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Johannes Waclawek:
"Entwicklung und Charakterisierung eines Photovoltaikmoduls optimiert für schwachen Lichteinfall";
Betreuer/in(nen): J. Summhammer; Atominstitut, 2012; Abschlussprüfung: 13.07.2012.

The aim of this diploma thesis was the development and characterization of a photovoltaic module optimized for light incidence at weak intensities. The optimization of a module for faint light irradiation conditions was achieved by optimizing the line pattern of the current approval on the frontside of a solar cell.
For this purpose an optimized design of the forefront metallization was calculated and subsequent modules were manufactured and measured over several months at a real location, while being compared to standard modules. The measurement was done automatically by means of an electronic circuit [designed by the author] and a software program [written by the author] for controlling the electronics and for storage and analysis.
What must be considered when optimizing solar cells to accommodate low levels of light irradiance is that global solar irradiance values of 1000 Wm-2 at latitudes such as those in Austria are very infrequently reached within a year. The standard design of commercial photovoltaic modules are optimized for such irradiation conditions (standard test conditions). Since approximately 65 % of hours of light per year exhibit low levels of global irradiance (region Vienna), namely, up to 300 Wm-2, a module optimized for light incidence at weak intensities should provide a higher
yearly yield compared to a standard module.
In order to optimally use the irradiated light for the production of electron-hole pairs, the shadowing effects at the front side of the solar cell by the disturbed metallization process should be as low as possible, that is to say very thin fingers and busbars should be available. To this end arises the need to keep ohmic losses from the emitter´s coating low, preferably low resistance- and contact losses in and at the fingers, as well as low serial resistance losses from the busbars. In determining a suitable design for the forefront metallization optimized for light incidence at weak intensities, the multi parametric problem needed to be solved.
The optimization of the pattern for low global irradiance was carried out by calculating the single power losses of the forefront metallization of two different designs (one and two busbars respectively) and for different irradiation conditions. The calculation of the yields was carried out by means of measurement data for global and diffused irradiance taken by the meteorological station Wien Hohe Warte during the period 2001 - 2010 [provided by the Zentalanstalt fürr Meteorologie and Geodynamik]. In this way a modified design of the standard cell with a lower number of fingers was created, which showed a higher absolute and specific yearly
yield in comparison to the standard module. The calculation of the total power losses and of the yearly yield shows that cells optimized for an irradiation of 300 Wm-2 theoretically provide a 0,24 % higher yearly yield and a 1,93 % higher specific yearly yield in comparison to the standard design. For this determined design a layout for the screen print was drawn. The cells were produced by the
Falconcell company, the modules were manufactured by the PVT-Austria company.
The characterization of the manufactured Modules was carried out by an automatically continuous current-voltage-measurement over 106 days in the period from September 2011 till February 2012, while being compared with standard modules. For this purpose a total of four modules were mounted on a roof (two modules optimized for light incidence at weak intensities and two standard modules). The
IU -characteristics of each module were measured approximately every one and a half minutes. From these measurements, typical values for characterization were taken. The results of the analysis of the test reading show that the highest absolute yield achieved in this period - in contrast to the theoretical prediction - was achieved
by the standard modules. They showed an average increase of 2,32 % in comparison to the modules optimized for light incidence at weak intensities. However, the optimized modules achieved a higher average specific yield. It rose about 2,03 % above those of the standard modules.
A possible explanation for the difference in the yield between the theoretical calculation and the practical measurement of the modules is that the modules optimized for light incidence at weak intensities were worse than advance predictions due to
the fact that the number of cells produced was quite low. Since not very many cells were produced, it was not possible to separate them into narrow current classes. Because of the high dispersion of the cell current within one module, within this module it became more likely that some cells had a reduced short-circuit current, thus decreasing the efficiency of the whole module.
The specific increase of the optimized modules corresponds, however, very closely to the theoretical prediction. This underlines the general accuracy of the consideration taken when designing the cell optimized for light incidence at weak intensities.
This work shows the theoretical potential for increasing the absolute yield of a photovoltaic module by optimizing the front pattern to account for irradiation conditions throughout the year, tailored specifically for locations with a light incidence at lower intensities. Through the production of a high number of optimized cells, modules with a lower dispersion of the cell current could be completed. Consequently these modules should deliver a higher absolute yearly yield in comparison to the standard
design.

photovoltaic module, solar cell, energy yield