It depends on the terms of the net metering.

If it's the ancient practice of crediting on a one for one basis, yeah that doesn't help. (A look around says that's probably where PR is now). If they credit power delivered to the grid based on conditions when it was delivered, then that might help. With appropriate controls, storage can increase grid stability. It would probably be more cost effective to do utility scale storage projects, but project management is difficult in PR; letting those with personal capital hook up solar+batteries and send some of that onto the grid when demand is high seems useful?