Given energy costs, in the UK lots of retailers are now selling domestic 'on-grid storage and self-consumption' kits "for storing cheap night-time energy (off-peak tariffs e.g. Octopus) for use during the day", e.g. a kit with Multiplus II 48/5000/70-50 and 14kWh of batteries, "more battery modules can be added at any time", and PV at later date - https://www.bimblesolar.com/ongrid/self-consumption/5kVA-On-grid-Victron-ESS-14kwh
With 14kWh of 6000 cycle, 95% DOD batteries I'm expecting to be able to store all my elec need at night (@ 7p/kWh) and not use any grid elec in the day (@ 47p/kWh). When we add solar PV, 5kWp will mean we are mostly self-sufficient for 5 months of the year (according to https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html ). But, with a 4kw inverter the above Multiplus seems underrated for 14kWh of batteries. We typically use 7Kwh night and 7kWh day but with occasional peak demand of 8kW (cooking, kettle etc). The expectation was to have all loads via the inverter - 'critical' on AC out 1 - otherwise the system doesn't pay for itself. Also we're rural and have frequent, short duration power outages and thus need the UPS functionality. Am I misunderstanding something here? I'm assuming that, in the day, all power needs can be supplied by the batteries and thus via the inverter and thus the 4kW inverter seems wrongly matched with the 14kWh batteries?