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rebalancing, and a constant rate of electrolyte decay losses (rED, also in units of % capacity loss per cycle), which must be remediated using alternate servicing methods. We encompass all non- crossover losses in the electrolyte decay rate, which refers to side reactions and/or active species decay (the latter only applying to finite-lifetime chemistries). We elect to ignore any non- electrolyte losses, such as membrane fouling or electrode decay, because these components generally degrade on timescales longer than those anticipated for electrolyte crossover and decay (i.e., require replacement every five to ten years [6,19]) and their degradation is assumed to be independent of the symmetry or lifetime of the chemistry, the focus of this work. The capacity accessed in a given cycle is equal to the product of the nominal battery size and fcap, the fraction of original capacity accessible at that time. This fraction changes as the battery experiences electrolyte decay/crossover and subsequent remediation: 𝑓 =100%−b𝑟 ∗𝑛Q (𝑡)d−[𝑟 ∗𝑛S (𝑡)] (III-2) B6M NO BPB 0R BPB where 𝑛K and 𝑛L are the number of cycles passed since the last rebalancing event (i.e., t = R) !/! !/! and the number of cycles passed since the last servicing event (i.e., t = S), respectively. These counters increase each cycle and reset once rebalancing or servicing occurs and capacity is regained. These terms are further defined in Equation III-3. We note that servicing also resets the rebalancing counter, as we assume servicing achieves total capacity recovery. nR/S (t) = ì0, t = 0 or upon rebalancing (R) or servicing (S) (III-3) cyc ínR/S (t -1) +1, t > 0 and not rebalancing (R) or servicing (S) To determine when to service or rebalance the system, we define a lower capacity limit (caplim); once the accessible capacity declines to the caplim, capacity remediation is performed. In the case of symmetric and pseudo-symmetric chemistries, rebalancing will occur, which regains the capacity lost to crossover but not that lost to electrolyte decay. This process repeats until the total accessible capacity upon rebalancing has decayed to the caplim (i.e., 𝑐𝑎𝑝 ≤ 100% − 𝑟 ∗ &$T IU 𝑛L (𝑡)), at which point electrolyte servicing is performed. Where rebalancing is not feasible (i.e., !/! asymmetric chemistries), rebalancing is not employed and instead a servicing event occurs each time the accessible capacity decays to the caplim. This iterative capacity fade and recovery process is illustrated in Figure III-1, which exemplifies a simulation of the capacities of a generic symmetric and asymmetric RFB as a function of time. The nominal capacity rating is maintained î cyc 46PDF Image | Bringing Redox Flow Batteries to the Grid
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