A. Antonini

Optical efficiency of solar concentrators by a reverse optical path method

A method for the optical characterization of a solar concentrator, based on the reverse illumination by a Lambertian source and measurement of intensity of light projected on a far screen, has been developed. It is shown that the projected light intensity is simply correlated to the angle-resolved efficiency of a concentrator, conventionally obtained by a direct illumination procedure. The method has been applied by simulating simple reflective nonimaging and Fresnel lens concentrators.

Monitoring of concentrated radiation beam for photovoltaic and thermal solar energy conversion applications

Methods for evaluating the light intensity distribution on receivers of concentrated solar radiation systems are described. They are based on the use of Lambertian diffusers in place of the illuminated receiver and on the acquisition of the scattered light, in reflection or transmission mode, by a CCD camera. The spatial distribution of intensity radiation is then numerically derived from the recorded images via a proprietary code. The details of the method are presented and a short survey of the main applications of the method in the photovoltaic and thermal solar energy conversion field is proposed. Methods for investigating the Lambertian character of commercial diffusers are also discussed.

Characterization of CPC solar concentrators by a laser method

In this paper we present a method of optical characterization of solar concentrators based on the use of a laser beam. The method, even though constrained by lengthy measurements, gives nevertheless interesting information on local mirror surface defects or manufacturing defects, like internal wall shape inaccuracies. It was applied to 3D-CPC-like concentrators and the measurements were supported by optical simulations with commercial codes. The method, simple to apply, requires just a laser to scan the CPC input aperture following a matrix-like path, at a controlled orientation of the beam. Maps of optical efficiency as function of the laser beam incidence angle are obtained by matching the CPC exit aperture with a photodetector with an efficient light trapping. The integration of each map gives the CPC efficiency resolved in angle of incidence, so curves of optical transmission (efficiency) as function of incidence angle can be drawn and the acceptance angle measured. The analysis of the single maps allows to obtain interesting information on light collection by the different regions of CPC input area. It reveals, moreover, how the efficiency of light collection depends on several factors like surface reflectivity, number of reflections of the single beam, local angle of incidence, local surface defects, and so on. By comparing the theoretical analysis with the experimental results, it is possible to emphasize the effects directly related to manufacturing defects.

Optical Methods for Indoor Characterization of Small-Size Solar Concentrators Prototypes

The light collection properties of different types of solar concentrators have been investigated by applying conventional and innovative methods of characterization [1, 2]. Four types of optical methods were applied: i) a “direct” method using a laser beam as light source; ii) a “direct” method using a parallel beam simulating the direct component of solar light; iii) a “direct” integral method using a lambertian light source simulating the diffuse component of solar light; iv) an “inverse” method using a lambertian light source applied at the receiver side, thereby reversing the light path. The optical properties derived by applying the above three methods were: i) the local optical collection efficiency, resolved on the entrance point and direction of incidence ii) the overall optical collection efficiency under collimated light, resolved on direction of incidence; iii) the spatial and angular distribution of flux on the receiver.

Double-cavity radiometer for high-flux density solar radiation measurements

A radiometric method has been developed, suitable for both total power and flux density profile measurement of concentrated solar radiation. The high-flux density radiation is collected by a first optical cavity, integrated, and driven to a second optical cavity, where, attenuated, it is measured by a conventional radiometer operating under a stationary irradiation regime. The attenuation factor is regulated by properly selecting the aperture areas in the two cavities. The radiometer has been calibrated by a pulsed solar simulator at concentration levels of hundreds of suns. An optical model and a ray-tracing study have also been developed and validated, by which the potentialities of the radiometer have been largely explored.

Rondine PV concentrators: Field results and progresses

In this work the experimental results of two pilot installations of 3.8 kWp and 4.9kWp of Rondine PV concentrators installed in Italy are presented. These concentrating modules have a medium concentration level (25x) and employ silicon solar cells. The non-imaging optics of the concentrator allows for larger angular acceptance respect to many CPV modules, giving us the possibility to employ trackers for standard PV modules. The effect of soiling in these first installations is evaluated as well as their working conditions in different weather situations.