Volume 23: Sustainable Energy Solutions for a Post-COVID Recovery towards a Better Future: Part VI

Dynamic modelling of an Organic Rankine Cycle Compressed Heat Energy Storage (ORC-CHEST) system integrated with a cascaded phase change materials (PCM) based packed bed unit Alessio Tafone, Roberto Pili, Alessandro Romagnoli

Abstract

Carnot batteries represent an emerging thermomechanical energy storage technology based on the
conversion of surplus electricity into medium-low temperature
heat, and subsequent conversion of the heat into electricity. A
promising configuration of the Carnot battery is represented
by the Organic Rankine Cycle Compressed Heat Energy Storage
(ORC-CHEST) that combines a high-temperature heat pump
(charge phase), an Organic Rankine Cycle (ORC) system
(discharge phase) and a thermal energy storage (TES) system.
Indeed, TES is a crucial component in the overall ORC-CHEST
system, since it thermally links the charge and discharge
phases (operating asynchronously) guaranteeing optimal
operation and ensuring significantly high round trip
efficiencies. Most of literature on ORC-CHEST have so far
only focused on preliminary analyses in order to define the
general thermodynamic potential and to identify the limits of
the overall system. Indeed, a detailed analysis of ORC-CHEST
with focus on TES modelling is lacking. This paper presents
such an analysis by developing a dynamic numerical model of
the discharge phase of ORC-CHEST system with a novel packed
bed solution for the TES system. Indeed, we developed for the
first time a plant model in MATLAB that blends together
algebraic and differential sub-models detailing the transient
behaviour of the thermal storage stages and the ORC unit. In
addition, a novel configuration of the TES system design is
proposed utilizing a cascade of multiple phase change
materials (PCMs) in place of the cascade of sensible and single
PCM proposed in literature, enhancing simultaneously both
the TES energy density and the round trip efficiency of the
system. The results are of great interest for academia and
industry and contribute significantly to the development of an
efficient and cost-effective thermal energy storage system,
capable to simultaneously increase the ORC-CHEST round trip
efficiency and energy density by 7 % and 77 %, respectively,
compared to the state-of-the-art solution.

Keywords CHEST, ORC, Phase Change Material, Renewable energy, Packed bed.