You can just use the vertical air line as an unpressurized vent line. A second vertical line could carry water up and down, between the surface and the storage tanks on the sea floor. This would be a classic pumped hydro system. The air line is vented to atmosphere, relieves pressure in the storage tanks, and allows water to be pumped freely up & down the water line. When water flows down to the storage tanks, electricity is generated. When water flows up and out of the tanks, energy is being stored. The generator/pump system could float about 50 meters below the surface to protect it from weather, facilitate servicing, and be in close proximity to a group of floating wind turbines.

The system would have 3500 meters of height, or "head". In comparison, the Hoover Dam has only about 158 meters of head, on average. This system would therefore generate 22-times more electricity per liter of water than the Hoover Dam.