The problem here is not renewable energy sources, it's buffering their output. Improvements to battery technology and short-term energy storage are key to cracking this problem.

If energy is free or even profitable to consume you'd make money pumping water uphill during the day and using that potential energy later to produce power through conventional hydro-electric means. This is completely insane if you have to pay for power at conventional rates, but we're entering a new era where time of day costs might go all over the place without arbitrage like this to even things out.