Energy Analysis of a Solid Oxide Fuel Cell – Stirling Engine Hybrid Power Plant with Cascaded Waste Heat Recovery

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DOI https://doi.org/10.15407/pmach2026.03.056
Journal Journal of Mechanical Engineering – Problemy Mashynobuduvannia
Publisher Anatolii Pidhornyi Institute of Power Machines and Systems
of National Academy of Science of Ukraine
ISSN  2709-2984 (Print), 2709-2992 (Online)
Issue Vol. 29, no. 3, 2026 (September)
Pages 56-70
Cited by J. of Mech. Eng., 2026, vol. 29, no. 3, pp. 56-70

 

Authors

Dmytro D. Hrinchenko, Anatolii Pidhornyi Institute of Power Machines and Systems of NAS of Ukraine (2/10, Komunalnykiv str., Kharkiv, 61099, Ukraine), e-mail: dimag628@gmail.com, ORCID: 0009-0001-8648-8099

Viktoriia O. Tarasova, Anatolii Pidhornyi Institute of Power Machines and Systems of NAS of Ukraine (2/10, Komunalnykiv str., Kharkiv, 61099, Ukraine), e-mail: vat523710@gmail.com, ORCID: 0000-0003-3252-7619

Abstract

A schematic design for a hybrid power plant based on a solid oxide fuel cell (SOFC) and Stirling engines, which involves the cascaded recovery of the thermal potential of the SOFC exhaust streams, is proposed. The objective of this study is to enhance the efficiency of fuel energy utilization in the SOFC–Stirling engine hybrid power plant by developing a configuration that employs the energy potential of the SOFC exhaust streams in a cascade, recovering waste heat sequentially across Stirling engines operating at different temperature levels. A mathematical model of the system has been developed, accounting for the material and energy balances of its core components, as well as regenerator efficiency, dead volumes, and temperature differences within the Stirling engines. A parametric analysis was conducted to examine the impact of regeneration efficiency and the temperature difference between the gas stream and the working fluid on the plant’s energy performance. For a configuration featuring a single Stirling engine, it was found that increasing the regenerator efficiency from 0.5 to 0.8 raises the thermal efficiency from 16.32–16.33% to 28.41–28.54%, and the electrical power output – from 116 kW to 202.72 kW. Under these conditions, the hybrid power plant achieves a maximum energy efficiency of 77.30% among the studied operating modes. It has been shown that after the first stage of waste heat recovery and the regenerative preheating of the cathode air, the temperature of the exhaust gas stream remains in the range of 474–528 °C. To utilize this thermal potential, the installation of a second Stirling engine – operating at a lower heat-input temperature level – is proposed. Calculations indicate that its electrical power output ranges from 103.29 to 108.17 kW, bringing the total electrical power output of the hybrid power plant to 810.85 kW. Among the analyzed operating modes, the highest calculated energy efficiency for the two-stage plant is 89.19%, achieved with regenerator efficiencies of e1=e2=0.8 and temperature differences of ΔTh,1=20 К and ΔTh,2=50 K. These results confirm the viability of using a cascaded approach to recover the thermal potential of SOFC exhaust streams via Stirling engines operating at different temperature levels, thereby generating additional electrical energy.

 

Keywords: solid oxide fuel cell, Stirling engine, hybrid power plant, cascaded waste heat recovery, heat regeneration, temperature difference, energy efficiency.

 

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Received 12 August 2026
Accepted 01 September 2026
Published 30 September 2026