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Waste heat is one of the major problems associated with the energy system. This paper discusses an energy, exergy, and emissions approach for the hybrid system by utilizing waste heat to the maximum extent. A thermoelectric generator (TEG) is incorporated to utilize the low-temperature waste heat from a hybrid model of a solid oxide fuel cell (SOFC) and a combined heat and power (CHP) system. SOFC is an electrochemical cell that generates power at high temperatures through an electrochemical reaction. The high-temperature, unutilized fuel leaves the SOFC, which is burned in the afterburner. The afterburner temperature controls the operating temperature of SOFC. Here, three recuperators are used to utilize this high-temperature waste heat to improve the performance of SOFC and simultaneously generate heat power from the water or gas recuperator. TEG is an auxiliary power production technology that converts waste heat into energy. A novel integration of TEG with SOFC–CHP hybrid system to utilize the low temperature waste heat, is employed. The main goal of this study is to analyze a novel SOFC–CHP-TEG hybrid system in terms of its thermodynamics and emissions. A Two stage TEG is integrated with the SOFC–CHP hybrid system. The simulation model of high temperature fuel cell (SOFC) is developed on MATLAB and validated with published results. This study analyses the impact of pressure ratio and afterburner temperature on the performance of SOFC–CHP-TEG. To do this, perform energy and exergy assessments using the principles of the first and second laws of thermodynamics. A novel exergy-based sustainability index with emissions analysis for the proposed SOFC–CHP is presented. The achieved overall energy efficiency is 62.54% at a pressure ratio of 12 and an afterburner temperature of 1000 K. With an increase in pressure ratio and temperature, the level of CO emissions reduces significantly. [Display omitted] • A novel energy exergy for SOFC–CHP-TEG system is presented. • Exergy based performance is compared and achieve 56.62. • Utilization of waste heat via TEG. • Energy efficiency of SOFC–CHP-TEG is 62.54% at rp = 12 and afterburner temperature of 900 K. [ABSTRACT FROM AUTHOR]

In this paper, six novel modified exergy relations are explored to determine the precise estimation of exergy destruction and to identify which component has the most improvement potential. For this, three power generation cycles are considered, i.e., simple gas turbine (SGT), recuperated gas turbine (RGT), are compared with a novel hybrid system (SOFC-RGT: Solid Oxide Fuel Cell-RGT), which operates with fuel flexibility as well as enhanced work-output and thermal efficiency. For energy, exergy, and sustainability studies, numerical modeling is conducted using MATLAB. At r p = 4, TIT = 1250 K, an exclusive comparison has been made between proposed configurations based on thermodynamic modeling and exergy-based sustainability index. It is found that with the inclusion of a recuperator and a fuel cell in the proposed cycles, the thermal and sustainability performance tend to increase significantly. Whereas, exergy destruction increases but has minimal impact on comparing thermal performance and sustainability index. In terms of sustainability, RGT is 30.76% more sustainable than SGT, while SOFC-GT is 63.39% more sustainable than RGT. [Display omitted] • The gas turbine exhaust waste heat generated has been examined for powering the fuel cell. • A comparative sustainable, qualitative and quantitative performance comparison has been made between SGT, RGT and SOFC-RGT. • As per sustainability index the performance order is SGT < RGT < SOFC-RGT (lower to higher). • 6-Modified exergy indicator is used for performance comparison. • A novel performance map has been drawn for SGT, RGT and SOFC-RGT. [ABSTRACT FROM AUTHOR]