Eric - having an EV and having solar panels, with or without export, are entirely separate.
Be it a mobile battery (EV car) or fixed battery (Solar) or even a thermal battery (storage radiators) and for that matter when appliances switch on (dishwasher, washing machine, and tumble drier) what matters it two things, how long, and can the supplier control it.
If the supplier can switch it off, be it with a teleswitch, or the EV charging unit, or even a dual output smart meter, they can when there is a shortage, turn off part of the supply to the household, without turning off the whole supply, and so they can reward the user by giving them a better rate.
But if all they can do is try to persuade you to use electric at certain times, and not everyone wants to do their gardening at night even if Anglia Ripon does, then the reward is less. And the longer the off-peak is, also the less reward we get.
I have a 60 amp supply (13.8 kW) so in 5 hours I can import 69 kWh, in real terms far less, as we could not ensure it did not go over if on the edge, so 7 kW EV charger could import 35 kWh, my solar panel battery has no option to reduce charge rate if there are other loads, so likely more like 5 kWh imported during off-peak.
If someone needs more than 35 kWh they could opt for Eco 7, and get 49 kWh, so £6.95 or £7.19 for 7 hours at 7 kW. Eco 7 is the cheaper of the two. Although the Eco 7 day rate is higher.
To get the EV lower rate, it needs to be controlled by the supplier, but the same applies to the solar panel rated, allow the supplier to control your inverter in both cases you get a better rate.
The problem is, to work out the best deal one needs to be a clever at maths, the comparison sites are useless once one includes export into the calculations, and of course as I found out to my cost, promises which they don't or can't deliver. It would not matter now what British Gas offered, I would simply take it with a pinch of salt. I know now, even if I had got the MPAN number when with them, they could not have back paid me.
When we went to Octopus, British Gas tried charging me for electric bought from Octopus, OK not their fault and once the meter reading given to them, it was corrected, but even with a Smart meter, they, it seems, could not get a final reading. And I wonder if we lost anything when by default British Gas took over our account when the last supplier went to the wall?
I hope Octopus don't fail, as at the moment £534.57 in credit. Once with them a year, I will adjust payments, but don't know winter costs yet.
But be it cost to run a dishwasher, washing machine, or tumble drier, there are that many programs and that many tariffs, it is near impossible to work out. Up to date this month, it has cost less than a £1, to run the dishwasher, not including price of detergent, so why is anyone worried?