Linear Fresnel Plant with Primary Reflectors Movable around Two Axes

In Linear Fresnel solar concentration systems, in addition to the main thermal losses due to convection and radiation, there are some energy losses due to the arrangement of the primary reflectors. An important loss of geometric type is caused by the fact that the primary reflectors have only one degree of freedom. Therefore, the accuracy of the solar tracking, at the ends of the collector, cannot be guaranteed. The phenomenon, in these types of system, is accentuated by the considerable distance to which the absorber must be placed with respect to the reflectors. The latter problem could be solved by making the primary reflectors placed at the ends of the plant movable around two axes. In the work, the mathematical law has been obtained, in an analytical way, for the determination of the position that each of these reflectors must assume at every moment of the day. The study shows that they must be moved independently in each direction. For the purposes of reducing the cost of the plant, a configuration was studied in which, around an axis, the reflectors are moved with a single motor, differentiating the movement only around the other axis of rotation. Thanks to the presence of the secondary reflector, the tracking error committed with this simplification is not significant. Finally, the advantages, in terms of performance, obtained thanks to the adoption of the above-mentioned reflectors, both for plants oriented in the North-South direction, and for plants oriented in the East-West direction, are illustrated.