I thought the idea was to use the difference in potential energy between the surface level and the sphere as the storage. ie, you'd store energy by emptying the sphere, and release energy by dumping water into it through a turbine. If that's the case, I don't get where the pressure comes into it.
You are right, this is basically a gravity energy storage. It's the same idea as moving a 14m3 blob of water 100m up and down. Unfortunately, gravity storages have really bad energy densities.
Let's see.
E = mgh
E is the energy, m the mass, g the gravitational acceleration, h the difference in height.
m = 14e3kg
g = 10m/s2
h = 100m
E = 14e6J = 3.9kWh
The only gravity storages that have been proved to be scalable so far are hydroelectric. And they have huge lakes behind them.
