Hi,
From what i have read now there is a smaller unit available, and it is rechargeable a lot more times, like 5000 vs only 500 times.
I dont think we can rely on the power companies to sell back power because they will not like that. If everyone did that they would not make any money, and that will lead to cuts in the buy-back price. Someone mentioned infrastructure, which we would have to analyze to figure out how much of the cost actually went for that. If it was significant, then we're beat.
This is still such a new area for our civilization. Changes are bound to happen over and over again until something emerges that actually works, or we keep trying forever until we die off.