Rooftop solar panels become new enemy of U.S. firefighters

[Robaroni]

Originally Posted by Exeric

I'm no technical expert on PV but I'd like to know where you got your information here. My understanding is that non-microinverter grid tied PV systems have several modules in series supplying DC voltage up to 300 or 400 volts at the inverter. Also, I'm a big enthusiast for PV systems and I'd like to one day install a system at my house. Rob, why do think that someone like me has some grudge or is in opposition to the solar industry? I'm no firefighter but I'm a human being. Its called empathy Rob. How would a firefighter know ahead of time if a house has a grid tied system, non grid tied, or a grid tied micro-inverter system, all of which can impact the level of risk?

Again, it gets back to the problem of people getting their back up, (like an angry cat) when they see a technical problem as a threat to their affinity group. Don't be so tribal. It not us and them.

It's none of that, I'm not angry, I'm using common sense.

Intertie systems have modules in series, whether that system uses microinverters or a single inverter. Series resistors, batteries, etc. have zero volts when the string is broken. You would have to literally pick up the disconnected wires, clean off the insulation, take off your gloves and hold the wires in opposite hands to get a shock. Not a very likely scenario for a fireman on a roof, is it?

Modules are rated at 12 or 24 volts with a VOC (open circuit voltage) of anywhere from 35 to 45 volts DC in most cases( 24V module). Not enough to give anyone a shock.

Off grid systems can run on 12V up to about 150V into the battery charge controller. Battery charge controllers usually peak out at around 150VDC because of internal MOSFETS (metal oxide silicon field effect transistors) and power ratings. But even off grid systems can only run what one module can deliver, just like an intertie, if the string is broken modules must be in a series string to get to the 150VDC level so no voltage is present.

So it really doesn't matter very much whether it's an on or off grid system.

Again, I'm just using common sense and logic, not anger or rage.

Rob

[Exeric]

Actually, this is where you are going wrong. You can be shocked with an open system. It's highly illegal but you can kill a lot of fish by putting two wires, one attached to a high voltage, and the other attached to ground into water. People die through this kind of means all the time. All that would need to happen is some ponding on the roof of a non-microinverter grid tied system where damage has been done to the mechanical protection of the wires and a decent ground somewhere on the roof that the water has reached. If a firefighter is up there he's in potential trouble.

More to the point, this could happen even on the ground by a firefighter who is inadvertently grounded and spraying water on the roof where the hot wire is exposed. Yes, I agree that one need a number of things to occur to add up to a big shock. But it's only a matter of statistics, not a matter of impossibility that it occurs. It's easy to say, "hey fireman, get up there and do your job!" when you are not the one facing that very real risk. That's why I was advocating putting in grounding at the fire hydrant and through the hose. That way any electricity coming back through the column of water will take the easy path to ground instead of through the firefighter.

[NeilBlanchard]

You can be shocked with any electrical system. Why are solar PV panels any different?

[Exeric]

Ok, I finally throw in the towel. The firefighters are on their own. The fact that there is 300 to 600 volts dc on wires going all the way down to the main inverter on a non microinverter grid tied system during daylight hours before power is physically turned off at the first disconnect is not a problem in the least. The fact that the firefighter does not know what kind of system it is before he gets to the fire is not a problem either. The fact that a system like this can be physically damaged by the fire in such a way that the normal safety backups don't work is not a problem. The fact that this situation is not like the normal grid connection where the meter can be removed and all potential for powering the house is removed does not matter in the least. Do I have all this right?

I just want to make sure that I've got it right that the official policy on this forum is that any firefighters' concerns are not our concern because we are for PV, period. Have I got that right?

[NeilBlanchard]

Hi Eric,

That's not how most solar PV systems work; on homes anyway. They have micro-invertors and so it is a 120v / 20A / 60Hz circuit that ties them into the panel. And, when the grid goes off, the panels go off. They don't want production during a power outage.

[Exeric]

Well, I know that microinverters are the newest and best for grid tied systems but I'm sure there are tons of legacy grid tied systems out there. They are also much cheaper systems than microinverter types, though I don't know how much longer that will be the case.

One thing this discussion has convinced me of: When I finally get around to installing a PV system a grid tied microinverter system will be what I get. I'm just not convinced the other type can ever be made to be safe in a fire. The main thing is to inform firefighters what system you have and have them trained well enough to understand the varying inherent risks of the different systems.

[Robaroni]

Originally Posted by Exeric

Actually, this is where you are going wrong. You can be shocked with an open system. It's highly illegal but you can kill a lot of fish by putting two wires, one attached to a high voltage, and the other attached to ground into water. People die through this kind of means all the time. All that would need to happen is some ponding on the roof of a non-microinverter grid tied system where damage has been done to the mechanical protection of the wires and a decent ground somewhere on the roof that the water has reached. If a firefighter is up there he's in potential trouble.

More to the point, this could happen even on the ground by a firefighter who is inadvertently grounded and spraying water on the roof where the hot wire is exposed. Yes, I agree that one need a number of things to occur to add up to a big shock. But it's only a matter of statistics, not a matter of impossibility that it occurs. It's easy to say, "hey fireman, get up there and do your job!" when you are not the one facing that very real risk. That's why I was advocating putting in grounding at the fire hydrant and through the hose. That way any electricity coming back through the column of water will take the easy path to ground instead of through the firefighter.

OK, several things have to happen before the FF gets zapped by a system. Let's say that he's spraying water on a roof with PV modules going to a central inverter, not a series of microinverters. He shuts off the main power to the house which is something you normally do on any house with AC in an area you are trying to control a fire. This removes the main inverter from the system. Now you have a string of PV modules in series totaling 600 volts going to that off converter AND it's daytime AND you haven't sprayed the modules with foam to effectively shut them off AND you have no protective rubber boots or rubber gloves on AND the smoke from the fire isn't cutting the power to the modules. Lets also say that the fire has burned the insulation off the wires and you spray the bare wires with water. How is the electricity going to get down the non conductive hose to you? If it does anything it will travel down the route of least resistance to ground and that's most likely the water run off, water isn't running down the hose, it's running away from the hose.

The fish scenario is not a open system, open systems do not conduct electricity. You need a closed system. The water between the wires is conducting electricity. If you were to stand in the water with rubber boots on you would not get a shock. PV arrays have specific grounding code requirements. DC wiring coming into a house must be encased in metal tubing

Fireman are equipped to deal with electricity in fires, it's not saying, "do your job." they know their job whether it is a chemical fire of unknown chemicals, or an EV with a 360 volt battery bank. They train for different confrontations. I respect how hard they work but they don't go to a fire unprotected. There's a reason they wear protective clothing. It isolates them from fumes and electricity.

How many fireman around the world have been killed from PV arrays? I don't know of any. Do you think they aren't prepared for PV arrays on houses that are on fire? I don't.

Each module must have aground going to it that returns to a ground rod 8 feet in the ground. Grounding has specific code requirements.

Again, any PV sending DC to an inverter that can't be shut off from the ground has to be encased in metal, here's my system.

I'm not trying to be hard to you or the fireman, they provide a wonderful service. I'm talking about the facts of PV systems from the perspective of an electronic engineer who has worked with electricity his whole life.

[Exeric]

I think this discussion is getting more into a bragging match than something constructive. One doesn't stand next to the end of the hose that is attached to the fire hydrant. Then one WOULD be insulated by the hose itself. Rather, one stands next to the other end of the hose and holds the part next to the nozzle. In this case there is no real insulating value of hose protecting you from being shocked by the stream of water being used as a conducting medium.

I'm convinced that danger is real and I'm not sure the statistics on whether it has happened already to firefighters is publicly available. Are you sure it hasn't happened or are you guessing?

I've got 20 years experience working on aircraft avionics. But I always say that by the time one can't stand on the arguments themselves and you have to appeal to the strength of your credentials that something has been lost in the discussion. Let's both give it a rest.

[Robaroni]

Originally Posted by NeilBlanchard

You can be shocked with any electrical system. Why are solar PV panels any different?

Because the voltage is too low. Low voltage DC from a single module is under 44 volts.

IF you grabbed the ends of series modules that amounted to enough voltage to travel through your body you would get a shock. The human body has very high resistance in the order of Megaohms. When I was a teen working in a TV repair shop I got hit from the second anode on cathode ray tubes from a color TV a technician left on a bench, it was 25 KV. It didn't kill me because the current was low. (When I recovered I did kill him, however!)

I do know PV installers who got careless and got shocks from strings. It didn't kill them, I don't know anyone who has been killed from a high voltage string, I think the current is too low.

Rob

[Robaroni]

Originally Posted by Exeric

I think this discussion is getting more into a bragging match than something constructive. One doesn't stand next to the end of the hose that is attached to the fire hydrant. Then one WOULD be insulated by the hose itself. Rather, one stands next to the other end of the hose and holds the part next to the nozzle. In this case there is no real insulating value of hose protecting you from being shocked by the stream of water being used as a conducting medium.

I'm convinced that danger is real and I'm not sure the statistics on whether it has happened already to firefighters is publicly available. Are you sure it hasn't happened or are you guessing?

I've got 20 years experience working on aircraft avionics. But I always say that by the time one can't stand on the arguments themselves and you have to appeal to the strength of your credentials that something has been lost in the discussion. Let's both give it a rest.

Sure, I'm sorry if I'm coming across aggressively I'm not trying to. Please accept my apology if it appears that way.

Rob