Currently, there are no inverters (the ‘brains’ behind the system) on the market which are compatible with the Tesla Powerwall AND specifically designed for Off Grid solutions. The Tesla Powerwall IS able to be used in Off Grid solutions, once there are off-grid able AND Tesla Powerwall compatible inverters available.
If you have the money to do so, once the off grid compatible inverters are available, you can definitely go off grid using the Tesla Powerwall. You will need a generator for last resort backup power and multiple Tesla Powerwalls.
If you CAN stay connected to the grid, save yourself around $10-25,000+ by staying connected to the grid which removes the need for a generator and extra Tesla Powerwalls to store the power needed to cover you for multiple cloudy and/or rainy days in a row (a requirement for off grid solutions).
Even if you stay connected to the grid you would only use grid power when your batteries are completely drained. If you don’t end up using any grid power, you only need to pay the service fee from your energy provider.
Depending on your Feed-In Tariffs, once your house power needs are met and your Tesla Powerwall(s) are fully charged, you are able to sell your excess power back to the grid which in many cases will even cover your service fee and potentially even get a credit from your energy provider!
To expand on the selling power back to the grid concept, if you add Reposit Power to your system, you will be able to sell your stored power back to the grid in times where there is excessive demand on the grid (such as really hot days in Summer where everyone is running their air conditioners) and the grid supply can’t meet the demand at around $1 per kWh. These specific events statistically happen around 77 times a year and adding Reposit Power to your system will help you become even more cash flow positive meaning your solar system is paid off quicker than those without Reposit Power. More details to be made available in April 2016.