Fusing solar panels?

Depends where you are in the world as to what standards applies. In Australia, yes you do.
The manufacturers spec sheet for your panels will say the fuse size per string.
The correct type has to be used for PV, called gPV basically high DC voltage rated, fast blow types.
Usually 38mm x 10mm size.
 
Since the OP is in Germany, that kinda narrows it down to his location ;)
I agree with Repacket. It depends on the building codes in your area. But most likely, you do need to fuse your panels.

You also should have at least 1 cutoff switch that is easily accessible outside of your building. This is for first responders or if you need to shut it down asap.
I believe some even install a separate cutoff for each series connection run for added safety.

I know you are asking about fuses, but I figure that cuffoff panels would be soon to follow as well ;)
 
How could such a cutoff panel look like? Any pictures or links?

Would an automatic circuit breaker do the job. Both in one?
 
Either a standard breaker panel box rated for DC loads, or a manual pull handle style used on A/C units.

You can use a breaker that "looks" similar to what is in a standard breaker box, however it MUST be rated for DC loads. These breakers are usually a little more expensive and a bit beefier as they have to handle directional current instead of alternating current.

For a good explanation, please watch bigclivedotcom's video on the subject:
 
I can only find very expensive ones of these. Any cheaper models available? Or any other possibilities to fuse and disconnect the solar panels?
 
You could get something like this:
https://www.homedepot.com/p/GE-30-Amp-120-240-Volt-240-Watt-Fused-AC-Disconnect-TF30RCP/100576894
30 Amp 120/240-Volt 240-Watt Fused AC Disconnect
$11USD

They have heavy copper lugs and can handle high arcs during disconnect. They are nice because you can pull the disconnect, turn it upside-down and re-insert it as there's a built in holder, close the box so it doesn't accidentally get turned on.

Here's the exact same model that Clive was showing:
https://www.amazon.co.uk/Circuit-Breaker-Solar-Single-TOB1Z-63/dp/B017Q6DL2Y
it's only about $11USD as well
 
I have a combiner/disconnect at the PV array on outside of house per city code. It happens to be circuit breakers because the Midnight Solar combiner box with 'all-off-handle' encourages them. But electrically I don't see why an actual 'fuse' (overload/short) function of the circuit breaker would be needed as panels can be shorted and not hurt anything.

I also have a circuit breakers on the combined PV array strings just before the Charge Controller. Not sure if this is required by code or not. This serves as PV array cutoffs inside the house conveniently located next to the Charge Controllers. For this combined circuit (of several strings of panels) I'm pretty sure a circuit breaker is recommended to protect the wire and/or Charge Controller - but not sure what that would be. There are already lightning (surge) arresters at the outside combiner boxes to take of lightning - so what else could cause a 'surge' beyond the rated capacity of the wire / system might be the question.

Interesting topic - maybe the simple on/off (which is convenient and for safety working on system) is so often provided by circuit breaks that fusing (overload) is combined because no makes simple on/off switches that snap into combiner boxes.
 
OffGridInTheCity said:
But electrically I don't see why an actual 'fuse' (overload/short) function of the circuit breaker would be needed as panels can be shorted and not hurt anything.
Click to expand...

A single panel shorted won't do anything, but a string of panels shorted will create a blinding flash. Depending on how many panels you have, shorting the wires could easily become as powerful than a welder, or more so. Not to mention all that current flowing as well. I'd hate to be in between those wires.

What is the voltage that your solar panel string operates at?

OffGridInTheCity said:
I also have a circuit breakers on the combined PV array strings just before the Charge Controller. Not sure if this is required by code or not. This serves as PV array cutoffs inside the house conveniently located next to the Charge Controllers. For this combined circuit (of several strings of panels) I'm pretty sure a circuit breaker is recommended to protect the wire and/or Charge Controller - but not sure what that would be. There are already lightning (surge) arresters at the outside combiner boxes to take of lightning - so what else could cause a 'surge' beyond the rated capacity of the wire / system might be the question.

Interesting topic - maybe the simple on/off (which is convenient and for safety working on system) is so often provided by circuit breaks that fusing (overload) is combined because no makes simple on/off switches that snap into combiner boxes.
Click to expand...

A circuit breaker in a combiner box would basically be replacing the fuse. I think what Redpacket was alluding to was having the fuse as a failsafe. Just in case the circuit breaker didn't, well, break as expected. When dealing with high voltages, more points of controlled failure is desired. You never know when one will fail and the other saves your, or others, lives.

But, with that said, most homes only have 3 breakers. Mains at the pole, mains in the house panel, and one for each circuit. So having 2 breakers already may be good, but a 3rd wouldn't hurt ;)
 
The fuse per string is for safety in the event of a fault where panels in a string go short & the rest of the array dumps energy into them causing a roof top fire.
This has happened more than a few times, hence the fuse requirement.
"Hard shading" on panels increases the likelihood (stresses the bypass diodes more) and so does panels that have been physically stressed (numpty installer walking on them, yes some did) &/or "snail trails" (micro cracked silicon panel cells).

Breakers usually have much slower acting time curves - these gPV fuses are quick quick acting.

Like Korishan was saying, DC causes arcs that don't easily go out so you need special DC gear & rated for the voltage.
 
Korishan said:
OffGridInTheCity said:
But electrically I don't see why an actual 'fuse' (overload/short) function of the circuit breaker would be needed as panels can be shorted and not hurt anything.
Click to expand...

A single panel shorted won't do anything, but a string of panels shorted will create a blinding flash. Depending on how many panels you have, shorting the wires could easily become as powerful than a welder, or more so. Not to mention all that current flowing as well. I'd hate to be in between those wires.

What is the voltage that your solar panel string operates at?
Click to expand...
Each string is 3 panels in series with 39.7v (Voc) / 31.3v (Vmpp) and 9.8a (Isc) / 9.2a (Impp). So nominally its 93.9v @ 9.2a with max of 119.1v and 9.84a at short circuit. Each string has a 15amp circuit breaker in the combiner box. 4 strings per combiner give 93.9v @36.8a = 3,445wattstraveling to the Controller area.
Its not clear to me (other than lightning) how a string would trip the 15amp circuit breaker. I guess 2 or morestrings (wiring)could cross connect on roof under the panels and overload the wiring (10 awg) for a single string with more than 15amps... so circuit breakers work to protect the wiring of each string?
 
OffGridInTheCity said:
Each string is 3 panels in series with 39.7v (Voc) / 31.3v (Vmpp) and 9.8a (Isc) / 9.2a (Impp). So nominally its 93.9v @ 9.2a with max of 119.1v and 9.84a at short circuit. Each string has a 15amp circuit breaker in the combiner box. 4 strings per combiner give 93.9v @36.8a = 3,445wattstraveling to the Controller area.
Its not clear to me (other than lightning) how a string would trip the 15amp circuit breaker. I guess 2 or morestrings (wiring)could cross connect on roof under the panels and overload the wiring (10 awg) for a single string with more than 15amps... so circuit breakers work to protect the wiring of each string?
Click to expand...

So say one of the 4 strings has a short fault, the other three dump energy into that one = 3x 9.84 = 29.52A, breaker pops?
 
Redpacket said:
OffGridInTheCity said:
Each string is 3 panels in series with 39.7v (Voc) / 31.3v (Vmpp) and 9.8a (Isc) / 9.2a (Impp). So nominally its 93.9v @ 9.2a with max of 119.1v and 9.84a at short circuit. Each string has a 15amp circuit breaker in the combiner box. 4 strings per combiner give 93.9v @36.8a = 3,445wattstraveling to the Controller area.
Its not clear to me (other than lightning) how a string would trip the 15amp circuit breaker. I guess 2 or morestrings (wiring)could cross connect on roof under the panels and overload the wiring (10 awg) for a single string with more than 15amps... so circuit breakers work to protect the wiring of each string?
Click to expand...

So say one of the 4 strings has a short fault, the other three dump energy into that one = 3x 9.84 = 29.52A, breaker pops?
Click to expand...

That leads to the next question. How 'big' should we use a fuse for our solar panels? Let's say about 10 A max current, would we take a 10 A fuse or 15 A maybe even 20A fuse? What would you choose?
 
Maniac_Powerwall said:
Redpacket said:
OffGridInTheCity said:
Each string is 3 panels in series with 39.7v (Voc) / 31.3v (Vmpp) and 9.8a (Isc) / 9.2a (Impp). So nominally its 93.9v @ 9.2a with max of 119.1v and 9.84a at short circuit. Each string has a 15amp circuit breaker in the combiner box. 4 strings per combiner give 93.9v @36.8a = 3,445wattstraveling to the Controller area.
Its not clear to me (other than lightning) how a string would trip the 15amp circuit breaker. I guess 2 or morestrings (wiring)could cross connect on roof under the panels and overload the wiring (10 awg) for a single string with more than 15amps... so circuit breakers work to protect the wiring of each string?
Click to expand...

So say one of the 4 strings has a short fault, the other three dump energy into that one = 3x 9.84 = 29.52A, breaker pops?
Click to expand...

That leads to the next question. How 'big' should we use a fuse for our solar panels? Let's say about 10 A max current, would we take a 10 A fuse or 15 A maybe even 20A fuse? What would you choose?
Click to expand...
The manufacturer's spec sheet should give the correct fuse size. It'd likely be a 15A size for these panels, mine are similar & are15A max. A 10A fuse could just work too but be a bit close to the wind.
 
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