What you have described would last for 1000 days used to even out daily (solar) power demand/supply. So for a 25yr capability it would cost 8x more? I would hop

What you have described would last for 1000 days used to even out daily (solar) power demand/supply. So for a 25yr capability it would cost 8x more? I would hope not, and I think you could get 3000 cycles by restricting temperature and charge/discharge, but that still requires 2.5-3x higher cost and puts this solution as very competitive with current battery solutions.