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.

The invention relates to a thermal energy storage with at least one thermal energy storage volume. The thermal energy storage comprises at least one primary borehole extending from ground level to a first predetermined depth in a rock body; at least one set of secondary boreholes located around the at least one primary borehole; and at least an upper and a lower fracture plane extending in a radial and/or oblique plane from the at least one primary borehole towards adjacent secondary boreholes. At least one fracture plane permits a hydraulic flow between at least one of the secondary boreholes and the primary borehole. Each thermal energy storage volume is defined by one set of secondary boreholes and its upper and lower fracture planes. The set of secondary boreholes diverge away from the at least one primary borehole at each fractured plane level, without intersecting the at least one primary borehole.

A device for energy transfer and for energy storage in a liquid reservoir includes a water heat exchanger and an air heat exchanger arranged above the water heat exchanger, wherein the water heat exchanger is arranged in a liquid reservoir, and wherein the device includes an outdoor air inlet from which an outdoor air flow can be induced to an air outlet through the air heat exchanger, includes a heat exchanger which is designed to direct exhaust air flowing in from an exhaust air inlet for energy transfer via the liquid reservoir (FR) into a peripheral area of the heat exchanger, from which the exhaust air can be supplied as an extract air flow to the air heat exchanger, in which the outdoor air flow and the extract air flow mix.

A cooling system transfers thermal energy from a temperature-critical reservoir to a heat sink. The system has an intermediate reservoir which is thermally interposed between the temperature-critical reservoir and the heat sink. The intermediate reservoir serves as an energy buffer between the two reservoirs by accepting thermal energy from the temperature-critical reservoir, storing that energy, and then transferring it to a heat sink by means of a temperature-driven process rather than by means of a heat pump. Transfer of thermal energy from the intermediate reservoir to the heat sink is temporally coordinated with naturally occurring temperature variations of the heat sink so that all thermal energy transfer processes conducted by the system are temperature-driven.

A compressed air energy storage system may have an accumulator and a thermal storage subsystem having a cold storage chamber for containing a supply of granular heat transfer, a hot storage chamber and at least a first mixing chamber in the gas flow path and having an interior in which the compressed gas contacts the granular heat transfer particles at a mixing pressure that is greater than the cold storage pressure and the hot storage pressure and a conveying system operable to selectably move the granular heat transfer particles from the cold storage chamber, through the first mixing chamber and into the hot storage chamber, and vice versa.

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.

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 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 compressed air energy storage system may have an accumulator and a thermal storage subsystem having a cold storage chamber for containing a supply of granular heat transfer, a hot storage chamber and at least a first mixing chamber in the gas flow path and having an interior in which the compressed gas contacts the granular heat transfer particles at a mixing pressure that is greater than the cold storage pressure and the hot storage pressure and a conveying system operable to selectably move the granular heat transfer particles from the cold storage chamber, through the first mixing chamber and into the hot storage chamber, and vice versa.

Disclosed techniques include gas liquefaction using hybrid processing. A gas is compressed adiabatically to produce a compressed gas at a first pressure. The compressing a gas adiabatically is accomplished using one or more compressing stages. Heat is extracted from the compressed gas at a first pressure. The heat that is extracted is collected in a thermal store. The compressed gas at a first pressure is further compressed. The further compressing is accomplished using a first liquid piston compressor. The further compressing produces a compressed gas at a second pressure. The first liquid piston compressor is cooled using a liquid spray. The compressed gas at a second pressure is cooled using a heat exchanger. The cooling accomplishes liquefaction of the compressed gas at a second pressure. The gas that was liquefied is stored for future use. The gas that was liquefied is used to perform work.