This one, I already have. I paid more than that for two Tesla powerwalls. I use them for load shifting. I charge at night when electricity is cheap and use them during the day. They already paid for themselves in savings. Oh yeah, no more power outages either.
How? Where do you live that electricity is that expensive during the day and arbitrage rate is that high to create a thousand dollars a year in savings? I run my AC 24 hours a day at fifteen or more degrees below outdoor ambient on a decent sized house, with appliances that are better than twenty years old, and my total yearly electricity cost is under two grand. This math doesn't work.
I live in the US, where the federal government subsidized half the system cost (at least when I installed it) via tax credits. I save about a 100 bucks a month on electric, since I can charge my car at night at a discount, which requires a special meter enabled by the system.