Greece has immediate access to deep ocean for cheap storage, and plenty of sunshine and wind year-round. Transmission lines out to the rest of Europe could make them a major exporter.
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.
I am curious about what you mean, can you please elaborate?
But pumping water and air, driving winches, and building pressure vessels are all mature tech.