87The realization of a simple solar tracking concentrator for university research applications

R.Y. Nuwayhid et al. / Renewable Energy 24 (2001) 207–222
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the two areas is the concentration ratio (CR). In two-dimensional concentrators (parabolic troughs for example) the focus is a line, whereas in the three-dimensional case (the parabolic dish and heliostat system) the focus is a point. In two-dimensional concentrators, the CR is relatively small, thus moderate temperatures are generated at their receivers, normally in the range of a few hundred degrees Celsius. Applications are therefore restricted in this temperature range to water distillers, heating circuits and power cycles using relatively large areas. On the other hand, in threedimensional concentrators where high CRs are achievable, temperatures at the receiver could reach several thousand degrees. Concentration ratios of up to 50,000 have been reported for relatively large-sized parabolic systems [2]. With threedimensional systems power generation could be quite feasible even at moderate scales. Candidate heat-engine cycles include Stirling, thermoelectric or possibly Rankine-type or Brayton-type cycles. However, at very elevated temperatures it takes little insight to realize that the best application ought to be one that makes the most technoeconomic use of the high-quality heat collected at some effort and expense. High-temperature chemical reactions producing valuable products are an example of such applications [3]. It is not easy to identify candidate chemical reactions, but an example is the limestone decomposition reaction that is of importance in the cement industry [4]. A serious challenge in concentration remains the cost and effort required in full solar tracking. It makes little sense, for example, to track the sun in order to produce, say, 50 W of power or 50°C hot water that could be simply and cheaply obtained from flat collectors. Thus one can either find a suitable application or attempt to significantly reduce the cost of concentrator systems. The proposed project addresses a reasonably low-cost fully tracking system with feedback control. This will be tackled by first looking at the concentrator surface (the dish), followed by the tracking mechanism and control. Simple test runs are conducted to assess the performance of the system.
Nomenclature is the latitude of the location of the site (Beirut), i.e. the angle between the line drawn from the earth center to the location and its projection on the equator plane. is the longitude of the site. Greenwich is 0°. LLoc a is the solar altitude, the angle between the sunray and the horizontal plane of the sight. n is the day of the year. d is the declination, that is the angular position of the sun at solar noon (the highest position of the sun in the sky at a given day) with respect to the plane of the equator. North positive, and varies between Ϫ23.45° and +23.45° and could be calculated roughly by the equation d=23.45 sin(360/365×(284+n)). w is the hour angle, that is the angular displacement of the sun east to west of the local meridian due to the rotation of the earth. It is set to vary 15° per hour, morning negative, noon is 0° and positive in the afternoon. is the solar azimuth, that is the deviation of the projection of the gs sunrays on the horizontal surface and the local meridian (north to south line). Zero due south, east negative, west positive, depending on the season but roughly varies between +180° and Ϫ180°. Zenith is the point directly upwards, that is a perpendicular line to the horizontal plane at location and a point in the sky. q is the angle of incidence, that is the angle between the normal to the concentrator plane and the beam of radiation (ray from the sun). In a concentrator this is to be minimized. g is the surface azimuth, that is the angle between the projection of the normal to the concentrate plane to the horizontal and the local meridian. Apply the same conventions of the solar azimuth, with regard to signs. b is the angle between the surface and the horizontal. L
0960-1481/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 0 - 1 4 8 1 ( 0 0 ) 0 0 1 9 1 - 9
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R.Y. Nuwayhid et al. / Rnewable Energy 24 (2001) 207–222 www.elsevier.nl/locate/renene
The realization of a simple solar tracking concentrator for university research applications
Abstract A tracking parabolic concentrator was built from easily available and affordable components. Simplicity and ease of assembly were prime considerations. Considerable experience was gained in the design, assembly and testing. The system performed reasonably well considering its simplicity and rapid assembly. As an educational tool, demonstrating both energy conversion and control, or for simple high temperature experiments and applications, any university could easily set up a similar working concentrator at a very low cost. 2001 Elsevier Science Ltd. All rights reserved.