When a Tree Falls on the Array

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PWDickerson

Senior Member
Location
Clinton, WA
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Solar Contractor
I was conducting a training for our local fire department yesterday evening, getting them up to speed on Rapid Shutdown. After the training, one of the fire fighters asked what they should do if they arrive at a home where a tree has fallen on a roof-mounted solar array. If the system has module level rapid shutdown, there shouldn't be any point in the array that exceeds the module Voc, and so it should be safe to cut the tree away. But what should I tell them to do if it is an older system without rapid shutdown? What would I instruct my crew to do if we were called to make it safe for the fire fighters? I have been thinking about that this morning and thought I would let the forum chew on it.
 
Kind of brainstorming from scratch here, but ideally...

1) DC disco(s)off
2) harnesses on
3) hot gloves on
4) if there are separate arrays connected in any way to the damaged one, disconnect them (unplug connectors) first
4) lift panels from the outside edges or array one by one and disconnect connectors
5) test voltage from any unplugged connectors to the racking as you go. Use extra caution if detecting anything over a single panel voltage

If you are lucky enough to have a string map, stategically remove panels in an order that breaks up strings to reduce max possible voltage.

If firefighters are doing this, their PPE is probably enough protection to remove panels with regular tools? Most difficult thing would be getting the appropriate plastic tool for unfastening the panel connectors.
 
RSD under 690.12 and UL 3741 is designed to operate on an undamaged PV array. If the PV array is damaged then there is no guarantee that the system can be rendered safe. That's not to say that all methods of implementing RSD will not work on a damaged array but some won't and therefore it's safer to assume a damaged array is not rendered safe by RSD.
That being the case I would treat a PV array under a downed tree to be live until verified by an electrician as safe.
 
There is a spray on product from an Australian company designed to use on PV modules to block sunlight and not damage them. You peel it off after you are done with it. The company is PVStop. Has anyone used this?
 
pv_n00b said:
There is a spray on product from an Australian company designed to use on PV modules to block sunlight and not damage them. You peel it off after you are done with it. The company is PVStop. Has anyone used this?
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How are you going to get to all the modules to spray that stuff on them when there is a tree lying on the array?
 
letgomywago said:
Headlamps and temp strings wouldn't put out enough light to be dangerous on the panels too
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Of course I was not being serious, but that said, I once got shocked pretty good from an indoor teaching PV array on a roof mockup when the only light source was a couple of fluorescent light tubes overhead on a 20 foot ceiling. I'm sure the Isc was pretty low but the Voc was about 380V. I fell off the roof onto the floor when it happened but it was only a foot or two; if it had been a real roof in bright sunlight I might not have survived.
 
ggunn said:
Of course I was not being serious, but that said, I once got shocked pretty good from an indoor teaching PV array on a roof mockup when the only light source was a couple of fluorescent light tubes overhead on a 20 foot ceiling. I'm sure the Isc was pretty low but the Voc was about 380V. I fell off the roof onto the floor when it happened but it was only a foot or two; if it had been a real roof in bright sunlight I might not have survived.
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So can a spectrum be chosen that isn't picked up by the panels. They have a range
 
ggunn said:
Of course I was not being serious, but that said, I once got shocked pretty good from an indoor teaching PV array on a roof mockup when the only light source was a couple of fluorescent light tubes overhead on a 20 foot ceiling. I'm sure the Isc was pretty low but the Voc was about 380V. I fell off the roof onto the floor when it happened but it was only a foot or two; if it had been a real roof in bright sunlight I might not have survived.
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Good thing one of the instructors did not let a mockup squirrel loose on the mockup roof. ;)
 
pv_n00b said:
Good thing one of the instructors did not let a mockup squirrel loose on the mockup roof. ;)
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It's even worse: I was the instructor. :D

Luckily I was setting up for a class and no student witnessed my act of flagrant stupidity.

For my next lesson I shall set myself on fire...
 
letgomywago said:
Headlamps and temp strings wouldn't put out enough light to be dangerous on the panels too
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But the typical firefighting scene lights can result in a hazardous voltage where the outputs are open circuited and a someone comes into contact with the conductors.
 
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