I haven't ran any numbers, but have seen that you could save £900 a year by having one installed on economy 7. Now, I take sales figures with a pinch of salt, and to save £900 a year means you had to be spending £900 a year in the first place.
But let's say this thing runs on E7, and (for arguments sake, not done much looking) E7 off-peak is half the cost of peak. And for the sake of keeping things simple, let's say this powerwall will keep an average house running all day. So essentially, that means your electricity bill is halved. Let's say my bill was £400 for electric, surely that means I can save £200 a year. Okay, the boxes are about £5k which will put repayment at 25 years, but the boxes are surely going to come down in price in the foreseeable future.
Sorry, very basic maths etc, but I reckon this is going to have a lot more potential than solar. If you already have solar, this stuff is going to double it's usefulness.
