Thermodynamic optimization for dye-sensitized solar cell-thermoelectric generator hybrid device with external and internal irreversibilities

This study develops a finite-time-thermodynamic model of dye-sensitized solar cell-thermoelectric generator (DSSC-TEG) hybrid device. Considering external heat transfers, optical loss, Fourier heat leakage, Joule heat, Thomson effect, convection and radiation losses, expressions for energy conservation equations and performance parameters are derived by combining thermodynamics and heat transfer. Under a fixed overall heat exchanger thermal conductance, the maximum power, maximum efficiency and optimal DSSC operating temperatures are provided by simultaneously optimizing thermal conductance distribution, current density, thin-film thickness, thermoelectric leg length and thermoelectric element number. The design parameters and irreversibilities effects on optimal performance are investigated, the DSSC-TEG hybrid device and standalone DSSC device performances are compared, and a modified performance comparison method is proposed. Results indicate that TEG can effectively recover DSSC waste heat, and hybrid device delivers higher power than standalone DSSC. DSSC operating temperature and TEG operating temperature-difference first decrease and then increase with current density, and DSSC power is larger than TEG power in hybrid device. External thermal resistances, Thomson effect, convection and radiation losses degrade the optimal performance. At optimal performance, the total thermal conductance is distributed almost equally between two heat exchangers. The temperature-dependent coefficients affect hybrid device performance, which decrease as they increase.