Off Grid Solar System - 250 amps of Inverter capacity - What load center do I use?

Question

I have four Sol-Ark 15k inverters (Although I'd like to size things so that I have room to add more in the future if needed). Each inverter can supply up to 62.5 amps of continuous power. So 62.5 multiplied by 4 inverters = 250 amps of total continuous output. Also keep in mind we'd like to size things such that we might add an additional inverter in the future, which would push total output to 312.5 continuous amps. (Effectively 400 amp service)

This power needs to be divided among a few different buildings: A house, a shop, and a couple smaller buildings. We would like to supply "200 amp service" to the house and shop with smaller service to the smaller buildings.

I was originally thinking I would just buy a 400amp load center: And have each inverter connect to said Load Center via an 80 amp breaker (yes this would derate their output to 60 amps but that's fine). So this would mean four separate 80 amp breakers, each connected to one inverter. Then in that same load center install one 200 amp breaker for the house, and another 200 amp breaker to the shop, etc.

However as I started to search for the required parts, I realized it's nearly impossible to find a load center that handles more than 200 amps, and just as impossible to find breakers rated over 100-150 amps.

I know 400 amp service isn't common: but I thought it was done routinely enough that it would be possible to find load centers and breakers of that size.

So here are my questions:

1. Is there a 400 amp load center out there that can support 200 amp breakers? IE: If I had 400 amp service from the grid and I wanted to divide that to multiple buildings: How would I do that?
2. If "No" to #1: Can I run two separate sets of wires, each connected to a 100 amp breaker, and then combine them at the load center on the house or shop to feed a single 200 amp "main breaker" on that buildings sub-panel?
3. Is there a simpler solution here that I'm not seeing?

Answer 1

Your options are...limited

Normally, at the 400A mark, one is dealing with commercial work, and thus is using a full commercial panelboard instead of a residential-style loadcenter; hence, 400A loadcenters are rare, despite 400A both being a common service size and a common size for lower-end panelboards. However, there are a few 400A loadcenters out there.

For your application (solar combiner), presuming you can mount the panel either outdoors or in an unfinished (service) space, your best bets are either an Eaton BR1224L400R or a Siemens W0606ML1400CU. The latter provides a copper bus option, and is less costly, but limits your flexibility as it's only labeled for 6 breaker positions despite having 24 single pole spaces. (You'll need to lean on the tap rules to pull power off the 400A panel's main lugs to a 200A main breaker loadcenter if you use the latter option, even.)

This is fortunate at least though, as your option #2 would violate NEC 225.30. Were you to have a 400A grid service, the normal practice would be to use either a Class 320 meter base with 2 200A main breaker panels, or a 400A meter main that contains both the meter base and the service disconnects, with 200A panels downstream of that main.

As to 200A branch breakers, both Eaton and Siemens make them: Eaton's is the BJ2200, while the Siemens counterpart is the QN(R)2200, with the R version having a reverse orientation.

Keeping things in place

With all that said, though, the main problem with using a loadcenter as a multiple-feed combiner in an off-grid system like yours, though, is that the solar system breakers in it need retainers to meet NEC 408.36(D):

(D) Back-Fed Devices

Plug-in-type overcurrent protection devices or plug-in type main lug assemblies that are backfed and used to terminate field-installed ungrounded supply conductors shall be secured in place by an additional fastener that requires other than a pull to release the device from the mounting means on the panelboard.

as NEC 705.30(E) no longer applies when you are on the grid-forming (vs the grid-interactive) side of a multimode inverter (such as your Sol-Arks):

(E) Fastening

Listed plug-in-type circuit breakers backfed from electric power sources that are listed and identified as interactive shall be permitted to omit the additional fastener normally required by 408.36(D) for such applications.

and residential-style loadcenters often only support breaker retention in a small number of positions as it's generally only needed when using the panel in a backfed main breaker configuration. Furthermore, I wasn't able to find any documentation online about whether the panels I mentioned above support breaker retention or what breaker positions they support for such use, for that matter.

With this in mind, we look to something that straddles the boundary between a residential loadcenter and a commercial panelboard, namely the QONQ line of merchandised panelboards that Square D offers as 400A loadcenters for QO. The QONQ30LS400 with its matching MH50 enclosure can support 200A branch breakers (QO2200s, to be precise) and also can be flush mounted using the correct cover, in addition to supporting backfed breakers at arbitrary positions using bolt down style QOB breakers. However, it is restricted in its use with a NEMA 3R box (you need to use the MH62D9VWP vented enclosure with a NQ12RDE extension, which limits you to a single 200A branch breaker as well atop being 9" deep), is wider than a typical loadcenter (20" vs the more typical 14" loadcenter cabinets), and requires a non-standard cover (NC50VS3P or NC50VF3P) to work with the QO2200 branch breakers.

Answer 2

Option 1: Get a 400A meter pan

Wire it exactly like a bog-standard 400A residential service, where the meter pan has double lugs for dual 250 kcmil wire, which then has double output lugs to split to two 200A main panels. The 400A meter pan is acting as a combiner for all inverters, and then (whatever the inverters generate) is split asymmetrically to two 200A panels (i.e. it splits as it needs to).

You get a useless meter out of the deal, but you also have a setup that any inspector will instantly recognize and feel comfortable with.

How does this 400A setup work in a normal house? The meter feeds two run-of-the-mill "200A main breaker + 16-40 breaker spaces" panels, e.g. two Siemens PN4040B1200C fed off a Milbank RS3548-X (with correct lugs). This isn't for you; I'm just giving you a baseline for the normal practice.

For you, my option 1A is replace the plain ole panels above with Ranch/Trailer panels. These beauties have

• a main breaker
• 4-12 breaker spaces
• "THRU LUGS" to carry the "full 200A" onward to another panel.

An example is the Siemens PNW0816B1200TC. Again not expensive equipment, two at $200 a pop + meter pan - $700 of equipment so far. You have two large buildings you want to deliver 200A to; each one is fed off the bottom "thru lugs" of one meter. If one building is taking 200A the other one can take up to 50A (though of course nothing enforces this). The 8 breaker spaces also provide you places to install feeders to smaller loads.

Option 1B: An "All-In-One" Ranch Panel. This is a peculiar beast that provides most of the above in a much more compact form factor. An example is the Siemens MC0816B1400RLTM.

The only thing it doesn't give you is an 8-space panel off the second 200A breaker, but you may not need that, and it may be worth the reduced box count.

Option 2: move one inverter to its own panel.

Now you're at 187.5 amps give or take, well within the capacity of a resi 200A load center.

You don't have to destroy it; you can give it its very own 70A or larger load center and have it supply some loads. You'd have to figure out for yourself which loads make sense for that.

Option 3: Conservation > Generation: Get more efficient appliances

What's got me puzzled is why an off-grid house needs 250A of inverter. It's very common for off-gridders to just "default to" the bog-standard American resistance electric dryer, resistance electric water heater, or the inefficient (and annoying) resistance cooktops. Because they're cheap.

But they're not cheap to provision electricity to when you generate it yourself. The heat pump dryers and water heaters cost $1500 instead of $800, but their much smaller footprint on your NEC 220.82 Load Calculation saves you thousands on generator or solar/battery/inverter.

Technology Connections has a great video on these new appliances and the relevant part for you starts at 4:58 - now Alec is talking about avoiding costly service upgrades and making an all-electric home work on 100A service, but the principles are the same.

Heat pump dryers and water heaters can plug into common 120V sockets, however since the vast majority are replacing resistance units, many are made with the same 240V/30A connection so the homeowner doesn't have to have an electrician in to rewire the circuits to 120V. Their power consumption is what matters. Some dryers, since they have 30A on-hand, include the old resistance element to provide startup heat And since they have 30A at hand, some of the dryers include a resistance element used to provide the initial heat (then recycled by the heat pump).

Not to mention the thing where a resistance dryer pushes conditioned air out of the house, sucking in outside air, burdening your HVAC and filtration further. That goes away with the heat pump dryer, for further energy savings.

Option 4: Manage EV charging

So you have big EVs, many EVs, and expect more. That's not bad news forcing you into larger and larger service - it's good news allowing you less and less. Because EVs have service limiting baked in. Every EV from the Taycan to the Wheego LiFe.

When EVs were developed, manufacturers were well aware that most people would need service upgrades to add 40-60-100A circuits to their panels to charge a car, and that due to range anxiety, most people would not settle for a 20A circuit that would actually fit their needs. This would be a sales-killer, but knowing this, they included technology in the EV standard to fit in ANY service and charge anyway. To understand why, you need to discover the secret that most appliances only take power when you are using them. Technology Connections has a fantastic video on that here.

To understand how EVs can even do that, TC also has a video on that, because of course Alec does LOL.

So the first swing at service capacity conservation is to use the tech so gracefully provided by the manufacturer, using an EVSE ("charger") capable of EVEMS / service limiting. Listen carefully here: it installs a power monitor on the main service wires coming into your service, and then wires those to the EVSE. The EVSE then dynamically adjusts EV charge rate so that the programmed service load will not be exceeded.

So if you set up, say, 187A service, your F150 Lighting will rock at 80A actual until you dryer, compressor, saw and A/C all just happen to be all on at once, driving non-EV load to 95A. You've set a 160A limit so it reduces EV charge to 65 amps for a few moments until the compressor finishes. As discussed, this doesn't happen often enough to matter to your charge rate, but it does beautifully clip the peak so you can provision less service equipment.

The Wallbox Pulsar Plus is a proven performer here in the States; Zappi in Europe, and Emporia has an unproven solution that is all-WiFi.

The second tool is Power Sharing. I don't know if any of your ATVs are sophisticated enough to have J1772 charging - if they're not, their load is probably too small to matter. If they do have J1772, you can set up a row of EVSEs and link them with another tech called Power Sharing (available from several makers). You allocate a fixed amount of current to the entire group and it dynamically shares among the vehicles. As such you can have an unbounded number of vehicles, but nonetheless bound their total consumption and thus their space in the service Load Calculation.