German Solar Already Covering 50% Power Demand
Compare this graph with a post from May this year to see that Germany is making progress with breakneck-speed. And clearly, if a country can cover 50% of its electricity needs from solar during peak hours, it also can cover 100%, provided sufficient storage facilities are available. The big difference between Germany and the US probably largely has to do with cost.
Here is an article with a lot of solar data, like cost.