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.
