It sounds right to me, if you get 4.1p /kWh and pay 5p / kWh then it will be 9p /10kWh. You are on a good rate with Octopus, enjoy it whilst you can! At some point it might be worth installing a battery to store your solar or cheap overnight rate, especially for Nov-Feb when your solar pv will not give you as much. VW and other companies are developing car-2-home for their EV’s, so that you can utilise your car battery to power your home and also sell back to the grid at peak times but re-charge at off-peak, so that might be an option for your next car.
I have looked at battery storage until I was quoted around £4,000 + and £8,500 for a Tesla system, I would however be interest in the V2G/V2H when it comes online in this country ,fortunately our Outlander PHEV is one of the few capable and approved by the manufacture of supporting the system. Figure of £2,000 are being branded about for a V2G charger when they come available ?
Unfortunately I have suffered a brain injury and occasionally I get confused and often say the wrong thing.