Optimum aperture size and operating temperature of a solar cavity-receiver

For solar cavity-receivers operating at high temperatures, the optimum aperture size results from a compromise between maximizing radiation capture and minimizing radiation losses. When the absorbed solar energy is utilized as high temperature process heat, the energy conversion efficiency can be represented as the product of the energy absorption efficiency and the Carnot efficiency. We describe a simple, semiempirical method to determine the optimum aperture size and optimum operating temperature of a solar cavity-receiver for which its energy conversion efficiency is maximum. Such optimization strongly depends on the incident solar flux distribution at the aperture plane of the receiver. We analytically examine the case of a Gaussian distribution of the incident power flux, and we compare theoretical results with the results obtained when using an optically measured flux distribution. Using Monte-Carlo ray tracing, we further investigate the influence of sunshape on the optimal parameters of a cavity-receiver in a paraboloidal concentrator.