Its not just about enough sun and wind capacity. There is already over supply in lot of the world. But the supply curve doesnt match the daily DYNAMIC demand curve so grid ops still dependent on coal and gas for different reasons. It becomes about what happens during unpredicted demand spikes, or when congestion on those wires happens whose load gets priority? which producers get curtailed? etc etc That moves probs into the political domain. You can watch daily grid ops live and see the probs. Wars and the weather randomly take down wires and substations all the time. If you can move people and factories to follow the wind and the sun then maybe you get demand and supply curves to match easier.