Analysis of the image produced by Scheffler paraboloidal concentrator

Abstract

Our purpose is to help projects of receivers for Scheffler concentrators in order to avoid losses of energy at the entrance of thermal radiation absorbers. The Scheffler concentrator is a paraboloidal solar concentrator that works in a two axes track system and, thus, maintains the focal image fixed in its stopped absorber with the variation of the solar declination and azimuth. The image formed by Scheffler concentrator is presented. The reflector geometry is defined by a lateral section of a paraboloid and its reflector has elliptical profile. At equinox, these rim angles are approximately 49.6 and 109.6 degrees from the paraboloid axis. However the tracking system for adjusting to the variation in solar declination causes a change in these rim angles. An analysis of the effect of these variations over the image of the focus, the aperture area to the Sun, and the concentration ratio is performed. The effect of the variations of rim angles was found to cause variations in the size of the focal image ofScheffler reflectors in two axes, and these variations differ among these axes. Were also found that the aperture area can vary twice, and, the concentration ratio, once during the year.

Stationary point focus solar concentrators—A review

“…Since the Sun makes a cone of angle 0.54 at every point on the reflector surface, the reflected rays from these points also form a cone resulting in an elliptical image at the focal plane. 30 The reflected light cone from the topmost point E1 envelops the images created by the light from all other points.…”

Combined use of volumetric expanders and Scheffler receivers to improve the efficiency of a novel direct steam solar power plant

“…38 Solar rays trace a cone with an angle 2θ s , with θ s ≈ 0.27 on the surface of the Earth. 39 The image on the focal plane perpendicular to the center line of the reflected ray will ideally assume an amplitude Δr given by Equation (12), where p is the distance from the generic point R x R ,y R ð Þon the surface of the concentrator to the focal point F as shown in Figure 2 40 :…”

Technical analysis of an oven with coupled receiver for scheffler solar concentrator tested under cloudy weather conditions

“…The effects of aperture area variations in the focal image size were studied mathematically by Dib and Fiorelli (2015), and by photogrammetry and Ray Tracing by Ruelas, Pando, Lucero, and Tzab (2014) Ruelas, Palomares, and Pando (2015). Considering a perfect concentrator and perfect tracking system, Dib and Fiorelli found that the variations in aperture area reach the limits of +37% and -38% between both solstices, and when the image is smaller, the aperture area is larger and the concentrated ratio is highest.…”