[_FKS_]

Nothing happens at night, there's no electricity output. You need some kind of storage on the back-end if you want to store the day's surplus electricity. Molten salt or hydro work well and can store the electricity, in order to distribute it at night time.

But in practice, this is mitigated by the actual power grid, another plant(s) somewhere else would take over at night. On a coal plant it is harder to adjust the load factor on the fly, it is not instantaneous. On a gas plant or a hydro dam, it is a matter of minutes, the turbines can start very quickly. That's why usually when such utility-scale renewable plants are installed, they need to be paired with another load-following plant, such as gas. Nevertheless, a renewable+gas/coal plant means less CO2 emissions, so I guess it's a good thing.