PDF Publication Title:
Text from PDF Page: 011
the system, in spite of the gassing problem, 1n order to check out the system design concept and controls and to ga1n some operat1ng experience. These goals were accomplished in spite of the operational difficulties. In addi- t1on, some charge-acceptance and polarizatlon data out to the des1gn power level were acquired, and the system was operated briefly ln conjunction with the 5-kW (peak) solar photovoltaic array. Nonetheless, the five-cell stack of rebalance cells was unable to keep up w1th the system gas evolution rate, so the two reactants were always chemically out of balance. Therefore it was decided to completely rebuild the four stacks, taking advantage of a techn1que newly developed by G1ner, Inc., for effect1vely catalyzing carbon felt for chromlum electrodes. Laboratory tests had shown such electrodes to generate hydrogen in very modest amounts. This perlod would also be used to redesign and rebuild the flve-cell rebalance stack. As each of the four stacks was rebuilt, it was checked out 1ndividually. As expected, the hydrogen evolution rates had become almost negl1gible. The average reslstance of stack cells, about 12 mfi, compared well wlth labo- ratory results. However, the shunt-current power losses, as indicated by the steady-state current (taper current) attalned whlle charglng at a fixed voltage, were about twice as large as calculated. Most of this discrepancy has been shown to result from shunt paths unaccounted for 1n the mathematical model. These paths are effect1vely el1m1nated by using a polyethylene gasket to prevent the flow1ng flulds in the port slots (f1g. 8) from contacting the membranes. Table 2 shows, for five-cell stacks, the h1story of shunt loss reduction as cells have been made to conform more closely to the model. In this table the cell conf1guration resulting in a 28-mA taper current 1S the same as ln the l-kW system. The insertion of the polyethylene gaskets reduced taper current to 12 mAo It can be 1nferred from these data that a reduction in shunt loss of about 50 percent would result from this simple modification to the cells of the l-kW system. The reassembled l-kW system 1S shown in figure 9. Testing began in mid-November 1980. The init1al work, whose focus was to characterize the performance of the Redox system, conslsted of polarizat1on tests, charge- discharge cycles, and performance-versus-flow-rate measurements (flow mapping). In these evaluations, all 156 cells were act1ve and system charg- lng was done wlth a dc power supply. Also, for the reasons mentioned earller, power suppl1es were used to power the pumps, 1nstruments, and controls. Figure 10 presents the polarizatlon curves for the 156-cell Redox system, taken at three d1fferent states of charge and presented in terms of average cell voltage versus current dens1ty. The dlP in the discharge curve for the lowest state of charge (SOC) occurred when the weaker cells of the system fell off in performance. The voltage of such cells tends to drop to near zero and then stab1l1ze. The rise in the charg1ng curve for the highest state of charge was accompanied by the onset of a considerable increase in the hydrogen evolution rate, which is typical for h1gher charging voltages. The linear segments of the discharge curves have a slope equivalent to 15 mfi/cell, about 25 percent greater than measured when the stacks were tested indiv1dually. It was determined that this rise in cell resistance resulted from the lnab1lity of the heatlng system in the shed houslng the l-kW system to keep the reactant temperature above 50° F ln midwinter. Prior tests had been performed at a controlled 70° F. Th1S temperature- induced lncrease in cell reslstance results in a decrease in system energy efficlency. 8PDF Image | NASA Redox Storage System Development Project 1980
PDF Search Title:
NASA Redox Storage System Development Project 1980Original File Name Searched:
19830006412.pdfDIY PDF Search: Google It | Yahoo | Bing
Salgenx Redox Flow Battery Technology: Power up your energy storage game with Salgenx Salt Water Battery. With its advanced technology, the flow battery provides reliable, scalable, and sustainable energy storage for utility-scale projects. Upgrade to a Salgenx flow battery today and take control of your energy future.
CONTACT TEL: 608-238-6001 Email: greg@salgenx.com (Standard Web Page)