Net energy assessment of front water spectral splitters in concentrated photovoltaic/thermal systems

Concentrated photovoltaic/thermal (CPV/T) systems employing spectral splitting have attracted considerable attention because they enable simultaneous electrical and thermal energy production. However, most previous investigations primarily focused on optical and thermal performance while neglecting the influence of hydraulic pumping power and coolant residence-time constraints on the overall net energy balance. The objective of the present work is to develop a comprehensive coupled opto-thermo-electrical-hydraulic framework for evaluating the net energy performance of a CPV/T system incorporating a front-facing pure-water spectral splitter and to compare its performance with that of a conventional back-cooled configuration under identical operating conditions. The proposed model combines wavelength-dependent Beer-Lambert optical absorption, a spectrum-based photovoltaic electrical model, conjugating heat transfer within the PV/T receiver, and hydraulic pumping-power calculations based on the Darcy-Weisbach formulation while enforcing residence-time constraints to determine feasible operating conditions. System performance is assessed using electrical power, thermal power, photovoltaic efficiency, outlet temperature, hydraulic pumping power, and the proposed Net Utilization Factor (UF_net). The analysis reveals a distinct performance inversion. At low coolant flow rates (< 0.1 kg/s), the water-splitter configuration becomes heat-capacity limited, resulting in higher PV temperatures than the conventional back-cooled system. Beyond this threshold, enhanced thermal recovery enables superior overall performance. At a concentration ratio of 10, the maximum UF_net increases from approximately 0.63 to 0.84, corresponding to a 33% improvement, while the positive-energy operating envelope extends by approximately 15% before hydraulic pumping losses dominate. These results demonstrate that pure-water spectral splitting represents a promising approach for integrated CPV/T poly-generation systems when hydraulic operating conditions are properly optimized.