> If powerwalls are that great, it should be more cost effective to install giant banks of them in cheap warehouses outside major metros since you'll have economies of scale on installation and maintenance.

This works only if the electrical grid has the ability to consume back your stored power. Most electrical grids in the US would have problems doing that.

For example, UCSD has their own generating facility; however, SDG&E was sufficiently backward that UCSD was unwilling to go through the grief necessary to put energy back into the grid. Therefore, UCSD only does load shifting or disconnects the campus from the grid during rolling blackouts.

Because of the poor energy grid transport, storage batteries make the most sense when you can consume the stored energy locally to minimize your grid consumption during high energy prices--ie. you have a high-rise office with lots of air conditioning or a manufacturing facility.