So, let's say that the whole stuff (before solar cells go below a meaningful percentage of efficiency) will last in total 27 years[0], that is three cycles of 9

So, let's say that the whole stuff (before solar cells go below a meaningful percentage of efficiency) will last in total 27 years[0], that is three cycles of 9 years. It is likely that he will need in the next 18 years another charge controller and another set of batteries, so between: 35+2+4+2+4=47 thousands/27=1,740 US$/year and 35+2+16+2+16=71 thousand/27=2,630 US$/year I believe that the issue about the lead batteries is due to them being "in a cabinet", most probably they can be relocated or however the cabinet made ventilated for far less than the difference between lead and lithium batteries. Still, even if lead batteries can be used, it does look like expensive. [0] and it has to be seen how much it will be the cost for the disposal of the panels