Marcus Zettl

Indoor Characterization of Photovoltaic Modules under Various Conditions

Usually photovoltaic modules are characterized under standard testing conditions by subjecting them to an irradiation of 1000 W/m2 with an AM 1.5 spectrum and a cell temperature of 25°C. However, not all modules perform the same under real conditions since their efficiency is strongly affected by environmental fluctuations. To get real operation data, expensive outdoor test are performed. However, for most of the new thin film technologies, these data are not available yet. The experiments were conducted in an indoor solar simulator, which fulfills the requirements of irradiation level and solar spectrum within a homogeneous area of 2 by 2.5 meters. In this contribution we compare different PV modules, including first generation, thin films and emerging technologies, in order to understand their behavior under various conditions. The modules were tested as a function of incident angle and diffused versus direct irradiation. Another aspect that is also taken under consideration is the influence of temperature on the module performance. These measurements are necessary in order to make a correct assessment of energy yield in several geographical locations for residential, commercial and utility applications.

Specific energy yield comparison between crystalline silicon and amorphous silicon based PV modules

As emerging thin-film PV technologies continue to penetrate the market and the number of utility scale installations substantially increase, detailed understanding of the performance of the various PV technologies becomes more important. An accurate database for each technology is essential for precise project planning, energy yield prediction and project financing. However recent publications showed that it is very difficult to get accurate and reliable performance data of theses technologies. This paper evaluates previously reported claims the amorphous silicon based PV modules have a higher annual energy yield compared to crystalline silicon modules relative to their rated performance. In order to acquire a detailed understanding of this effect, outdoor module tests were performed at GE Global Research Center in Munich. In this study we examine closely two of the five reported factors that contribute to enhanced energy yield of amorphous silicon modules. We find evidence to support each of these factors and evaluate their relative significance. We discuss aspects for improvement in how PV modules are sold and identify areas for further study further study.

Simulation of point light concentration with parabolic trough collector

As the amount of solar generated energy usage increases worldwide, researches are turning to more advanced methods to increase collection efficiencies and drive down system costs. In this paper, four different optical system designs for solar concentrator applications are discussed. Each of the designs studied utilizes a parabolic trough optical element. The use of the parabolic trough in conjunction with a secondary optical component eliminates the need for expensive complicated 2-axis tracking, whilst still allowing the precise point focus normally only possible with more complex paraboloid systems. The result is an optical system, which offers all the advantages of a linear focus geometry combined with the possibility to utilize point focus concentration. The results were obtained using photometric geometrical ray tracing methods. Ideal surface simulations were initially used to separate surface from geometrical loss contributions. Later, more realistic simulations, including surface and reflectivity data of typical manufacturing methods and materials, were used to compare optical output power densities and system losses. For the systems studied, the minimum and maximum optical efficiencies obtained were 76.73% and 81% respectively. The AM 1.5 solar spectrum power densities in the absorption plane ranged from 50 to 195.8Wm-2.