Solar Tracking System for a Linear Fresnel Plant with Two Degrees of Freedom Reflectors.

The mirrors of a traditional Fresnel system are moved with a tracking system that allows rotation around a single axis. However, this type of movement in the LFR generates high losses at its ends. The paper aims to study a configuration in which the primary reflectors that generate the aforementioned losses are made movable around two axes to increase the efficiency of the plant. The work presents the kinematic system for moving the field of mirrors in which the control of solar tracking is carried out with the open loop technique. From a constructive point of view, the mechanical components necessary for the purpose are identified. To allow a robust solar tracking, not influenced by external forces, the rotation of the mirrors is managed by "stepper" type servomotors. In particular, the use of the aforementioned motors generates a motion by steps, of which it is necessary to know in detail the temporal characteristics and the driving logic of the motors. The behavior of the whole set of "electric motor - mechanical system" will be modeled numerically in order to define the control logic of the servomotor that allows the execution of the steps at the right moment, evaluating the torque and the errors in the motion. In fact, the adoption of too small pitches improves solar tracking but needs the presence of a complex reduction system, with numerous gear wheels, which requires too high torque values.