Get some old batteries from a car place, cheap solar panel and a cheap invertor and you have back up. I did this in new zealand when I lived in the bay of islands. The power kept going out so i got some decent batteries taken from a car just out of warranty. $20.00 got me a solar panel and i paid next to nothing for a 300w invertor. I put led lights up in the house and it was enough to power the lights and modem so I could still surf the net. I have the same set up in the uk but bigger batteries and a 2000w invertor. Never really needed to use them though.
Another option is wind power those little wind generators create some decent wattage.
Leisure Batteries (Caravan Batteries) will be better than Car Batteries as Car Batteries are designed to give out a large charge to start a vehicle while Leisure Batteries are designed to give out a consistent charge suitable for lights and household goods.
Leisure batteries/deep cycle batteries is what it I have here 2 X 6v Trojan linked together, but mine are only really to play with. They are much more expensive to buy. I sometimes get used one as we use them in our industry. I suggested car batteries as only because sometimes they get thrown away. My 2000w modified signwave inverter was about £25.00
if your looking for something to power a pc you can get 12v to 12v power supplies so no inverter needed
this also saves you going from 12v to 240v and then back to 12v