The Powerwall comes in two sizes: 7 kilowatt hours (kWh), which cost $3,000 and 10kWh, or for $3,500. Any home or business that needs more capacity, can install up to nine units together for a maximum 90kWh. The average four-person household uses between 20.9kWh and 21.6kWh of electricity per day. So for about $7,000, plus the cost of solar panels, a family of four would be good to go, or rather stay in, and watch TV, even at night. On top of generating their own electricity, in many states electric utilities are required to buy back any excess electricity that homeowners generate. So, once the Powerwalls are topped off, homeowners could potentially turn a profit.
Electric utilities aren't happy about this arrangement, or about the increasing number of homeowners who are generating their own electricity. They're often quoted as saying things like, "The grid isn't built for this." Well, that's true enough. But it's also true that we lose as much as fifty percent of the electricity we generate in current plants during transmission in our current antiquated grid.
To demonstrate the effectiveness of his company's new product, Musk used them to power the entire press conference at which he announced the Powerwall's release. Musk also announced that Tesla was taking orders for new units that could be delivered within the next three months.
So, if you're looking to move off the grid, or if you just want to go solar and hang on to all of the energy from the sun you produce, the this may be the product for you. It seems likely that Powerwall or something like it will become a standard part of solar systems installed in people's homes. Imitations are likely, as Musk has open sourced the design. When asked about this unconventional move, Musk explained that this is a revolution in power generation that needs to happen, but that he and Tesla won't be able to make it happen alone. Musk is clear that he's going to need competition, and according to him, the fastest way get competition is to make it.
(Sources: phys.org, NPR)