That is one alternative. Another is to pump air down a hose to force water out of a deep cavity. A third is to winch a float down toward a seafloor-mounted pulley. Methods that put the electrical equipment on shore are generally cheaper than the ones that put it at the sea floor.

Energy storage is mostly freshman-level physics (E = Fx, E = mgh), chemical schemes excepted. Undersea methods can often be adapted to an under-groundwater form.

The winning energy storage methods will be the cheapest ones, even at the expense of round-trip efficiency. But forms that are shippable, such as liquified ammonia synthesis, have an advantage than can overcome both higher cost and lower efficiency.

Most places will rely on a mix.