Over paneling conductors

[hwy17]

I am playing around with the concept of conductor over paneling that I just recently picked up from other discussions around here.

I was aware of charge controller over paneling, but it had not previously occurred to me that overpaneling could potentially also achieve an economy on conductor wire as well. It gets a little precarious and may require using fixed voltage power points rather than MPPT, to avoid the tracking mode ever searching into intolerable low voltage high amperage power points.

If you're wondering why not just spend a little money once on bigger conductors, that's valid. I am just exploring the idea.

Here is an example of 17kW PV feeding into 11kW of charge controllers on just 4 12 AWG conductors. I believe individual string fusing would not be necessary since there only two arrays in parallel on each charge controller. 20A fuses directly after the parallel array combiner or splice provide protection for the long run of 12AWG conductor, in case of short circuit or charge controller overcurrent.

Code wise, I'm not sure there would be any way to fully justify it under the NEC. Article 690 probably has too many definitive statements that ignore the possibility of this concept entirely.

 

[Supervstech]

Fuse for the wire size, and you could be ok... but you could also have a lot of nuisance fails

 

[hwy17]

you could also have a lot of nuisance fails

That's what I'm hoping the high fixed voltage power point on the charge controllers would avoid. But Schneider calls it a target voltage, which doesn't sound like an assurance that it will always perfectly observe it.

 

[Brucey]

I am playing around with the concept of conductor over paneling that I just recently picked up from other discussions around here.

I was aware of charge controller over paneling, but it had not previously occurred to me that overpaneling could potentially also achieve an economy on conductor wire as well. It gets a little precarious and may require using fixed voltage power points rather than MPPT, to avoid the tracking mode ever searching into intolerable low voltage high amperage power points.

If you're wondering why not just spend a little money once on bigger conductors, that's valid. I am just exploring the idea.

Here is an example of 17kW PV feeding into 11kW of charge controllers on just 4 12 AWG conductors. I believe individual string fusing would not be necessary since there only two arrays in parallel on each charge controller. 20A fuses directly after the parallel array combiner or splice provide protection for the long run of 12AWG conductor, in case of short circuit or charge controller overcurrent.

Code wise, I'm not sure there would be any way to fully justify it under the NEC. Article 690 probably has too many definitive statements that ignore the possibility of this concept entirely.

View attachment 208925

Can't you just upsize your 12AWG runs to 10AWG and then your potential 22A per combined string is well within spec? You'd still just have the two pairs for the home run.

 

[ricardocello]

That's what I'm hoping the high fixed voltage power point on the charge controllers would avoid. But Schneider calls it a target voltage, which doesn't sound like an assurance that it will always perfectly observe it.

The MPPT likely assumes that it can nearly short circuit the panels to find its optimum point.
At those current peaks, if it dwells there too long, the fuse could blow.
I’ve had this issue with my DC disconnect breakers, wasn’t expecting it.

Would be nice if we could set the min voltage/max current as an MPPT parameter.

 

[hwy17]

Can't you just upsize your 12AWG runs to 10AWG and then your potential 22A per combined string is well within spec?

Yes. But stick with me on the thought experiment for the sake of it.

The MPPT likely assumes that it can nearly short circuit the panels to find its optimum point.

By fixed voltage though I mean disabling MPPT functionality. You tell the charge controller to operate at 390v or 400v or whatever, and all it does is such as much current as it can get or take at that voltage. With an output limit of 5500W, that should limit from ever sucking more than 14A at 400v.

 

[Brucey]

Yes. But stick with me on the thought experiment for the sake of it.

By fixed voltage though I mean disabling MPPT functionality. You tell the charge controller to operate at 390v or 400v or whatever, and all it does is such as much current as it can get or take at that voltage. With an output limit of 5500W, that should limit from ever sucking more than 14A at 400v.

So you could have each pair of arrays east and west facing.

So controller 1 has an east facing array for early in the day and west facing for afternoon. And same with controller 2. Then chances of hitting 20A on each string is minimized.

 

[hwy17]

So you could have each pair of arrays east and west facing.

So controller 1 has an east facing array for early in the day and west facing for afternoon. And same with controller 2. Then chances of hitting 20A on each string is minimized.

Yes, but if the purpose of the over paneling is to get enough production in winter then I think it's possible south would still be best. Even straight south they might not be regularly exceeding 7 amps per string at mid day.

The system should still be self limiting to 14A by the charge controller limit, even when the array has all 22A available.

 

[Brucey]

Yes, but if the purpose of the over paneling is to get enough production in winter then I think it's possible south would still be best. Even straight south they might not be regularly exceeding 7 amps per string at mid day.

Yes if they are mobile ground mounts could swing them all south for max winter production then go east/west for longer duration summer production for A/C load?

 

[Hedges]

Yes, but if the purpose of the over paneling is to get enough production in winter then I think it's possible south would still be best. Even straight south they might not be regularly exceeding 7 amps per string at mid day.

For winter, how about one panel due south with optimal tilt, parallel with another panel straight up for overcast?
(How much power do we get from slight overcast, light source is entire cloudy sky?)

By fixed voltage though I mean disabling MPPT functionality. You tell the charge controller to operate at 390v or 400v or whatever, and all it does is such as much current as it can get or take at that voltage. With an output limit of 5500W, that should limit from ever sucking more than 14A at 400v.

Some equipment has that option. Older Sunny Boy (5000US) have "Turbine" and/or constant voltage.
Midnight Classic too.

Of course 14 awg through 10 awg has NEC rule limiting current lower than ampacity. So there is margin there.
The rules don't apply inside appliances.
Not sure the reason for that derating, but I'd guess convenience outlet circuits are routinely overloaded to the point of tripping breakers, so good to have them limited to ~2/3 of ampacity, 1/2 the power dissipation and temperature rise. Larger/dedicated circuits less likely to suffer that, so insulation life of about 100 overloads is sufficient.

(In other words, if code doesn't matter to you, go for it.)

 

[hwy17]

For winter, how about one panel due south with optimal tilt, parallel with another panel straight up for overcast?

But in the end are we really getting anything by dividing instead of just splitting the difference and pointing them all up at a sky facing 25 degrees?

Some equipment has that option. Older Sunny Boy (5000US) have "Turbine" and/or constant voltage.
Midnight Classic too.

Yeah my Schneider MPPT 100 600 does to. I wonder if Barcelona and Hawkes Bay do, but I would assume so.

Of course 14 awg through 10 awg has NEC rule limiting current lower than ampacity. So there is margin there.

Yes I like to keep that one in my back pocket as my backup safety factor. As long as a 20 amp fuse doesn't blow the 12awg wire should be fine.

 

[Hedges]

I'd say as long as 30A fuse doesn't blow, 12 awg would be fine. It just isn't code. (but don't also leave unused portion in a tightly coiled spool - ask me how I know!) And if sized for 1.56x Isc per NEC, you should really be fine.

Benefit of two orientations is lower peak current, I estimate based on presented area.
If SCC wattage rating clips current, that could also help, but not if wires get shorted so I guess don't rely on that.