Off-Grid System: Check my work

[dp09]

This is my first time posting to this forum but I’ve used it several times as a resource. I want to make sure I have this system planned out correctly before I purchase all of the equipment. I have never installed a solar system of this size before and I’m going to try my best to include all of the necessary information in this post. Any help is appreciated.

I'm in the process of building an off-grid home and over the next two months (Dec-Jan 2024) I will be ordering all of the components and putting together this system (I currently own the 250W panels). The house construction finishes in mid spring (2024) so I need to have the system completed by then and ready for county inspection.

I am responsible for wiring up the solar equipment and a licensed electrician will be handling running the AC power from the inverter to the main panel, an AC disconnect, and wiring up receptacles, lights, etc.

Site: Northern Midwest

System type: Full off-grid solar power

Mount: Galvanized steel ground mount

Distance: PV array is roughly 150’ from house

Inverter/Bat Location: Inverter and battery are located inside the house

Backup Power Source: WEN 11kW Dual Fuel Generator

Inspections: local county inspection



Equipment:

•EG4 18kPV w/2x PowerPro 14.3kWh batteries

•Watts247 4-2 combiner box

•18 used 240W SanTan panels

•24 new 365W Hyundai panels

•10AWG direct burial cable


Panels (I’m going to gloss over the series-parallel connections because I don’t have concern about this portion of the build):

Used 240W: VOC 37.2

New 365W: VOC 40.8

The panels will be wired up in series into 4 strings. Two strings consisting of 240W panels and two consisting of 365W panels. That will run into the combiner box to parallel those two like strings together.

Combiner box output will have two strings at about 350VDV (240W panels) and about 500VDC (365W panels).


Direct Burial Wire: (I have no plans to run conduit).

I’m using UL 4703 10AWG direct burial rated PV cable to run the power from the combiner box 150’ to the house where the 18kPV and batteries are located.

I haven’t been able to find specifics on how many cables I can bury in the same trench or spacing requirements or anything like that. I did get confirmation from the county that the trench needs to have 24” of soil on top of cables and schedule 80 PVC at ground entry and exit points at least 18” into the ground.

I will likely contact the county again to ask those questions but the plan as of now is to run 6 cables in the same trench, a positive and negative for each of the two strings and an extra set of two cables so I can add a third string of panels later on (since the 18kPV has three MPPT’s). Then surround the cables in a layer of sand before backfilling the trench to protect from sharp rocks, etc. I will be installing that magnetic marking tape in the ground to mark the wire location for future reference.

Grounding/Earthing:

The plan is to connect all of the aluminum PV frames to each other and to the galvanized steel ground mount and run that to an 8’ grounding rod located at the PV array. And also run the combiner box ground wire to this same grounding rod? (This I am unsure of.)


Everything else that needs grounding at the house (18kPV, 2 batteries, etc) will be connected to the grounding rod the electrician will install to ground the main panel.


Things I’m unsure of:

1. Best way to get generator power ran to the inverter.
2. Dry contact hookup to signal and auto start generator based on inverter criteria input. (This generator has an electric start with a key and I have attach the wiring diagram.) What is a good aftermarket controller that would best accomplish this?
3. Does the solar array grounding rod need connected to the grounding rod at the house? If so, does running a ground cable in the trench with the DC power cables from one grounding rod to the other satisfy that?
4. Are there any issues burying 6 - 10AWG UL 4703 direct burial rated cables together in the same 24” trench?

 

[12VoltInstalls]

Combiner box output will have two strings at about 350VDV (240W panels) and about 500VDC (365W panels).

I don’t know the specs on that equipment but thought I’d mention that confirmation of VOC @ -40* versus the EG4 specs should be done

have no plans to run conduit

i myself would probably at the very least encapsulate the run in black poly water pipe as a measure of frost/stone/vehicle traffic protecting. But that’s me…

connect all of the aluminum PV frames to each other and to the galvanized steel ground mount and run that to an 8’ grounding rod located at the PV array. And also run the combiner box ground wire to this same grounding rod? (This I am unsure of.)


Everything else that needs grounding at the house (18kPV, 2 batteries, etc) will be connected to the grounding rod the electrician will install to ground the main panel.

use your electrician to verify local code office compliance. NEC says one thing, sometimes jurisdictions diverge

Does the solar array grounding rod need connected to the grounding rod at the house? If so, does running a ground cable in the trench with the DC power cables from one grounding rod to the other satisfy that?

array ‘grounding’ and system grounding should be separate- but according to discussions here in the past some jurisdictions want them connected. But I would not want them connected! Your house system would have that system ground if/as required but the frames of the panels and mountings would be a second ground path in my mind.

What is a good aftermarket controller that would best accomplish this?

Buy a Champion, Honda, Yamaha. There are proven solutions available in the market for each of them. I’m wary of wen, predator, and westinghouse and ‘house brands’ but fir portables used in a ‘fixed’ installation those three have very low complaints considering their high market insertion. Imho. Ymmv but that’s my opinion .

 

[pvgirl]

Panels (I’m going to gloss over the series-parallel connections because I don’t have concern about this portion of the build):

Verify your currents are within the limits of the 18kpv, with more then 2 strings in parallel you could be exceeding the limits of the inverter.

Things I’m unsure of:

Best way to get generator power ran to the inverter.

While you could install a generator inlet, and wire that to the gen input on the inverter, with a small generator like yours, using the eg4 chrageverter connected to the generator, and to the battery may be the best option.

Dry contact hookup to signal and auto start generator based on inverter criteria input. (This generator has an electric start with a key and I have attach the wiring diagram.) What is a good aftermarket controller that would best accomplish this?

https://atkinsonelectronics.com/gscm-mini-60hz/ Contact them to make sure this will work with your generator

Does the solar array grounding rod need connected to the grounding rod at the house? If so, does running a ground cable in the trench with the DC power cables from one grounding rod to the other satisfy that?

A separate ground rod at the array is not required or recommended, all metal at the array will need to be bonded together, and connected to a ground wire run with PV wires to the inverter, where it will be connected to the houses ground system. Where exposed the ground must be at least 6 AWG for protection from damage, where in conduit or underground you can use 10 AWG.

Are there any issues burying 6 - 10AWG UL 4703 direct burial rated cables together in the same 24” trench?

You can run as many cables in a trench as you want, but the same derating rules apply as if they were in conduit. For 6 conductors the current capacity of the wire would be reduced 80%, but you can use the 90c rating for this if your wire is 90c rated. You will also need a ground wire in the trench to the house, to bond the grounds together

 

[dp09]

I don’t know the specs on that equipment but thought I’d mention that confirmation of VOC @ -40* versus the EG4 specs should be done

i myself would probably at the very least encapsulate the run in black poly water pipe as a measure of frost/stone/vehicle traffic protecting. But that’s me…

use your electrician to verify local code office compliance. NEC says one thing, sometimes jurisdictions diverge

array ‘grounding’ and system grounding should be separate- but according to discussions here in the past some jurisdictions want them connected. But I would not want them connected! Your house system would have that system ground if/as required but the frames of the panels and mountings would be a second ground path in my mind.

Buy a Champion, Honda, Yamaha. There are proven solutions available in the market for each of them. I’m wary of wen, predator, and westinghouse and ‘house brands’ but fir portables used in a ‘fixed’ installation those three have very low complaints considering their high market insertion. Imho. Ymmv but that’s my opinion .

I went back and double checked my numbers at the coldest temp around here and both strings came in under the max inverter input. 405V @ 13.22a and 574.8V @ 18.54a

I’ll look into the black poly piping but, I’m pretty confident it’ll be fine given the location on the property it’s being trenched. No vehicle traffic and not a rocky soil.

I’ll double check the grounding with the county since they will be the ones pass/failing it.

I forgot to add that I already own the WEN generator unrelated to this solar build and was hoping to be able to use it.


Thanks for the input.

 

[dp09]

Verify your currents are within the limits of the 18kpv, with more then 2 strings in parallel you could be exceeding the limits of the inverter.



While you could install a generator inlet, and wire that to the gen input on the inverter, with a small generator like yours, using the eg4 chrageverter connected to the generator, and to the battery may be the best option.

https://atkinsonelectronics.com/gscm-mini-60hz/ Contact them to make sure this will work with your generator

A separate ground rod at the array is not required or recommended, all metal at the array will need to be bonded together, and connected to a ground wire run with PV wires to the inverter, where it will be connected to the houses ground system. Where exposed the ground must be at least 6 AWG for protection from damage, where in conduit or underground you can use 10 AWG.

You can run as many cables in a trench as you want, but the same derating rules apply as if they were in conduit. For 6 conductors the current capacity of the wire would be reduced 80%, but you can use the 90c rating for this if your wire is 90c rated. You will also need a ground wire in the trench to the house, to bond the grounds together

Both strings max currents are within the inverter max input limits. I just went back through the numbers to double check.

Okay I’ll look up the eg4 chargeverter and see what the use cases are. I’m assuming I’ll still need to use a generator control module with the eg4 chargeverter to auto start the generator or does the chargeverter have something like that built in?

That makes much more sense than having a separate grounding rod at the solar array. When you say “connected to the houses ground system” are you meaning to run that 10AWG ground wire from the panel array directly to the grounding rod at the house?

I’ll have to contact the manufacturer to see about 90c rating. It lists temp rating from -40°C to 90°C.
When you say the current capacity will be reduced do you mean reduced to 80% or reduced by 80%? I just want to make sure I understand correctly. The cable is rated for 40a so I’m assuming that means the max current is now 32a being as that’s 80%.

 

[pvgirl]

Okay I’ll look up the eg4 chargeverter and see what the use cases are. I’m assuming I’ll still need to use a generator control module with the eg4 chargeverter to auto start the generator or does the chargeverter have something like that built in?

You'll still need a generator control module to take the simple contact close interface of the 18kpv, and handle cranking and stopping the generator.

That makes much more sense than having a separate grounding rod at the solar array. When you say “connected to the houses ground system” are you meaning to run that 10AWG ground wire from the panel array directly to the grounding rod at the house?

The ground wire from the array will run to the inverter and connect to the ground bar there, which be connected to the main panel ground and to the rest of the grounds in the house.

I’ll have to contact the manufacturer to see about 90c rating. It lists temp rating from -40°C to 90°C.
When you say the current capacity will be reduced do you mean reduced to 80% or reduced by 80%? I just want to make sure I understand correctly. The cable is rated for 40a so I’m assuming that means the max current is now 32a being as that’s 80%.

Yes that cable is now rated 32amp instead of 40amps, which isn't a real issue as 10awg is limited to 30amps by NEC 240.4(D) Small Conductors. any ways.

 

[12VoltInstalls]

double check the grounding with the county since they will be the ones pass/failing it

 

[eod1991]

Why are you using the combiner boxes? Is that a local inspection requirement?

Dp09 I have a similar setup to yours if you want to check my build thread in my signature it may help some.

 

[dp09]

Why are you using the combiner boxes? Is that a local inspection requirement?

I’m using the combiner boxes as a way to parallel the series strings of panels.

Dp09 I have a similar setup to yours if you want to check my build thread in my signature it may help some.

Okay cool, I’ll check it out here in a bit when I have some free time.

 

[eod1991]

I’m using the combiner boxes as a way to parallel the series strings of panels.

Okay cool, I’ll check it out here in a bit when I have some free time.

I used the mc4 parallel connectors. I am also In a rural area with no inspections.

 

[12VoltInstalls]

I used the mc4 parallel connectors. I am also In a rural area with no inspections.

I have a couple of those- fine for a while, but I discovered that I liked paralleling after the breakers inside. Then I can control the strings independently if I want to do something different or have a problem at some point.
Yes- this costs more in cabling but on the grand scale? Not that much. (I’m using thhn in conduit do not terribly expensive comparatively)

For quick setup and easier waterproof connections they work fine, especially if not on a rooftop.

Why are you using the combiner boxes

So in my situation I considered combiner boxes. But I had three colors ~1500’ of 12thhn on hand. I still see the appeal with lightning arrestor inside and everything tidy. But the ‘out’ cable to a big SCC would be required, and at this point the appeal of ~140V strings to multiple SCC’s offers redundancy and the option of shutting one/some down manually in the sunny season is a benefit (for my setup).

Instead of a combiner box, 250V terminal blocks offer ‘local’ ease of connection and junction box function but I probably should figure out a lightning arrestor.

 

[dp09]

I used the mc4 parallel connectors. I am also In a rural area with no inspections.

I thought about using those initially but decided I liked the extra protections that come with the combiner box. The one I’m using is only a couple hundred dollars so it’s worth it for the low cost.

I looked through your build thread, nice setup. I saw you ended up needing to order two additional batteries to handle the overnight usage. I was kinda worried I’d end up with the same issue so I went ahead and upped mine to three batteries.

 

[eod1991]

I thought about using those initially but decided I liked the extra protections that come with the combiner box. The one I’m using is only a couple hundred dollars so it’s worth it for the low cost.

I looked through your build thread, nice setup. I saw you ended up needing to order two additional batteries to handle the overnight usage. I was kinda worried I’d end up with the same issue so I went ahead and upped mine to three batteries.

Yea honestly I probably could have gotten by without it but I hate the thought of the generator running often. I haven’t had any issues the past 7 days but it’s also been warmer.

Welp I spoke to
Soon! Woke up this morning to no power, it shut itself off at 655am about 30 minutes before the sun starts making power.