I'm going to qualify what I say right at the start by saying I'm no expert so if anyone contradicts me later they may well be right.

That said, I don't see how you could break anything but things might not be quite what you expect. Eventually, you only have one cable from the grid to your house and your import or export is simply a measurement of the net flow of electricity in one direction or the other. Therefore, if you charge your car at 7kW at the same time you're telling your battery to discharge at 3.6kW then the car will charge from your home battery and will pull extra from the grid to get up to the full 7kW. That's not ideal since you're not going to be paid for the energy being discharged from the battery and you're also wearing your home battery unnecessarily.

You should also bear in mind the likely lifetime of your battery vs its initial cost so you can get an idea of how much a charge/discharge cycle costs. You may well find that the 8p difference between export price and cheap import price isn't as much after all. I've been through it and found playing the "import now to export later" game gives only relatively low payback.

All that said, you're quite right that a bit of home automation is the way to go to get much better control (along with keeping an open mind on tariffs too, of course). Assuming you're talking specifically about Home Assistant, I'm sure there's plenty we could do to help reduce the confusion so shout if you want help.

@majordennisbloodnok I should probably clarify: I wasn't expecting that it would charge at 7kW and simultaneously export 3.6 for payment just not interfere with each other (or break something!!)  For the evenings where I do charge the car, and assuming it is ok to discharge at the same time, I'm expecting my export payment to be zero.  But I offset that small loss against having to change the configuration twice every time I plug the car in.  I'd ask my installer but he's currently on paternity leave and I don't want to bother him.

As for Home Assistant (I keep getting that "A" in the acronym mixed up), if I need some help I'll be sure to ask.  It will be related to hooking in to the Octopus API and re-configuring the SigGen batteries for a smart schedule.  Anyway that's a different thread!!

Understood, @andrewj.

It might be simpler if you remember that the EV charger isn't a special device from your inverter's point of view; it's just another load the same as a phone charger, a laptop or an oven. If your fridge is still running whilst you're discharging your home battery then the only thing that'll change when you try charging your EV is the size of the load.

Does that help?

@majordennisbloodnok Well, I tried it and nothing burned down 😀  Actually, I forgot to think about the 8kW inverter so what happened was that the battery entered its forced discharge and 7kW ended up in the car and 1kW ended up in the grid so all works fine and I don't need to be messing with configs.  Although, of course, I won't be getting paid the £1.05 for that 7kW so it would seem unlikely I'll be a millionaire this time next year!