BTW, on the subject of batteries being too expensive it might be an interesting experiment to see how far you'd get using a common full sine wave UPS with a number of external batteries. Charge the external batteries using the inverter, pull power out of the UPS. Expenditure would consists of a UPS - you'll find these on auction sites, often without or with expired battery packs - and a number of batteries. A reasonably-sized UPS which can deliver a kilowatt or more often uses 24/48/72 volt battery packs, i.e. 2 to 6 lead-acid batteries in series. If you have a way of getting these for a reasonable price it may be worth experimenting with if you're the experimenting type (I am).

Our inverter is built for high-voltage batteries (120V to 580V) so I'm aiming for either using expired EV batteries or - once prices go down more - LiFePO4 battery stacks. As it stands prices are still too high which - calculated over the life span of the batteries combined with compound interest on the investment - makes power from such batteries cost around the same as power taken from the 'net. Battery prices are steadily going down so this situation should change, hopefully within 3 years they'll have gone down so far as to make it a worthwhile investment.