Patent Application
20070072067
The present disclosure relates to battery storage systems, and more specifically, to vanadium redox battery systems.
Domestic and industrial electric power is generally provided by thermal, hydroelectric, and nuclear power plants. N/ew 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 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 may include cells holding anolyte and catholyte solutions separated by a membrane. A vanadium redox energy storage system may also rely on a pumping flow system to pass the anolyte and catholyte solutions through the cells.
The present embodiments will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that the accompanying drawings depict only typical embodiments, and are, therefore, not to be considered to be limiting of the invention's scope, the embodiments will be described and explained with specificity and detail in reference to the accompanying drawings in which:
It will be readily understood that the components of the embodiments 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 various embodiments, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of various embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.
The phrases “connected to,” “coupled to” and “in communication with” refer to any form of interaction between two or more entities, including mechanical, electrical, magnetic, electromagnetic, fluid, and thermal interaction. Two components may be coupled to each other even though they are not in direct contact with each other. The term “abutting” refers to items that are in direct physical contact with each other, although the items may not necessarily be attached together.
V2+V3++e− Eq. 1.1
The positive compartment 18 contains a catholyte solution 24 in electrical communication with the positive electrode 20. The catholyte solution 24 may be 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. By way of example, in a VRB-ESS 10 the charge-discharge redox reaction occurring at the positive electrode 20 in the catholyte solution 24 is represented by Equation 1.2:
V4+V5++e− Eq. 1.2
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 known in the art. Typically, aqueous NaOH is not included within the scope of the anolyte solution 22, and aqueous HCl is typically not included within the scope of the catholyte solution 24. In one embodiment, the anolyte solution 22 is 1M to 6M H2SO4 and includes a stabilizing agent in an amount typically in the range of from 0.1 to 20 wt %, and the catholyte solution 24 may also be 1M to 6M H2SO4.
Each cell 12 includes an ionically conducting membrane 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 membrane 26 serves as a proton exchange membrane and may include a carbon material which may or may not be purflomatorated.
Although the membrane 26 disposed between the anolyte solution 24 and the catholyte solution 22 is designed to prevent the transport of water, vanadium and sulfate ions, typically some amount of water, vanadium and sulfate transport occurs. Consequently, after a period of time, the cells 12 become imbalanced because water, vanadium and sulfate crossover. Each crossover typically occurs in one direction (i.e., from the anolyte solution 24 to the catholyte solution 22 or from the catholyte solution 22 to the anolyte solution 24 depending on what type of membrane is used). In order to balance the system 10, the catholyte and anolyte solutions 22, 24 may be mixed which completely discharges the battery system 10.
In conventional systems, the cells 12 in the cell stack are either all anion-selective membranes or all cation-selective membranes. Having all anion membranes or having all cation membranes results in unidirectional water transport and unidirectional vanadium transport. According to the embodiments described herein, at least one cell has an anion-selective membrane and at least one cell has a cation-selective membrane. The membrane configurations are discussed in greater detail in conjunction with the description accompanying
Additional anolyte solution 22 may be 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 may communicate 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 may have a variable speed to allow variance in the generated flow rate. The heat exchanger 38 transfers heat generated 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 suitable devices known to those having skill in the art.
The supply line 30 may include one or more supply line valves 40 to control the volumetric flow of anolyte solution. The return line 32 may also communicate with one or more return line valves 44 that control the return volumetric flow.
Similarly, additional catholyte solution 24 may be 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 may communicate with a pump 54 and a heat exchanger 56. The pump 54 may be a variable speed pump 54 that enables flow of the catholyte solution 24 through the catholyte reservoir 46, supply line 48, positive compartment 18, and return line 50. The supply line 48 may also include a supply line valve 60, and the return line 50 may include 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 may be disposed in series between the power source 64 and each negative electrode 16. Likewise, a load switch 70 may be 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
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 the load switch 70 and opening the power source switch 68. This causes the 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.
An anolyte supply line 130 may provide the negative compartment 114 with anolyte solution 122 from an anolyte reservoir (not shown in
The negative and positive electrodes 116, 120 in the cell stack 111 are in electrical communication with a power source 164 and a load 166. By way of example, a power source switch 168 may be disposed in series between the power source 164 and each negative electrode 116. Likewise, a load switch 170 may be disposed in series between the load 166 and each negative electrode 116. In charging the cell stack 111, the power source switch 168 switch is closed, and the load switch 170 is opened. During a discharge process, electricity is drawn from each cell 112 by closing load switch 170 and opening power source switch 168.
Each cell 112 includes a membrane disposed between the positive and negative compartments 114, 118 and is in contact with the catholyte and anolyte solutions 122, 124 to provide ionic communication therebetween. One cell 112 of the cell stack 111 includes a cation membrane 171. The cation membrane 171 may be any commercially available cation exchange membrane such as a Nafion 115 membrane.
In the cell adjacent the cell containing the cation membrane 171, an anion membrane 172 may be disposed between the positive and negative compartments 114, 118 and is in contact with the catholyte and anolyte solutions 122, 124. The anion membrane 172 may be any type of commercially available anion exchange membrane as would be known to those having skill in the art.
In one embodiment, the cells 112 containing cation membranes 171 are alternated with cells 112 containing an anion membrane 172, such that each cell 112 having a cation membrane 171 is adjacent a cell 112 having an anion membrane 172, and each cell 112 having an anion membrane 172 is adjacent a cell 112 having a cation membrane 171. However, one having skill in the art would recognize that alternative configurations of cells 112 are envisioned. For example, the number of cation membrane-containing cells may not be equal to the number of anion membrane-containing cells, and/or the positioning of each may not be alternating as shown in the embodiment of
With cation exchange membranes 171, water crossover or transport across the membrane occurs in one direction, such as from the anolyte solution 122 across the membrane 171 to the catholyte solution 124. Furthermore, during the discharge process of the cell stack 111, vanadium ion transport across the cation membrane 171 typically occurs from the anolyte solution 122 to the catholyte solution 124 depending on factors such as electrolyte concentrations, pressure and current densities.
However, with anion exchange membranes 172, water transport across the membrane occurs in a second direction which is opposite from the cation membrane-containing cell. Additionally, vanadium transport across the anion membrane 172 typically occurs from the catholyte solution 124 to the anolyte solution 122 during the discharge process of the cell stack 111.
By having a combination of anion exchange membranes 172 and cation exchange membranes 171 in different cells 112, the net crossover of water in the cell stack 111 is improved. In one cell 112 the water transfer occurs in one direction (because it contains an anion membrane 172), and in another cell 112 water transport occurs in the opposite direction (because it contains a cation membrane 171). Thus over each cycle of the vanadium redox battery, there tends to be an improvement of efficiency and more balance than achieved in conventional systems.
This improvement in water management strategy in VRB-ESSs does not require the mixing of catholyte and anolyte solutions 124, 122 in order to balance the system which results in the discharge of the battery as is employed in conventional systems. This may be particularly beneficial in some applications, such as uninterruptible power supply (“UPS”) applications.
Additionally, by having a plurality of cells 112 containing a cation exchange membrane 171 and a plurality of cells 112 containing an anion exchange membrane 172, net vanadium transport between the catholyte solution 124 and the anolyte solution 122 is restricted. This results in an enhanced performance compared to conventional systems in terms of DC to DC efficiency evidenced by improved coulombic efficiency and reduced equalization losses.
Furthermore, a combination of cation exchange membranes 171 and anion exchange membranes 172 may result in a decrease in the overall change of proton and sulfate concentrations in the catholyte and anolyte solutions 124, 122. By way of example, a portion of the charge, proportional to the ratio of cation to anion membranes 171, 172, is supported by proton transport across the membrane from the catholyte solution 124 to the anolyte solution 122. Whereas the other portion of the charge in the other cells is supported by sulfate ions and is transported across the membrane from the anolyte solution 122 to the catholyte solution 122. Therefore, the change in ionic strength and conductivity is less than the entire charge supported by the transport of either proton or sulfate ions individually.
Each cell 212 includes an ionically conducting membrane disposed between positive and negative compartments. As heretofore described, a plurality of cells 212 contain a cation exchange membrane while the remaining plurality of cells 212 contain an anion exchange membrane. In some embodiments the cation membrane-containing cells are alternated with the anion membrane-containing cells. This improves water crossover and restricts net vanadium transport and net change of proton and sulfate concentrations.
According to the VRB-ESS 210 of
Similarly, additional catholyte solution is held in a catholyte reservoir 246 that is in fluid communication with the positive compartment of each cell 212 through a catholyte supply line 248 and a catholyte return line 250. The catholyte supply line 248 may be coupled to a pump 254 that enables flow of the catholyte solution through the catholyte reservoir 246, supply line 248, positive compartment of each cell 212, and return line 250. As with the anolyte pump 236, the catholyte pump 254 may also be a variable speed pump to allow variance in the generated catholyte flow rate.
By way of example, a distributor 280 may be used to distribute the anolyte solution from the anolyte supply line 230 to the negative compartment of each cell 212. A distributor 280 may also be used to distribute the catholyte solution from the catholyte supply line 248 to the positive compartment of each cell 212. The distributors 280 may also provide the catholyte and anolyte solutions from the positive and negative compartments of each cell 212, respectively to the catholyte and anolyte return lines 250, 232.
Referring to
The membranes 26 in each cell 12, 112, 212 may be alternated so that each cell having a cation membrane 171 is adjacent a cell having an anion membrane 172 and each cell having an anion membrane 172 is adjacent a cell having a cation membrane 171. Water and vanadium transport across each anion exchange membrane 172 occurs in a direction from the anolyte solution 22, 122 toward the catholyte solution 24, 124 during a discharge process of the VRB-ESS 10, 210. Furthermore, water and vanadium transport across each cation exchange membrane 171 occurs in the opposite direction from the catholyte solution 24, 124 to the anolyte solution 22, 122.
A net change of proton and sulfate concentrations are also restricted in the anolyte 22, 122 and catholyte 24, 124 solutions. It should be apparent that each step or action of the methods described herein may be changed by those skilled in the art and still achieve the desired result. Thus, any order in the detailed description is for illustrative purposes only and is not meant to imply a required order.
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.
