Characterization of optical losses due to tracking systems on a linear solar thermal concentrator
- Autores: Fabienne Sallaberry
- Directores de la Tesis: José Luis Torres Escribano (dir. tes.), Ramón Pujol Nadal (codir. tes.)
- Lectura: En la Universidad Pública de Navarra ( España ) en 2015
- Idioma: español
- Tribunal Calificador de la Tesis: Adolfo de Francisco García (presid.), Almudena García Gorostiaga (secret.), Loreto Valenzuela Gutiérrez (voc.)
- Materias:
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- Resumen
Solar thermal energy is able to provide a considerable fraction of the current and future energy demand in both, industrial and domestic sectors. This fact is reflected by the growing interest during the last decade in the design of new solar collectors in order to satisfy the increasing heating demands.
For a wide range of operational temperatures, solar collectors can use optical concentration systems to optimize their efficiency. However, as optical concentration relies on beam radiation, it is necessary to use a solar tracker following the sun direction to maximize the amount of useful solar radiation received.
The selection of the appropriate tracking systems matching the optical concentration factor is essential to achieve an optimal collector efficiency. Otherwise, the concentrator will experience high optical losses due to the inadequate focusing of the beam solar radiation onto its receiver, regardless of its quality.
Even though the concentrating solar collectors are mentioned in the International Standards, the general testing methods cannot always be easily applied to unusual collector designs. Moreover, those testing methods consider the solar tracker as part of the solar collector so they do not characterize the impact of its precision on the overall efficiency.
For those reasons, this thesis aims to contribute to the improvement of tracking errors estimation on single-axis solar trackers on a solar thermal collector, in particular linear through collectors. And therefore, it also aims to estimate the optical losses resulting from the tracker. This study consisted in the three following stages: First, a testing procedure was defined for solar trackers by adapting a testing method from an International Standard for photovoltaic double-axis trackers. The experiments were carried out using a simple procedure to determine the tracking elevation error.
Second, the optical characterization of different concentrating solar collectors was performed through simulation and experiment. The optical behavior of the concentrator aimed to determine the dependency of its efficiency to the angular tracking error. For the simulation, a ray tracing program was employed, and for the experiment some tests of the collector optical efficiency were carried out. A good agreement was found between the simulation and the experimental results considering the measurement uncertainties.
Third, the long-term optical losses due to the tracking error were estimated using the transversal incidence angle modifier obtained previously by ray-tracing simulation or by experiment, and the tracking errors distribution estimation. The impact of the maximum tracking error angle upon the optical efficiency has been determined on different concentrating/tracking collector types.
Finally, this thesis describes the points defined in the International Standards that should be improved in order to ascertain the influence of the tracking on the overall efficiency of concentrating/tracking solar collectors. Some points have been proposed for a future Standard testing procedure on trackers for solar thermal collectors.
