Overpaneling over a 100% of what a controller can take. Offgrid

[zanydroid]

Solar charge controllers do not require external over current protection. Any additional fuses on Solar circuits are there to protect the panels from each other.

Sure, they rely on the limited fault current to protect themselves.

I was referring to how much current an appliance can handle. You are not allowed to wire appliances designed for 15A circuits into 50A circuits.

Also solar panels are somewhat unique in that the downstream equipment like SCC is able to short the PV without significant consequence. Do that to almost other things and it’s a bad day.

Suppose there is a SCC that has a 30A relay that shorts the inputs (there was another thread recently talking about how victron SCC has one). This implies a 30A Isc limit on the attached array.

 

[timselectric]

Sure, they rely on the limited fault current to protect themselves.

I was referring to how much current an appliance can handle. You are not allowed to wire appliances designed for 15A circuits into 50A circuits.

Also solar panels are somewhat unique in that the downstream equipment like SCC is able to short the PV without significant consequence. Do that to almost other things and it’s a bad day.

Suppose there is a SCC that has a 30A relay that shorts the inputs (there was another thread recently talking about how victron SCC has one). This implies a 30A Isc limit on the attached array.

I'm not sure what point you are trying to make.
I have not seen any failure due to overpaneling.
Victron equipment could be a special exception. But, that would be covered in their warranty.

 

[zanydroid]

I'm not sure what point you are trying to make.
I have not seen any failure due to overpaneling.
Victron equipment could be a special exception. But, that would be covered in their warranty.

Well separate from overpaneling I was correcting the concept that fusing is only to protect wires, not equipment. NEC is clear on that.

As for overpaneling.

I’m saying assuming unlimited Isc is unrealistic given other analogous situations in electrical engineering and electrical code, and the fact that the design of an SCC can theoretically take advantage of the limited fault current.

I’ll note also that microinverters often do quote a max Isc. Which makes me question why string inverters should not be considered to have one, or be given a more specific reason why, from engineering or safety standard first principles

Anyway to make a more concrete contribution. I think it’s safe to overpanel to probably 2-3x with Isc or watts computed for site conditions. For both diffuse scattered light conditions where all panels in all directions are generating and hard light conditions where most of the power output is concentrated in one place.

 

[Crowz]

I typed out a long reply with me going on and on about there being tons of power up the line on the ac side of circuits in a house etc and then decided that wasn't apples to apples.

I think that the only reason not to over panel beside reverse polarity protection would be short circuit protection.

So to me if someone wants to cover all bases on this then install a breaker on the pv side which we all should have anyways. If a dead short happens that fixes that. Otherwise over panel till the cows come home as long as you don't go over max voltage. Well that and make sure you don't hook up the pv backwards somehow if your over max amps but if your using mc4 connectors that only comes into play at the install time of the charge controller.

 

[zanydroid]

Well separate from overpaneling I was correcting the concept that fusing is only to protect wires, not equipment. NEC is clear on that.

422.11 E for non motor appliances:

https://up.codes/viewer/texas/nfpa-70-2020/chapter/4/equipment-for-general-use#422.11_%28A%29

 

[zanydroid]

So to me if someone wants to cover all bases on this then install a breaker on the pv side which we all should have anyways. If a dead short happens that fixes that. Otherwise over panel till the cows come home as long as you don't go over max voltage. Well that and make sure you don't hook up the pv backwards somehow if your over max amps but if your using mc4 connectors that only comes into play at the install time of the charge controller.

Yeah I think having the breaker or fuse at a reasonable size will address my concerns basically 100% since it restores the available fault current to something a lot more similar to the arrays that majority of people are using

Running without one is foolhardy. When you overpanel you anyway have an idea of the max power, from running PVwatts etc.

 

[timselectric]

The only downside to overpaneling is the higher possibility of wasted available production. It's not the best option for efficiency. But it's sometimes a cheaper option. Because it only requires additional panels. Instead of other more expensive equipment.

 

[zanydroid]

If you connect in reverse polarity, yes. The isc limits are directly related to reverse polarity protection. Every now and then some monkey hooks it up the wrong way

I think that the only reason not to over panel beside reverse polarity protection would be short circuit protection.

I thought the blocking FET in reverse polarity circuit was mainly limited by the voltage rating of the FET? Would glad to have an explanation of my understanding gap.

 

[squowse]

I only know Victron explicitly state max Isc and the reasons for it. There are internal fuses but they tend to blow after the equipment is damaged.

I’ve not seen other manufacturers do this hence they mostly come up with a fairly arbitrary figure based on percentage of panel W compared to max charge W.

You would think that the other manufacturers equipment has exactly the same issues as the Victron with panels over the max Isc. It’s only really in a malfunction or installation error scenario that it matters and extra fuses will hopefully stop any fire.