I'm interested in Powerwall for backup; in fact, I was one of the first to click and "order" one. After further research, it strikes me if you are going to buy Powerwall for backup you almost certainly should add a small solar system, even here in Houston where there are no local incentives and I can buy all the 100% wind generated electricity I want for 12c per kWh. Here's why. Let's say a 10 kWh Powerwall backup system costs $7k including inverter and installation. For that I get 10 kWh of power if the grid fails, then nothing. What if I add a small solar system to the mix? A 3 kW system would ordinarily come to about $9k (@ $3 per watt), but since I'm already paying for the inverter and electrical installation let's say it adds $7k to the bill, so $14k total. Now comes the fun part. The whole system, including the battery, now qualifies for a 30% federal tax credit on residential solar systems. So the net cost is about $10k. And I now have a system that (1) generates about $400 of electricity per year, and (2) delivers 10 kWh of power per day if the gird fails. Way more attractive to me. A couple important details I learned while researching this. To fully be covered by the federal tax credit on solar systems, a battery must only be charged from the solar. This isn't really an issue for a backup application, but it may in part explain some of the strange comments people have been hearing from Solar City. Also, the federal tax credit expires at the end of 2016 and I don't have much confidence it will be renewed so I need to try to get this project completed before then: fingers crossed that Tesla can deliver!