I know rooftop solar is not the grand solution, it's just a little piece. We would indeed have to build out solar & wind farms of appreciable size.
But I cannot fathom how the entire total global roof area can only power 8% of Poland. Evidence?
See, even with superb photovoltaics only single story homes have the right area to power use ratio to make sense to use solar as main power source. These cause transportation problems that probably eat all the benefit...