Operating electrical power grids requires a very careful balance between production and consumption. Long term trends are regulated on the consumption side through pricing, short term jitter is regulated on the production side through switching power plants on and off.

Traditionally, a power grid only had medium and large power plants, and they are not only connected to the power grid but also a control network. Adding many small power generators poses a problem in how you communicate and coordinate with them.

"Connecting Solar to the Grid is Harder Than You Think" https://www.youtube.com/watch?v=7G4ipM2qjfw