Infrastructure cost for 100% is the same as infrastructure cost for 10%? That's not true. The distribution network is the part that can't be scaled, but it can also be reused for either source, so it doesn't double in cost.
No, I'm saying infrastructure cost for 100% is the same as infrastructure cost for 100%. You can't build 10% as much fossil fuel infrastructure and expect it to carry 100% of the load when solar isn't working. And obviously I'm talking about generation here, not distribution.