Adiabatic salt energy storage

Abstract

Efficient energy storage is provided by using a working fluid flowing in a closed cycle including a ganged compressor and turbine, and capable of efficient heat exchange with heat storage fluids on a hot side of the system and on a cold side of the system. This system can operate as a heat engine by transferring heat from the hot side to the cold side to mechanically drive the turbine. The system can also operate as a refrigerator by mechanically driving the compressor to transfer heat from the cold side to the hot side. Heat exchange between the working fluid of the system and the heat storage fluids occurs in counter-flow heat exchangers. In a preferred approach, molten salt is the hot side heat storage fluid and water is the cold side heat storage fluid.

1 . An energy system operable in at least a refrigerator mode and a heat engine mode, the system comprising:
 a turbomachinery system arranged to consume net energy when the system operates in the refrigerator mode and to generate net energy when the system operates in the heat engine mode, the turbine machinery system comprising at least one compressor and at least one turbine;   a working fluid path arranged to circulate a working fluid in communication with the turbomachinery system, the working fluid path including a high pressure (HP) side and the low pressure (LP) side;   a hot side heat exchanger arranged in communication with the working fluid on the HP side of the working fluid path to transfer heat between the working fluid and a hot side heat storage medium; and   a cold side heat exchanger arranged in communication with the working fluid on the LP side of the working fluid path to transfer heat between the working fluid and a cold side heat storage medium,   wherein the working fluid path is arranged to flow in a closed Brayton cycle including, in sequence, the at least one compressor, the hot side heat exchanger, the at least one turbine, and the cold side heat exchanger.   
     
     
         2 . The energy system of  claim 1 , further comprising:
 a hot side hot heat storage tank;   a hot side cold heat storage tank;   wherein the hot side heat storage medium flows from the hot side cold heat storage tank to the hot side hot heat storage tank in the refrigerator mode.   
     
     
         3 . The energy system of  claim 2 , wherein the hot side heat storage medium comprises molten salt. 
     
     
         4 . The energy system of  claim 3 , wherein the molten salt comprises a eutectic mixture of sodium nitrate and potassium nitrate. 
     
     
         5 . The energy system of  claim 2 , further comprising:
 a cold side hot heat storage tank; and   a cold side cold heat storage tank,   wherein the cold side heat storage medium flows from the cold side hot heat storage tank to the cold side cold heat storage tank when the system operates in the refrigerator mode.   
     
     
         6 . The energy system of  claim 5 , wherein the cold side heat storage medium comprises water. 
     
     
         7 . The energy system of  claim 6 , wherein the cold side heat storage medium further comprises an antifreeze compound. 
     
     
         8 . The energy system of  claim 1 , wherein the working fluid is air. 
     
     
         9 . The energy system of  claim 1 , wherein the working fluid is Argon. 
     
     
         10 . The energy system of  claim 1 , wherein the working fluid path is arranged to transfer heat to the hot side heat storage fluid in the refrigerator mode. 
     
     
         11 . The energy system of  claim 1 , wherein the working fluid path is arranged to transfer heat to the cold side heat storage fluid in the heat engine mode. 
     
     
         12 . The energy system of  claim 1 , wherein the working fluid path is arranged to transfer heat to the working fluid from the hot side heat storage medium in the heat engine mode. 
     
     
         13 . The energy system of  claim 1 , wherein the working fluid path is arranged to transfer heat to the working fluid from the cold side heat storage medium in the refrigerator mode. 
     
     
         14 . The energy system of  claim 1 , wherein the hot side heat exchanger is arranged within the working fluid path between the at least one compressor and the at least one turbine on the HP side. 
     
     
         15 . The energy system of  claim 1 , wherein the cold side heat exchanger is arranged within the working fluid path between the at least one turbine and the at least one compressor on the LP side. 
     
     
         16 . The energy system of  claim 1 , wherein the at least one compressor is mechanically coupled with the at least one turbine. 
     
     
         17 . The energy system of  claim 1 , further comprising a waste heat exchanger operable to dissipate waste heat to reduce entropy of the system. 
     
     
         18 . A method of operating an energy system, the method comprising:
 circulating a working fluid within a working fluid path through, in a closed Brayton cycle, in sequence, at least one compressor, a hot side heat exchanger, at least one turbine, and a cold side heat exchanger, wherein the working fluid path includes a high pressure (HP) side and a low pressure (LP) side, wherein circulating includes communicating the hot side heat exchanger with the working fluid on the HP side of the working fluid path to transfer heat between the working fluid and a hot side heat storage medium, and communicating the cold side heat exchanger with the working fluid on the LP side of the working fluid path to transfer heat between the working fluid and a cold side heat storage medium,   wherein circulating includes consuming net energy when the system operates in a refrigerator mode and generating net energy when the system operates in a heat engine mode.   
     
     
         19 . The method of  claim 18 , including, operating the system in the refrigerator mode, comprising flowing the cold side heat storage fluid from a cold heat storage tank to a hot heat storage tank.