DIY PV System to Save Money AND for SHTF

[Skvez]

8* 80W panels is 640W 'rated'.
You work with a figure of 730kWh / year.
My tests suggest a value of 220kWh/year would be closer to typical for 640W of solar in the UK.
You also don't consider the efficiency losses of your inverter, the spec sheet isn't clear about this but it suggests it's possibly 91% efficient although from some of the other figures they give I calculate 86% … who really knows. And in either case that’s the efficiency at full power, lower power is probably less efficient.

Certainly a viable system, I'd be tempted to charge the batteries from the solar and only switch to the inverter when they were topped up (rather than bother with the AC charger).
I'd also very seriously consider DC lighting (as others have suggested).