diy solar

diy solar

Is there such a thing as a Class K PV wire? Can any 10 AWG single conductor wire be used as PV wire?

If you use this: https://www.solar-electric.com/imo-si32-pel64r-4-true-dc-solar-isolator.html you'd get your isolator and way to transition to a fine strand cable. You also then get ability to disconnect PV array power near the MPPT RS so it would be safe to work on if need be. Run whatever cable you want from the PV array to that isolator and then use fine strand cable from the isolator to the MPPT RS. I'm not clear what kind of connection is in that IMO isolator so you made need to use a ferrule on the fine strand cables to connect them.

This is an elegant and very good solution.

Unfortunately we just realized our solar panels have MC4 connectors made by Staubli that apparently say to not use bare copper PV wire, but rather to use tinned copper. So it looks like we're gonna have to replace three thousand feet of PV wire anyway.

Because we just assumed that PV wire, with an MC4 connector, rated for the voltage and amps, was good to go.

This entire solar adventure has been like this. I'm just waiting for some manual (that we had to dig up and convert from Chinese text to English) to say "do NOT use sun for photovoltaics except during a lunar eclipse" or something similar next. Can't count on anything just being obvious.
 
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Unfortunately we just realized our solar panels have MC4 connectors made by Staubli that apparently say to not use bare copper PV wire, but rather to use tinned copper. So it looks like we're gonna have to replace three thousand feet of PV wire anyway.
You don't have to do that. Just use a combiner box or some junction box if you don't need the breakers near the panels so you just replace the few feet from the panels to combiner and use what you have from the combiner to the charge controller/IMO isolator.
 
MC4 connectors work with the 84 strand PV wire, but not the 7 strand and vice versa, and I'll have to figure out how to make it all connect
A less elegant solution I’ve done a couple of times to mate thhn to fine strand or whatever is to use a hex crimp tool that swages a wicked tight crimp and two layers of heat shrink with tape over them.
I use a thick, bare butt-splice crimp of a size large enough for both stripped cables to bypass each other in the crimp fitting and then crimp the middle and each end which crushes the cables together which results in 100% contact and very tight.
Im sure some will poo-poo this but I’ve never had a warm-running splice even on 2ga battery cable the few times I’ve found it necessary to do this (I like uninterrupted home-runs but like in your case that isn’t always desirable or even possible).

Just a thought. YMMV
 

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OR just use another one of those isolators near the panels.

That's a good idea. Maybe make a little plastic box near each array with that isolator in it to do that switch. Then for maintenance on the system, I can flip the switches by the array to isolate them, and switch the circuit breakers inside the solar shed for double isolation to ensure the panels aren't connected before working on things.

Tinned copper cable going from panels to isolator, transition to 7 strand bare copper, long run to solar shed into a 2P circuit breaker, transition to multi-thread tinned copper wire into the MPPT.
 
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That IMO isolator is rated for outdoors (NEMA 4X) it doesn't need to be inside anything to protect it.

I saw in another thread where you use Midnite PV surge protectors. I wonder if I could use that instead of the outside isolators instead to do the transition? Having PV surge protection is probably a good idea with these bifacial panels and frigid temps anyway.
 
The Midnite surge protectors just have wires dangling out of them. They have to be connected in parallel with the PV wires inside something like the Midnite transition box I mentioned. They aren't meant to protect against high voltage in winter, they are used to protect from surges from lightning hits.
 
The Midnite surge protectors just have wires dangling out of them. They have to be connected in parallel with the PV wires inside something like the Midnite transition box I mentioned. They aren't meant to protect against high voltage in winter, they are used to protect from surges from lightning hits.

Hopefully my math worked out well enough then. It's confusing for me with BiFacials because they have so many numbers on the spec sheet.

7 panels connected in series:
  • Voc [%/°C] -.26
  • Open Circuit Voltage (Voc) [V] - STC 46.0
  • Open Circuit Voltage (Voc) [V] - BiFi100 46.0
  • Open Circuit Voltage (Voc) [V] - BiFi200 46.0
  • Open Circuit Voltage (Voc) [V] - STC* 48.9
  • Open Circuit Voltage (Voc) [V] - BiFi100** 48.9
  • Open Circuit Voltage (Voc) [V] - BiFi200** 48.9
Temp correction where we're at is 1.23

7 * 48.9 * 1.23 = 422V

Our charge controllers can only handle 450V.

Would be nice to have something on the PV side that could prevent more than 450V from going to the charge controllers in case of some freak drop in temps. For the temp correction I used the lowest recorded historical temp for my location, which is likely to be at night. So I think it's conservative enough but would be nice to have a device to add some extra insurance just in case.

We don't get as cold as you get I don't imagine. Lowest I've seen is -9F. But weather is changing, although it seems to be warming up here near the arctic.
 
A less elegant solution I’ve done a couple of times to mate thhn to fine strand or whatever is to use a hex crimp tool that swages a wicked tight crimp and two layers of heat shrink with tape over them.
I use a thick, bare butt-splice crimp of a size large enough for both stripped cables to bypass each other in the crimp fitting and then crimp the middle and each end which crushes the cables together which results in 100% contact and very tight.
Im sure some will poo-poo this but I’ve never had a warm-running splice even on 2ga battery cable the few times I’ve found it necessary to do this (I like uninterrupted home-runs but like in your case that isn’t always desirable or even possible).

Just a thought. YMMV
I transitioned at the disconnect but I don't see why you couldn't use a Wago.
 
I asked since you need to keep in mind that you have to design for the Victron MPPT RS using 8 * your float voltage as the maximum Voc and not assume 450V is the maximum you can use. It seems like your system would be okay. See page 8 of the manual:
When the MPPT switches to float stage it reduces battery charge current by increasing the PV Power Point voltage. The maximum open circuit voltage of the PV array must be less than 8 times the minimum battery voltage when at float.
For example, where a battery has a float voltage of 54.0 volts, the maximum open circuit voltage of the connected array cannot exceed 432 volts.
Where the array voltage exceeds this parameter the system will give a "Over-charge Protection" error and shut down.
I used the calculator here: https://www.midnitesolar.com/sizingTool/index.php and it shows even at -20F air temp you'd be fine since the Voc stays the same even when you get more reflection on the back.
Screenshot 2023-02-19 at 10.37.05 AM.png

I'm also planning on adding this charge controller which is why I've looked at it extensively.

I also agree that LG bifacial data sheet is very poorly organized. I've seen much better arranged bifacial spec sheets that make it easier to understand.
 
I asked since you need to keep in mind that you have to design for the Victron MPPT RS using 8 * your float voltage as the maximum Voc and not assume 450V is the maximum you can use. It seems like your system would be okay. See page 8 of the manual:

I used the calculator here: https://www.midnitesolar.com/sizingTool/index.php and it shows even at -20F air temp you'd be fine since the Voc stays the same even when you get more reflection on the back.
View attachment 135651

I'm also planning on adding this charge controller which is why I've looked at it extensively.

I also agree that LG bifacial data sheet is very poorly organized. I've seen much better arranged bifacial spec sheets that make it easier to understand.

Thanks so much for sharing that, that's very helpful. I had no idea about that.
Float.png
 
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