Strain energy accumulator

An energy storage system comprising:

• a reversible pump/motor having a first inlet/outlet and a second inlet/outlet;
• a shaft coupled to the reversible pump/motor;
• and
• an expandable accumulator and reservoir assembly having a first port in communication with the first inlet/outlet via a first fluid line and a second port in communication with the second inlet/outlet via a second fluid line, the expandable accumulator and reservoir assembly including
• a housing defining an interior chamber configured to contain a working fluid therein,
• an expandable accumulator positioned at least partially within the housing, the expandable accumulator including at least one flexible member configured to be at least partially immersed in the working fluid contained within the interior chamber, wherein an interior of the expandable accumulator is coupled with the first port,
• a rigid support member positioned in the interior chamber and outside of the expandable accumulator to surround the at least one flexible member, wherein the rigid support member has at least one aperture to allow passage of the working fluid, and
• an additional flexible member positioned outside the rigid support member to surround the rigid support member, the additional flexible member having perimeter portions sealed to the outside of the rigid support member, the additional flexible member defining a flexible boundary between a primary reservoir inside the additional flexible member and a secondary reservoir outside the additional flexible member, wherein the second port is in communication with the primary reservoir.