Hmm, let’s try, shall we? Assume $300/kW-hr and 4,000 charge cycles. That means a total of 4000 kW-hrs can be stored for $300. (I’m being charitable and ignoring the cost and efficiency losses of the power inverters, and efficiency of charge/discharge of the batteries.) So that means each kW-hr stored costs 7.5 cents just for the batteries. If you add in all that other stuff, I’m sure the total cost is much worse. No bargain.

You are far better off putting extra energy generated into your PHEV (or fridge, or AC unit, or pool heater….) and getting any electricity needed at night from the grid. The grid will even be happy as you are drawing at off-peak hours and supplying yourself at on-peak hours.