Proposal of a parabolic-trough-type spectral splitting concentrating photovoltaic-photothermal (SSCPVT) system for combined power and heat generation

In order to improve the comprehensive utilization efficiency of full-spectrum solar energy, a novel solar parabolic-trough concentrated spectral splitting photovoltaic-photothermal (CSSPVT) system for combined power and heat generation is proposed. The optical path in this system and the structural parameters of the parabolic-trough primary concentrator, the hyperbolic secondary concentrator with SS and the heteromorphic prisms are primarily optimized. In this dual-axis tracking solar system, the incident full-spectrum sunlight undergoes three-stage concentration processes, with the focus-shape transformed from line to point, the geometric concentration ratio lifted up to 900, and the full-spectrum split from 500 to 1200 nm, to satisfy the equipment of GaAs cells. A comprehensive multiphysics model incorporating optical, flow and thermal consideration is established to simulate the system performances under design and off-design conditions. The results show that, under a direct normal irradiance (DNI) of 650 W m⁻², the system achieves a photovoltaic efficiency of 24.36 %, photothermal efficiency of 36.7 %, waste heat utilization of 11.58 %, resulting in a comprehensive solar utilization efficiency of 72.64 %. Furthermore, under the off-design condition, the optimal inlet velocity for the thermal oil was determined to be 0.1 m s⁻¹ at different DNI. Moreover, the annual performance in Dunhuang of Northwest China is evaluated on hourly basis. The results show that the annual combined heat and power generation can reach 1060.3 kW m⁻² with the heat-to-power ratio of 1.38, and the annual comprehensive solar energy utilization efficiency (η_th+PV) is up to 57.98 % with the thermal and photovoltaic efficiencies are 33.61 % and 24.37 %, respectively, while the maximum daily combined power and heat outputs can reach 253.86 kW. Finally, LCOE model is established for heat and power economic analysis, and the results show that the LCOEs of electricity and steam are 0.048 $·kWh⁻¹ and 30.1 $·ton⁻¹, respectively. This work can provide some inspiration and assistance for the design of the novel and high-efficient full-spectrum solar energy utilization system.