OK, I'm working on the premise:

1) Panels are cheap and it's best if you install all you can at the start while there's scaffolding etc.

2) Ideally I would like to be off-grid, but PV production in the middle of winter is b....ks, so I'll still use a grid connection then. But I would like to maximise PV production in the shoulder seasons.

3) I have a 1P / 100A grid connection to UKPN.

So, I'm planning about 48kWp of panels split across 4 roofs (in 2 pairs) in various orientations. And then:

1) Asking the DNO to allow a 12kW 1P inverter with grid connection for the house (ASHP, DHW with immersions, kitchen etc) which will support 24kWp of panels on the house (2x clipping). This will be integrated single stack (probably Sig) with as yet unknown amount of battery.

2) Having a separate 12kW 1P for the other 24kWp of panels on the 'cart lodge' but disconnected from the rest of the house circuits and the grid. This will only be used for car charging.

What do you think?

Edited 1 hour ago1 hr by Alan Ambrose

Firstly, with a 100A connection why start with the premise of only exporting 12kw? At least ask the utility if they can support higher export? Then it's simple and easy. Even if they limit export below generation it seems like keeping things simple would be better. Having said that, you might not even get 12kw so that then creates another problem for you.

I'm not sure your approach does anything more than make things complex. A 24kwh battery is not enough to fully charge a car and even if you are mostly just topping up you will likely come across times when you empty the batteries in the off-grid system before you charge the car. Also, if the off-grid system had spare solar stored in it's battery but the house did not, you would have no way to use that capacity. So I would look for everything to be grid connected (with ability to continue operation without the grid). That way you get the full capacity of all batteries available.

If you have significant excess generation that can't be exported what are you going to do with it? Seems like a huge waste to spend a fortune on install and not have anything to use it for.

If you plan a workshop with potential for 3p machines then an alternative setup would be to use inverters to generate the 2 other phases (all connected to the same battery). 1 inverter is connected to the grid, the other two phases purely rely on solar/battery (inc charging from the grid connected inverter). I doubt this is a common option but I know you can do it with some inverters (Victron). Still I'm not sure it makes much sense from a financial POV.

Just over clock the inverters, fit PV to run at max amps or max voltage. We have 6.5kW PV on a 3.6kW inverter and 2kW on a 1kW inverter. Any excess is just clipped, but rarely does it clip anything.

But if going with hybrid inverters and battery you can put as much PV as you want on the DC side as long as you stick each array in it's own MPPT.

Battery and inverter I would investigate if you are running on a cloud and walk away if you are. Our GivEnergy is a good example it can be run in full local mode, so when GivEnergy went belly up everything just carried on working. A cloud based system you stuffed. Sig I believe need a web connection to have full functioning - so if that's the case, I would look elsewhere.

Also if you want full house functionality in a power cut, look for a system that has a gateway, that will allow full inverter output to house with grid off. Most normal hybrid just give a small ups output which is great if you just want a light on.