I’ve already got a 4kWh solar system, and am also with Octopus, getting 4hrs per night cheap rate. I find that it’s not worth the hassle doing other than just charging my Kona at night on the cheap rate, at 7kWh. However in May we’re due to have an additional 4kWh system plus 16kWh of batteries, at that point we will schedule to run off the the batteries, topping those up at the cheap rate when the panels haven’t produced enough.