Well, the vast majority that are plugged into the electric grid are. The issue is more that wind and solar don't change their generation capacity in response t

Well, the vast majority that are plugged into the electric grid are. The issue is more that wind and solar don't change their generation capacity in response to demand (it's either sunny or windy that day or it isn't), so you need a battery of some sort to store up output in excess of current demand and/or the ability to add generating capacity when hit with peak demand; that's where natural gas / coal plants are necessary given present technology.