Batteries and flywheels are simple indeed. You might not have noticed, since they seem to stay within budget and timeframe. But they are a standard solution.
Synchronous condenser example from Germany:
https://www.siemens-energy.com/global/en/home/press-releases/siemens-energy-technology-stabilizes-german-power-grid.html
From Ireland:
https://www.siemens-energy.com/global/en/home/stories/irelands-great-grid-stabilizer.html
And so on:
https://new.abb.com/motors-generators/synchronous-condensers
#Renewables #GridStability #PowerGrid #Flywheel #SynchronousCondenser #nuclear