Grid storage generally means water, wheel, or heat. Green electricity is especially problematic for grid stability. As wind can hugely fluctuate and large clouds can dramatically effect solar output. These huge and rapid transient events can be significantly smoothed with some form of grid storage. The result is improved grid stability. The problem is, an outage of the storage (battery fire, and has repeatedly happened in the past), can knock the total segment capacity offline. Which means, for reliability you still need fossil or nuclear to back it. Which means idle surplus capacity equal to that farm's capacity. Which now means the green cost is green + grid storage + fossil backing capacity which you're demanding to remain idle. So yaaa... more expensive electricity for the same reliability.