- Did you need/use an electrician to set this up? - How much KWh capacity do your batteries have? - What about fire safety? Did you install outside, or inside? - I assume dec/jan are the months you're not fully self-sufficient, are you allowed to charge from grid to do arbitrage over time, or is that another can of worms?
The battery is 16kWh. Effectively around 14kWh, since you never fully discharge. LiFePo4, so no chance of spontaneous combustion like other battery chemistries.
I'd say the months Nov→Feb are tricky, although since I have quite a bit of excess solar capacity there are even in December plenty of days where the battery pulls me through the night.
Charging/discharging from/to the grid is possible, since I have a retrofit inverter (AC to battery), but not doing it yet, have to do a bit more research (dynamic pricing, tax is >50% of the kWh price in NL, etc).
UK specific note: note that since the changes in 2013 under the ""Part P"" building regulations, almost all electrical work other than trivial replacement is illegal to DIY. Additionally, renewables work requires extra MCS certification.
Which is why balcony solar is a good deal, it requires none of that.