Patent Publication Number: US-9853306-B2

Title: System and method for optimizing efficiency and power output from a vanadium redox battery energy storage system

Description:
RELATED APPLICATIONS 
     This application is a divisional of and claims priority to U.S. patent application Ser. No. 11/032,280 filed Jan. 10, 2005 now U.S. Pat. No. 8,277,964, entitled “System and Method for Optimizing Efficiency and Power Output from a Vanadium Redox Battery Energy Storage System,” which claims the benefit of U.S. Provisional Application No. 60/536,662 filed on Jan. 15, 2004, and entitled “System and Method for Optimizing Efficiency and Power Output from a Vanadium Redox Battery Energy Storage System” and to U.S. Provisional Application No. 60/541,534 filed on Feb. 3, 2004, and entitled “System and Method for Optimizing Efficiency and Power Output from a Vanadium Redox Battery Energy Storage System,” all of which are herein incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This invention relates to vanadium redox battery energy storage systems and associated automated control systems to enhance performance. 
     BACKGROUND OF THE INVENTION 
     Domestic and industrial electric power is generally provided by thermal, hydroelectric, and nuclear power plants. New developments in hydroelectric power plants are capable of responding rapidly to power consumption fluctuations, and their outputs are generally controlled to respond to changes in power requirements. However, the number of hydroelectric power plants that can be built is limited to the number of prospective sites. Thermal and nuclear power plants are typically running at maximum or near maximum capacity. Excess power generated by these plants can be stored via pump-up storage power plants, but these require critical topographical conditions, and therefore, the number of prospective sites is determined by the available terrain. 
     New technological innovations and ever increasing demands in electrical consumption have made solar and wind power plants a viable option. Energy storage systems, such as rechargeable batteries, are an essential requirement for remote power systems that are supplied by wind turbine generators or photovoltaic arrays. Energy storage systems are further needed to enable energy arbitrage for selling and buying power during off peak conditions. 
     Vanadium redox energy storage systems have received very favorable attention, as they promise to be inexpensive and possess many features that provide for long life, flexible design, high reliability, and low operation and maintenance costs. A vanadium redox energy storage system include cells holding anolyte and catholyte solutions separated by a membrane. 
     The vanadium redox energy storage system relies on a pumping flow system to pass the anolyte and catholyte solutions through the cells. In operating a vanadium redox energy storage system, flow rates, internal temperatures, pressure, charging and discharging times are all factors that influence power output. Thus, it would be an advancement in the art to provide a system and method for optimizing the efficiency of a vanadium redox energy storage system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more particular description of the invention briefly described above will be rendered by reference to the appended drawings. Understanding that these drawings only provide information concerning typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which: 
         FIG. 1  is a block diagram of an embodiment of a vanadium redox battery energy storage system; 
         FIG. 2  is a block diagram illustrating an embodiment of a power conversion system; 
         FIG. 3  is a block diagram of an embodiment of a control system; 
         FIG. 4  is a graph illustrating a state of charge curve; 
         FIG. 5  is graph illustrating a state of charge curve for ideal open circuit voltages; and 
         FIG. 6  is a block diagram illustrating a control methodology for use in the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The presently preferred embodiments of the present invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the apparatus, system, and method of the present invention, as represented in  FIGS. 1 through 6 , is not intended to limit the scope of the invention, as claimed, but is merely representative of presently preferred embodiments of the invention. 
     A vanadium redox battery energy storage system, hereinafter referred to as VRB-ESS, includes all sizes of vanadium redox batteries (VRB) in both absolute KVA rating and energy storage duration in hours. The VRB-ESS includes storage reservoirs to hold vanadium electrolyte, an energy conversion mechanism defined as a cell, a piping and pumping flow system, and a power conversion system (PCS). 
     The VRB-ESS is in electrical communication with a control system that monitors and controls aspects of the performance of the components of the VRB-ESS. The control system may be implemented in any number of ways but, in one embodiment, includes a control program running on a suitable platform, such as programmable logic controller, microprocessor, or the like. The control system controls and manages the performance of the VRB-ESS in such a manner as to optimally meet the fundamental parameters of efficiency and safe operation. The control system further provides for self protection in the event of an external or internal fault or failure of a critical component, accurate controlled output as determined by dynamic load requirements or preset performance thresholds, and ambient conditions prevailing from time to time in each cycle. 
     The present invention provides a system and method for optimally controlling the power output, charging and discharging times, and efficiency of a VRB-ESS or any system that uses vanadium based electrolyte solution as the energy storage component of a battery. There are several key parameters which control the operation of a VRB. For any given concentration of electrolyte solution, the key parameters include temperature, volumetric flow rates, pressure within and across the cell stacks, and state of charge of the electrolyte and load as evidenced by the current drawn or supplied. The load may be seen as positive or negative. If negative, then the load is actually supplying power to the VRB. All of these parameters change in a dynamic manner continuously and vary with age. 
     In order to optimize the overall performance of the VRB, the present invention employs a control system provides algorithms with control strategies. The control system allows the VRB-ESS to operate in an automatic mode to ensure that the highest possible efficiency is achieved as measured from the alternating current input to alternating current output on a round trip basis. The control system adjusts according to the age of the VRB-ESS or as dynamic changes in any of the components occurs. The control system provides optimized efficiency by controlling the charging and discharging, pump flow rates, and associated pressures within the VRB-ESS. 
     Referring to  FIG. 1 , a block diagram of a VRB-ESS  10  for use with the present invention is shown. A suitable energy storage system is required for remote power system applications that are supplied by either photovoltaic arrays or wind turbine generators. For such applications, low life-cycle cost and simplicity of operation are major requirements. 
     The system  10  includes one or more cells  12  that each have a negative compartment  14  with a negative electrode  16  and a positive compartment  18  with a positive electrode  20 . Suitable electrodes include any number of components known in the art and may include electrodes manufactured in accordance with the teachings of U.S. Pat. No. 5,665,212, which is hereby incorporated by reference. The negative compartment  14  includes an anolyte solution  22  in electrical communication with the negative electrode  16 . The anolyte solution  22  is an electrolyte containing specified redox ions which are in a reduced state and are to be oxidized during the discharge process of a cell  12  or are in an oxidized state and are to be reduced during the charging process of a cell  12  or which are a mixture of these latter reduced ions and ions to be reduced. The positive compartment  18  contains a catholyte solution  24  in electrical communication with the positive electrode  20 . The catholyte solution  24  is an electrolyte containing specified redox ions which are in an oxidized state and are to be reduced during the discharge process of a cell  12  or are in a reduced state and are to be oxidized during the charging process of the cell  12  or which are a mixture of these oxidized ions and ions to be oxidized. 
     The anolyte and catholyte solutions  22 ,  24  may be prepared in accordance with the teachings of U.S. Pat. Nos. 4,786,567, 6,143,443, 6,468,688, and 6,562,514, which are hereby incorporated by reference, or by other techniques well known in the art. The anolyte solution  22  refers to an electrolyte containing specified redox ions which are in a reduced state and are to be oxidized during the discharge process of a redox battery or are in an oxidized state and are to be reduced during the charging process of a redox battery or which are a mixture of these latter reduced ions and ions to be reduced. The catholyte solution  24  refers to an electrolyte containing specified redox ions which are in an oxidized state and are to be reduced during the discharge process of a redox battery or are in a reduced state and are to be oxidized during the charging process of the redox battery or which are a mixture of these oxidized ions and ions to be oxidized. Further, aqueous NaOH is not included within the scope of anolyte solution  22 , and aqueous HCl is not included within the scope of a catholyte solution  24 . In one embodiment, the anolyte solution  22  is 1M to 6M H.sub.2 SO.sub.4 and includes a stabilizing agent in an amount typically in the range of from 0.1 to 20 wt % and the catholyte solution  24  is 1M to 6M H.sub.2 SO.sub.4. 
     Each cell  12  includes an ionically conducting separator  26  disposed between the positive and negative compartments  14 ,  18  and in contact with the catholyte and anolyte solutions  22 ,  24  to provide ionic communication therebetween. The separator  26  serves as a proton exchange membrane and may include a carbon material which may or may not be purflomatorated. 
     Additional anolyte solution  22  is held in an anolyte reservoir  28  that is in fluid communication with the negative compartment  14  through an anolyte supply line  30  and an anolyte return line  32 . The anolyte reservoir  28  may be embodied as a tank, bladder, or other container known in the art. The anolyte supply line  30  communicates with a pump  36  and a heat exchanger  38 . The pump  36  enables fluid movement of the anolyte solution  22  through the anolyte reservoir  28 , supply line  30 , negative compartment  14 , and return line  32 . The pump  36  has a variable speed to allow variance in the generated flow rate. The heat exchanger  38  transfers generated heat from the anolyte solution  22  to a fluid or gas medium. The pump  36  and heat exchanger  38  may be selected from any number of known, suitable devices. 
     The supply line  30  includes one or more supply line valves  40  to control the volumetric flow of anolyte solution. The return line  32  communicates with a return line valves  44  that controls the return volumetric flow. 
     Similarly, additional catholyte solution  24  is held in a catholyte reservoir  46  that is in fluid communication with the positive compartment  18  through a catholyte supply line  48  and a catholyte return line  50 . The catholyte supply line  48  communicates with a pump  54  and a heat exchanger  56 . A variable speed pump  54  enables flow of the catholyte solution  22  through the catholyte reservoir  46 , supply line  48 , positive compartment  18 , and return line  50 . The supply line  48  includes a supply line valve  60  and the return line  50  includes a return line valve  62 . 
     The negative and positive electrodes  16 ,  20  are in electrical communication with a power source  64  and a load  66 . A power source switch  68  is disposed in series between the power source  64  and each negative electrode  16 . Likewise, a load switch  70  is disposed in series between the load  66  and each negative electrode  16 . One of skill in the art will appreciate that alternative circuit layouts are possible and the embodiment of  FIG. 1  is provided for illustrative purposes only. 
     In charging, the power source switch  68  is closed and the load switch is opened. Pump  36  pumps the anolyte solution  22  through the negative compartment  14  and anolyte reservoir  28  via anolyte supply and return lines  30 ,  32 . Simultaneously, pump  54  pumps the catholyte solution  24  through the positive compartment  18  and catholyte reservoir  46  via catholyte supply and return lines  48 ,  50 . Each cell  12  is charged by delivering electrical energy from the power source  64  to negative and positive electrodes  16 ,  20 . The electrical energy derives divalent vanadium ions in the anolyte solution  22  and quinvalent vanadium ions in the catholyte solution  24 . 
     Electricity is drawn from each cell  12  by closing load switch  70  and opening power source switch  68 . This causes load  66 , which is in electrical communication with negative and positive electrodes  16 ,  20  to withdraw electrical energy. Although not illustrated, a power conversion system may be incorporated to convert DC power to AC power as needed. 
     A number of control parameters influence the efficiency of the system  10 . A key control parameter is the temperature of the anolyte and catholyte solutions  22 ,  24 . The temperature is influenced by ambient conditions and load requirements. Another control parameter is the pressure of the solutions  22 ,  24  which is influenced by flow rates, state of charge (SOC), temperature, and plant design. A further control parameter is the flow rate which is controlled through variable speed drives. Other control parameters include charging current and duration of constant current periods, as determined by SOC. 
     Another control parameter is hydrogen evolution. The hydrogen evolution is minimized in the control strategy and is influenced by temperature, SOC, load and rates of charge and discharge which are ramp rates. Another control parameter is the remixing of concentrations of the anolyte and catholyte solutions  22 ,  24  with respect to volumes. Pressure differentials develop over time as reservoirs  28 ,  46  have different electrolyte levels due to crossover. Concentrations also vary and system optimization must factor the remixing parameter. 
     Recharge and discharge periods are additional control parameters. The rate of charge and discharge impact the evolution of hydrogen. In addition, during discharge, heat is developed and the temperature of the anolyte and catholyte solutions  22 ,  24  is raised. Viscosity is thus affected and pump flow rates need to be adjusted accordingly. The optimal time for charge and discharge is selected within the maximum rates that the system can handle as well as within the loads requirements, i.e. time available in a day. 
     Referring to  FIG. 2 , an interconnection of cells  12  of a VRB-ESS  10  to a PCS  100  is shown. The PCS  100  serves as the load  66  generally referenced in  FIG. 1 . The PCS  100  is illustrative of any number of configurations and is provided as one example. One or more cells  12  are coupled to the PCS  100  through a load switch  70 . The cells  12  provide a direct current to a coupling circuit  102  that may include a capacitor  104  and diode  106  in series. The coupling circuit  100  is in communication with an inverter  108  to convert the direct current to alternating current. The inverter  108  couples to a main switchboard  110  to provide local distribution. 
     One or more transformers  112 , such as pole mount transformers, are in electrical communication with the main switchboard  110  to step up the localized voltage for remote distribution. A distribution feeder  114  is coupled to the transformer  112  to enable long range power transmission. 
     A panel board  116  is coupled to the main switchboard  110  for local power distribution. This is particularly useful if the system  10  is located in a remote location with limited power access. The panel board  116  is in electrical communication with the pumps  36 ,  54  to power their operation. One or more power lines  118  are in communication with the panel board  116  to provide high voltage supply to one or more applications such as lighting, HVAC, and so forth. A transformer  120 , in electrical communication with the panel board  112 , steps down the voltage for wall outlets and delivers the voltage to a sub panel  122 . The sub panel  122  is in electrical communication with one more wall outlets  124 . 
     Referring to  FIG. 3 , a block diagram of one embodiment of a control system  200  that interfaces with the system  10  of  FIG. 1  is shown. The control system  200  may be embodied as a programmable logic computer with a processor  202  for executing applications of the present invention. The processor  202  is in electrical communication with a memory  204  that receives and stores executable applications and data. The memory  204  may be embodied in various ways and may collectively include different memory devices such as ROM, RAM, non-volatile memory, such as a magnetic hard drive, and the like. The control system  200  further includes an input  206  and an output  208  to enable user interaction. 
     A user enters control settings  210  into lookup tables  212  in the memory  204 . The control settings  210  include real time pricing requirements, anticipated demand peak limits, and projected charge and discharge periods for a VRB-ESS  10 . 
     The control system  200  is in communication with the various components of the system  10  through a control communications interface  214 , that may be embodied as a RS485 using a MODBUS protocol. The components in electrical communication with the control system  200  include pumps  36 ,  54 , heat exchangers  38 ,  56 , supply valves  40 ,  60 , return valves  44 ,  62 , power source switch  68 , and load switch  70 . The control system  200  further communicates with an equalization/mix control  215  that equalizes the anolyte and catholyte solutions  22 ,  24  in the reservoirs  28 ,  46 . As required, the equalization/mix control  215  increases or decreases the volume of electrolytes in the reservoirs  28 ,  46  to maintain approximate equalization of anolyte and catholyte solutions  22 ,  24 . The equalization/mix control  215  may provide additional anolyte and catholyte solution  22 ,  24  from auxiliary reservoirs (not show) or reduce solution  22 ,  24  through drains (not shown). 
     The control system  200  communicates with sensors  216  through a monitor communications interface  218  that may be similar to the control communications interface  214 . The sensors  216  are disposed within the system  10  to monitor performance. The sensors  216  may include anolyte and catholyte thermometers  220   a ,  220   b  to monitor electrolyte temperatures. The anolyte and catholyte thermometers  220   a ,  220   b  are in contact with the anolyte and catholyte solutions  22 ,  24  and may be disposed at any number of locations throughout the VRB-ESS  10 . The sensors  216  further include an ambient thermometer  222  to monitor the external ambient temperature. Electrolyte level sensors  224   a ,  224   b  are disposed in the anolyte reservoir  28  and the catholyte reservoir  46  respectively to monitor levels of anolyte and catholyte solutions  22 ,  24 . Anolyte and catholyte flow rate sensors  226   a ,  226   b  are disposed in the supply and/or return lines  30 ,  32 ,  48 ,  50  to measure volumetric flow rate of the anolyte and catholyte solutions  22 ,  24 . Anolyte and catholyte pressure sensors  228   a ,  228   b  are disposed in the system  10  to measure the pressure of the anolyte and catholyte solutions  22 ,  24  in the supply and/or return lines  30 ,  32 ,  48 ,  50 . One or more emission sensors  230  are disposed in the system  10  to monitor the quantity of H2 emissions generated by the cells. 
     The communications interface  218  is further in electrical communication with the cells  12  to determine the Voc (open-circuit voltage) or to a reference cell inside the cell stack  12  of the system  10 . The communications interface  218  is also in electrical communication with the PCS  100  to receive signals indicative of voltage and current delivered to and received from the PCS  100 . All sensor input is collectively referred to as operational data  228  which is relayed to the control system  200  and stored in the memory  204 . 
     The control system  200  includes a control module  232 , resident in memory  204 , that controls and monitors system performance. The control module  232  monitors the operational data  228  for enhancements and determination of changes in performance. The control module  232  is an algorithmic application that evaluates the dynamic conditions of the system  10  by reviewing the operational data  228  and adjusts the control variables of system components to maximize the efficiency within the given design requirements. The control module  232  takes into account the effects of hysterisis and lag times in terms of response. 
     In operation, meeting grid demands is a dynamic situation. As load increases, the control system  200  meets the demand by increasing pump speeds to supply more power. Accordingly, as load decreases, the pump speeds are decreased. Furthermore, the more charge in the electrolyte solution, the slower the pump speed to meet a demand. Conversely, the less charge in an electrolyte solution, the faster the pump speed to meet a demand. In charging a VRB, the less charge in the electrolyte, the slower the pump speed needed to charge the electrolyte, whereas the greater charge in the electrolyte the faster the pump speed needed to charge the electrolyte. Furthermore, different pump speeds are employed based on the different types of electrolytes and concentrations. 
     The control module  232  employs the following control strategy equation:
 
SOC=( A+B*Voc   C )/( D+Voc   C ),
 
     where SOC is the state-of-charge and Voc is the open-circuit voltage. A, B, C, and D are constants. The control strategy equation defines a fundamental relationship between Voc and the SOC. Referring to  FIG. 4 , a graph is shown illustrating one example of the shape of a plot of Voc as a function of SOC. Referring to  FIG. 5 , a graph illustrating an ideal Voc as a function of SOC is shown. The relationship may also be confirmed against a reference cell. 
     The variables, A, B, C, and D are determined by physical design factors such as the pressure of cell stacks, ambient temperature, internal temperature, length of pipes, molar concentrations of electrolyte, and other design and operating factors. Although the plot shown in  FIG. 4  may vary and shift based on variables, the fundamental curve shape remains. The control module  232  uses the above equation to calculate the SOC based upon the open-circuit voltage Voc. A unique consideration of the present invention is that not all variables need to be actively controlled. Some variables are dependent upon others with definite time lags total system  10  operates as a feedback mechanism. 
     The flow rates of the anolyte and catholyte solutions  22 ,  24  may be varied to affect the Voc, SOC, and, consequently, power output. The control system  200  operates the pumps  36 ,  54  and heat exchangers  38 ,  56  to vary pump speeds and temperature and control the flow rate in the supply and return lines  30 ,  32 ,  48 ,  50 . The control system  200  can control flow rates to yield a constant power output, a constant current or a constant voltage. The control module  232  monitors the generated Voc and SOC to determine if the system  10  is performing efficiently. If performance is below expectations, the control module  232  alters key parameters of pump speed and temperature to improve performance. In this manner, the control module  232  adapts and improves control of the system  10 . 
     In discharging the system  10 , the control system  200  operates the pumps  36 ,  54  and heat exchangers  38 ,  56  to adjust the flow rate to optimize efficiencies and available power. With SOC at higher states and when discharging, the anolyte and catholyte solutions  22 ,  24  are pumped slower so that more charge can be removed on each pass. With SOC at lower states and when discharging, the pumping speeds are increased to the maximum allowable under pressure rating limits. 
     As the anolyte and catholyte solutions  22 ,  24  discharge, they become more viscous so flow rates can increase without equivalent pressure build up. To extract more power down to 10 percent SOC, it is necessary to increase the flow rate. When discharging, there is an exothermic reaction when the anolyte and catholyte solution  22 ,  24  states change. This typically results in a rising temperature of the electrolyte, unevenly from positive to negative sides. Temperature limits are typically set at a minimum of 5 Celsius and at a maximum of 40 Celsius. The control system  200  determines lead and lag times associated with each charge/discharge cycle and establishes set points. The set points determine when the control system  200  operates the heat exchangers  38 ,  56  to extract heat from the anolyte and catholyte solutions  22 ,  24 . Ambient conditions impact this process so that the condition is continuously dynamic. 
     During charging of the system  10 , the control system  200  controls the pumping speed at the extremes of the SOC in order to optimize the power input and output and to enhance round trip efficiency. With SOC at higher states and when charging, faster pumping prevents charged electrolyte from being trapped and developing heat and gas emission and potentially V 2 O 5 . With SOC at lower states and when charging, slower pumping allows maximum energy transfer each pass to reduce gas emission. 
     By use of emission sensors  230 , the control system  200  monitors any hydrogen gas evolution under bad conditions within each cell  12  during the charging process. In general, H 2  gas evolves during the charging cycle. Gas evolution is generally higher at a higher SOC and the control system determines the optimal performance criteria. If excess H 2  is produced, the efficiency drops off. During charging, the temperatures of the anolyte and catholyte solutions  22 ,  24  do not rise and may decline depending upon starting points and rates of charge. 
     Referring to  FIG. 6 , a block diagram illustrating a specific control methodology  300  performed by the control module  232  is shown. In a first process, the control module calculates  302  the SOC of the system  10 . In the previously discussed equation, SOC is calculated from the Voc of the cells  12  or reference cell. 
     Next the control module  232  calculates  304  the dynamic pumping speed for each pump  36 ,  54 . Pumping speed is determined by the calculated  302  SOC, and anolyte and catholyte pressures. Furthermore, pumping speed is adjusted by the calculated  312  charge and discharge rates, calculated  310  system efficiency, and cell H2 emissions. The optimal pumping speeds are transmitted from the control system  200  to each pump  36 ,  54 . 
     The control module  232  further calculates  306  an optimal temperature range for the anolyte and catholyte solutions  22 ,  24  based on the calculated  302  SOC and calculated  304  pumping speeds. The control module  232  operates the heat exchangers  38 ,  56  in accordance with the ambient and electrolyte temperature range. During charge and discharge, heat is generated and is measured to maintain an optimal range. As needed, heat is removed to maintain an optimal temperature range. In sufficiently cold environments, no heat exchangers are required as the ambient air provides the needed cooling. 
     During operation, the control module  232  monitors the levels of the anolyte and catholyte solutions  22 ,  24  and determines  308  if equalization of reservoir levels is needed. The control module  232  operates the equalization/mix control  215  to adjust the reservoirs  28 ,  46  as needed. 
     The control module  232  calculates  310  system efficiency based on a ratio of power output versus power input. System efficiency is determined from voltage and current generated by the cells  12 , calculated  314  power factor, and voltage and current delivered to the PCS  100 . System efficiency is used in calculating  304  the pump speeds. 
     The control module  232  accesses the control settings  210  to retrieve available charge and discharge periods. The control module  232  then calculates  312  charge and discharge rates to minimize demand peaks and to optimize efficiency. The charge and discharge rates are calculated initially and then may be updated and calculated under dynamic demand conditions. The charge and discharge rates are used in calculating  304  the pump speeds. 
     The control module  232  calculates  314  a power factor based on voltage and current received and delivered to and from the PCS  100 . The control module  232  further calculates  314  the optimal charge and discharge rates based on the calculated  312  charge and discharge rates. The control module  232  may modify the projected charge and discharge rates based on prior rates. The control module  232  may communicate the charge and discharge rates to the PCS  100  for anticipated performance. 
     In operation, meeting grid demands is a dynamic situation. As load increases, the PCS  100  meets the demand by increasing pump speeds to supply more power depending on the SOC. Accordingly, as load decreases, the pump speeds are decreased. Furthermore, the more charge in the electrolyte solution, the slower the pump speed to meet a demand. Conversely, the less charge in an electrolyte solution, the faster the pump speed to meet a demand. In charging a VRB, the less charge in the electrolyte, the slower the pump speed needed to charge the electrolyte, whereas the greater charge in the electrolyte the faster the pump speed needed to charge the electrolyte. 
     The processes disclosed in the methodology  300  frequently operate in parallel and, as illustrated, interrelate with one another. The system&#39;s dynamic conditions require constant monitoring of system variables, such as Voc, pressure, temperature, and so forth. The control module  232  continuously updates the pump speeds, electrolyte temperatures, and reservoir levels to optimize performance. The control module  232  may be implemented in various ways including a neural networks or more simply with standard logic programming. 
     It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by the following claims.