WO2025230842A1

WO2025230842A1 - Direct contact thermal storage of pumped heat energy storage system

Info

Publication number: WO2025230842A1
Application number: PCT/US2025/026464
Authority: WO
Inventors: Samar SHAH
Original assignee: Malta Inc
Current assignee: Malta Inc
Priority date: 2024-04-29
Filing date: 2025-04-25
Publication date: 2025-11-06
Anticipated expiration: 2026-10-29

Abstract

A pumped heat energy storage ("PHES") system is operable in a generation mode and a charge mode. In the generation mode, the PHES includes a fluid circuit for circulation of a working fluid therethrough, including a heat exchanger system and a turbine system for expanding the working fluid received from the heat exchanger system to generate rotational drive. A thermal storage system receives an extracted portion of the working fluid for mixture with cold side thermal storage fluid for direct contact heat exchange.

Description

DIRECT CONTACT THERMAL STORAGE OF PUMPED HEAT ENERGY STORAGE SYSTEM

BACKGROUND

[0001] Pumped heat energy storage (“PHES”) systems can be used to store thermal energy and generate power from the stored energy storage. In a charge mode, the PHES system can be used to increase the thermal energy in a hot side thermal storage system that is in fluid communication with cycle working fluid via a heat exchanger system.

[0002] In a generation mode, a feed fluid system can move the working fluid through the heat exchanger system to transfer heat from the hot side thermal storage system to the working fluid. The heated working fluid can be expanded within a turbine system to produce work and/or electrical power at a generator, which can be distributed for use, such as in an electrical grid. The working fluid can be cooled to lower temperatures and re-cycled through the fluid circuit.

SUMMARY

[0003] According to an aspect of the present disclosure, a pumped heat energy storage (“PHES”) system may be operable in an energy storage mode and a power generation mode. The system may include a fluid circuit for circulation of a working fluid therethrough. The fluid circuit in the generation mode may include a pump system for assisting circulation of the working fluid within at least a portion of the fluid circuit; a heat exchanger system through which the working fluid circulates in use; a hot side thermal reservoir operable to transfer stored heat to the working fluid via the heat exchanger system; a turbine system configured to expand the working fluid received from the heat exchanger system to generate rotational drive; a thermal interface line in communication with the turbine system at a separation point to receive an extracted portion of the working fluid; and a cold side thermal storage system configured to store cold side thermal energy. The cold side thermal storage system may include a cold side thermal storage tank arranged to receive the extracted portion of the working fluid from the thermal interface line for mixture with thermal storage fluid within the thermal storage tank for direct contact heat exchange.

[0004] In some embodiments, the extracted portion of the working fluid may be steam. The thermal storage fluid may include condensate water. The heat exchanger system may include a hot-side heat exchanger. The hot side thermal storage tank may be arranged in fluid communication with the hot-side heat exchanger for thermal communication with the working fluid.

[0005] In some embodiments, in the generation mode, the hot-side heat exchanger may transfer heat from the hot side thermal storage tank to the working fluid. In some embodiments, the high temperature reservoir may include thermal storage fluid for passing through the hot- side heat exchanger in thermal communication with the working fluid.

[0006] In some embodiments, an auxiliary heat exchanger system may be arranged to receive a discharge portion of the working fluid from the turbine system for transfer of waste heat out from the fluid circuit and the auxiliary heat exchanger system is arranged to transfer waste heat to ambient. The extracted portion of the working fluid may include intermediate extraction taken between stages of the turbine system. The extracted portion of the working fluid may be extracted at an intermediate location of a low pressure turbine of the turbine system.

[0007] In some embodiments, condensate from the thermal storage system may be circulated to the heat exchanger system. The thermal storage system may include at least a warm portion and a cold portion for thermal storage fluid. Condensate circulated to the heat exchanger system from the thermal storage system may be from the cold portion of the thermal storage system.

[0008] In some embodiments, the PHES system may be operable in the charge mode to extract thermal energy from the thermal storage system and to store thermal energy within a high temperature reservoir arranged in thermal communication with the heat exchanger system. [0009] According to another aspect of the present disclosure, a method is provided of operating a pumped heat energy storage (“PHES”) system capable of operation in at least one of a charge mode and a generation mode. The system may include a fluid circuit for the circulation of a working fluid therethrough. The method may include, in the generation mode, assisting circulation of the working fluid within at least a portion of the fluid circuit; passing the working fluid through a heat exchanger system to receive heat from hot side thermal storage; expanding the working fluid received from the heat exchanger system with a turbine system to generate rotational drive; extracting a portion of the working fluid at a separation point through a thermal interface line; directing the extracted portion of the working fluid through the thermal interface line to a thermal storage tank; mixing the extracted portion of the working fluid with thermal storage fluid within the thermal storage tank for direct contact heat exchange; and storing thermal energy from the extracted portion of the working fluid in the hot side thermal storage.

[0010] In some embodiments, the extracted portion of the working fluid may be steam. The thermal storage fluid may include condensate water. The heat exchanger system may include a hot- side heat exchanger.

[0011] In some embodiments, the method may include transferring heat from thermal storage fluid in a high temperature reservoir to the working fluid in the heat exchanger system in the generation mode. The method may include directing a discharge portion of the working fluid from the turbine system to an auxiliary heat exchanger system for transfer of waste heat out from the fluid circuit. The method may include transferring the waste heat to ambient.

[0012] In some embodiments, the method may include extracting the portion of the working fluid from between stages of the turbine system. Extracting the portion of the working fluid may include extracting from an intermediate location of a low pressure turbine of the turbine system.

[0013] In some embodiments, the method may include circulating condensate from the thermal storage system to the heat exchanger system. Circulating condensate may include circulating condensate to the heat exchanger system from a cold portion of the thermal storage system. In some embodiments, the method may include operating the PHES system in the charge mode to extract thermal energy from the thermal storage system and to store thermal energy within a high temperature reservoir arranged in thermal communication with the heat exchanger system.

[0014] According to another aspect of the presented disclosure, a pumped heat energy storage (“PHES”) system may be operable in a generation mode and a charge mode. The system may include a fluid circuit for circulation of a working fluid therethrough. The fluid circuit may include, in the generation mode, a heat exchanger system through which the working fluid circulates in use. The heat exchanger system may include a hot-side heat exchanger and a high temperature reservoir arranged in fluid communication with the hot- side heat exchanger to transfer heat from the high temperature reservoir to the working fluid in a generation mode. The system may include a turbine system configured to expand the working fluid received from the heat exchanger system to generate rotational drive and a thermal storage system configured to store cold side thermal energy. The thermal storage system may include a thermal storage tank arranged to receive an extracted portion of the working fluid for mixture with thermal storage fluid within the thermal storage tank for direct contact heat exchange. Condensate from the thermal storage system may be circulated to the heat exchanger system.

[0015] These as well as other aspects, advantages, and alternatives, will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a schematic diagram of a pumped heat energy storage (PHES) system, according to disclosed embodiments.

[0017] FIG. 2 is a schematic diagram of a portion of the PHES of FIG. 1 showing an thermal interface flow path for extracting working fluid for direct contact thermal transfer.

DETAILED DESCRIPTION

[0018] Referring to FIG. 1, a pumped heat energy storage (PHES) system 10 is shown which can use thermodynamic cycle(s), embodied as a Rankine cycle, to generate electrical power from stored thermal energy by operating in a generation mode, and to gather thermal energy into storage by operating in a charge mode for later recovery, for example, in the generation mode. In the generation mode, the PHES circulates a working fluid in use in a fluid circuit 12 that includes a heat exchanger system 20 in thermal contact with a hot side of a thermal storage system 34. A cold side thermal storage system 100 of the thermal storage system 34 can provide heat during the generation mode. In the illustrative embodiment, the heat exchanger system 20 includes a first heat exchanger 22, a second heat exchanger 24, a third heat exchanger 26, and a fourth heat exchanger 28, each of which provides thermal communication with the thermal storage system 34 as discussed in additional detail herein. In some embodiments, the heat exchanger system 20 may include a single heat exchanger or any suitable number of heat exchangers in series or parallel. In some embodiments, heat exchanger 24 may be omitted.

[0019] In the illustrative embodiment, each of the heat exchangers 22, 24, 26, 28 of the heat exchanger system 20 are embodied as hot-side heat exchangers in the generation mode, further embodied as shell and tube heat exchangers for transferring heat from the thermal storage system 34 to the working fluid for use in generation power via the turbine system 60. In some embodiments, the heat exchanger system 20 may include any suitable manner of conventional heat exchangers, printed circuit heat exchangers, plate type heat exchangers, moving bed heat exchangers, fluidized bed heat exchangers, or packed bed thermocline.

[0020] In the illustrative embodiment, the thermal storage system 34 includes a hot side thermal storage system 36 including a high temperature reservoir 30 and a warm temperature reservoir 32. The hot side thermal storage system 36 includes hot side thermal storage fluid for passing through the hot-side heat exchangers 22, 24, 26, 28 of the heat exchanger system 20 in thermal communication with the working fluid. In the generation mode, the hot side thermal storage fluid is illustratively passed from the high temperature reservoir 30 at a high temperature, through the heat exchanger system 20 providing heat to the working fluid, resulting in a warm temperature, and onto the warm temperature reservoir 32, to extract stored thermal energy from the hot side thermal storage system 36 to the working fluid for use in power generation. In the charge mode, the hot side thermal storage fluid is illustratively passed from the warm temperature reservoir 32 at the warm temperature, receiving heat for storage via heat pump cycle 180, and on to the hot reservoir 30 to store thermal energy within the thermal storage system 34 as discussed in additional detail herein. In the illustrative embodiment, the thermal storage fluid flowing between the high temperature reservoir 30 and the warm temperature reservoir 32 is molten salt (including binary mixtures, ternary mixtures or the like); but in some embodiments, the thermal storage fluid may include thermal oil, water, fluidized particulate such as aggregate sand or stone, concrete, encapsulated phase-change materials, bulk phase-change materials, a combination therein, or any other material suitable for use in a PHES high temperature reservoir. In some embodiments, the reservoirs 30, 32 are each a single vessel or a plurality of vessels. In some embodiments, the hot side thermal storage system 34 may include thermocline tanks having separation between warm and hot zones.

[0021] The PHES system 10 includes a feed fluid system 80 for assisting circulation of working fluid within at least a portion of the fluid circuit 12 of the PHES system 10. The feed fluid system 80 illustratively includes a fluid pump 50, embodied as a high pressure feed water pump electrically driven by a motor 82, for increasing pressure of condensate feed water circulation to the heat exchanger system 20. The feed fluid system 80 is fluidly connected with the heat exchanger system 20 to provide feed fluid condensate thereto to facilitate the transfer of thermal energy from the hot side thermal storage system 36 and to the working fluid via the heat exchanger system 20. As discussed in additional detail herein, the feed fluid system 80 illustratively includes another pump 94 electrically driven by a motor 96, embodied as a low pressure feed water pump for pressurizing feed water condensate from a condenser heat exchanger system 40.

[0022] In the illustrative embodiment, the thermal storage system 34 includes a cold side thermal storage system 100 for storage (and recovery) of cold side thermal energy. As discussed in additional detail herein, the cold side thermal storage system 100 includes a cold side thermal storage reservoir 102 arranged to receive an extraction of working fluid for mixing with storage working fluid to achieve a cold side storage temperature. The cold side storage working fluid is illustratively embodied as storage condensate working fluid. The storage working fluid from the cold side thermal storage system 100 can be provided to the feed fluid system 80 for circulation to the heat exchanger system 20.

[0023] In the generation mode, the PHES system 10 transfers thermal energy from the thermal storage system 34 to the working fluid via the heat exchanger system 20 to generate electricity via turbine system 60. At a location upstream from the feed fluid system 80 and downstream of the heat exchanger system 20, the working fluid is at a lower temperature and pressure than passing through the heat exchanger system 20. The pressure of the working fluid within the fluid circuit 12 at an inlet of the pump 94 of the feed fluid system 80 is illustratively the lowest temperature and pressure of the fluid circuit 12 over the course of one cycle through the fluid circuit 12, and at an inlet of the pump 50 is illustratively an intermediate pressure with only incidentally higher temperature from the pump 94 operation. In some embodiments, the feed fluid pressure upstream of the pump 50 can be about 0.1 MPa to about 0.4 MPa.

[0024] The feed fluid system 80 illustratively includes a feed fluid heating system 52. The feed fluid heating system 52 includes a feed fluid heat exchanger for receiving heat from working fluid bleed-extracted from other portions of the fluid circuit 12 having greater thermal energy than the working fluid from the pump 50. The feed fluid heat exchanger is embodied as a shell and tube heat exchanger, but in some embodiments, may include any suitable manner of conventional heat exchangers, printed circuit heat exchangers, or plate type heat exchangers. In the illustrative embodiment, bleed-extraction working fluid is provided from an intermediate portion of the turbine system 60 via line 51 at a bleed temperature and pressure to the feed fluid heating system 52 to transfer heat to the feed working fluid for preheating, and bleed side return working fluid is directed to the inlet of the pump 50 via line 53.

[0025] Working fluid is pressurized and discharged from the feed fluid system 80 at a feed pressure at an outlet of the feed fluid system 80. The feed pressure at the outlet of the feed fluid system 80 is illustratively the highest pressure of the working fluid over the course of one cycle through the fluid circuit 12. In some embodiments, the pressure at the outlet of the pump 50 is illustratively within the range of about 3 MPa to about 35 MPa. The working fluid then enters an inlet of the heat exchanger system 20 and thermal energy is transferred from the high temperature reservoir 30 to the working fluid to increase the temperature of the working fluid. In the generation mode, the working fluid is circulated through the turbine system 60 to generate rotational drive. In the illustrative embodiment, the turbine system 60 includes a high- pressure (HP) turbine 62, the intermediate pressure (IP) turbine 64, and the low pressure (LP) turbine 66, which are each fluidly connected to the fluid circuit 12 and arranged to receive working fluid from the heat exchanger system 20. In some embodiments, greater or fewer turbine stages/pressures may be applied. While FIG. 1 depicts the high-pressure turbine 62, the intermediate pressure turbine 64, and the low-pressure turbine 66 as separate components, the high-pressure turbine 62, the intermediate pressure turbine 64, and the low-pressure turbine 66 may be partly or wholly combined or formed by one or more multi-stage turbines. The working fluid exits the heat exchanger system 20 at high temperature and is expanded within the turbine system 60, producing shaft work. Expansion of the working fluid within the turbine system 60 decreases the pressure of the working fluid. Work generated by the turbine system 60 exceeds the work input to the feed fluid system 80 in the generation mode of operation due to the recovery of thermal energy from the thermal storage system (hot side thermal storage), and excess energy is, at least in part, converted to electrical power by one or more generators 68 driven by one or more of turbines 62,64,66, for example, for feeding into an electrical grid (not shown). A portion of generated electricity is provided to feed fluid pumps, although in some embodiments, feed fluid pumps may be driven as turbomachinery-driven (e.g., via extracted steam) working fluid pumps, and/or mechanically-coupled with the turbine system 60.

[0026] In the illustrative embodiment in the generation mode, working fluid enters the heat exchanger 22 and receives heat from the hot side thermal storage system 36. The heat exchanger 22 is illustrative embodied as an economizer generating steam from feed water condensate. Working fluid (steam) discharged from the heat exchanger 22 enters heat exchanger 28. In the illustrative embodiment, a recirculation line 23 can recirculate liquid from the economizer to the economizer inlet. The heat exchanger 28 is illustratively embodied as a evaporator/superheater in subcritical conditions or as a superheater in supercritical conditions, transferring heat from the thermal storage system 36 to heat the steam working fluid. In the illustrative embodiment, hot side thermal storage fluid from the high temperature reservoir 30 is passed to the heat exchangers 24, 26, 28 and then serially on to the heat exchanger 22, and on to the warm temperature reservoir 32.

[0027] Working fluid discharged from the heat exchanger 28 is expanded in HP turbine 62 to generate power. Working fluid discharged from the outlet of the HP turbine 62 is passed through heat exchanger 26. The heat exchanger 26 is illustratively embodied as a reheat heat exchanger, transferring heat from hot side thermal storage system 36 to re-elevate the temperature of the working fluid lost during expansion in the HP turbine 62. Working fluid discharged from the heat exchanger 26 is expanded in the IP turbine 64 to generate power. Working fluid discharged from the outlet of the IP turbine 64 is passed through heat exchanger 24. The heat exchanger 24 is illustratively embodied as another reheat heat exchanger, transferring heat from hot side thermal storage system to again re-elevate the temperature of the working fluid lost during expansion in the IP turbine 64. In the illustrative embodiment, hot side thermal storage fluid from the high temperature reservoir 30 is provided to the heat exchangers 24, 26, 28 in parallel with each other at the same high temperature. The working fluid discharged from the outlet of LP turbine 66 is passed to a condenser heat exchanger system 40.

[0028] An extracted portion of the working fluid is drawn from the turbine system 60 via a thermal interface line 90. In an the illustrative embodiment, the extracted portion of the working fluid is steam, extracted at a pressure of approximately 1.13 bar and temperature of approximately 337° C. The thermal interface line 90 is arranged to introduce the extracted portion of the working fluid from the turbine system 60 to a cold side thermal reservoir 102 of the thermal storage system 100.

[0029] The thermal interface line 90 of the fluid circuit 12 provides a flow path for extracted portion of the working fluid to flow from the turbine system 60 to the cold side thermal reservoir 102. The flow of the extracted working fluid through the thermal interface line 90 defines a thermal storage interface flow path of the PHES system 10. The cold side thermal reservoir 102 is defined as a portion of a cold side storage system 100 and may include one or more flow control valves 164, 172 for controlling flow of working fluid as shown in Fig. 2. The cold side thermal reservoir 102 is illustratively arranged to receive the extracted portion of the working fluid for mixture with thermal storage fluid within the cold side thermal reservoir 102 for direct contact heat exchange. In the illustrative embodiment, the cold side storage fluid is condensate water, and the extracted working fluid is steam. The extracted portion of the working fluid illustratively transfers heat to the storage fluid to raise a temperature of the cold-side storage fluid within the range of approximately 74° C to approximately 98° C, and generally condenses the extracted steam into condensate.

[0030] In the disclosed embodiments, the extracted portion of the working fluid is directly injected into the cold side thermal storage system 100 through mixing devices, embodied, e.g., as spargers, that incrementally raise the bulk temperature of the thermal storage reservoir 102, embodied as a tank. The extracted steam may be injected at an appropriate level (height) within the thermal storage reservoir 102 so that the steam is injected against a desired hydrostatic head of the thermal storage reservoir 102. In some embodiments, the desired hydrostatic head of the thermal storage reservoir 102 is approximately fixed with minor variations occur due to density change. In some embodiments, the desired hydrostatic head of the thermal storage reservoir 102 is approximately 35m to 40m. The steam may be illustratively injected into the thermal storage reservoir 102 at an appropriate level to ensure enough mixing to distribute temperature uniformly throughout the thermal storage reservoir 102. The injected steam removed here from the working fluid circuit 12 can be compensated for by drawing relatively colder condensate from a lower portion (e.g., bottom) of the thermal storage tank 102 and passing such condensate to working fluid circuit at, e.g., the feed fluid system 80, using the hydrostatic head of the thermal storage reservoir 102. Thus, in comparison to separate non-contact thermal storage (e.g., via heat exchangers), an interface heat exchanger, thermal fluid transfer circulation pumps, and/or steam/condensate -related hardware systems can be eliminated (or reduced at a minimum) by disclosed embodiments.

[0031] Resulting cold-side thermal storage fluid (illustratively, condensate) can be passed to the feed fluid system 80. In the illustrative embodiments, the cold side thermal storage system 100 includes at least a warm portion (upper) and a cold portion (lower) of thermal storage fluid by gravity; although in some embodiments, baffles and/or other reservoir structures may encourage temperature gradient. In the illustrative embodiment, the thermal storage fluid flows to the feed fluid system 80 at about 74° C, from the cooler portion of the system 100; although in some embodiments, the thermal storage fluid may flow to the feed fluid system 80 at a pressure of approximately 1.13 bar and a temperature within the range of approximately 74° C to approximately 98° C. The disclosed embodiments can allow the heating of the storage fluid, while eliminating certain hardware for the system by comparison to the hot side thermal storage system.

[0032] The fluid circuit 12 illustratively includes auxiliary condenser heat exchanger system 40 arranged to receive a discharge portion of the working fluid from the outlet of the turbine system 60 for transfer of waste heat out from the fluid circuit 12. The condenser heat exchanger system 40 illustratively includes a condenser heat exchanger adapted to return the discharge working fluid to substantially the initial conditions, both in temperature and pressure, illustratively as condensate, before once again entering the feed fluid system 80 via the low pressure feed fluid pump 94. In the illustrative embodiment, the condenser heat exchanger system 40 passes the discharge working fluid in thermal contact with an auxiliary heat transfer fluid embodied in an ambient air as a radiator or water as a water-cooled condenser, but in some embodiments may be any suitable manner of waste heat exchange, such as ambient water and/or other waste heat uses such as district heating, low grade heat manufacturing process, or similar uses.

[0033] In the charge mode, the PHES system 10 transfers thermal energy to the hot side thermal storage system 36 utilizing, e.g., a heat pump cycle 180. The cycle 180 is illustratively embodied as a vapor compression cycle in thermal communication with each of the hot side and cold side of the thermal storage system 34 to receive heat from the cold side thermal storage system 100 and provide heat for storage in the hot side thermal storage system 36. In the illustrative embodiment, the heat pump cycle 180 is shown as distinct from the components operating in the generation mode; however, in some embodiments, machinery and/or components can be partly or wholly shared, for example, such as portions of fluid circuit 12, working fluid, and/or heat exchanger system 20 may be applied to transfer heat from the working fluid into the hot side thermal storage system 36 in the charge mode using the heat pump cycle 180. The cycle 180 illustratively receives cold side thermal storage fluid from the cold side thermal reservoir 102 in thermal contact with working fluid of the cycle 180 via a heat exchanger to transfer heat from the cold side thermal reservoir 102 to the working fluid of the cycle 180. The cycle 180 illustratively includes compression and throttling machinery and components to transfer heat for storage into the hot side thermal storage system 36. Compression in the cycle 180 is primarily provided by electrical power drive, but in some embodiments, may be supplemented by turbomachinery drive. In some embodiments, the cycle 180 may be formed as a reverse Brayton cycle, vapor absorption cycle, Stirling cycle, or other suitable heat pump cycle.

[0034] In the illustrative embodiment, the cold side thermal storage system 100 enables the charge mode working fluid (wet steam) to absorb heat (above ambient) from the storage fluid within the thermal storage reservoir 102. The storage fluid provides thermal energy during the charge mode that was extracted from previous generation cycle(s). The PHES system 10 is operable in the charge mode to extract thermal energy from the thermal storage system 100 and to store thermal energy within the high temperature reservoir 30.

[0035] Referring to FIG. 2, extraction of working fluid in the generation mode for direct- contact cold side thermal storage is shown in additional detail. The extracted portion of the working fluid includes intermediate extraction taken between stages of the turbine system 60. In the exemplary embodiment, the steam is extracted from the working fluid between turbine stage 66a and turbine stage 66b of turbine 66. In the illustrative embodiment, the extracted working fluid is taken from the LP turbine 66, but in some embodiments, the extracted working fluid may be taken between high-pressure stages, between high and intermediate pressure stages, between intermediate-pressure stages, between intermediate and low pressure stages, and/or between any suitable turbine stages. The steam is extracted into the thermal interface line 90 at a separation point 162. The thermal interface line 90 includes the control valve 164 that may be selectively opened and closed during the generation mode to govern extracted working fluid (e.g., steam) from between the stages. [0036] As mentioned above, the extracted working fluid is injected into the thermal storage reservoir 102 to transfer heat to a storage fluid in the thermal storage reservoir 102 to raise a temperature of the thermal storage fluid. A control valve 172 may be selectively opened and closed during the generation mode to control return of condensate in the thermal storage reservoir 102 to the feed fluid system 80.

[0037] Governing of related control components such as valves and related operators is illustratively conducted according to a governing control system, embodied to include at least one processor executing instructions stored on memory and communication circuitry communicating signals to/from the processor according to processor commands.

[0038] Within the presented disclosure, in a generation mode, heat from high temperature storage can be directed partly or wholly for other heat consuming needs, such as district heating, industrial process heat, or the like.

[0039] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

CLAIMS What is claimed is:

1. A pumped heat energy storage (“PHES”) system operable in an energy storage mode and a power generation mode, the system comprising: a fluid circuit for circulation of a working fluid therethrough, the fluid circuit in the generation mode comprising: a pump system for assisting circulation of the working fluid within at least a portion of the fluid circuit, a heat exchanger system through which the working fluid circulates in use, a hot side thermal storage system operable to transfer stored heat to the working fluid via the heat exchanger system, a turbine system configured to expand the working fluid received from the heat exchanger system to generate rotational drive, a thermal interface line in communication with the turbine system at a separation point to receive an extracted portion of the working fluid, and a cold side thermal storage system configured to store cold side thermal energy, the cold side thermal storage system comprising a cold side thermal storage tank arranged to receive the extracted portion of the working fluid from the thermal interface line for mixture with thermal storage fluid within the thermal storage tank for direct contact heat exchange.

2. The PHES system of claim 1 , wherein the extracted portion of the working fluid is steam.

3. The PHES system of claim 1, wherein the thermal storage fluid comprises condensate water.

4. The PHES system of claim 1, wherein the heat exchanger system includes a hot-side heat exchanger.

5. The PHES system of claim 4, wherein the hot side thermal storage system includes a high temperature thermal reservoir arranged in fluid communication with the hot-side heat exchanger for thermal communication with the working fluid.

6. The PHES system of claim 5, wherein in the generation mode the hot-side heat exchanger transfers heat from the high temperature thermal reservoir to the working fluid.

7. The PHES system of claim 5, wherein the high temperature thermal storage reservoir includes thermal storage fluid for passing through the hot-side heat exchanger in thermal communication with the working fluid.

8. The PHES system of claim 1, further comprising an auxiliary heat exchanger system arranged to receive a discharge portion of the working fluid from the turbine system for transfer of waste heat out from the fluid circuit.

9. The PHES system of claim 8, wherein the auxiliary heat exchanger system is arranged to transfer waste heat to ambient.

10. The PHES system of claim 1, wherein the extracted portion of the working fluid comprises intermediate extraction taken between stages of the turbine system.

11. The PHES system of claim 10, wherein the extracted portion of the working fluid is extracted at an intermediate location of a low pressure turbine of the turbine system.

12. The PHES system of claim 1, wherein condensate from the thermal storage system is circulated to the heat exchanger system.

13. The PHES system of claim 12, wherein the hot side thermal storage system includes at least a warm portion and a cold portion for thermal storage fluid, and condensate circulated to the heat exchanger system from the thermal storage system is from the cold side thermal storage system.

14. The PHES system of claim 1, wherein the PHES system is operable in the charge mode to extract thermal energy from the cold side thermal storage system and to store thermal energy within the high temperature reservoir arranged in thermal communication with the heat exchanger system.

15. A method of operating a pumped heat energy storage (“PHES”) system capable of operation in a charge mode and a generation mode, the system having a fluid circuit for the circulation of a working fluid therethrough, the method comprising, in the generation mode,: assisting circulation of the working fluid within at least a portion of the fluid circuit, passing the working fluid through a heat exchanger system to receive heat from hot side thermal storage, expanding the working fluid received from the heat exchanger system with a turbine system to generate rotational drive, extracting a portion of the working fluid at a separation point through a thermal interface line, directing the extracted portion of the working fluid through the thermal interface line to a thermal storage tank, mixing the extracted portion of the working fluid with thermal storage fluid within the thermal storage tank for direct contact heat exchange, and storing thermal energy from the extracted portion of the working fluid in cold side thermal storage.

16. The method of claim 15, wherein the extracted portion of the working fluid is steam.

17. The method of claim 15, wherein the thermal storage fluid comprises condensate water.

18. The method of claim 15, wherein the heat exchanger system includes a hot-side heat exchanger.

19. The method of claim 15, further comprising transferring heat from thermal storage fluid in a high temperature reservoir of the hot side thermal storage to the working fluid in the heat exchanger system in the generation mode.

20. The method of claim 15, further comprising directing a discharge portion of the working fluid from the turbine system to an auxiliary heat exchanger system for transfer of waste heat out from the fluid circuit.

21. The method of claim 20, further comprising transferring the waste heat to ambient.

22. The method of claim 15, wherein extracting the portion of the working fluid includes extracting from between stages of the turbine system.

23. The method of claim 22, wherein extracting the portion of the working fluid includes extracting from an intermediate location of a low pressure turbine of the turbine system.

24. The method of claim 15, wherein assisting circulation includes circulating condensate from the thermal storage system to the heat exchanger system.

25. The method of claim 24, wherein assisting circulation includes circulating condensate to the heat exchanger system from a cold portion of the thermal storage system.

26. The method of claim 1, further comprising operating the PHES system in the charge mode to extract thermal energy from the thermal storage system and to store thermal energy within a high temperature reservoir of the hot side thermal storage arranged in thermal communication with the heat exchanger system.

27. A pumped heat energy storage (“PHES”) system operable in a generation mode and a charge mode, the system comprising: a fluid circuit for circulation of a working fluid therethrough, the fluid circuit comprising in the generation mode: a heat exchanger system through which the working fluid circulates in use, wherein the heat exchanger system includes a hot- side heat exchanger and a high temperature reservoir arranged in fluid communication with the hot-side heat exchanger to transfer heat from the high temperature reservoir to the working fluid in a generation mode, a turbine system configured to expand the working fluid received from the heat exchanger system to generate rotational drive, and a thermal storage system configured to store cold side thermal energy, the thermal storage system comprising a thermal storage tank arranged to receive an extracted portion of the working fluid for mixture with thermal storage fluid within the thermal storage tank for direct contact heat exchange, wherein condensate from the thermal storage system is circulated to the heat exchanger system.