This looks to be a pretty big deal, especially if Tesla can actual scale to the potential here. And the timing is perfect given the ever growing fragility of the power grid to both natural and manmade damage.
There are layers here but the biggest I see is not only being able to daily store energy for solar/wind and other sources but equally powerful is to be able to effectively leverage peak load pricing of the base grid so that you charge the system at night during low load (and low rates) and use your own power - and even potentially sell some power back to the grid during peak power. The rate differential is 4 times or more virtually paying for the cost of the system. Wow.
If this works as hoped it should be clean, silent, simple, free to low cost and make our local power grids far more stable and secure. Win win for everyone (but the power company).
Call me a fanboy of Musk (I am) but he is the Thomas Edison of our time - changing finance (Paypal), transportation (Tesla), space travel (SpaceX), Clean Energy (SolarCity) and now our base power grid itself (Tesla Home Power). Through in Hyperloop and other ideas and he is simply a great practical get-it-done engineer in the classic style.