The performance of central tower solar plants is strongly dependent on the pointing accuracy of the heliostats when redirecting the solar radiation towards the receiver. Pointing errors are usually due to small misalignments in the heliostat tracking system, such as, for example, an incorrect leveling of the pedestal when it is installed in the field. Furthermore, pointing errors typically depends on time. Because of this, the reflected solar radiation travels over the receiver along the day, what is known as drift.
Drift and its possible causes have been subject of study for many years. However, all the studies have focused on heliostats with azimuth- elevation based tracking system, since they are the most common. IMDEA Energy has carried out a detailed study of all the possible causes of drift and its effects on heliostats with a tracking system based on roll and pitch. This study, that has been recently published in Solar Energy journal*, shows a catalogue of all the possible causes of drift and sorts all of them according to their impact on the field performance. The study concludes that the most undesirable factors are the lack of perpendicularity between the two axes of the tracking system, a rotation of the pedestal and its inclination along the east-west axis.
(*) Drift analysis in tilt-roll heliostats. Alejandro Martínez-Hernández, Iván B. Gonzalo, Manuel Romero, José González-Aguilar. Solar Energy, vol. 211, 15 November 2020, Pag. 1170-1183 doi.org/10.1016/j.solener.2020.10.057
More information: José González, Head of the High Temperature Processes Unit, email@example.com
a) Heliostat with tilt-roll tracking system. b) Misalignments of the tracking system. c) Misalignment of the face