Handbook of Energy Storage for Transmission or ... - W2agz.com
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Handbook of Energy Storage for Transmission or ... - W2agz.com

Handbook of Energy Storage for Transmission or ... - W2agz.com Handbook of Energy Storage for Transmission or ... - W2agz.com

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EPRI Proprietary Licensed Material Regenesys Electricity Storage Technology sulfide solution at the negatives in discharge dissolves in excess sodium sulfide that is present to form sodium polysulfide. The bromine produced at the positives in charge dissolves in excess sodium bromide to form sodium tribromide. Unlike the situation in zinc/bromide batteries, the bromine active material remains in solution in the tribromide ion form until it is consumed by the discharge reaction at the positives. Note also that the electrolyte for the positive electrodes is relatively inexpensive, and that used in the negative compartments of the cells is very inexpensive. A block diagram of a Regenesys energy storage plant is shown in Figure 1. 1 Figure 1 Flow Schematic of Regenesys Electricity Storage System The cation-exchange membranes that are a vital part of the electrochemical operability of Regenesys batteries serve to separate the differing electrolytes in the positive and negative compartments of each cell, yet provide a path for the passage of sodium ions. A rupture of a membrane in one of the cells will allow the electrolyte in the positive compartments and that in the negative compartments to mix together. This mixing is undesirable, so the Innogy technology based on this chemistry includes measures to detect and isolate any membrane ruptures. Even when operating properly, no membrane is 100% effective, of course, so the coulombic efficiency of Regenesys cells is typically 99%, and some material can pass from one side of the membranes to the other, thereby causing a build up of a sodium sulfate in the 1 Unless otherwise noted, all figures, diagrams and photos in this chapter are credited to Innogy/Regenesys Technologies, Ltd., which organization retains the copyright thereto. These graphics were downloaded from www.regenesys.com, and this acknowledgment is included in the current document as required as a condition of downloading and reproduction. There is no mention that specific authority to reproduce these graphics is required. Page 3

EPRI Proprietary Licensed Material Regenesys Electricity Storage Technology electrolyte for the negative compartments. This contaminating material must be removed as discussed in the following technology section. Regenesys Technology Here, we use the term “technology” to encompass the components and equipment that are necessary to allow operation of a rechargeable battery system with the chemistry described in the preceding section of the chapter. The design approach adopted by Innogy for their Regenesys technology is quite different than that of other flow battery developers, or indeed developers of any other battery technology. The Innogy design approach results from the needs dictated by the Regenesys chemistry and by the background of Innogy (i.e., National Power) personnel as employees of an electric utility generating company, as now indicated: • Innogy have chosen to design on a basis that efficiency is a much less important factor than capital cost for electric utility applications, so they employ higher current densities, by a factor of two or so, than other flow battery developers, particularly as compared to the design approach used by Sumitomo Electric Industries for their vanadium redox battery (VRB). • All the flow battery developers use carbonaceous materials in one form other another for both electrodes and for the bipolar element of their cell-stacks. (See Figure 2) In Innogy stacks, the electrochemical reactions occur at the specially prepared faces of the bipolar electrodes; unlike VRBs and other redox batteries, carbon felts are NOT used in either cell compartment. • Significantly larger electrodes (up to 1 square meter instead of a few hundreds of square centimeters, i.e., a small fraction of square meter) are used by Innogy as compared to other battery developers. (See Figure 3) • Innogy uses higher voltage, 300V versus ~100V or less, and much large capacity cell-stacks, 100kW versus 5-10kW, (larger electrodes, more cells in series/stack) as compared to other flow battery developers. (See Figure 4) • Unlike other flow battery developers, Innogy utilizes single large tanks for the positive and the negative electrolytes, together with correspondingly large pumps and other auxiliaries, as opposed to the modularized tanks and auxiliaries used by US flow battery developers. (See Figure 5) Page 4

EPRI Proprietary Licensed Material<br />

Regenesys Electricity <strong>St<strong>or</strong>age</strong> Technology<br />

electrolyte <strong>f<strong>or</strong></strong> the negative <strong>com</strong>partments. This contaminating material must be removed as<br />

discussed in the following technology section.<br />

Regenesys Technology<br />

Here, we use the term “technology” to en<strong>com</strong>pass the <strong>com</strong>ponents and equipment that are<br />

necessary to allow operation <strong>of</strong> a rechargeable battery system with the chemistry described in the<br />

preceding section <strong>of</strong> the chapter. The design approach adopted by Innogy <strong>f<strong>or</strong></strong> their Regenesys<br />

technology is quite different than that <strong>of</strong> other flow battery developers, <strong>or</strong> indeed developers <strong>of</strong><br />

any other battery technology. The Innogy design approach results from the needs dictated by the<br />

Regenesys chemistry and by the background <strong>of</strong> Innogy (i.e., National Power) personnel as<br />

employees <strong>of</strong> an electric utility generating <strong>com</strong>pany, as now indicated:<br />

• Innogy have chosen to design on a basis that efficiency is a much less imp<strong>or</strong>tant fact<strong>or</strong> than<br />

capital cost <strong>f<strong>or</strong></strong> electric utility applications, so they employ higher current densities, by a<br />

fact<strong>or</strong> <strong>of</strong> two <strong>or</strong> so, than other flow battery developers, particularly as <strong>com</strong>pared to the design<br />

approach used by Sumitomo Electric Industries <strong>f<strong>or</strong></strong> their vanadium redox battery (VRB).<br />

• All the flow battery developers use carbonaceous materials in one <strong>f<strong>or</strong></strong>m other another <strong>f<strong>or</strong></strong><br />

both electrodes and <strong>f<strong>or</strong></strong> the bipolar element <strong>of</strong> their cell-stacks. (See Figure 2) In Innogy<br />

stacks, the electrochemical reactions occur at the specially prepared faces <strong>of</strong> the bipolar<br />

electrodes; unlike VRBs and other redox batteries, carbon felts are NOT used in either cell<br />

<strong>com</strong>partment.<br />

• Significantly larger electrodes (up to 1 square meter instead <strong>of</strong> a few hundreds <strong>of</strong> square<br />

centimeters, i.e., a small fraction <strong>of</strong> square meter) are used by Innogy as <strong>com</strong>pared to other<br />

battery developers. (See Figure 3)<br />

• Innogy uses higher voltage, 300V versus ~100V <strong>or</strong> less, and much large capacity cell-stacks,<br />

100kW versus 5-10kW, (larger electrodes, m<strong>or</strong>e cells in series/stack) as <strong>com</strong>pared to other<br />

flow battery developers. (See Figure 4)<br />

• Unlike other flow battery developers, Innogy utilizes single large tanks <strong>f<strong>or</strong></strong> the positive and<br />

the negative electrolytes, together with c<strong>or</strong>respondingly large pumps and other auxiliaries, as<br />

opposed to the modularized tanks and auxiliaries used by US flow battery developers. (See<br />

Figure 5)<br />

Page 4

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