Title: Influence of boundary conditions on the exergetic performance of the combination of a thermal energy storage system and an organic Rankine cycle

Authors: Andreas König-Haagen; Dieter Brüggemann

Addresses: Centre of Energy Technology (ZET), University of Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany ' Centre of Energy Technology (ZET), University of Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany

Abstract: The combination of a high-temperature packed bed thermal energy storage (TES) with an organic Rankine cycle (ORC) - named ORCTES - is analysed and optimised numerically for different boundary conditions from an exergetic point of view. The temperature dependency of all relevant material properties is taken into account. Characteristic curves from literature are used to model the ORC. Pressure and heat losses as well as convection, diffusion and radiation in the packed bed are included in the TES model. To identify the optimisation potential and interactions in the system, a detailed exergetic evaluation method is applied. For one set of boundary conditions, an optimisation is performed and compared with a previous publication. These two cases refer to the highest and lowest overall exergetic efficiency in the non-optimised case. Interestingly, the effect of physical aspects on the exergetic efficiency can be higher or lower for the TES itself compared to the effect on the overall system and these effects strongly depend on the boundary conditions. The optimisation raised the exergetic overall efficiency from 36.1% to 43.4% and from 7.6% to 28.0%.

Keywords: exergetic evaluation; thermal energy storage; TES; organic Rankine cycle; ORC; optimisation.

DOI: 10.1504/IJEX.2021.118718

International Journal of Exergy, 2021 Vol.36 No.2/3/4, pp.227 - 242

Received: 13 Nov 2020
Accepted: 14 Feb 2021

Published online: 29 Oct 2021 *

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