[nhaehnle]

Those batteries can come in useful even when you're still connected to the grid.

Right now, some locations have laws and/or regulation that force grid companies to buy solar-generated electricity from home owners at fixed rates. This makes a lot of sense right now as a measure to encourage the adoption of solar, as a way to get off fossil fuels. In the long term, it might become a less useful measure, and we might want to allow market mechanisms for time-of-day-based pricing. This is already happening on the big players' market, where you see drops of the spot price of electricity at noon on sunny days. Extending these market mechanisms to individual homes makes sense, as long as home owners are empowered by technology to make use of it.

A large battery is an important piece of such empowering technology (combined with being able to set a smart policy for when to run off the battery, when to run off the grid, and when to feed back into the grid).