I also have a new Tesla 10 kWh battery back-up that Solar City recently installed in my garage to back up my solar panels in case of an outage ... and it will work independently from the grid, should there be a black-out, and will power everything in my home (including charging my Model S) indefinitely because my solar panels will continuously recharge it. However, I missed the original $10/month lease program, so I opted to buy it for $15,800 ... with SDGE giving a whopping $10,800 rebate! That makes the out of pocket $5,000, with a ten year warrantee. Still not a bad deal. There is not problem with SDGE here near San Diego, as far as installing these units, as they are cooperating fully. And also, you might like to know that I was told by the Tesla technician that the batteries in my unit were absolutely brand new and NOT used in any way. I received the early model in September, but he said that a smaller, upgraded model will be on the way for 2014, when Tesla expects to be selling about 10,000 of these battery back-up units. My system is now temporarily off-line pending SDGE installing the meter, hopefully within the month ... then it will be on full time. And, since there is a warranty for 10 years, I am not worried about any degradation. Oh, by the way, these batteries have no heating and cooling as do the cars - at least that is what the Tesla tech told me - so he said that because of this (no heating or cooling draw) there is no drain from the system when they are not being used, as with the cars.