Geothermal energy is increasingly recognized as a useful energy source for both industrial and residential purposes. Disclosed herein are units for subterranean heat exchange comprising a polymer block with ‘mini-channels’ adapted and/or sized for highly efficient heat exchange. In some embodiments such units can, as needed, be manufactured off site, spooled for transport, and conveniently installed in boreholes. Other arrangements are also described for conduits located within a borehole for heat exchange, without a polymer block. Also disclosed are geothermal heat exchange systems including those that employ such units, for example with direct expansion of a two-phase heat-exchange fluid such as carbon dioxide.

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.

Thermal energy storage systems are disclosed in this application. Systems of the inventive subject matter are designed to reduce maintenance requirements by sequestering, for example, corrosive fluids that might otherwise damage difficult-to-fix internal components are kept out of those components by introducing a non-corrosive heat transfer fluid to facilitate heat transfer between a thermal energy storage medium (e.g., molten sulfur) and a potentially corrosive working fluid. Thus, the potentially corrosive fluid is kept out of a thermal energy storage tank containing the thermal energy storage medium, which, by design, is difficult to repair when internal components corrode or otherwise require maintenance.

A heat storage unit includes: a heat storage material that contains water and high polymers that exhibit hydrophilicity or hydrophobicity depending on a temperature; a heat exchanger that causes heat exchange to be performed between a heating fluid and the heat storage material to heat the heat storage material and store heat in the heat storage material, and causes heat exchange to be performed between a heat utilization fluid and the heat storage material to receive heat from the heat storage material and cause heat to be transferred from the heat storage material; and a container that is filled with the heat storage material and houses the heat exchanger.

A heat storage unit includes: a heat storage material that contains water and high polymers that exhibit hydrophilicity or hydrophobicity depending on a temperature; a heat exchanger that causes heat exchange to be performed between a heating fluid and the heat storage material to heat the heat storage material and store heat in the heat storage material, and causes heat exchange to be performed between a heat utilization fluid and the heat storage material to receive heat from the heat storage material and cause heat to be transferred from the heat storage material; and a container that is filled with the heat storage material and houses the heat exchanger.

A thermal energy storage apparatus is disclosed. The apparatus may include a base and fluid flow plates which cooperate with the base to define a cavity; a phase change material contained within the cavity; an external seed crystal reservoir trigger assembly at least partially positioned within the phase change material; and end plates which cooperate with the fluid flow plates to define fluid flow channels. The apparatus may include a housing that holds a heat exchanger and phase change material. Inlet and outlet ports allow for the ingress and egress of a heat exchange fluid into the fluid flow channels or heat exchanger. In operation, actuation of the external seed crystal reservoir trigger assembly to an open state induces solidification of at least a portion of the phase change material from a supercooled liquid state to a solid state, releasing thermal energy, allowing for the transfer of thermal energy across the fluid flow plates or heat exchanger from the phase change material to the heat exchange fluid.

Disclosed are systems and methods of flexibly cooling thermal loads by providing a thermal energy storage cooling system having a nucleation cooling system for at least initiating nucleation of a phase change media within the thermal energy storage system.

A sintered material exhibiting the following chemical composition, as percentages by weight: iron oxide(s), expressed in the Fe.sub.2O.sub.3 form, ≥85%, CaO: 0.1%-6%, SiO.sub.2: 0.1%-6%, 0.05% ≤TiO.sub.2, 0≤Al.sub.2O.sub.3, TiO.sub.2+Al.sub.2O.sub.3≤3%, and constituents other than iron oxides, CaO, SiO.sub.2, TiO.sub.2 and Al.sub.2O.sub.3: ≤5%. The CaO/SiO.sub.2 ratio by weight is between 0.2 and 7. The TiO.sub.2/CaO ratio by weight is between 0.2 and 1.5.

A heat sink cooling apparatus of the present invention includes a thickened Phase Change Material (PCM) and an aluminum profile container for superior cold storage, heat transfer and efficiency of defrost. The PCM is a composition including a brine solution and a thickening agent resulting in increased holdover capacity in a no-leak, safe food grade PCM, and a tubular aluminum profile manufactured with a highly conductive aluminum alloy, which can be triangular, with optional internal and/or external fin-tube configurations maximizing surface area for heat transfer. The heat sink cooling apparatus is capable of removing heat from (but not limited to) a transport cargo area (truck body) through the processes of conductive and convection heat transfer via the aluminum profile filled with a PCM, either in a passive form of cooling via free convection (hanging mount) or in a forced air plenum chamber.

A heat sink cooling apparatus of the present invention includes a thickened Phase Change Material (PCM) and an aluminum profile container for superior cold storage, heat transfer and efficiency of defrost. The PCM is a composition including a brine solution and a thickening agent resulting in increased holdover capacity in a no-leak, safe food grade PCM, and a tubular aluminum profile manufactured with a highly conductive aluminum alloy, which can be triangular, with optional internal and/or external fin-tube configurations maximizing surface area for heat transfer. The heat sink cooling apparatus is capable of removing heat from (but not limited to) a transport cargo area (truck body) through the processes of conductive and convection heat transfer via the aluminum profile filled with a PCM, either in a passive form of cooling via free convection (hanging mount) or in a forced air plenum chamber.