Batteries are getting cheaper, and have high charge/discharge rates. Flywheels can maybe double as AC/DC conversion, but their role is closer to a capacitor than a battery.
What distinguishes H2 is that it is transportable/exportable energy, that also has alternate chemical uses. It is ideal aviation fuel. Sure making it has some expense/loss, but storing it is $1/kwh electric (also contains heat energy that when used in a fuel cell matches the typical domestic hot water energy fraction). Transporting H2 energy by truck is cheaper than electricity by wire. Because H2 can be produced at convenience (solar surplus), and made available for user convenience later, it can be cheaper energy overall, and improve the total utilization of renewable+battery/static storage systems.
Batteries are getting cheaper, and have high charge/discharge rates. Flywheels can maybe double as AC/DC conversion, but their role is closer to a capacitor than a battery.
What distinguishes H2 is that it is transportable/exportable energy, that also has alternate chemical uses. It is ideal aviation fuel. Sure making it has some expense/loss, but storing it is $1/kwh electric (also contains heat energy that when used in a fuel cell matches the typical domestic hot water energy fraction). Transporting H2 energy by truck is cheaper than electricity by wire. Because H2 can be produced at convenience (solar surplus), and made available for user convenience later, it can be cheaper energy overall, and improve the total utilization of renewable+battery/static storage systems.