FWIW our experience is much the same. Originally fitted 7.1 kW, charging this from PV was fine but not leaving enough for the immersion diverter. Also not enough storage to run the electric cooker at breakfast time without cheap rate top-up.richbee wrote: ↑Thu May 11, 2023 9:23 am My feeling is about the same, based on 6 months of having only 1x 5kWh battery with Solar PV. There is a lot of time where the battery is full and exporting, but then the battery is empty the following morning. Also the discharge rate of 2.5kW is not enough to run things like a kettle fully.
I have now fitted a 2nd 5kWh battery and it seems to have made a huge difference - in May so far I have inly imported <10kWh and usage is well over 90%, even though we have had less PV generation on average compared to April.
So added nearly as much PV again, also added third battery module to make the figures below. Would agree this is a sweet spot; is enough to keep the lights on all evening in winter with a bit to spare and in summer to survive on PV alone. Won't increase capacity any further, heat pump will have to fend for itself, though I am contemplating 200 litre thermal store to charge up from E7 before the heat demand begins in the morning. Subjec to what I can get an installer to agree to, may have to DIY or retrofit.