Experimental Characterization of a Revolved Compound Parabolic Concentrator for Enhanced Optical Capture in Solar Thermal Receivers

This article presents the outdoor experimental characterization of a revolved compound parabolic concentrator (CPC) as a passive secondary optical element for compact central receiver concentrated solar power (CSP) systems. The development of supercritical CO2(sCO2) Brayton power cycles, which target thermal efficiencies approaching 50% but require receiver outlet temperatures exceeding 700∘C, place enhanced demands on optical concentration at newer, more compact receiver apertures. A prototype CPC with a 31.5 deg acceptance half-angle was fabricated from electropolished 6061-T6 aluminum and integrated with multi-element BPW34 photodiode arrays coupled to custom transimpedance amplifier circuitry. Two-stage outdoor characterization was performed: (1) surface reflectivity measurement using a collimated laser source, yielding a surface reflectivity of ρ=0.716±0.022 across 24 sampled locations of the reflective surface, and (2) angular concentration mapping via a motorized rotation stage sweeping 0–90 deg under direct solar illumination. The measured integrated energy gain was Gmeas=1.186×, with a reflectivity-corrected geometric concentration of Ggeo=1.647× against a theoretical maximum of Cideal,2D=1.93×. Peak local gain of 2.16× was observed near the design acceptance angle. Spatial analysis revealed systematic beam migration consistent with ray-transfer geometry. Sweep repeatability was confirmed at coefficient of variation (CV) = 0.20% (N = 5) and analysis of variance (ANOVA) p = 0.9997.