Fluid displacement energy storage systems and processes to enable pressure equilibrized subsea tank

A system for storing and generating power comprising:

• a first storage reservoir near the surface of a body of water and configured to store a first fluid;
• a second storage reservoir located below the surface of the body of water and configured to store a second fluid which has a higher density than the first fluid;
• a first pump fluidly connected to the first fluid;
• a second pump fluidly connected to the second fluid;
• a first turbine fluidly connected to the first fluid and configured to generate power;
• a second turbine fluidly connected to the second fluid and configured to generate power;
• and
• a pressure compensator for maintaining pressure equilibrium between the second reservoir and the adjacent body of water;
• wherein the first pump, the second pump, and the first and the second reservoir are operatively connected such that power is stored by pumping the first fluid from the first storage reservoir into the second storage reservoir using the first pump and by pumping the second fluid from the second storage reservoir into the first storage reservoir using the second pump;
• and
• wherein the first turbine, the second turbine, and the first and the second reservoir are operatively connected such that power is generated by transferring the second fluid from the first storage reservoir into the second storage reservoir through the second turbine and transferring the first fluid from the second reservoir to the first reservoir through the first turbine;
• and
• wherein the first fluid is a liquid and the second fluid is a liquid.