Internally shielded receivers for parabolic trough solar concentrators operating with supercritical carbon dioxide: Analytical assessment

Abstract

An urgent need to enable the operation of parabolic trough concentrators at higher temperatures for higher efficiency of the coupled power cycles is manifested in the state-of-art literature. Supercritical carbon dioxide is a promising fluid for the next generation of these concentrators. However, the inflated radiative thermal losses at elevated temperatures are the main challenge, and the relatively large absorber diameters are questionable for supercritical pressures. This study proposes a novel 1-D analytical model, coupled with Monte Carlo ray tracing, for evaluating internally shielded receivers based on the absorber tube’s diameter and eccentricity, the heat shield’s opening angle, as well as the operating conditions. The results suggest that increasing the tube diameter reduces the performance dependency on tube eccentricity, but also reduces the optical performance. Shielding the receiver is favorable for opening angles up to 160°. The impact of operating pressure is marginal, compared to flow rate and temperature. A shielded receiver with an opening angle of 160°, eccentricity of −10 mm, and tube diameter of 50 mm maximizes the exergy efficiency up to 45.9%, whereas a receiver with corresponding values of 80°, −15 mm, and 80 mm, respectively, maximizes the energy efficiency up to 77.2%. Shielded receivers also boost the efficiency by up to 10.6%, compared to conventional 70 mm receivers. These performance enhancements are expected to elevate the efficiency of the integrated systems with minimal economic and environmental impacts due to the simplicity of the proposed solution.