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Fusing solar panels?
#11
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.
Running off solar, DIY & electronics fan :-)
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#12
(05-28-2019, 02:37 AM)Korishan Wrote:
(05-28-2019, 02:21 AM)OffGridInTheCity Wrote: 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.

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?
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 = 3,445watts traveling 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 more strings (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?
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#13
(05-28-2019, 10:25 AM)OffGridInTheCity Wrote: 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 = 3,445watts traveling 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 more strings (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?

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?
Running off solar, DIY & electronics fan :-)
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#14
(05-28-2019, 11:04 AM)Redpacket Wrote:
(05-28-2019, 10:25 AM)OffGridInTheCity Wrote: 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 = 3,445watts traveling 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 more strings (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?

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?

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?
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#15
(06-10-2019, 06:23 AM)Maniac_Powerwall Wrote:
(05-28-2019, 11:04 AM)Redpacket Wrote:
(05-28-2019, 10:25 AM)OffGridInTheCity Wrote: 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 = 3,445watts traveling 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 more strings (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?

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?

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?
The manufacturer's spec sheet should give the correct fuse size. It'd likely be a 15A size for these panels, mine are similar & are 15A max. A 10A fuse could just work too but be a bit close to the wind.
Running off solar, DIY & electronics fan :-)
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