A hydraulic compressed air energy storage system includes air and liquid tanks, each of which includes interdependent volumes of liquid and air. Each tank includes dedicated passages through which incoming air may be fed, forcing outflow of liquid, or incoming liquid may be fed, forcing outflow of air. Compressed air tanks are connected to a first group of the air and liquid tanks. The system further includes a pump and a liquid turbine, the liquid turbine being electrically connected to a generator for generating electric power. During charging of the system, liquid is pumped through the first group of air and liquid tanks, and air is expelled from the first group of air and liquid tanks and compressed in the compressed air tanks. During discharging of the system, compressed air is released from the compressed air tanks, and said compressed air pumps liquid through the liquid turbine, thereby generating electricity.

A compressed gas energy storage system may include an accumulator for containing a layer of compressed gas atop a layer of liquid. A gas conduit may have an upper end in communication with a gas compressor/expander subsystem and a lower end in communication with accumulator interior for conveying compressed gas into the compressed gas layer of the accumulator when in use. A shaft may have an interior for containing a quantity of a liquid and may be fluidly connectable to a liquid source/sink via a liquid supply conduit. A partition may cover may separate the accumulator interior from the shaft interior. An internal accumulator force may act on the inner surface of the partition and the liquid within the shaft may exert an external counter force on the outer surface of the partition, whereby a net force acting on the partition is less than the accumulator force.

A compressed gas energy storage system may include an accumulator for containing a layer of compressed gas atop a layer of liquid. A gas conduit may have an upper end in communication with a gas compressor/expander subsystem and a lower end in communication with accumulator interior for conveying compressed gas into the compressed gas layer of the accumulator when in use. A shaft may have an interior for containing a quantity of a liquid and may be fluidly connectable to a liquid source/sink via a liquid supply conduit. A partition may cover may separate the accumulator interior from the shaft interior. An internal accumulator force may act on the inner surface of the partition and the liquid within the shaft may exert an external counter force on the outer surface of the partition, whereby a net force acting on the partition is less than the accumulator force.

An axial piercing mechanism for a pressurized gas canister includes a housing, electric motor assembly, pushrod assembly, and lancet. The housing defines one or more radial exhaust ports and coaxial internal cavities. The electric motor assembly and pushrod assembly are disposed in the respective first and second cavities. The pushrod assembly is coupled to the electric motor assembly and is rotatably driven along the longitudinal axis thereby. The lancet is coupled to the pushrod assembly. The housing includes a second end that receives or couples to a sealed end of the pressurized gas canister proximate the lancet such that the electric motor assembly, when energized, causes the pushrod assembly and lancet to translate along the longitudinal axis, pierce a sealed end/diaphragm of the canister, and release pressurized gas through the exhaust port. A system includes the axial piercing mechanism and the pressurized gas canister.

Method is for operating fluid-processing plant configured to generate and store pressurized fluid, and spaced apart from body of water. Method includes: (A) positioning variable-buoyancy assembly in body of water in such way that buoyancy force urges variable-buoyancy assembly to move toward surface of body of water; (B) positionally anchoring, at least in part, non-collapsible fluid-line assembly underground in such way that non-collapsible fluid-line assembly extends, at least in part, into body of water; (C) fluidly connecting, via non-collapsible fluid-line assembly, fluid-processing plant and variable-buoyancy assembly together in such way that non-collapsible fluid-line assembly conveys pressurized fluid between fluid-processing plant and variable-buoyancy assembly; and (D) transmitting an anchoring force, via non-collapsible fluid-line assembly, from ground to variable-buoyancy assembly in such way that anchoring force substantially counteracts buoyancy force acting on non-collapsible fluid-line assembly, and anchoring force substantially urges variable-buoyancy assembly to remain below surface of body of water.

A modular subsea fluid storage unit comprises a variable-volume inner tank having a rigid top panel and a peripheral wall that is flexible by virtue of concertina formations. The peripheral wall is extensible and retractable vertically while the horizontal width of the tank remains substantially unchanged. A side wall of a lower housing part surrounds and is spaced horizontally from the peripheral wall of the inner tank to define a floodable gap between the peripheral wall and the side wall that surrounds the tank. An upper housing part extends over and is vertically spaced from the top panel of the inner tank and overlaps the side wall to enclose the inner tank. The floodable gap and the upper housing part enhance thermal insulation and trap any fluids that may leak from the inner tank.

A compressed gas energy storage system may include an accumulator for containing a layer of compressed gas atop a layer of liquid. A gas conduit may have an upper end in communication with a gas compressor/expander subsystem and a lower end in communication with accumulator interior for conveying compressed gas into the compressed gas layer of the accumulator when in use. A shaft may have an interior for containing a quantity of a liquid and may be fluidly connectable to a liquid source/sink via a liquid supply conduit. A partition may cover may separate the accumulator interior from the shaft interior. An internal accumulator force may act on the inner surface of the partition and the liquid within the shaft may exert an external counter force on the outer surface of the partition, whereby a net force acting on the partition is less than the accumulator force.

An underwater compressed air storage device with at least one underwater compressed air tank, positioned on the floor (7) of a body of water and provided with at least one water outlet opening and at least one inlet opening (11, 13) for a mixture of water and air. A tank which has at least one compressed air storage volume provided with two connecting ducts (9, 11) between said volume and a collection chamber (5) for the water and air mixture, a first duct (9) located in the upper part of the volume ensuring the passage of compressed air in the volume and a second duct (11), at an altitude lower than the first duct (9), ensuring the passage of the water and air mixture in the volume, said tank also having at least one opening for discharging the degassed water into the body of water.

A portable subsea storage tank for the storage of gas products under pressure or oil products consisting of pipeline sections in an array which can be coated in specialist coatings and recovered for inspection and re-use. A method of self-installing the subsea storage tank is also described.

A modular subsea fluid storage unit has a variable-volume inner tank having a rigid top panel and a peripheral wall that is flexible by virtue of concertina formation. The peripheral wall is extensible and retractable vertically while the horizontal width of the tank remains substantially unchanged. A side wall of a lower housing part surrounds and is spaced horizontally from the peripheral wall of the inner tank to define a floodable gap between the peripheral wall and the side wall that surrounds the tank. An upper housing part extends over and is vertically spaced from the top panel of the inner tank and overlaps the side wall to enclose the inner tank. The floodable gap and the upper housing part enhance thermal insulation and trap any fluids that may leak from the inner tank.