STUDY OF KINEMATIC SYSTEM FOR SOLAR TRACKING OF A LINEAR FRESNEL PLANT TO REDUCE END LOSSES

Linear Fresnel Plants are composed of flat mirrors that reflect direct radiation towards a fixed receiver tube parallel to the reflectors. In traditional plants, mirrors are able to rotate around a single axis. This type of solar tracking system generates high losses at its ends. In the paper a new configuration is studied in which the mirrors placed at the ends are moved around two axes. The proposed system is thus able to recover the direct radiation which, otherwise, would not reach the receiver tube. The rotation of the mirrors is managed by stepper servomotors. They allow a robust solar tracking, not influenced by external forces. The work presents the kinematic system for moving the field of mirrors actuated with open loop control. Stepper motors generate a motion by steps; in order to execute each step at the exact moment, the logic of movement is properly defined. It is necessary to know in detail the temporal position and the law of motion for each rotation to identify the driving logic of the motors. The behaviour of the "electric motor - mechanical system" is numerically modelled, evaluating the torque and the errors in the motion.