Tools for experimental evaluation of the precision of an automatic tracking system for concentrating solar plants
S. Barotti, L. Castiglioni, M. De Chirico,
"Tools for experimental evaluation of the precision of an automatic tracking system for concentrating solar plants",
Proceedings of the Solar Energy Tech 2010,
8th July 2010, Milano, Italy, pp.45-54,
ISBN 978-1-4467-3765-1
Abstract:
To ensure good performance in a concentrating solar plant (CSP) based on Fresnel technology, is essential to build a very high precision tracking system. The overall system performance is mainly influenced by the error in positioning the mirrors; this error is due to the imprecision of the algorithm used to detect the position of the sun added to inevitably inaccuracies and backlash of the kinematic chain used to move the mirrors.
In the examined project, to validate the used tracking system, a low cost and high resolution sensor was considered in order to measure the overall accuracy of the system in terms of angular error between the light beam reflected from the mirror and the target angle.
In literature, sensors designed for Fresnel plants that are used to measure the distribution of the light radiation on the collector tube are described, however, these systems are very expensive and need a complex image processing algorithm to measure the reflected beam position. It was therefore decided to test the feasibility of a sensor using low cost components available on the market in order to detect the positioning error of a mirror with a resolution of 0.15 mrad.
To this end we conducted a theoretical study of the shape of light beams reflected by the mirrors used in this plant and then we tested and evaluated different photosensitive elements and identified the best suited for the particular application. After this first test step was then possible to identify the most appropriate geometry of photosensitive elements according to the resolution target and was developed an algorithm to process the signals acquired in order to identify the positioning error of the mirror.
The result of this research was the creation of a low-cost sensor that has been tested and validated in different lighting conditions and integrated in the automation and control suite eXPert of SDI Automazione Industriale, the sensor was capable of measuring the error with a resolution of 0.15 mrad.
The operating principle of the sensor, designed for Fresnel systems, can be easily extended to the measurement of the position of the beam in all concentrating solar systems that require high precision.
Keywords:
Fresnel, sun tracking systems, concentrating solar plants
References:
Kalogiru,S.A.:Design and construction of a one-axis sun-tracking system. Solar Energy. 1996. Vol. 57, 6, pp. 465-469
Optoelettronics, PerkinElmer. Photoconductive Cells and Analog Optoisolators