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the latter at 108 mH/cm2, using two-molar reactants. In both cases the re- actant cost was assumed to be about $22/kWh. The results of the UTC study (ref. 31) indicate a system cost of S74/kWh for the 500-kwh system and $63/kWh for the 100-MWh system. These cast projec- tions were encouraglng. Although they were greater than the then-existing estimates for several competing technologies, they were much less than some of the more djre predicttdns; and they fell within the goals put forward for the major target applications. For both system sizes the preponderant portion of the cost was associated with the reactants and their tankage. This amounted to 81 percent for the smaller system wjth ite t.xtended cycle length and 58 ~ercentfor the large, shorter-term system. Thus the results of the reactant cost i l ~ d w'er~e ~ awaited wSth Lome anticipation. RF~OXreactant costs. - Six processing routes for the ction ot +he --- comp'ete Redox system reactant package, whicb, included aclz ~queoussoiu- ticits of ferrous-ch1c:'lue and chromic chloride, were aaalyzc -,the two coc- tyactors. A l l brocesses began with either chromite ore (Cr/Fe = 1.58 mass ratio), f~:rochrome(Cr/Fe = 1.64). or the chemical intermediate. sodium chro- ;,ute. rz; rhe sodium chromate starting material the necessary iron would be supplied to the process as scrap iron. Of the processes examined, only those i ~ v o l v i n gthe reductive chlorination of chromite ore would require new or un- certain technology. The remaining processes are wel? understood and their associated cost estimates are therefore accepted as being quite accurate. These studies are presented in detail in references 32 and 33. The results of the two studies, adjusted t o a comnon basis, are sumnarized i n table 111. The specific costs in dollars per kilowatt-hour assume an 80-percent utilization of reactants and an average cell discharge voltage of 0.9 V. If the assumed reactant cost of $22/kWh, which was used in tke UTC system cost analysls, i s adju;ted t o the same basis, i t becomes $lS.SO/kWh. This I s roughly equal to the most expensive process evaluated by Allied and CRA. The remaining processes that were evaluated indicated reactant costs as low as about 45 percent of the most expensive. For example, the reactant cost for the methanol reduction of sodium chromate, a process evaluated and well underst-;U by thr Allied Chemical Co. i s projected to be about $lO/kWh. Since this i s about S6/kWh less than the UTC assumption, it can be inferred that the total jystcm costs would be closer t o $57 t o $68/kWh than $63 t o $74/kWh. The results of the system and reactant cost analyses served to lend further credibility to the ambient-temperature iron-chromiurr, Redox storage system concept. To the attractive characteristics inherent i n flow batteries and the proven technical viability of the systen~,economic viability had now been added - provided, of course, that the assumed performance levels were attainable. Performance of Ambient-Temperature Iron-Chromlam Redox System I n spite of a l l of the posltlve aspects of the amblent-temperature iron- chromium flow battery, as evidenced especially i n the development and operation of the 1-kW system and i n the various cost analyses, it yet failed to satisfy the perceived technical requirements of the marketpiace. The problem was thatPDF Image | NASA Redox Storage System Development Project
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