Concentrating solar power, particularly parabolic trough system with solar concentrations less than 50, requires spectrally selective solar absorbers that are thermally stable at high temperatures of 400°C above to achieve high efficiency. In this work, the solar-thermal energy conversion performance of a selective multilayer metafilm absorber with excellent thermal stability is characterized along with a black absorber for comparison by a lab-scale experimental setup that measures the steady-state absorber temperature under multiple solar concentrations. Heat transfer analysis is employed to elucidate different energy conversion modes and validate the solar-thermal experiment. The solar-thermal efficiency was measured to be 38% from the experiment and projected to be 86% without parasitic heat losses for the selective metafilm-on-Si absorber at the temperature of 336°C under 9.1 suns, in comparison with measured 30% and projected 55% efficiency for the black absorber at a lower temperature of 266°C under the same solar concentration. In addition, the metafilm absorber deposited on the flexible cost-effective stainless steel foil achieves the solar-thermal efficiency 57% at a steady-state temperature of 371°C under 10 suns during the lab-scale experiment with losses, while a highest efficiency of 83% was projected under the same conditions for practical solar thermal applications. The results here will facilitate the research and development of novel solar materials for high-efficiency solar thermal energy conversion.