Dionyz Gasparovsky, PhD.

Ilkovicova 3, 812 19 Bratislava, Slovak Republic
Tel.: +421 903 455 035, Fax: +421 2 654 25 826
e-mail: hung@elf. stuba. sk

Introduction

Many solar applications require temperatures higher than those that can be achieved by common flat-plate collectors. Temperatures over 100 °C are necessary e. g. for industrial process heat. Such temperatures can be obtained by means of solar energy concentrators.

Advantages of concentrating the solar radiation can bring in addition to higher temperatures also decrease in heat losses and material savings due to smaller size of absorber, if taking into account that costs for material absorber per square meter can be possibly higher than costs for e. g. concentrating mirrors. On the other hand, using the concentration, two other kinds of losses will raise: losses of diffuse radiation and optical losses.

There exist a variety of solar energy concentrators for different purposes. For low — temperature applications, inexpensive concentrators of diffuse radiation can be used. For these concentrators, acceptance angle 0A defines the ability to concentrate the diffuse radiation and also its concentration factor C. To this class of concentrators belongs e. g. nonimaging types like CPC (Compound Parabolic Concentrator), V-trough types, cylindrical concentrators etc.

This paper deals with development of a new type of concentrator, novel concept of which is based on functionality of CPC by means of flat mirrors, primarily designed for needs of SME’s (Small and Medium Enterprises). The CLON project is being ellaborated under the 5th Framework Programme of the EU.

Background

In many publications one can meet the solutions of solar energy concentrators, which seem to be similar to the CLON concentrator by shape, however, conceptually they are different. Analyses of those similar designes showed that their properties do not reach many of advantages of the CLON. In first order they are not single-reflecting, they have a lack of satisfactory concentration factor or they are not able to concentrate diffuse radiation.

Concepts similar to CLON are usually named as „V-trough" concentrators (with multiple mirrors), mainly in english written publications. Russian authors, who developed a variety of such designs, name the device like „Flat Focline" [1], [2], [3] (symmetrical single-mirror concentrator), „Single Focline" [2], [3] (non-symmetrical concentrator with one only flat
mirror). Device with multiple mirrors is described e. g. in [4] and [3] but only the direct solar radiation is focusable.

A common property of all the mentioned concepts is flat shape of absorber at the output area. There exist also a concept of concentrator for frontal placement of absorber [5], [6],

[7] and [8], however, this is not a concept following the principle of CPC rather a parabolic trough concentrator.

As an example, concept proposed first by Grilikhes and Zaitsev, furtherly improved by Vartanian [3] is most similar to the concept of CLON. Difference is, in fact, that this concentrator focuses only direct radiation incoming exactly at 0°. Vartanian found out the optimal angle for first zone of the concentrator to be equal to 01 = 67° 30′. Inclination angles and sizes of the rest zones can be found using the following algorithm with results presented also in table 1.

Goals

The project CLON is built upon idea of novel concept of solar energy concentration, not approximating the curvature of CPC, rather simulating the functionality of the CPC. CLON aims, in general, to the development of concentrating collector of practical output for SME’s, including three chosen installations: 1. Industrial plant (process heat), 2. Swimming pool, 3. Agriculture (drying of products).

The current stage of the project is oriented to ellaboration of the novel concept in details with creating the mathematical model of the concentrator and analyses of its properties, as a preparatory work for construction of the device and manufacturing of the prototypes. Goals of the first stage can be briefly listed as follows:

• To formulate the functioning principle of the concentrating device and its general optical scheme.

• Based on the optical scheme of well-known and well-studied type of solar energy concentrator — the CPC, to achieve the same effect of single reflecting concentration in the framework of defined angular range by the means of inexpensive flat mirrors.

• To define the basic parameters of the concentrator.

• Based on the optical scheme, to derive the graphical method of calculation of the concentrator.

• Optimalisation of graphical method and derivation of numerical method for calculation.

• Analyses of geometrical properties of the concentrator.

Further goals of the first stage include selection of materials for each of the components, detailed analyses of optical properties and mechanical model of the collector. These tasks are actually under ellaboration.