Thermoelectric energy storage system

Abstract

A thermoelectric energy storage system and method are provided for storing electrical energy by transferring thermal energy to a thermal storage in a charging cycle, and for generating electricity by retrieving the thermal energy from the thermal storage in a discharging cycle. The thermoelectric energy storage includes a working fluid circuit configured to circulate a working fluid through a heat exchanger, and a thermal storage conduit configured to transfer a thermal storage medium from a thermal storage tank through the heat exchanger. The working fluid includes a zeotropic mixture. The working fluid is in a mixed vapor and liquid phase and has continuously rising or continuously falling temperature during heat transfer due to the working fluid including the zeotropic mixture.

What is claimed is: 
     
         1 . A thermoelectric energy storage system for storing electrical energy by transferring thermal energy to a thermal storage in a charging cycle, and for generating electricity by retrieving the thermal energy from the thermal storage in a discharging cycle, the thermoelectric energy storage system comprising:
 a working fluid circuit configured to circulate a working fluid through a heat exchanger; and   a thermal storage conduit configured to transfer a thermal storage medium from a thermal storage tank through the heat exchanger,   wherein the working fluid includes a zeotropic mixture.   
     
     
         2 . The thermoelectric energy storage system of  claim 1 , wherein the zeotropic mixture is selected such that the temperature of the working fluid in the heat exchanger changes from a first temperature to a second temperature. 
     
     
         3 . The thermoelectric energy storage system of  claim 1 , wherein the heat exchanger includes a counter flow heat exchanger. 
     
     
         4 . The thermoelectric energy storage system of  claim 1 , wherein the flow of the working fluid through the heat exchanger is controlled such that a temperature difference between the working fluid and the thermal storage medium is less than 50° C. 
     
     
         5 . The thermoelectric energy storage system of  claim 1 , comprising:
 a valve configured to control the flow in the working fluid circuit.   
     
     
         6 . The thermoelectric energy storage system of  claim 1 , wherein the thermal storage tank includes a hot storage tank, and the thermal storage conduit includes a hot storage conduit configured to transfer a hot storage medium between a first hot storage tank and a second hot storage tank through the heat exchanger. 
     
     
         7 . The thermoelectric energy storage system of  claim 1 , wherein:
 the storage tank includes an intermediate storage tank; and   the heat exchanger includes a stream splitter configured to divide the flow of the thermal storage medium from a first storage tank into a flow to the intermediate storage tank and to a second storage tank.   
     
     
         8 . The thermoelectric energy storage system of  claim 1 , comprising:
 a compressor configured to compress the working fluid in vapor phase from a lower pressure to a higher pressure during the charging cycle, such that electrical energy for driving the compressor is injected into the thermal energy storage system.   
     
     
         9 . The thermoelectric energy storage system of  claim 1 , comprising:
 an expansion device configured to expand the working fluid in liquid phase from a higher pressure to a lower pressure during the charging cycle.   
     
     
         10 . The thermoelectric energy storage system of  claim 1 , comprising:
 a pump configured to pump the working fluid from a lower pressure to a higher pressure during the discharging cycle.   
     
     
         11 . The thermoelectric energy storage system of  claim 1 , comprising:
 a turbine configured to expand the working fluid from a higher pressure to a lower pressure level for generating electrical energy during the discharging cycle.   
     
     
         12 . A method for storing and retrieving electrical energy, the method comprising:
 storing electrical energy by transferring thermal energy to a thermal storage in a charging cycle; and   retrieving electrical energy by changing the thermal energy from the thermal storage into mechanical energy in a discharging cycle,   wherein the charging cycle and the discharging cycle comprise transferring heat between a working fluid and a thermal storage medium, and   wherein the working fluid is in a mixed vapor and liquid phase and has continuously rising or continuously falling temperature during heat transfer due to the working fluid including a zeotropic mixture.   
     
     
         13 . The method of  claim 12 , comprising:
 controlling the flow through the heat exchanger such that a temperature difference between the working fluid and the thermal storage medium is less than at least one of 50° C., 10° C. and 3° C.   
     
     
         14 . The method of  claim 12 , comprising:
 dividing the flow of the thermal storage medium in the heat exchanger such that heat transfer in the heat exchanger has two different rates.   
     
     
         15 . The thermoelectric energy storage system of  claim 2 , wherein the zeotropic mixture is selected such that a temperature of the working fluid in the heat exchanger continuously changes from a first temperature to a second temperature. 
     
     
         16 . The thermoelectric energy storage system of  claim 4 , wherein the flow of the working fluid through the heat exchanger is controlled such that the temperature difference between the working fluid and the thermal storage medium is less than 10° C. 
     
     
         17 . The thermoelectric energy storage system of  claim 4 , wherein the flow of the working fluid through the heat exchanger is controlled such that the temperature difference between the working fluid and the thermal storage medium is less than 3° C. 
     
     
         18 . The thermoelectric energy storage system of  claim 4 , comprising:
 a valve configured to control the flow in the working fluid circuit.   
     
     
         19 . The thermoelectric energy storage system of  claim 1 , wherein the thermal storage tank includes a cold storage tank, and the thermal storage conduit includes a cold storage conduit configured to transfer a cold storage medium between a first cold storage tank and a second cold storage tank through the heat exchanger. 
     
     
         20 . The thermoelectric energy storage system of  claim 6 , wherein the thermal storage tank includes a cold storage tank, and the thermal storage conduit includes a cold storage conduit configured to transfer a cold storage medium between a first cold storage tank and a second cold storage tank through the heat exchanger. 
     
     
         21 . The thermoelectric energy storage system of  claim 20 , wherein:
 the storage tank includes an intermediate storage tank; and   the heat exchanger includes a stream splitter configured to divide the flow of the thermal storage medium from a first storage tank into a flow to the intermediate storage tank and to a second storage tank.   
     
     
         22 . The thermoelectric energy storage system of  claim 20 , comprising:
 a compressor configured to compress the working fluid in vapor phase from a lower pressure to a higher pressure during the charging cycle, such that electrical energy for driving the compressor is injected into the thermal energy storage system.   
     
     
         23 . The thermoelectric energy storage system of  claim 20 , comprising:
 an expansion device configured to expand the working fluid in liquid phase from a higher pressure to a lower pressure during the charging cycle.   
     
     
         24 . The thermoelectric energy storage system of  claim 20 , comprising:
 a pump configured to pump the working fluid from a lower pressure to a higher pressure during the discharging cycle.   
     
     
         25 . The thermoelectric energy storage system of  claim 20 , comprising:
 a turbine configured to expand the working fluid from a higher pressure to a lower pressure level for generating electrical energy during the discharging cycle.   
     
     
         26 . The method of  claim 12 , comprising:
 joining the flow of the thermal storage medium in the heat exchanger such that heat transfer in the heat exchanger has two different rates.   
     
     
         27 . The method of  claim 13 , comprising:
 dividing the flow of the thermal storage medium in the heat exchanger such that heat transfer in the heat exchanger has two different rates.   
     
     
         28 . The method of  claim 13 , comprising:
 joining the flow of the thermal storage medium in the heat exchanger such that heat transfer in the heat exchanger has two different rates.