After closer consideration I decided to buy the Powerwall for my house in Florida. We don't have a natural gas service, so a generator is not an option. Solar is not an option due to hurricanes and low energy prices (12c per kWh). I will likely buy the 10kwh battery from solarcity for 7140$. It provides a reasonable backup solution for the most important systems in my house. Power outages usually last 1-5h after powerful t-storms. Furthermore it adds value to my house, so I don't see it as an investment to save money, just like people don't buy a natural gas generator to produce electricity for less money than the grid is offering. Plus it looks awesome in my garage.