System and method for converting electric energy into thermal energy and for storing thermal energy

Abstract

System and method of operating the system. The system having a heat pump cycle, a turbine cycle, a medium storage cycle and a water storage cycle. By way of the heat pump cycle, heat of a working fluid can be transferred to a thermal medium (M) for storing thermal energy. By way of the turbine cycle, heat of the thermal medium (M) can be transferred to a working fluid (F). In so doing electric energy can be converted into thermal energy or transferred from thermal energy into electric energy by operating either the heat pump cycle or the turbine cycle. The thermal coupling between the water storage cycle and the heat pump cycle is provided by a water-to-fluid heat exchanger and the thermal coupling between the water storage cycle and the turbine cycle is provided by a fluid-to-water heat exchanger. The water storage cycle additionally contains an air-cooled water-cooling unit that can be operated independent from the water-to-fluid heat exchanger.

1 . A system for converting electric energy into thermal energy and for storing thermal energy, comprising:
 a heat pump cycle in which a working fluid (F) can be circulated comprising a first compressor unit for compressing the working fluid (F), an expander unit for expanding the working fluid (F), and a medium heating unit that are fluidly connected so that the medium heating unit is fluidly connected downstream of the first compressor unit and up-stream of the expander unit, wherein a water-to-fluid heat exchanger is fluidly connected to the heat pump cycle downstream of the expander unit, wherein the medium heating unit is adapted to heat a thermal medium (M) that can be circulated in a medium storage cycle, wherein the water-to-fluid heat exchanger is adapted to transfer heat from water (W) that can be circulated in a water storage cycle to the working fluid (F),   a turbine cycle in which a working fluid (F) can be circulated comprising a turbine unit, a medium cooling unit and a fluid-to-water heat exchanger that are fluidly connected so that the medium cooling unit is upstream of the turbine unit and the fluid-to-water heat exchanger is downstream of the turbine unit, wherein the medium cooling unit is adapted to cool the thermal medium (M) of the medium storage cycle, wherein the fluid-to-water heat exchanger is adapted to transfer heat from the working fluid (F) to the water (W) of the water storage cycle,   wherein the water storage cycle comprises a hot water tank, a controllable valve unit downstream of the hot water tank having a first outlet port and a second outlet port, and wherein the first outlet port is fluidly connected via the water-to-fluid heat exchanger with a cold water tank and/or with the fluid-to-water heat exchanger and the second outlet port is fluidly connected via an water cooling unit with the cold water tank and/or with the fluid-to-water heat exchanger.   
     
     
         2 . The system of  claim 1 , wherein the water storage cycle is a closed loop. 
     
     
         3 . The system of  claim 1 , wherein the water cooling unit is air cooled with ambient air. 
     
     
         4 . The system of  claim 1 , wherein the medium storage cycle is a closed loop comprising a hot medium reservoir downstream of the medium heating unit and a cold medium reservoir downstream of the medium cooling unit. 
     
     
         5 . The system of  claim 1 , wherein the first compressor unit is driven by an electric motor. 
     
     
         6 . The system of  claim 1 , wherein the turbine cycle comprises a second compressor unit that is driven by a turbine rotor or shaft of the turbine unit. 
     
     
         7 . The system of  claim 1 , wherein the heat pump cycle comprises a first heat exchanger that has a heat discharge section that is fluidly connected downstream of the medium heating unit and upstream of the expander unit. 
     
     
         8 . The system of  claim 1 , wherein the expander unit comprises a first expander device and a second expander device. 
     
     
         9 . The system of  claim 8 , wherein downstream of the first heat exchanger a first fluid valve is provided for splitting the working fluid in two split streams, wherein one of the split streams is conducted to the first expander device and the other of the split streams is conducted to the second expander device, and wherein a second fluid valve is provided downstream of the first expander device and the second expander device, that mixes the working fluid streams delivered from the two expander devices. 
     
     
         10 . The system of  claim 9 , wherein the first fluid valve is adjusted or controlled to adjust the mass flow of the split streams of the working fluid (F), such that the fluid streams delivered from the two expander devices have particularly a desired temperature and/or a desired pressure. 
     
     
         11 . The system of  claim 7 , wherein the first expander device and/or the second expander device is fluidly connected downstream of the heat discharge section of the first heat exchanger. 
     
     
         12 . The system of  claim 7  wherein the heat pump cycle comprises a second heat exchanger has a heat discharge section that is fluidly connected downstream of the first heat exchanger and upstream of the second expander device. 
     
     
         13 . The system of  claim 12 , wherein a heat charging section of the second heat exchanger is fluidly connected downstream of the first expander device and upstream of the heat charging section of the first heat exchanger. 
     
     
         14 . The system of  claim 12 , wherein a control unit is present that is adapted to control the controllable valve unit depending on at least one environmental parameter (Ta, Tf). 
     
     
         15 . A method of operating a system according to  claim 1 , comprising the following steps:
 if electrical energy shall be stored in form of thermal energy: driving the first compressor unit in order to transfer heat from the working fluid (F) of the heat pump cycle to the thermal medium (M) of the medium storage cycle;   if electrical energy shall be produced by the turbine unit: transferring heat from the thermal medium (M) of the medium storage cycle to the working fluid (F) of the turbine cycle, supplying working fluid (F) to operate the turbine unit thereby transferring heat from the working fluid (F) of the turbine cycle to the water (W) of the water storage cycle by a fluid-to-water heat exchanger, wherein the amount of water (W) supplied to the water-to-fluid heat exchanger and/or the amount of water (W) supplied to the water cooling unit is controlled by a controllable valve unit.