LABORATORY FOR TEACHING PHOTOVOLTAICS

An introductory course on photovoltaics is an interdisciplinary endeavor involving semiconductor physics and inorganic chemistry, electrical and mechanical engineering and even economics and finances. In general, students taking these courses can arrive with very different backgrounds, experiences and motivations and therefore it is of paramount importance that the teaching approach takes into consideration all these differences. The introduction of practical exercises in the laboratory are one of the strategies to overcome these challenges. Lab work will develop better understanding of key concepts, enhance the critical analysis of the phenomena and promote team work within a heterogeneous group.
In this paper we will describe a set of experiments that have been tested, replicated and tuned in the photovoltaic course of the MSc in Energy and Environment Engineering at the University of Lisbon. The first set of experiments deals with the characterization of solar cells. Taking a lab-made solar cell, its spectral response is measured using a in-house developed setup which includes a monochromator for selecting light wavelength, a lock-in and a reference cell, for calibration. From the spectral response of the test solar cell, the students are asked to determine the expected short circuit current under standard solar spectrum (AM1.5) and under the typical spectrum of an halogen lamp. Then, the characteristic curve of the solar cell is measured in a 4-point probe based IV tracer, with temperature control and halogen illumination, also developed in-house. For that measurement, the students are asked to adjust the illumination by taking into consideration the lamp used. The final discussion of the work includes the determination of the expected ‘true’ IV curve of the solar cell under the standard solar spectrum. A second set of experiments discusses the association of solar cells and modules in series and parallel. This time, the IV curves are traced by using a variable resistance as load of the solar circuit. A simple setup using a 300W projector, multimeters and a few resistances allows the determination of the electrical parameters of the solar modules, as well a in depth discussion of the power losses due to temperature and shading.
We will present the detailed set up and procedure for these experiments and guidelines for discussion illustrated with sample data.