I am just filling out the Tesla Energy thing. Seems like you buy a powerwall which Tesla controls to import export. They then charge 8p/kWh on imported energy irrespective of time of day and also pay 8p/kWh is you export any power from SolarPV. I currently spend around £2,500 per year on electricity (3 EVS, electric heating, electric cooking and a workshop) so even with the install cost of nearly £10K it look slike a potential 6 to 8 year payback.