EG4 18kPV AC Couple Questions

[thepetersms]

I see $325/500ft of #1 THHN. Wire is sort of a "pay once use it for decades" thing.

Going to 500VDC will save 1/2 size on the wire, however you will still need two circuits to hit 18k on the inverter. Maybe just send 12K to the 18kpv. You can also 1/2 the size of the AC back to the grid. It won't mean 1/2 the cost though.

You can also choose to send part of the array through 18kpv and the rest directly to grid. It depends on if you think you can use all that electricity in the shed, otherwise you're losing money b/c of not exporting it.

There's a couple ways to avoid a return line, although the return line gives you the most options. You can also choose to reconfigure it later (you should probably flag the direct bury or conduit nicely though, in case you need to dig again. Don't want to hit it).

For instance you can send solar to grid without going through the inverter. This effectively makes the 18kpv a backup battery for the shop. Sometimes people with batteries in outbuildings reduce the size of the feeder to those buildings. Since the inverters can provide the surge loads from the battery. And then overnight (or whenever the building isn't being used) the battery slowly charges to full again. What you lose here is the ability to form a grid when the power is out (You can still do this by rewiring in a power outage but I'm not sure there's a 100% safe way, you can start a thread though to see if someone can advise a safe way. The tough part is keeping grid vs solar array energy straight). Is that important to you?

Can you send me a link to that $325 for 500ft of #1 THHN?

 

[zanydroid]

1 AWG THHN/THWN-2 Aluminum Cable PVC Insulation Nylon Jacket 600V

Specifications : Size AWG : 1, Stranding : 18, Conductor Diameter Inches : 0.299, Insulation Thickness Inches : 0.55, Jacket Thickness Inches : 0.007, O.D. Inches : 0.413, New Weight lb/1000FT : 110 lbs, Ampacity at 90°C : 115 Amps. Standards : UL standard 83, 1685, CUL, Federal Specification...

nassaunationalcable.com

Shipping might be expensive AF though. There should be stacks and stacks of this locally.

I buy stuff online when it's a specialty type (like PV cable, I have to drive more than I care to locally), or the local places don't cut it. And usually the stuff that local places won't cut, are not that heavy.

 

[thepetersms]

1 AWG THHN/THWN-2 Aluminum Cable PVC Insulation Nylon Jacket 600V

Specifications : Size AWG : 1, Stranding : 18, Conductor Diameter Inches : 0.299, Insulation Thickness Inches : 0.55, Jacket Thickness Inches : 0.007, O.D. Inches : 0.413, New Weight lb/1000FT : 110 lbs, Ampacity at 90°C : 115 Amps. Standards : UL standard 83, 1685, CUL, Federal Specification...

nassaunationalcable.com

Shipping might be expensive AF though. There should be stacks and stacks of this locally.

I buy stuff online when it's a specialty type (like PV cable, I have to drive more than I care to locally), or the local places don't cut it. And usually the stuff that local places won't cut, are not that heavy.

Thanks,

https://nassaunationalcable.com/pro...X9b8zaucJOza8sHp9fnC692TLsdr_ePYaArCAEALw_wcB

It's still cheaper to go the 2-2-4-6 route

 

[zanydroid]

You probably need #1, unless you are pushing #2 to 90C (ground might be too hot for that). You probably cannot use the extra allowed capacity on #1 for a shed like you can for a dwelling (dwelling can do #2 for 100A)

 

[thepetersms]

I see $325/500ft of #1 THHN. Wire is sort of a "pay once use it for decades" thing.

Going to 500VDC will save 1/2 size on the wire, however you will still need two circuits to hit 18k on the inverter. Maybe just send 12K to the 18kpv. You can also 1/2 the size of the AC back to the grid. It won't mean 1/2 the cost though.

You can also choose to send part of the array through 18kpv and the rest directly to grid. It depends on if you think you can use all that electricity in the shed, otherwise you're losing money b/c of not exporting it.

There's a couple ways to avoid a return line, although the return line gives you the most options. You can also choose to reconfigure it later (you should probably flag the direct bury or conduit nicely though, in case you need to dig again. Don't want to hit it).

For instance you can send solar to grid without going through the inverter. This effectively makes the 18kpv a backup battery for the shop. Sometimes people with batteries in outbuildings reduce the size of the feeder to those buildings. Since the inverters can provide the surge loads from the battery. And then overnight (or whenever the building isn't being used) the battery slowly charges to full again. What you lose here is the ability to form a grid when the power is out (You can still do this by rewiring in a power outage but I'm not sure there's a 100% safe way, you can start a thread though to see if someone can advise a safe way. The tough part is keeping grid vs solar array energy straight). Is that important to you?

I thought about setting it up without a return line as well. I was going to connect two strings of 12 panels each to the inverter but then I figured I would be wasting electricity that would previously be sold back to the grid since I won't be out in the shop that often.

 

[zanydroid]

I thought about setting it up without a return line as well. I was going to connect two strings of 12 panels each to the inverter but then I figured I would be wasting electricity that would previously be sold back to the grid since I won't be out in the shop that often.

If you’re not in the shop that often, how often do you want to be able to recharge the shop from solar panels when the grid is down?

I would think emergency grid down power is more useful in the house.

 

[thepetersms]

If you’re not in the shop that often, how often do you want to be able to recharge the shop from solar panels when the grid is down?

I would think emergency grid down power is more useful in the house.

I'm building out a living area and office/game room in the shop so eventually the power draw will be higher.
Eventually the plan is to move everything over to another 18kPV and a couple more batteries to put the house critical loads on that.

 

[zanydroid]

Have you considered putting a small structure near your service to hold the inverters and batteries? They are outdoor rated so it may not need to be much.

Then you can power house and shop. There would likely be less wire (but I’m not convinced the wiring cost is a big deal in the grand scheme of things), as compared to the different functionality you get.

There are a couple philosophies about whether you want central or distributed system. Each have their place and I’m not able to gain enough experience as a DIYer to weigh in on which one is better.

 

[thepetersms]

Have you considered putting a small structure near your service to hold the inverters and batteries? They are outdoor rated so it may not need to be much.

Then you can power house and shop. There would likely be less wire (but I’m not convinced the wiring cost is a big deal in the grand scheme of things), as compared to the different functionality you get.

There are a couple philosophies about whether you want central or distributed system. Each have their place and I’m not able to gain enough experience as a DIYer to weigh in on which one is better.

Yes I considered that but decided not to go that route.
My mind is going 10 different ways right now and I have no idea which route I want to take when setting these up now.
Part of me wants to remove all of the IQ7+ micros to eliminate them from the system and run 4 strings in series back to the inverter. Then run my sell back grid line to the meter under my panels.
Part of me wants to do it the easier way and leave the IQ7+ micros in place and run it into the GEN lugs and out the GRID lugs.

I thought I had the right 10 gauge PV cable but the insulation is not thick enough for the MC4 connectors, I bought it from Lowes.

 

[zanydroid]

I think a way to do this is write down the ideas and pros/cons, without working them all out in detail (well, you can work a few if you want).

Going DC into the AIOs lets you save on wire and will get tighter control over export than if you AC coupled (export control is tricky if sun is out). It will also likely be a few % more efficient, & less potential AC coupling problems.

Off hand I think putting the inverters/batteries outside at the service will have the downsides of shorter lifespan from baking in a shed, and will likely have to run the battery heaters a lot more than if it was in space that you occupy and are already conditioning.

I thought I had the right 10 gauge PV cable but the insulation is not thick enough for the MC4 connectors, I bought it from Lowes.

That sucks, what did you buy? I thought 19 strand PV cable would work in general (maybe you got smaller strand count, which you're not supposed to use for connecting to panels)

 

[thepetersms]

I bought this stuff. 500ft in black and 500ft in red. The thickness of the insulation is thinner than your typical "PV" wire

https://www.lowes.com/pd/Southwire-500-ft-10-AWG-Stranded-Red-Copper-THHN-Wire-By-the-Roll/50189563

 

[zanydroid]

I bought this stuff. 500ft in black and 500ft in red. The thickness of the insulation is thinner than your typical "PV" wire

https://www.lowes.com/pd/Southwire-500-ft-10-AWG-Stranded-Red-Copper-THHN-Wire-By-the-Roll/50189563

Yeah that's the wrong kind of wire. I don't think it's allowed for exposed runs under a solar array, though I don't have a code reference (it will at least need to be sunlight resistant, plus the incompatibility with the MC4 rules it out. All the exposed wire that typically goes under a solar panel is really thick).

You can consider using it to run 3 to 4 runs of DC strings. The big input on the 18kpv is too big for a single #10 (or right at the threshold)

You can buy Red and Black PV online, I used black only and distinguished with MC4 end, it seemed OK except when going into a JB.

 

[thepetersms]

Yeah that's the wrong kind of wire. I don't think it's allowed for exposed runs under a solar array, though I don't have a code reference (it will at least need to be sunlight resistant, plus the incompatibility with the MC4 rules it out. All the exposed wire that typically goes under a solar panel is really thick).

You can consider using it to run 3 to 4 runs of DC strings. The big input on the 18kpv is too big for a single #10 (or right at the threshold)

You can buy Red and Black PV online, I used black only and distinguished with MC4 end, it seemed OK except when going into a JB.

I can run one string of 12 panels into one mppt on the 18kPV and still be below the 600v max input

 

[zanydroid]

I can run one string of 12 panels into one mppt on the 18kPV and still be below the 600v max input

I was talking about the current limit.

30/1.56 or 35/1.56 (or worse. Depends on derating and your risk tolerance)

 

[thepetersms]

I was talking about the current limit.

30/1.56 or 35/1.56 (or worse. Depends on derating and your risk tolerance)

I found a decent deal on Amazon for PV wire and going that route. I'll run 1 or 2 strings into the 18k to get my shop powered up and running. I might as well put a new combiner box out by the solar breaker panel too.

 

[zanydroid]

I found a decent deal on Amazon for PV wire and going that route. I'll run 1 or 2 strings into the 18k to get my shop powered up and running. I might as well put a new combiner box out by the solar breaker panel too.

I’m kind of scared of buying critical wiring and connectors on Amazon. I’ve done it a handful of times. For your ground mount the risk is well managed (mine are on my roof and I don’t want melted wires up there, for fire risk and for the PITA to service).

 

[thepetersms]

Have you considered putting a small structure near your service to hold the inverters and batteries? They are outdoor rated so it may not need to be much.

Then you can power house and shop. There would likely be less wire (but I’m not convinced the wiring cost is a big deal in the grand scheme of things), as compared to the different functionality you get.

There are a couple philosophies about whether you want central or distributed system. Each have their place and I’m not able to gain enough experience as a DIYer to weigh in on which one is better.

You got me thinking about moving the inverter and batteries to a shed out by the panels and main electrical panel and meter. I have a nice 12x16 shed that I can move and use that to house the inverters and batteries. That would be best for my future ideas of putting the house on batteries. Save me a bunch of money for cable runs lol .

 

[thepetersms]

Have you considered putting a small structure near your service to hold the inverters and batteries? They are outdoor rated so it may not need to be much.

Then you can power house and shop. There would likely be less wire (but I’m not convinced the wiring cost is a big deal in the grand scheme of things), as compared to the different functionality you get.

There are a couple philosophies about whether you want central or distributed system. Each have their place and I’m not able to gain enough experience as a DIYer to weigh in on which one is better.

I moved my 10x16 shed by the array. Moving inverter and batteries tomorrow.
I think that's the smartest thing to do for my future plans

 

[wheisenburg]

I believe I would disconnect the 3 lines coming into my solar electric panel at the top (those lines come from a 100amp feeder breaker at my main panel)
Run 3 new lines back to my shop and into my 18kPV into the Generator lugs. Then run 3 more lines out of the 18kPV from the GRID lugs and tie them back into 3 lines that I previously disconnected.

First, I would ask yourself this question. Are you sure you really want to AC couple those 48 micro inverters into your system? What you have to understand about AC coupling (I know it sounds like a great idea on the surface), is this. A grid tied inverter is designed to sync to an incoming grid connection and then import as much power as possible back into the grid. So if these are IQ7s they have a rating of 250 watts. If you have an IQ7+ those have a 295 watt rating. You have 48 of these inverters. If you lose the grid, that means your system needs to be designed such that it can handle 12,000 watts. I have two inverters for a much smaller array. Now the hybrid inverter can frequency shift the micros to reduce their output, but this is not perfect and it takes some time to do that. The IQ7s may take longer to respond than an IQ8. Until the the inverter power is curtailed, the hybrid inverter must store the power into the batteries. So that means your inverter will need take 12,000 watts of AC current and be able to send 240 amps of charging current into the battery. If the batteries are fully charged when you lose power, you are going to have a real problem. I think part of the reason they are using the "Gen" terminals is that they can control it. They will just disconnect, the array until there is a significant drop in the battery charge state.

Check on this forum if anyone has been able to AC couple a 12,000 watt array.

One issue on your system is that you are using a 100 amp back feed breaker. When a panel has multiple feeds to the bus, they limit the total current to 120% of the bus limit and require the back feed breaker be on the opposite end of the panel than the main breaker. That would allow for a 40 amp breaker. Now you are removing the feed from the PV array. However when you hook your hybrid inverter "Grid" connections back into this breaker, it becomes a feeder breaker too because it will export the PV from panel back through this connection. Will this burn anything down? Probably not, but it won't pass inspection either if that matters to you.

Another thing to remember it that you are lengthening the wire run for the PV array. It will need to go all the way to the shop and then back to this outdoor panel. Because this is a power source you actually get more voltage rise the longer the distance is. If the voltage gets too high, the micros won't work. You can check out this video. They explain some things about AC coupled systems.

 

[thepetersms]

First, I would ask yourself this question. Are you sure you really want to AC couple those 48 micro inverters into your system? What you have to understand about AC coupling (I know it sounds like a great idea on the surface), is this. A grid tied inverter is designed to sync to an incoming grid connection and then import as much power as possible back into the grid. So if these are IQ7s they have a rating of 250 watts. If you have an IQ7+ those have a 295 watt rating. You have 48 of these inverters. If you lose the grid, that means your system needs to be designed such that it can handle 12,000 watts. I have two inverters for a much smaller array. Now the hybrid inverter can frequency shift the micros to reduce their output, but this is not perfect and it takes some time to do that. The IQ7s may take longer to respond than an IQ8. Until the the inverter power is curtailed, the hybrid inverter must store the power into the batteries. So that means your inverter will need take 12,000 watts of AC current and be able to send 240 amps of charging current into the battery. If the batteries are fully charged when you lose power, you are going to have a real problem. I think part of the reason they are using the "Gen" terminals is that they can control it. They will just disconnect, the array until there is a significant drop in the battery charge state.

Check on this forum if anyone has been able to AC couple a 12,000 watt array.

One issue on your system is that you are using a 100 amp back feed breaker. When a panel has multiple feeds to the bus, they limit the total current to 120% of the bus limit and require the back feed breaker be on the opposite end of the panel than the main breaker. That would allow for a 40 amp breaker. Now you are removing the feed from the PV array. However when you hook your hybrid inverter "Grid" connections back into this breaker, it becomes a feeder breaker too because it will export the PV from panel back through this connection. Will this burn anything down? Probably not, but it won't pass inspection either if that matters to you.

Another thing to remember it that you are lengthening the wire run for the PV array. It will need to go all the way to the shop and then back to this outdoor panel. Because this is a power source you actually get more voltage rise the longer the distance is. If the voltage gets too high, the micros won't work. You can check out this video. They explain some things about AC coupled systems.

Thanks for the reply. I will look into that for sure regarding the excess power coming in from micro inverters.

Regarding the backfeed breaker, I was actually just researching that. It seems the current 100amp breaker that's in right now is not correct given my main panel is only rated for 200amp bus bars so it's far over the 125% rule. I'm royally confused how it's not melting anything given all 48 micro inverters are back feeding the grid.
The solar was installed by the local electric power company with the previous owners of the house 2 years ago.