What is the volume of fossil fuel we extract from the ground every year and try to imagine getting there from zero. Fact is we have easily 100K sq miles of useless desert as-is. We can fit a Rhode Island-sized solar farm in Nevada and nobody would notice. China built a solar farm of 162 sq mi in Tibet and are still expanding it. But realistically we will also be building wind, hydro and enhanced geothermal along too. It will be a lot of work, but it's absolutely achievable in a matter of decades with enough popular and political will.