How useful are alternative energy sources?

Question

Internet of Things

Faced with a contradiction when delving into Smart Grid technology (intelligent power grids): on the one hand, smartgrids largely rely on increasing the share of distributed energy production systems and
renewable energy sources and increasing the flexibility of power supply. That is, in simple terms, alternative energy sources are used whenever possible, and there is frequent switching between different sources. On the other hand, people who understand a little more than me say that it is much more expensive for power plants to change the operating mode than to work stably with a heavy load.
How then do smartgrids benefit from this?
I confess that the question is not quite IT (what is there, far-fetched, but not on the mail. Answers should go with it), although I ran into it within the framework of IS.