There will likely be lots of wind energy too which could alleviate the solar problem, though this is based on luck. Passed that the ideal solution is nuclear energy and in the future fission based reactors if they are economically viable.
What’s most feasible today in most places would be burning gas. I know it’s not perfect and still emits plenty of CO2 but the plants are much faster, cheaper and easier to build than nuclear, and gas burns much cleaner than coal or oil. Plus it can be stored and transported fairly efficiently by LNG container ships.