David Strachala

Effect of negative potential on the extent of PID degradation in photovoltaic power plant in a real operation mode

Abstract This paper deals with Potential Induced Degradation (PID) of p-type monocrystalline PV modules (Evergreen) from a photovoltaic power plant that has been in operation mode for 7 years. Within the PV module affected by the PID degradation, the effect of the electric field on individual PV cells is studied. The distribution of the electric field was simulated by SolidWorks software. The results show a random distribution of affected PV cells not related to the size and distribution of the electric field intensity. Furthermore, the dependencies of negative voltage potential on the range of PID degradation of individual PV modules located in the negative pole of the PV string is made. From measured current voltage characteristics (measured at STC), it is evident that the value of negative voltage potential is not directly proportional to the PID occurrence. These results are supplemented by electroluminescence images which confirm this finding.

Rheological Properties of Heat Transfer Liquids for Solar Thermal Systems

This article discusses the rheological properties of heat transfer fluids used in all year round solar systems. Four commercially known media were measured. Two of them were glycols based media and two of them alternative heat transfer fluids based on glycerol. Parameters of viscosity and density were measured in a wide range of temperature. Measured dependencies were mathematically approximated by Vogel-Fulcher-Tammanovou equation that very accurately describes their shape. The temperature coefficient of volumetric expansion β is another parameter of heat-transfer fluids described in this article. β plays a very important role in the construction of the solar system. The last parameter determining the year round operation is the freezing point. Freezing point was measured by the cryoscopic methods.