Solar panel fires!

[max2k]

Yes, I did.


Still no. The formula you quoted is for electric field of a current. It doesn't apply to what I said which is static electricity. Again Google is your friend if you don't know the difference. In static electricity, there's no current until the point of discharge. Only potential or voltage matters in attracting oppositely charged ions. Even at the point of discharge, people don't normally use current as figure of merit. Because 1M amps in 1us doesn't say very much. It's normally in joules.

1M amps in 1 uS says a lot- it means 1 coulomb of charge passed through that point. It doesn't say anything about energy, you're correct. If you knew the difference in el. potential which caused that amount of charge to move then you could find the energy involved.

Dry air arcs at electric field level of 30,000 V/cm AC or DC. You need very high voltage to start arching this way. Static electricity provides such voltages, tens of kV, depending on a cat . Electric charges of the same polarity repel so to get them somewhere you need external force (petting the same cat would do). Sharp electrodes arch easier because of their shape which increases intensity of electric field, not number of charges. Static electricity also doesn't have much energy so when someone get shocked by static he/she generally survives and it is impossible to set building on fire with just static. This all is not relevant to solar due to level of voltages involved.

Another kind of arching is caused by bad contact and high current trying to get through. This possibility is very relevant to solar and also to any other power line carrying current > 1 A. Due to local elevated resistance such spot becomes very hot very quickly as a lot of power get converted to heat due to voltage drop over bad contact. No magic electric or magnetic fields take part in this process. This 'arching' can start a fire if there's something to burn, like wire insulation, jug of gasoline, etc. Solar cells are made of silicon and it is hard chemical to burn- it ignites at temps around 1000 C, a lot of other materials will be burning before that point.

I don't think solar creates any extra fire hazard compare to your conventional power wiring: I had breaker burnt in my hose power panel due to bad contact, I had power wall outlet wire arching inside (very dangerous due to proximity of wood) but that's just life. Some posts in this thread provided very useful advices how to maintain these systems, at kW levels they deserve respect. Micro inverters if I understand this correctly somewhat mitigate the problem by decreasing current level in the common rail due to higher output voltage compare to raw DC output from the panels. Still, somewhere all that energy gets connected together and becomes dangerous.

[vav925]

whoa!

[inetdog]

I think that is a very unhappy cat. Bruce Roe

He might just be mad at the cameraman. Or was that a selfie?

[bcroe]

Cat

I am tempted to censor that post on the grounds that it encourages cruelty to animals.

I think that is a very unhappy cat. Bruce Roe

[inetdog]

Me thinks someone in this thread needs to by everyone in their home one of these.

I am tempted to censor that post on the grounds that it encourages cruelty to animals.

[Sunking]

Me thinks someone in this thread needs to by everyone in their home one of these.

[sensij]

Still no. The formula you quoted is for electric field of a current. It doesn't apply to what I said which is static electricity. Again Google is your friend if you don't know the difference. In static electricity, there's no current until the point of discharge. Only potential or voltage matters in attracting oppositely charged ions. Even at the point of discharge, people don't normally use current as figure of merit. Because 1M amps in 1us doesn't say very much. It's normally in joules.

The formula I originally supplied was for voltage drop, and was from a source that erroneously equated voltage drop with electric field. That was a bad mistake on my part, and I've replaced the equation with a paper that properly calculates the static electric field generated outside of a current carrying conductor. The equations are more complicated, but the cliff notes version is that for an ideal conductor, there is zero electric field outside of it, but in the real world, there is some charge density that builds up on the surface of the conductor that can create a weak field... in this case, orders of magnitude less than the charge generated on glass by wind.

Your use of the phrase "static electricity" is incorrect, and is leading to some mistaken ideas on your part, and some mistaken interpretations of your ideas by me and others. The true fire hazards of DC (or AC) conductors were explained by others much more clearly in the thread, and neither you nor I has contributed much of value to that discussion (except perhaps the article you linked).

[thejq]

You said the above...

Yes, I did.

And you don't see how the strength of an electric field is relevant? Yeah, there is no point to this at all. Mike's got it right.

Still no. The formula you quoted is for electric field of a current. It doesn't apply to what I said which is static electricity. Again Google is your friend if you don't know the difference. In static electricity, there's no current until the point of discharge. Only potential or voltage matters in attracting oppositely charged ions. Even at the point of discharge, people don't normally use current as figure of merit. Because 1M amps in 1us doesn't say very much. It's normally in joules.

[SunEagle]

All my inside connections are inside steel boxes; not likely to ever flame. But some possible failures
could be difficult and expensive to fix, think inverter. All 15KW feeds through a couple split bolt taps,
which aren't so easy to check being taped up. But I can at least check for warmth by hand and with
my infrared thermometer. Bruce Roe

An IR thermometer or camera is the perfect tool to detect poor electrical connections that have been taped up. As long as you have the camera set up correctly and use the thermometer within the desired distance of your target.

[bcroe]

Great to hear you have had no issues. Also good info that you found that the connections had changed over a period of time.

Yes I agree that a solar pv system is relatively "maintenance free", but all electrical wiring systems require spot checks every so often because they do change and usually not for the better.

As for the potential of a fire. Chances are higher that it will start inside the building from another source then from a failed pv wiring connection. And as Mike pointed out there really isn't much flammable material in a solar panel to burn.

So while this thread could be an eye opener for some, I wouldn't worry about your pv system going up in flames anytime soon.

All my inside connections are inside steel boxes; not likely to ever flame. But some possible failures
could be difficult and expensive to fix, think inverter. All 15KW feeds through a couple split bolt taps,
which aren't so easy to check being taped up. But I can at least check for warmth by hand and with
my infrared thermometer. Bruce Roe

[SunEagle]

That was one of the first things I thought about, and one of many reasons I have a ground
mounted array hundreds of feet from any building. I am going to add this which just might
relate to some fires.

After some 22 months of service, I have decided to join the "TIGHTEN ALL CONNECTIONS
REGULARLY" school. I have been running 15 KW out every sunny day not just at solar noon,
but for many of the daylight hours. None of the wiring is approaching its absolute limit,
but at the end of sun it can definitely be felt to be warmer than the surroundings.

There are a couple inverters, DC and AC disconnect boxes, several AC breaker boxes, and a
DC combiner box. All the connections were initially checked by me. About a year ago a
circuit breaker failed, apparently from heat at one of the line terminals. This month a DC
screw connection to a disconnect switch (carrying 21A @ 360 VDC) burned out. The
problem was detected & repaired in a couple hours, but the issue is, why did it happen
at all?

As others have suggested, perhaps the constant heat/cool cycles at significant power can
work these connections loose. Loose enough, the resistance will rise and they burn out.
I undertook (in the dark of course) to check them ALL for tightness. Sure enough, the
tightness of screws after 1.5 years varied A LOT. Since all were done by the same person,
often many the same day, some had apparently loosened up. My conclusion is that
these all need to be rechecked annually, at least until they ALL show some settling to
stability.

So far, no issues with split bolt or soldered connections. Bruce Roe

Great to hear you have had no issues. Also good info that you found that the connections had changed over a period of time.

Yes I agree that a solar pv system is relatively "maintenance free", but all electrical wiring systems require spot checks every so often because they do change and usually not for the better.

As for the potential of a fire. Chances are higher that it will start inside the building from another source then from a failed pv wiring connection. And as Mike pointed out there really isn't much flammable material in a solar panel to burn.

So while this thread could be an eye opener for some, I wouldn't worry about your pv system going up in flames anytime soon.

[sensij]

...With DC, if the wire is not shield properly, charged particles will accumulate around the wire. With the right voltage and humidity, arc occurs to release the energy build-up...

...High voltage DC can create a static field around the wires. If not properly shielded, can cause arcs or sparks...

I'm talking about static voltages. Think of it as a high voltage battery with +/- terminals that're pretty close. The + side attracts - particles, and - side, + particles. With enough build up and the right humidity, the two sides of particles (or ions) will some times touch and release the energy, in extreme case, produces an arc. If you enclose it in a metal conduit, the metal is a conductor that constantly neutralizes ions, so no charge build-up no arc. With AC, the polarity of the battery changes at 60Hz, so there's no time for charge to build-up.

You said the above...

I don't see the relevance of the electric field equation in this discussion, and the reason for keeping bringing it up...

And you don't see how the strength of an electric field is relevant? Yeah, there is no point to this at all. Mike's got it right.

[thejq]

OK, let's slow down. The equation I provided is not that of the magnetic field, it is the electric field. Large electric fields can be hazardous (corona discharge in extreme cases), but the electric field generated here is insignificant.

The hazards described in the article, or in the example of a battery terminal that arcs, are not due to the attraction of charged particles. They are due either to a termination failure or an insulation failure. In the case of insulation damage, dielectric breakdown can occur under the right conditions, and an arc can occur between + and -, or possibly to ground if it is not a floating system. However, just so it is clear, this has nothing to do with the accumulation of charged particles. Although grounded metal conduit serves many purposes, neutralization of ions is not one of them.

With undamaged insulation and proper terminations, I don't see how the risks of DC in PV systems are any greater than the risks of AC.

I don't see the relevance of the electric field equation in this discussion, and the reason for keeping bringing it up, since both you and I agree it's not the cause of arcing. I also failed to see what your point is after all these. The original questions was whether high voltage DC is more prone to causing fire, and microinverter is safer in that aspect. My point from the beginning was most likely yes. What is your point? I gave one simple example of what can cause arcing that's unique to high voltage DC. I never said it's the only nor necessary-and-sufficient reason. By regurgitating the points in the article I linked, logical you agreed with my main point, but your wording sounded like disagreeing. Reading your reply reminded me of the days of high school debate where triumph by confusion is often the winning strategy.

[Mike90250]

Ok, as a newbie following this thread, I got lost somewhere on the middle. I never thought about the fire aspect. ......

Thank user thejq for starting up a whole bunch of nothing.

In a modern Glass and silicon panel, there is a bit of EVA sealant, and a thin Tedlar backsheet. There is very little
in a PV panel to burn. It doesn't create mystery fields that will arc and torch your house. The AC/DC static field charge buildup bs is just nonsense.

But what can happen, is rats, squirrels, chewed insulation, nest materials, trapped leaves, palm fronds and that stuff can be lit off by damaged wires, and there goes the neighborhood.

And, yes, copper creep under pressure. Even bit me. Installer added a proper 40a conductor to a buss bar, and either forgot to torque and re-torque an hour later, or something, but the connection failed. Inside a UL box with UL wire. Scorched stuff, but no flames. I now have a gunsmiths torque driver to go through the ePanel with.

[bcroe]

I never thought about the fire aspect.

That was one of the first things I thought about, and one of many reasons I have a ground
mounted array hundreds of feet from any building. I am going to add this which just might
relate to some fires.

After some 22 months of service, I have decided to join the "TIGHTEN ALL CONNECTIONS
REGULARLY" school. I have been running 15 KW out every sunny day not just at solar noon,
but for many of the daylight hours. None of the wiring is approaching its absolute limit,
but at the end of sun it can definitely be felt to be warmer than the surroundings.

There are a couple inverters, DC and AC disconnect boxes, several AC breaker boxes, and a
DC combiner box. All the connections were initially checked by me. About a year ago a
circuit breaker failed, apparently from heat at one of the line terminals. This month a DC
screw connection to a disconnect switch (carrying 21A @ 360 VDC) burned out. The
problem was detected & repaired in a couple hours, but the issue is, why did it happen
at all?

As others have suggested, perhaps the constant heat/cool cycles at significant power can
work these connections loose. Loose enough, the resistance will rise and they burn out.
I undertook (in the dark of course) to check them ALL for tightness. Sure enough, the
tightness of screws after 1.5 years varied A LOT. Since all were done by the same person,
often many the same day, some had apparently loosened up. My conclusion is that
these all need to be rechecked annually, at least until they ALL show some settling to
stability.

So far, no issues with split bolt or soldered connections. Bruce Roe