A NONTRACKING, CYLINDRICAL SOLAR CONCENTRATOR WITH CIRCULAR CROSS-SECTION - THEORETICAL AND EXPERIMENTAL-ANALYSIS

This paper presents a theoretical and experimental analysis of a non-tracking, cylindrical solar concentrator with circular cross-section of radius R. The focal length of the concentrator oscillates between 0.5R and 0 with decreasing amplitude as the rim angle increases from 0 to 90 degrees. The dependence of local area-concentration on rim angle, and on distance from the cylindrical axis along the radial focal line is investigated. Based on the analysis, the circular cross-section of the concentrator is designed to have a rim angle of 45 degrees, and beyond that the reflector surface is a plane mirror extending tangentially up to the 60 degrees rim angle-chord of the circle. The concentrator has a half-linear aperture to maximum focal length ratio of 1.83, and the average concentration ratio in the focal plane is 4.4. Recommendations for the size, shape and placement of the absorber are made. Experimental investigations show that the concentrator is not very sensitive to the deviation of the Sun's rays, and needs adjustment to its orientation at intervals of one-half to one hour as against the continuous tracking for high concentration devices. The performance of the concentrator is compared with that of an analogous parabolic concentrator. These concentrators are best suited for applications in remote, rural areas of developing countries where lack of technical skill and financial resources prohibits the use of technically sophisticated and expensive devices. They can be manufactured inexpensively from indigenous materials, thus generating employment opportunities among rural communities.