Method of operating thermal energy storage system

Abstract

A method of operating a thermal energy storage system comprises operating a pump to circulate a heat transfer fluid from cold storage through a heating system to hot storage, supplying electric power from an electric power grid external to the thermal energy storage system to power an electric heater in the heating system that heats the heat transfer fluid as it circulates through the heating system to hot storage, regulating a flow rate of the heat transfer fluid through the heating system so that the heat transfer fluid enters hot storage at a specified temperature, and regulating the supplying of electric power from the electric power grid to the electric heater to balance supply of and demand for power on the electric power grid and maintain a frequency, a voltage, or a frequency and a voltage of electric power on the electric power grid at specified values.

What is claimed is: 
     
         1 . A method of operating a thermal energy storage system comprising cold storage, hot storage, a heating system, and a heat transfer fluid, the method comprising:
 operating a pump to circulate the heat transfer fluid from the cold storage through the heating system to the hot storage;   supplying electric power from an electric power grid external to the thermal energy storage system to power an electric heater in the heating system that heats the heat transfer fluid as it circulates through the heating system to the hot storage;   regulating a flow rate of the heat transfer fluid through the heating system so that the heat transfer fluid enters the hot storage at a specified temperature; and   regulating the supplying of electric power from the electric power grid to the electric heater to balance supply of and demand for power on the electric power grid and maintain a frequency, a voltage, or a frequency and a voltage of electric power on the electric power grid at specified values.   
     
     
         2 . The method of  claim 1 , comprising controlling an operating speed of the pump to regulate the flow rate of the heat transfer fluid through the heating system. 
     
     
         3 . The method of  claim 1 , comprising operating control valves to regulate the flow rate of the heat transfer fluid through the heating system. 
     
     
         4 . The method of  claim 1 , wherein regulating the supplying of electric power from the electric power grid to the electric heater comprises varying a voltage of the electric power delivered to the electric heater from the electric power grid. 
     
     
         5 . The method of  claim 1 , wherein regulating the supplying of electric power from the electric power grid to the electric heater comprises varying an electric current delivered to the electric heater from the electric power grid. 
     
     
         6 . The method of  claim 1 , wherein regulating the supplying of electric power from the electric power grid to the electric heater comprises interrupting the flow of electricity from the electric power grid to the electric heater using on-off control. 
     
     
         7 . The method of  claim 1 , wherein the electric heater is or comprises an electric resistance heater and regulating the supplying of electric power from the electric power grid to the electric heater comprises regulating the supplying of electric power from the electric power grid to the electric resistance heater to maintain a frequency of electric power on the electric power grid at a specified value. 
     
     
         8 . The method of  claim 7 , comprising controlling an operating speed of the pump to regulate the flow rate of the heat transfer fluid through the heating system. 
     
     
         9 . The method of  claim 7 , comprising operating control valves to regulate the flow rate of the heat transfer fluid through the heating system. 
     
     
         10 . The method of  claim 7 , wherein regulating the supplying of electric power from the electric power grid to the resistance heater comprises varying a voltage of the electric power delivered to the electric resistance heater from the electric power grid. 
     
     
         11 . The method of  claim 7 , wherein regulating the supplying of electric power from the electric power grid to the resistance heater comprises varying an electric current delivered to the electric resistance heater from the electric power grid. 
     
     
         12 . The method of  claim 7 , wherein regulating the supplying of electric power from the electric power grid to the resistance heater comprises interrupting the flow of electricity from the electric power grid to the electric resistance heater using on-off control. 
     
     
         13 . The method of  claim 1 , wherein the electric heater is or comprises an electric inductive heater and regulating the supplying of electric power from the electric power grid to the electric heater comprises regulating the supplying of electric power from the electric power grid to the electric inductive heater to maintain a voltage of electric power on the electric power grid at a specified value. 
     
     
         14 . The method of  claim 13 , comprising controlling an operating speed of the pump to regulate the flow rate of the heat transfer fluid through the heating system. 
     
     
         15 . The method of  claim 13 , comprising operating control valves to regulate the flow rate of the heat transfer fluid through the heating system. 
     
     
         16 . The method of  claim 1 , comprising regulating the supplying of electric power from the electric power grid to the electric heater to balance supply of and demand for power on the electric power grid and maintain a frequency and a voltage of electric power on the electric power grid at specified values. 
     
     
         17 . The method of  claim 16 , comprising controlling an operating speed of the pump to regulate the flow rate of the heat transfer fluid through the heating system. 
     
     
         18 . The method of  claim 16 , comprising operating control valves to regulate the flow rate of the heat transfer fluid through the heating system. 
     
     
         19 . The method of  claim 16 , wherein regulating the supplying of electric power from the electric power grid to the electric heater comprises varying a voltage of the electric power delivered to the electric heater from the electric power grid. 
     
     
         20 . The method of  claim 16 , wherein regulating the supplying of electric power from the electric power grid to the electric heater comprises varying an electric current delivered to the electric heater from the electric power grid. 
     
     
         21 . The method of  claim 16 , wherein regulating the supplying of electric power from the electric power grid to the electric heater comprises interrupting the flow of electricity from the electric power grid to the electric heater using on-off control.