Thermoelectric energy storage system having an internal heat exchanger and method for storing thermoelectric energy

Abstract

Exemplary embodiments are directed to a thermoelectric energy storage system (TEES) and method for converting electrical energy into thermal energy to be stored and converted back to electrical energy with an improved round-trip efficiency are disclosed. The TEES includes a working fluid circuit for circulating a working fluid through a first heat exchanger and a second heat exchanger, a thermal storage medium circuit for circulating a thermal storage medium, the thermal storage medium circuit having at least one hot storage tank coupled to a cold storage tank via the first heat exchanger. The arrangement maximizes the work performed by the cycle during charging and discharging for a given maximum pressure and maximum temperature of the working fluid.

1 . A thermoelectric energy storage system having a charging cycle for providing thermal energy to a thermal storage, and a discharging cycle for generating electricity by retrieving the thermal energy from the thermal storage, the thermoelectric energy storage system comprising:
 a working fluid circuit for circulating a working fluid through a first heat exchanger and a second heat exchanger; and   a thermal storage medium circuit for circulating a thermal storage medium, the thermal storage medium circuit having at least one hot storage tank coupled to a cold storage tank via the first heat exchanger,   wherein, the second heat exchanger is adapted to cool the working fluid at an output of the first heat exchanger during a charging cycle, and adapted to pre-heat the working fluid at an input to the first heat exchanger during a discharging cycle.   
     
     
         2 . The system according to  claim 1 , wherein, during the charging cycle, the second heat exchanger comprises:
 a first input from the first heat exchanger connected to a first output leading to an expander; and   a second input from a condenser connected to a second output leading to a compressor.   
     
     
         3 . The system according to  claim 1 , wherein, during the discharging cycle, the second heat exchanger comprises;
 a first input from a pump connected to a first output leading to the first heat exchanger; and   a second input from a thermodynamic machine connected to a second output leading to a condenser.   
     
     
         4 . The system according to  claim 1 , wherein at least one section of a charging cycle or a discharging cycle runs transcritically. 
     
     
         5 . The system according to  claim 1 , wherein either the charging cycle or the discharging cycle runs without the second heat exchanger. 
     
     
         6 . The system according to  claim 2 , wherein at least one section of a charging cycle or a discharging cycle runs transcritically. 
     
     
         7 . The system according to  claim 2 , wherein either the charging cycle or the discharging cycle runs without the second heat exchanger. 
     
     
         8 . The system according to  claim 3 , wherein at least one section of a charging cycle or a discharging cycle runs transcritically. 
     
     
         9 . The system according to  claim 3 , wherein either the charging cycle or the discharging cycle runs without the second heat exchanger. 
     
     
         10 . A method for storing and retrieving energy in a thermoelectric energy storage system, comprising:
 charging the system by heating a thermal storage medium, wherein the thermal storage medium circulates between at least one hot storage tank and a cold storage tank;   discharging the system by heating a working fluid in a working fluid circuit with heat from the thermal storage medium and expanding the working fluid through a thermodynamic machine;   cooling the working fluid output from a first heat exchanger during charging by means of a second heat exchanger; and   pre-heating the working fluid input into the first heat exchanger during discharging by means of a second heat exchanger.   
     
     
         11 . The method according to  claim 6 , wherein the step of cooling the working fluid output from the first heat exchanger during charging, comprises:
 transferring heat from the working fluid exiting the first heat exchanger to the working fluid output from an evaporator.   
     
     
         12 . The method according to  claim 6 , wherein the step of pre-heating the working fluid input into the first heat exchanger during discharging, further comprises:
 transferring heat from the working fluid exiting a thermodynamic machine to the working fluid input into the first heat exchanger.   
     
     
         13 . The method according to  claim 10 , wherein at least one section of a charging cycle or a discharging cycle is performed transcritically. 
     
     
         14 . The method according to  claim 10 , comprising:
 running either the charging cycle or the discharging cycle runs without the second heat exchanger.   
     
     
         15 . The method according to  claim 11 , wherein at least one section of a charging cycle or a discharging cycle is performed transcritically. 
     
     
         16 . The method according to  claim 11 , comprising:
 running either the charging cycle or the discharging cycle runs without the second heat exchanger.   
     
     
         17 . The method according to  claim 12 , wherein at least one section of a charging cycle or a discharging cycle is performed transcritically. 
     
     
         18 . The method according to  claim 12 , comprising:
 running either the charging cycle or the discharging cycle runs without the second heat exchanger.