New Forum Member - First Question about AC passthrough

[cliffstevens]

I have begun exploring a solar system for my small 1930s home in Arlington VA. I'm not sure yet about how many panels I can fit on my roof, and will certainly figure that out by talking to some solar installers, but right now I think only 25 or so panels, maybe 30 (of course depending on size). I have a good southern facing high up area of the roof, with minimal shade during most of the day. But I'm guessing right now I can only generate half of our monthly power needs of about 2000 kWh/hours a month towards the higher end in summer. I also want battery backup for the not infrequent storms in our area that often take out the strung power lines (from all the old trees).

My question is - if I was able to get a system like the EG4 18PVK and a couple of "matching" EG4 wall mount batteries installed, would AC passthrough from the grid supply all of the power I need that the solar system/batteries cannot produce at a given time through the inverter? So the inverter in the EG4 18 PVK is 12,000 watts continuous (with surge above that for some amount of time), or something like that. What if I need 20,000 watts at some time? I'm a total beginner and not sure if I have a load like that in my home, and will find out (maybe by installing an Emporia or something similar). But just from a system design standpoint, if I knew that the 18PVK could always draw from grid over 12000 watts and supplement that, then that is really helpful and makes designing the system a lot easier. I can only produce so much solar power, and probably not enough for our total needs. So we are going to be drawing from the grid no matter what. It would be nice if the AC added on top of the inverter capacity, rather than for example the load only running off the inverter or the grid, and not both at the same time

So here's my question. How does AC passthrough from the grid work on a system like this? Does it draw as much load as it can from the solar DC coming in and battery (up to the inverter capacity) and then add more AC load on top of that? Or can the 18PVK only supply 12000 watts AC (with whatever surge), even from the grid? If it worked that way, they maybe I'd need multiple 18PVK. I hope they don't work that way, but I don't know.

Also, I think I have a 200 amp grid line coming in. Obviously I"m going to be learning a lot more about my house electrical system, but I am a real beginner on this.

Thanks for any help.

 

[zanydroid]

The EG4 18kpv (and SolArk 15K) package the inverter with a 200A passthrough & transfer relay capability. So you can support the whole house load.

They both also (since they are high end hybrids) have the capability to supplement grid in the sense of serving 12kW from themselves and the balance served from grid. Doable since they are approved for parallel operation with grid and have CT sensors in the right places.

So a single inverter in this class is enough IMO for an average size home that is on grid.

I recommend installing an energy monitor like Emporia Vue2 or Vue3 to see how much you draw. (EDIT: I see you mentioned that)

 

[1201]

You can also achieve what you want to do without ac passthrough. Connect the grid input to a breaker at the main panel and the 18kpv can provide power to the main panel up to 12kw to reduce how much the main panel draws from the grid

 

[zanydroid]

Yup. The power of hybrid and being given permission to do this by POCO.

You will need to be able to install a CT though in the main. I’m surprised more people on this forum don’t complain about meter main combo that can’t accommodate CTs (and with rope CTs even being an issue)

Is it just an Enphase/non DIY forum thing or are people not actually setting up self consumption that way here.

 

[1201]

Yup. The power of hybrid and being given permission to do this by POCO.

You will need to be able to install a CT though in the main. I’m surprised more people on this forum don’t complain about meter main combo that can’t accommodate CTs (and with rope CTs even being an issue)

Is it just an Enphase/non DIY forum thing or are people not actually setting up self consumption that way here.

Enphase people are not diy and diy people generally don't set up this way

 

[zanydroid]

Enphase people are not diy and diy people generally don't set up this way

There are a decent number of introductory posts asking about self consume with equipment like SolArk 12K that lack 200A bypass or folks getting 15K/18kpv but don’t want to split their panel to use the bypass

So I’m wondering why I perceive there to be fewer people asking about how to workaround janky combo mains here vs other places (EG a neighbor reached out to me, not on a forum, about one)

 

[cliffstevens]

Thanks! Not sure if my home system could have a CT (current transformer?) in the main panel. Or whether I have a "meter main combo"? But it seems like it would be nice to tie the grid to the main panel at least optionally (with some kind of switch) in case the inverter dies and you want to route the grid directly to the panel, or you want to optionally run the inverter without AC passthrough (ie., have the inverter and the grid combine together as described in the main panel).

 

[zanydroid]

Thanks! Not sure if my home system could have a CT (current transformer?) in the main panel. Or whether I have a "meter main combo"? But it seems like it would be nice to tie the grid to the main panel at least optionally (with some kind of switch) in case the inverter dies and you want to route the grid directly to the panel, or you want to optionally run the inverter without AC passthrough (ie., have the inverter and the grid combine together as described in the main panel).

Yes CT is for Current Transformer

It’s pretty fast for someone to eyeball your situation. Take a picture with the door open and we can guesstimate the available clearance. Even better with the dead face off but that comes with risks. Last one I saw (either here or from neighbor) it would have required either rope CT (still tight) or opening up the plastic safety cover line side of the main breaker. Which may have its own code compliance/safety restrictions, as it is always energized and you will have wires coming off the CTs going into other stuff, that will be in close proximity (albeit with insulation) to wires that can’t be de energized without pulling meter.

There are some pictures here of crazy clever double interlock setups that allow backup flow into a main but these need to be figured out case by case.

 

[1201]

Thanks! Not sure if my home system could have a CT (current transformer?) in the main panel. Or whether I have a "meter main combo"? But it seems like it would be nice to tie the grid to the main panel at least optionally (with some kind of switch) in case the inverter dies and you want to route the grid directly to the panel, or you want to optionally run the inverter without AC passthrough (ie., have the inverter and the grid combine together as described in the main panel).

If you install it the way I mentioned the grid and inverter both feed the main panel at the same time so if the inverter dies the grid is still there and there is no break in service

 

[cliffstevens]

Here is my panel with the cover off. Is there a disadvantage to connecting the grid through the panel as opposed to using AC passthrough on the hybrid inverter? Would it be best to enable both options, with some kind of switch so the grid can go straight to the panel or routed to the hybrid inverter (18pkv for example)?

 

[1201]

Here is my panel with the cover off. Is there a disadvantage to connecting the grid through the panel as opposed to using AC passthrough on the hybrid inverter? Would it be best to enable both options, with some kind of switch so the grid can go straight to the panel or routed to the hybrid inverter (18pkv for example)?

You have space for CTs on the main legs but I don't see any space to land a breaker for the inverter.

Passthrough is more than likely going to cost quite a bit more. You need an expensive transfer switch

 

[zanydroid]

Here is my panel with the cover off. Is there a disadvantage to connecting the grid through the panel as opposed to using AC passthrough on the hybrid inverter? Would it be best to enable both options, with some kind of switch so the grid can go straight to the panel or routed to the hybrid inverter (18pkv for example)?

Did you look at the line diagrams yet in the 18KPV manual?

You can backfeed into this panel by consolidating a bunch of full breakers into tandems. Full of options here.

1. Connecting to the grid through this panel:

Pros: cheaper, can still local consume because you can easily fit CTs in here.
Cons: need to add a critical loads panel and feed it from the 18kpv. You will have to move individual circuits. However, this is doable one at a time at a slow DIY pace. There are some rules about triggering conversion to AFCI governed by how you end up extending the conductors, I don't know what the distance limit is off hand.

For backfeeding into this panel you most likely need to swap the main breaker down to 175A to meet 705.12. Unless this panel has a 225A busbar. In that case, 120% rule lets you get away with it (120% * 225 - 200A (main)) = 70A . On 200A, that works out to (120% * 200 -175) = 65A

2. Passthrough

Passthrough is more than likely going to cost quite a bit more. You need an expensive transfer switch

This is optional. If you want a service bypass switch, you will need to spend $700 for a 200A rated one. There are a number of forum members that decided to just do manual bypass by moving wires around. (EG, use some polaris style connectors to manually patch in / patch out the inverter).

Independent of service bypass switch, you will need a [service disconnect] - [18kpv] - [panel with all the circuits you have here]

This can be achieved by:
- add new main panel upstream of this panel, and convert this panel to a subpanel. The conversion is not supported by all panels. You will have to look at the wiring sticker on this panel to see if the ground can be unbonded.
- leave this panel as the main. Add a new subpanel downstream of the 18kpv. Move all circuits to this subpanel.

Note that you can migrate from (1) to (2) by feeding the new subpanel in (1) with a 200A rated feeder. Then you would move circuits one at a time to the new subpanel. Once you've moved all the subpanels you've arrived at option (2).

Note that the migration has a lot of details to maintain to maintain compliance with 705.12 at all times. I'm not really sure it's an appropriate use of our time to explain it unless you are close to doing it. It involves changing the size of the breaker / feed-through lug feeding the 18kpv as you progress through the project (you would start with a 40A-60A feeder to satisfy 705.12, at some point you will have too many loads on the second panel to feed it effectively, so you have to move all the rest over in one shot, after which you are allowed to switch to a feed-through lug... this sounds very annoying after writing this out, I think the only reason to do it is somehow you have enough $ to afford an 18kpv or 15K but too cheap to hire it out and think you have big enough britches to do it yourself. And practicing on the first 40A of load teaches enough about how to move the circuits to do the last bit quickly enough to not piss anyone off living at the house).

I don't believe this tricky sequence is in the 18kpv manual either. And it's only useful if you want to try to save some coin and move the circuits yourself. If you hire someone you need to be bold and figure out what is most appropriate to your goals then tell them to do it in one shot.

 

[zanydroid]

... Anyway. I don't think there's many irreversible decisions here after you determine what system to use for interconnection application.

That is baleful in the sense that you may not be allowed to increase the number of solar panels / size of inverter later.

Given the same size of solar panel / inverter, you are allowed to do whatever you want with the wiring inside your house as long as it complies with code. The consequence of picking the wrong approach (IE critical loads only) is just paying the electrician more money to switch it around later. Which could involve moving a lot of equipment on the wall or creating a ratsnest of wires.

 

[Hedges]

My question is - if I was able to get a system like the EG4 18PVK and a couple of "matching" EG4 wall mount batteries installed, would AC passthrough from the grid supply all of the power I need that the solar system/batteries cannot produce at a given time through the inverter? So the inverter in the EG4 18 PVK is 12,000 watts continuous (with surge above that for some amount of time), or something like that. What if I need 20,000 watts at some time? ...

Also, I think I have a 200 amp grid line coming in. Obviously I"m going to be learning a lot more about my house electrical system, but I am a real beginner on this.

Yes but, if you don't turn off those heavy loads when grid goes down, inverter won't be able to carry them and shuts off.
If battery runs down, shuts off.

So you could power entire panel through inverter, but unless you have automatic shutoff of loads, it may shut down.

Another way to go is feed inverter from main panel, or from grid (load or line side tap). Put critical and backed up loads on a sub-panel after the inverter. Then backfeed from inverter to an interlocked "generator" breaker in main panel. If power fails, you manually shut off heavy loads, shut off main breaker, slide interlock and turn on backfeed breaker. (If main panel also feeds inverter, turn off that breaker so inverter doesn't chase its tail.)

You have space for CTs on the main legs but I don't see any space to land a breaker for the inverter.

So replace some breakers with tandem breakers.

Passthrough is more than likely going to cost quite a bit more. You need an expensive transfer switch

Or large interlocked "generator" switch to bypass inverter when failed. (But you may still be asked to put in visible blade disconnect.)

I favor load or line side tap (inverter branches off after meter, before main panel). Feed backed up loads all the time, use manual interlock to backfeed main panel when desired. I'm doing that on a couple properties: Meter, Main breaker only box, Polaris tap, fan out to breaker panels and inverter disconnect.

That takes up space, would be nice to have a single breaker panel with multiple sections, but those are less available and expensive.

Cost for utility transformer installation?

slightly OT. There was a review of the Emporia Energy Monitor on Amazon, which mentioned that the house meter records more kwh usage when the pull is unbalanced between L1/L2. Is this a possibility ?

diysolarforum.com

 

[cliffstevens]

Wow thanks much. Will take me some time to digest. But couple of quick responses. I won’t DIY this but rather would use my very good electrician for all of the panel and inverter work (if he’s game despite not being a solar guy) or find an electrician/solar experienced person. And I would just have all the necessary panel work done in one swoop. Assuming I go with something like the 18pvk, the question for me is really what is the easiest way to go that’s code compliant. It seems like just feeding the panel from the 18pvk is easiest and rely on the AC pass through in the unit? But would probably want a grid service bypass switch if the inverter failed even if $1k. As for a critical loads panel fed by the inverter, is this absolutely required or just more convenient in event of grid power loss? If grid goes down, could I just manually shut down non critical loads and stay under inverter supply capacity? Or is a subpanel needed nevertheless (seems like it may be but again I’m a beginner). I have downloaded the 18pvk manual and intend to read more closely.

 

[Hedges]

You can have as much or as little automatically backed up as you wish.
Lights, communication, you probably want automatic.

There are panels from Reliance with double-pole switch behind every breaker, so individual circuits can be switched.

Yes a bypass for service is important. With interlocked breakers, figure $50 for the interlock + $50 for the breaker.

It is fairly likely you can't get anyone to install an inverter or PV panels that you buy.
If you have a design of breaker panels, interlocks, safety switch, that you should be able to get any electrician to do.
For inverter & PV, you probably have to find a company that sells and installs the sort of system you want, based on the equipment they offer.
The bigger name inverter brands may have a list of contractors.

 

[cliffstevens]

Yes I understand that contractor installation of self-purchased inverter/panels may be difficult/impossible but I may try to find someone. I probably don’t care as much about buying the panels so if someone could supply/install those to my spec then perhaps my electrician would install the inverter and wire everything inside the house where the panel wires, inverter, batteries go. Honestly it now seems that the preparatory panel work is more complicated than connecting the inverter to all that and the batteries and solar DC wires coming in.

 

[zanydroid]

Yes a bypass for service is important. With interlocked breakers, figure $50 for the interlock + $50 for the breaker.

I don't think interlocked 200A breakers would be this cheap. For that you would need the ON-OFF-ON 200A switch. Like this one:

Siemens General Duty Double Throw 200 Amp 240-Volt 2-Pole Outdoor Non-Fusible Safety Switch DTGNF224NR - The Home Depot

Double Throw switches are intended to transfer loads from 1 power source to another. All 2 and 3-pole double throw switches are suitable for use as service equipment including non-fusible versions when

www.homedepot.com

But there's an argument to not bother with 200A pass through. If you limit critical loads to 100A or 125A, IE the breaker sizes that you can readily use with interlock, you can save a lot of money. Similarly 100A ON-OFF-ON switches are cheap too.

FWIW the MidNite solar engineers (who are cult legends in US DIY solar industry) decided not to include 200A pass-through in their first hybrid (coming out in a few months), because they didn't think the use cases justified the cost. Instead they have 100A pass-through. That hybrid competes with the 18kpv. I think they put the money saved towards a handful of built-in load shed relays. The discussion is buried somewhere in this thread: https://diysolarforum.com/threads/m...their-new-10kw-aio-at-intersolar-today.76840/

For instance I'm quite sure the following switch will be cheaper than interlocked 100A breakers and a separate subpanel.

Eaton® 100-Amp 240V Outdoor Double Throw Safety Switch

The Eaton 100-amp 240-Volt double-throw safety switch is general duty and has a compact design with a rainproof painted galvanized steel enclosure. It features three-wires, two-poles, and includes a neutral. This double throw safety switch can be used to transfer service from a normal power...

www.menards.com

Now, it will be cheaper and more compact to put breakers in a main panel. Maybe an interesting combination would be 225A main panel with 175A main (225*1.2 - 175 = 95 ; the interlocked breakers only count once). You can then put two interlocked 90A breakers to 18kpv, and have unlimited number of branch breakers in the top main panel.

 

[Hedges]

true, I see a 40A QO for $42, 100A QO branch breaker for $130 (more than a 100A main breaker for 125A panel).
As you say, little reason to have 200A feed through an inverter that can deliver maybe 75A.

This stuff does really add up. Plan what you want to do so you buy the right things first time, and don't skimp or leave yourself without expansion options. I've spent more on wire and conduit than on breaker panels and safety switches. But it's my place and I don't care anymore, I'm going to put in what I want.

eBay saves me a lot (or maybe I buy too much and spend more), with patience I've picked up the switches and other hardware I need. Also lengths of 3/0 wire (shipping can add up.)

Here's where I've found good prices for conduit fittings as the like, half the price of home improvement stores (maybe electrical supply houses would be similar?)

Buy Electrical supplies Plumbing Supply - Lutron Dimmers, Circuit Breaker, Disconnect Switches, Load center, Heating System, American Standard, Solar Power System, Fan, Security System, Voice and Data, Tools, Faucets, Intercom - MrSupply.com

 

[cliffstevens]

After looking more at the 18pvk manual, the whole house backup method shown in the attached using a feeder tap seems best to me. I’m kind of not sure how a critical loads subpanel option would even work in my old house because I have some very strange circuits that supply weird groups of things. If grid goes down I can turn off high unnecessary loads at the device or maybe panel for a few things. I would just pay my electrician to create all pieces of this that I don’t have. This method also seems to allow me to switch to just running from the grid if the inverter dies.