SYSTEMATIC AND MULTI-CRITERIA OPTIMISATION OF SUBCRITICAL THERMALLY INTEGRATED CARNOT BATTERIES (TI-PTES) IN AN EXTENDED DOMAIN

Abstract

Thermally integrated pumped thermal energy storage (TI-PTES) is a flexibility option to recover lowgrade heat (i.e. < 100°C) and to provide overnight storage. Common criteria when optimising such system are the power-to-power efficiency (i.e. electricity recovery), the total exergy efficiency (i.e. combined heat and electricity recovery) and the energy density (i.e. storage size). However, these objectives are generally conflicting and multi-criteria optimisation is therefore required to discuss the trade-offs. Design guidelines have been proposed for some specific case studies but are still lacking for the remaining wide range of possible integration scenarios. This work therefore presents a systematic multi-criteria analysis of a TI-PTES consisting of a high temperature vapor compression heat pump, a sensible heat thermal storage and an organic Rankine cycle, in an extended integration domain (i.e. heat source from −25 to 100°C, sink from −25 to 50°C). The single objective optimisation reveals that the design trends are not uniform and that the tipping points are located where the difference between the source and sink temperatures is less than 30 K. The multi-criteria analysis shows that there is a region of the domain where the criteria do not conflict. The results also highlight that density and exergy efficiency are much less conflicting with each other than they are with power-to-power efficiency.