Experimental 4E analysis (energy-exergy-economic-environmental) of hybrid parabolic trough collector-thermoelectric generator-phase change material cogeneration system

Hybrid solar cogeneration systems are critical for enhancing energy utilisation and mitigating the intermittency of solar resources. This study presents a comprehensive 4E (Energy-Exergy-Economic-Environmental) experimental analysis of a novel hybrid system that uniquely integrates a Parabolic Trough Collector (PTC), a small-scale steam turbine, a Thermoelectric Generator (TEG) assembly, and a Phase Change Material (PCM) thermal storage unit. The system's performance was investigated under 15 distinct operating conditions, varying initial water masses (0.1, 0.15, 0.2 kg) and operating pressures (6, 8, 10, 12, and 14 bar). Experimental results demonstrated the system's adaptive cogeneration capabilities. At 14 bar and 0.2 kg, the system achieved its maximum Solar-to-Electricity efficiency of 0.42%. At this operating condition, the highest collector thermal efficiency was 25.25% (at 6 bar), and the maximum overall energy and exergy efficiencies were 8.43% and 1.45%, respectively. A key finding was the system's adaptive electrical output: at low pressures (6 bar), the TEG acted as a crucial co-generator, supplying up to 55% of the electricity, whereas at high pressures (14 bar), the turbine dominated, accounting for 88-90% of the output. Furthermore, the study experimentally confirmed that latent heat transfer was the dominant heat transfer mechanism for the PCM, with latent heat contributing ∼445 kJ (55%) of the 805 kJ total energy stored. The thermo-economic analysis confirmed the system's viability, yielding a Simple Payback Period (Spp) of 6.9 years and a competitive Levelised Cost of Energy (LCOE) of $0.101/kWh. The system is projected to save 118.8 kg of CO2 and 660 L of water annually. The results validate the thermodynamic and economic feasibility of the integrated PTC-Turbine-TEG-PCM concept as a flexible solution for small-scale solar cogeneration.