I'm going to install a 9kW solar grid on my roof in the next couple of months - capital cost is ~$40K USD. Without the Power Wall, I'd be selling power back to the utility at around $0.10 / kWh, and buying it back at $0.09 / kWh in the evenings. The Power Wall will also let me endure grid outages as well (you can't run your house on your solar panels directly).
I'm really curious about what the end-user cost is going to be for one of these batteries, after distributor markup and utility company rebates. Would be interesting to see if it pays for itself over the 10 year lifespan of the batteries.
I just reserved one.