Thermal and electrical effects caused by outdoor hot-spot testing in associations of photovoltaic cells

An outdoor test facility has been prepared for the evaluation of the thermal and electrical effects caused by outdoor hot-spot testing in crystalline silicon modules. Five module types have been subjected to an outdoor test programme with the purpose of analysing their hot-spot endurance. The worst-case cell in each module type has been detected by laboratory characterisation under reverse-bias operation of all the individual cells included in the module. These cells, encapsulated within the module, have been operated at different shading fractions with bypass diodes around 18 or 24 cells. A data acquisition system has monitored temperatures and current flows during the day, completing the tests via infrared characterisation during the hours of maximum irradiance. The influence of the type of module, the number of cells per bypass diode, the position and amount of shading and the leakage current Of the cell is presented. This information is useful for cell and module manufacturers and system installers who must select the necessary protection criteria to guarantee long lifetimes for PV systems; it also helps to clarify hot-spot testing procedures in international standards. Copyright (C) 2003 John Wiley Sons, Ltd.