In Texas, net metering is not required, so there are only a few plans that have "solar buyback".
Since we are at risk of hurricanes, our 4 PowerWalls should provide enough power to keep us off-grid (with essential devices) for days after a hurricane.
We're currently paying $.091/KWh for electricity on a standard rate plan, and using the solar panels and PowerWalls to provide as much electricity as possible, and trying to avoid sending any power back to the grid (because we aren't compensated for that).
A net metering plan would cost us $.149/KWh. Any electricity sent back to the grid would be credited at this rate. Because we are able to keep the power we send back to the grid close to zero, using the net metering plan would increase our electric bill by 63%!
With our 15.4KW of solar panels and 4 PowerWalls, we've been able to reduce our electric bills by over half. Using net metering and no PowerWalls, we would have seen a much smaller decrease in cost savings.
The combination of the cost savings and the ability to operate off-grid (after a hurricane) justified our PowerWall purchase.
Instead of net metering, we're looking at the possibility of using a "free nights" plan that would give us free electricity from 9PM to 9AM. We would be charge $.185/KWh for electricity during the day, and would plan to use grid power only during the free nights. We're projecting we may be able to reduce our electric bills by an additional 50% (even with the higher per KWh rate) because our PowerWalls can provide us enough power to keep our "day" time usage pretty low.
If you have access to smart metering data and you've been operating a system with a single PowerWall for at least several months, you should be able to look at the actual data and see if you'd benefit economically from adding a PowerWall.
Otherwise, the only advantage would be to extend off-grid operation, and the value of that depends upon your risk of losing power and for how long.
