Advanced exergoeconomic analysis of a Rankine type Carnot battery: Splitting avoidable and unavoidable costs

Carnot batteries store electricity as heat and are a leading candidate for large scale, geographically unconstrained energy storage, yet their economic assessment has so far relied on conventional exergoeconomic methods that cannot distinguish improvable from technologically fixed costs. This study presents an advanced exergoeconomic analysis of a Rankine type heat pump and organic Rankine cycle Carnot battery with sensible hot water storage in which both the destruction costs and the investment costs of all components are decomposed, a combination that the studies compiled in Table 1 do not cover. The complete advanced exergy machinery, comprising forty four real, ideal, hybrid and unavoidable cycle solutions per configuration, is verified case by case against a published reference model to within 0.018 K in all state temperatures and 0.006 kW in all decomposition terms. A cost layer based on the specific exergy costing (SPECO) method with zone resolved heat exchanger sizing then splits both the exergy destruction cost rates and the investment cost rates of all ten components into avoidable and unavoidable as well as endogenous and exogenous parts. Two structurally different turbomachinery cost correlation families, a third power based family applied strictly within its published validity ranges, and a Monte Carlo analysis with five thousand samples per configuration separate what is robust from what is conditional. The destruction side is robust at the design point: the ORC condenser carries the largest avoidable endogenous destruction cost under all three correlation families and all unavoidable condition sets, and it ranks among the top three total priorities in all ten thousand samples; only re solving the cycles with three point lower machine efficiencies promotes the expander instead, so the list is tied to the design point. The leader of the total ranking, in contrast, is decided by whether the correlation prices isentropic efficiency: under a volumetric correlation the compressor falls from first to fifth place, under the power based family to the last place, and under an efficiency pricing correlation it keeps the first place. This correlation family dependence of advanced exergoeconomic investment splittings is quantified here and applies equally to rankings obtained with a single correlation set. For the reference configuration the system reaches a round trip efficiency of 39.9% and regenerates electricity at 597 EUR per MWh under the volumetric set from 60 EUR per MWh charging power, while a pressurized 140 °C configuration with the low global warming potential pair R1233zd(E) and R152a improves the round trip efficiency to 42.8% and lowers the cost amplification from 9.95 to 7.02; assigning vessel costs and thermal losses to the store changes these results by less than 8 % and preserves the advantage of the pressurized configuration. A full factorial optimization of the four storage side and rejection side temperature differences in the reference configuration lowers the specific cost by 3.7 and 6.1% under the two correlation families, transferring its optimum settings to the pressurized configuration lowers the cost there by 7.4 and 12.1%, and the round trip efficiency rises by up to seven points; the two families prefer different optimum designs, which extends the correlation family conditionality from the ranking to the design itself. Under volumetric costing the results shift development effort toward heat rejection and storage side heat transfer, under efficiency pricing they keep the turbomachinery in focus, and in both readings they provide a transparent advanced exergoeconomic benchmark for Carnot battery research.