Patent ID: 8277964

Claim:
A rechargeable energy storage system configured to couple to an electrical grid, comprising: a vanadium redox battery energy storage system, including: a vanadium redox battery cell having anolyte and catholyte solutions, an anolyte line coupled to the battery cell to carry anolyte solution, an anolyte reservoir coupled to the anolyte line and having anolyte solution, an anolyte variable speed pump coupled to the anolyte line to provide an anolyte flow rate, a catholyte line coupled to the battery cell to carry catholyte solution, a catholyte reservoir coupled to catholyte line and having catholyte solution, a catholyte variable speed pump coupled to the catholyte line to provide a catholyte flow rate, an anolyte thermometer in contact with the anolyte solution, and a catholyte thermometer in contact with the catholyte solution; and a control system in electrical communication with the vanadium redox battery cell to receive signals indicative of an open-circuit voltage of the vanadium redox battery cell, the control system further configured to be in electrical communication with an electrical grid and to determine grid conditions, the control system further in electrical communication with the anolyte and catholyte variable speed pumps and the anolyte and catholyte thermometers, the control system including, a processor, and a computer-readable medium in electrical communication with the processor and having a control program stored thereon, the control program comprising computer instructions executable on the processor for performing the method of, receiving anolyte and catholyte solution temperature signals from the anolyte and catholyte thermometers, calculating a state-of-charge for the vanadium redox battery cell from the open-circuit voltage and anolyte and catholyte solution temperature signals, calculating charge and discharge rates of the vanadium redox battery energy storage system, calculating anolyte and catholyte pump speeds from the state-of-charge, the charge and discharge rates, and grid conditions, and transmitting signals to the anolyte and catholyte variable speed pumps to control pump speed.