Battery storage being built today is, correctly, almost all for shifting afternoon collection to evening usage, where batteries are best suited by their unlimited charge and discharge wattage, and their high cost per MWh stored matters least.
For storage beyond 4 hours, other considerations become important, particularly cost per MWh stored. You still need to extract plenty of wattage, but charge rate matters less. So, you need big or many turbines, but pumps can be slower. And, of course, retrofitting the many existing reservoirs is cheapest, so you do that before building anew.
Fuel storage similarly takes advantage of existing combined-cycle turbines, which are being adapted to burn a gradually increasing fraction of hydrogen. It remains to be seen whether they can be made to burn ammonia directly, or if the ammonia must first release its hydrogen. Stored fuel has the great advantage that it can be shipped, bought, and sold.
For storage beyond 4 hours, other considerations become important, particularly cost per MWh stored. You still need to extract plenty of wattage, but charge rate matters less. So, you need big or many turbines, but pumps can be slower. And, of course, retrofitting the many existing reservoirs is cheapest, so you do that before building anew.
Fuel storage similarly takes advantage of existing combined-cycle turbines, which are being adapted to burn a gradually increasing fraction of hydrogen. It remains to be seen whether they can be made to burn ammonia directly, or if the ammonia must first release its hydrogen. Stored fuel has the great advantage that it can be shipped, bought, and sold.