Optical Efficiency of Linear Fresnel Reflectors in Fixed, Variable and Optimal Distance between Mirrors: Theoretical and Experimental Studies

In linear Fresnel reflectors, field arrangement has a significant effect on optical efficiency. Three constant, optimal, and variable distance layouts are proposed for Fresdemo solar power plant. The study was carried out by simulation and experiment. The small-scale Fresnel concentrator was designed and built with the capability to implement these three arrangements. The optical efficiency of the solar power plant with optimal variable and constant gap between mirrors were compared, considering fixed conditions for all layouts, including overall dimensions of the plant, width, and number of mirrors and dimensions of the receiver. It was observed that the arrangement with the optimal variable, and fixed distance had the highest to the lowest energy efficiency. Besides, the mirrors farther from the center entail more losses due to the sharper tilt angles, hence more spaces between these mirrors is required to reduce the losses. Meanwhile, the last mirrors in fixed distance arrangement have severe losses of shading and blocking while, they produce almost the same energy as central mirrors in the optimal and variable distance arrangement. The experimental results of the developed prototype showed that the thermal efficiency for the optimal distance was the highest, while it was followed closely by variable distance arrangement. The fixed distance arrangement had the lowest thermal efficiency. In addition, the variable and optimal distance arrangements exhibited an efficiency of 54% and 55%, respectively.