Above I illustrated my calculations on just one hour of battery backup for US grid with lithium ion- would require 10x annual global production of lithium. Generally cost of battery backup looks like 35c/kWh and has limitations on duration so it must come back to fossils.
Solar makes a lot of sense if backup/storage/smoothing weren't needed since pv has gone down in cost. It still makes a lot of sense in many off grid applications, and for instance in my home we have solar concentrator lights and I would love to have solar water pre-heaters in the summer. But for on grid the capital requirements are much more complicated than generally illustrated, and ultimately the environmental impacts are greater than apparent at first glance.