The rapid surge in the global energy demands and the growing environmental degradation concerns has forced the world to pay attention to renewable energy. Solar energy is widely used renewable energy, and parabolic trough solar collector (PTC) is the most economically feasible and promising technology for solar power concentration. A typical PTC consists of a receiver tube and a parabolic reflector for facilitating the optical-thermal conversion. Therefore, PTC is critical in determining the cost and overall performance of the solar system.
Recently, extensive studies have been conducted to improve the performance of PTC using various methods, especially numerical and integration methods. The studies have been extended to improve the photo-thermal properties and coupling performance of PTC systems. Notably, various errors that commonly emanate from the practical installation and operation of solar can deteriorate the performance of PTC systems if not controlled. To this end, studying and understanding the effects of different errors associated with PTC systems have drawn significant research attention.
Despite the remarkable progress, most studies have focused on the thermal and optical properties of PTC and the structural performance of the absorber tube under designed conditions. However, there is limited research on the effect of reflector installation-related errors on the performance of PTC absorber tubes. These errors are due to the deviation between the actual position where the reflector is installed and the design position. Its effects include inducing high thermal stress that could overheat the absorber tube and causing drastic changes in the distribution of the energy flux on the surface of the absorber.
To address this research gap, Dr. Bin Yang, Dr. Shuaishuai Liu, Dr. Ruirui Zhang and Dr. Xiaohui Yu from Hebei University of Technology studied the influence of the reflector installation errors on the thermal and optical performance of PTCs. A three-dimensional (3D) optical-thermal numerical model based on Finite Volume Method (FVM) and Monte Carlo Ray Tracing (MCRT) methods was utilized to maintain PTC safety. The feasibility and robustness of the proposed model were verified by exploring the heat flux distribution and comparing the numerical and experimental results. The work is currently published in the journal, Renewable Energy.
The research team showed that the reflector installation error significantly reduced the optical and collector efficiency. The bilateral error with the geometry of θright = 7 mrad significantly degraded the optical-thermal performance of the PTC. For reflector installation errors greater than 7 mrad, the collector and optical efficiencies induced by the bilateral installation error decreased faster with when the installation error increased compared to that caused by the unilateral installation error.
When the bilateral installation error was increased from 7 to 14 mrad, the absorbed solar energy by the heat transfer fluid and the collector efficiency approached zero for an installation error of 12.2 mrad. Moreover, higher errors could reduce energy received and PTC efficiency. It could also cause local overheating of the receiver, which not only deformed the receiver but also shortened its service life. By keeping the installation error below 7 mrad, optical and collector efficiency of about 82.61% and 68.22%, respectively, as well as the overall PTC performance, could be effectively maintained.
In summary, the study proposed a 3D MCRT-FVM coupling model to study the complex energy transfer and influence of the reflector installation errors on the performance of the PTC system. The results showed the importance of avoiding installation errors as much as possible as a vital way of enhancing PTC performance. In a statement to Advances in Engineering, the authors explained their study provided important findings that would advance solar energy harnessing and utilization across different industries.
Yang, B., Liu, S., Zhang, R., & Yu, X. (2022). Influence of reflector installation errors on optical-thermal performance of parabolic trough collectors based on a MCRT – FVM coupled model. Renewable Energy, 185, 1006-1017.