My house is mostly in the shade, and most of my roof faces north and is steeply sloped, so all I could do is a small solar array of about 2.5kW, which now, at the end of october, is producing about 7kWh per day. This solar array cost about $8000. This feeds into a Tesla PowerWall, which is the cheapest such system available. It can store 13kWh with 89% round trip efficiency. This cost $19,000 installed. Tesla advertises $7,000, but you need a whole lot more ancillary equipment and a lot of wiring complexity. So, we're at $27,000 for something that can produce 260W continuously 24/7 if the grid is out. This isn't very much. It's enough to run the fridge and a LED light or two. I realize I'm limited by my solar panels, and if I had the roof space, I could double my available power for roughly another $3,000. (these prices are pre-30% tax incentive).
A tri-fuel (natural gas, propane, gasoline) hardwired generator would have been a better way to go. I wasn't expecting multi-day outages.