No it isn't. Storage capacity for energy is expensive, if you want to have a grid that is largely dependent on intermittent sources and still have a stable grid providing power at all times you need large amounts of storage as well as generating capacity.

For example if nuclear costs 1bn for a GW and solar+wind costs 0.6bn but you need to also install 0.5bn of storage to make the grid reliable to the safety margin you deem acceptable then it is no longer a cheaper system.

Amount of storage needed scales up rapidly as you get towards an grid with entirely intermittent generation.