A new form of solar photovoltaic-photothermal cascade conversion with multistage concentrating-spectrum splitting: thermodynamic discussion

This study proposes a multi-stage concentrating and spectrum splitting strategy for full-spectrum solar energy photovoltaic–photothermal (PV–PT) coupling utilization. A thermophysical model is established to investigate the effect of concentration ratio on the photothermal conversion of spectrum beam radiation. The effectiveness of concentration ratio on improving the output work potential of different spectra are analyzed. Moreover, a single-stage spectral splitting PV–PT system is optimized, and the impact of concentration variation on system performance is evaluated. Two multi-stage system configurations are investigated: one using the residual spectrum for direct high-temperature conversion of isothermal endothermic processes such as thermophotovoltaics; and the other applying residual spectrum for cascade heating to drive thermal power or thermal chemical cycles. The results indicate that the increasing concentration ratio is beneficial for enhancing the thermal conversion capacity of long-wavelength solar radiation. For effective PV–PT coupling conversion, the concentration ratio should be decoupled for different spectra. The multi-stage system reduces the required concentration ratio by over 40% compared to a single-stage system, enabling simpler and more cost-effective optical designs. In addition, the system efficiency is theoretically comparable to or exceeding that of the optimal single-stage system. The two-stage system with concentration ratio of 600 can achieve an efficiency of over 54%, even exceeding that of the single-stage system with concentration ratio of 1000 (53.87%). A three-stage non-isothermal endothermic coupling system can achieve efficiencies near 55%. This study provides practical guidance for the development of high-efficiency full-spectrum solar energy PV-PT coupling conversion systems.