moved more aggressively to fight the fire on the roof?  Or would they have elected to play it safe?

The solar industry can work to develop safer products - which microinverters surely are - but that won’t matter if local fire crews aren’t educated as to how best to fight these fires.  Interestingly, while local codes require solar installers to provide all sorts of largely useless signage on our arrays - for example, specifying the nominal AC voltage and current as if that would make the least difference to anyone - there is no requirement to indicate whether the type of inverter being used.  Absent such signage, how would a local fire crew know what they were facing?

Maybe our friends at Enphase can design a placard to attach to our AC disconnect switches that advises the local fire department that throwing that one switch renders the conductors coming down from the roof safe.

So much of what we must do in the solar industry is education - this is perhaps one area where we need to improve our efforts.



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Comment from:
4 stars
It seems that the Australians are ahead of us on this, or at least they make is sound like they are. Could you comment on arc fault protection and it’s use in fire prevention and safety? It is my understanding that micro-inverters are not necessarily immune from arcing and that nothing will ever completely eliminate the threat, except maybe something at the level of every single module. As you know, my solar business does deal with this issue from a preventative standpoint, however, I don’t need to be an expert (nor will I ever be), but I’d love to be able to direct my customers, particularly residential installers, somewhere. Thanks for the in-depth report. Your content is like non elsewhere, and you are providing a real service to the industry. P.S. I happened upon this, for those who really want and need to check into the issue in depth. http://bit.ly/18q37nb
09/03/13 @ 16:05
Comment from: Jim Jenal - Founder & CEO
Hi Spiffy - Thanks very much for the kind words - I really appreciate it. As I understand it, an arc fault occurs when you have two faults on a PV string, the second of which is on the leg that is set to detect ground faults. When the second fault occurs, the inverter is isolated from the string (due to the GFDI circuitry) but because you have two faults, you can have a complete circuit w/in the array. That could be in a single string, or it could be downstream from a combiner in which case you will have a much bigger issue on your hands. It is my understanding that it was such a double fault situation that created the arc fault that lead to the fire discussed here: http://solarprofessional.com/articles/design-installation/the-bakersfield-fire-a-lesson-in-ground-fault-protection Interestingly, the new Enphase microinverter - the M250 - should prevent arc faults since it can detect a fault on either leg of the DC connection. Of course, microinverters are far less of a concern for a dangerous arc fault since the DC “string” is only one module. (The earlier models, most notably the M215, had a more conventional GFDI circuit which could only detect a fault on one leg.) I discussed this benefit of the new M250 in this post: http://runonsun.com/~runons5/blogs/blog1.php/solnews/intersolar-2013-enphase-gen-4 Jim
09/03/13 @ 16:32
Comment from: John Drucker  
John Drucker
4 stars
I understand also that there was concern of collapse due to the buildings tilt slab construction. There are a number of photographs taken that seem to indicate that tilt slab collapse did occur due to the collapse of the supporting (bracing) roof assembly. A 40 Foot tilt slab dictates a minimum 60 foot collapse zone. I agree with Chief Holt a firefighters life is not worth jeopardizes over property with the numerous hazards at this facility.
08/23/15 @ 09:59
Comment from: Jim Jenal - Founder & CEO
John - that is a very good point - if the slabs of the building are in danger of collapse that would make it too dangerous for the fire fighters. But of course, that could be a risk in every tilt-up slab building out there, not just those with solar. Odd that nearly 2 years later and we haven’t heard anything about the cause of the fire. Jim
08/23/15 @ 10:07

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Jim Jenal is the Founder & CEO of Run on Sun, Pasadena's premier installer and integrator of top-of-the-line solar power installations.
Run on Sun also offers solar consulting services, working with consumers, utilities, and municipalities to help them make solar power affordable and reliable.

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