A thermal storage subsystem may include at least a first storage reservoir configured to contain a thermal storage liquid at a storage pressure that is greater than atmospheric pressure. A liquid passage may have an inlet connectable to a thermal storage liquid source and configured to convey the thermal storage liquid to the liquid reservoir. A first heat exchanger may be provided in the liquid inlet passage and may be in fluid communication between the first compression stage and the accumulator, whereby thermal energy can be transferred from a compressed gas stream exiting a gas compressor/expander subsystem to the thermal storage liquid.

A thermal energy storage system is provided, comprising an outer shell defining an outer shell volume, an energy transfer module, comprising an input port for providing energy to the energy storage system, an output port for retrieving energy from energy storage system, wherein the outer shell is provided with a fluid distribution network.

The present disclosure is directed to materials that can be used in a heat storage and transfer, and an improved method for storing thermal energy which includes a high heat capacity thermal energy storage system using pumped or flowing metallic phase change materials (MPCs). Heat is added by pumping a cold fluid of MPCs mixed with a fluid media such as a molten glass and/or salt from a tank through a heat exchanger, solar receiver, or electrical heater cell and returning the heated fluid to a tank, or solid MPCs can be transported physically, or via gas transport such as entrained flow or a circulating fluid bed. In the heat exchanger, heat can optionally be transferred directly to a counterflowing gas or other fluid, or indirectly through heat exchanger walls to a working fluid, which can be steam, CO.sub.2 or sCO.sub.2, He, H.sub.2, process gas, and/or heat transfer fluid. The MPCs (encapsulated MPCs, non-coated MPCs) are solid-liquid and/or solid-solid phase change particles, salts, metals, or other compounds with a melting point between the hot and cold fluid temperatures, and can optionally include high heat capacity, and/or energy absorbing (IR and divisible) nanoparticles.

A device for energy transfer and for energy storage in a liquid reservoir has a water heat exchanger arranged on a bottom and has an air heat exchanger arranged above the water heat exchanger, wherein the water heat exchanger is arranged in a liquid reservoir that is surrounded by an inner shell which delimits the device with respect to an outer shell covering the inner shell from the bottom, wherein the outer shell is at least partially inserted into an earth layer, and the device is closed upwardly by a lid in such a way as to make it possible to generate a flow of air from an air inlet to an air outlet of the air heat exchanger.

A thermal storage subsystem may include at least a first storage reservoir configured to contain a thermal storage liquid at a storage pressure that is greater than atmospheric pressure. A liquid passage may have an inlet connectable to a thermal storage liquid source and configured to convey the thermal storage liquid to the liquid reservoir. A first heat exchanger may be provided in the liquid inlet passage and may be in fluid communication between the first compression stage and the accumulator, whereby thermal energy can be transferred from a compressed gas stream exiting a gas compressor/expander subsystem to the thermal storage liquid.

An arrangement for storing thermal energy, including a shaft (1) and at least one tunnel (2), the shaft (1) and the tunnel (2) being in fluid communication with each other. The tunnel (2) includes at least a first (2a), a second (2b), and a third (2c) tunnel section. The second tunnel section (2b) is arranged between and connected to the first (2a) and third (2c) tunnel sections. The second tunnel section (2b) is sealed off at an end (4) connected to the third tunnel section (2c), and the third tunnel section is further connected the shaft (1). The shaft (1) and first (2a) and third (2c) tunnel sections hold fluid for thermal storage. The second tunnel section (2b) is an expansion space should a volume of the fluid expand beyond a volume of the shaft (1) and the first (2a) and third (2c) tunnel sections.

A heat storage arrangement for an intermediate storage of thermal energy. The heat storage arrangement includes at least one heat exchanger element which includes a liquid inlet and a liquid outlet, and at least one heat storage container which includes a heat storage medium. The at least one heat exchanger is stiff and has a liquid non-aqueous heat carrier having a freezing point of below −10° C. flow therein. The at least one heat storage container is flexible and closed, and is arranged to abut on the at least one heat exchanger element so that a heat transfer occurs between the liquid non-aqueous heat carrier and the heat storage medium.

An arrangement for storing thermal energy has at least two tunnels (1a, 1b) for holding a fluid. The tunnels (1a, 1b) are connected to each other by at least one channel (2), such that fluid communication is allowed between the tunnels (1a, 1b). Each of the inner tunnel (1a) and the outer tunnel (1b) is configured as a helix, the inner tunnel (1a) forming an inner helix and the outer tunnel (1b) forming an outer helix.

Methods and devices for long-duration electricity storage using low-cost thermal energy storage and high-efficiency power cycle, are disclosed. In some embodiments it has the potential for superior long-duration, low-cost energy storage.

A system and method of combining pumped hydro and thermal energy storage is disclosed that has upper and lower fluid storage reservoirs. The reservoirs are used as a pumped energy storage system in which excess electrical power is stored as gravitational potential energy by using it to transfer fluid up to the upper one. At a later time, the fluid is run back down through a turbine under the force of gravity to generate electricity. Either, or both, fluid storage regions are also used to store thermal energy transferred into the stored fluid via liquid-to-liquid heat exchangers. The stored thermal energy is later extracted out to be distributed in for use in either directly heating structures or to improve the heating efficiency of one or more heat pumps in a district heating system. The fluid may be water, or it may be any suitable high-density fluid such as drilling mud.