Structured Light Profilometry on m-PTC

Abstract

In concentrating solar systems, it is essential to study the optical losses of the collectors. A fundamental parameter is the intercept factor, namely, the fraction of sunrays reflected by the concentrator that reaches the receiver. Optical profilometry studies the relationship between the collector profile and the intercept factor, which influences the collection efficiency. Profilometric analyses were performed on a micro-parabolic trough collector (m-PTC), with reduced sizes and greater mirror curvature than a usual PTC. The proposed technique projects a luminous pattern (structured light) both on the collector with an opaque covering and on a flat reference plane. Measurement set-up and calibration technique were developed for m-PTC. A program coded in Python analyzed the images and reconstructs the mirror profile. The tilted reference plane was reconstructed using an original geometric model and a calibration procedure. The focal length of each parabolic section was calculated, providing information on surface defects in the mirror. An important parameter obtained was the displacement of the focus of the parabola with respect to the ideal position. Using this value, the intercept factor was estimated to be 0.89. The proposed technique was validated by comparing the results with an independent profilometric study applied to the same m-PTC.

Laser Profilometry on Micro-PTC

“…The global intercept factor is calculated averaging the values of the local intercept factor, giving a value of 0.91. This value is consistent with a measurement on the same object obtained with a different technique [33].…”

“…It is worth noting that this value only considers the profile contribution to this factor and the receiver tube is assumed to be in the ideal position. This value is in agreement with the results obtained with a measurement performed using a different technique on the same object [33]. If the solar half angle of 0.27 • at the earth's surface is taken into account in the calculation of the intercept factor, the value is 0.89.…”

“…The reconstruction of the mirror is reported in Figure 13a. The points of the reconstruction are not continuous, as happens with the structured light technique [33], but they are at a distance equal to the step of the scanning.…”

“…A new prototype of micro-PTC was optically designed, realized, and tested [30][31][32][33]. The micro-PTC was successively utilized for the realization of a concentrated solar power plant.…”

“…In Ref. [28], two methods were briefly introduced without details, then the authors proposed to use structured light profilometry (SLP) [33], adapting the fringe projection for this m-PTC. The SLP technique is fast and allows to examine the entire m-PTC in a unique measurement.…”