Patent ID: 7843076

Claim:
An energy storage system comprising: a fluid circuit comprising: a first fluid container situated so content of the first fluid container experiences a first pressure level; a second fluid container situated so that content of the second fluid container is at a second container pressure level, the second container pressure level being less than the first pressure level; a tank configured so that content of the tank is at a second pressure level, the second pressure level being less than the first pressure level; a first hydraulic motor/pump unit connected to communicate a first working fluid between the tank and the first fluid container; a second hydraulic motor/pump unit; a third hydraulic motor/pump unit; an electrical unit configured to operate as a motor in a first phase of operation and to operate as a generator in a second phase of operation, wherein in the first phase of operation electricity is supplied to the first hydraulic/motor unit Whereby the first hydraulic/motor unit transmits the first working fluid from the tank into the first fluid container, and wherein in the second phase of operation pressurized first working fluid in the first fluid container is transmitted from the first fluid container through the first hydraulic/motor unit to the tank thereby causing the electrical unit to generate electricity; wherein the second hydraulic motor/pump unit is operatively connected to the electrical unit and fluidically connected between the second fluid container and the third hydraulic motor/pump unit, wherein the third hydraulic motor/pump unit is fluidically connected between the second hydraulic motor/pump unit and the first fluid container; and wherein the second hydraulic motor/pump unit and the third hydraulic motor/pump unit are configured during the first phase of operation to operate as pumps to transmit fluid from the second fluid container to the first fluid container, and during the second phase of operation to operate as motors as fluid from the first fluid container is transmitted to the second fluid container; wherein the electrical unit is configured during the first phase of operation to operate as the motor for the second hydraulic motor/pump unit and during the second phase of operation to operate as a generator driven by the second hydraulic motor/pump unit.