So:
20A
Charger charging for 6.5 hours to give 130 Ah (1.6 kWh) to power 140 W computer for 7 hours.
Two 130 Ah
Batteries. I discover that it’s 130 Ah (C100) meaning it’s only 130 Ah if discharged over 100 hours. If discharged over say 10 hours the capacity is only around 90 Ah. So I’m charging up 130 Ah worth but only getting 90 Ah back because of internal losses which is a bit of a shame but never mind. I’m thinking of two batteries so that they’re not deep cycling the whole time which I presume wouldn’t do them any good.
3 kW
Inverter which might even let me run a 1 kW fan heater for an hour on sunny but cold winter day
I can’t retrofit a battery to my PV system so I’m hoping this will take me near off-grid between May and October. The panels would charge the batteries over day, with anything over the 240 W (20 A @ 12 V) being used by my existing controller to heat my immersion. I think that’s a cloudy but reasonably bright day. It all doesn’t take up too much room either, will need to allow for air flow but a block about 35l x 40w x 40h cm.
Tl:dr Costs around £310 and assuming a future price of 50p/kWh hopefully gives a repayment time of around 20 months.