Thin Film Modules Characterization under Standard Test Conditions

Abstract

Photovoltaic modules based on the relatively new thin film technology are gaining importance in the photovoltaic market. Some of these modules are made of silicon, consisting of layers of amorphous silicon or microcrystalline silicon. Other thin film PV modules are made of CIS, Cadmium Telluride (CdTe) or less frequently organic compounds. The materials used in thin film technologies pose problems in terms of measuring how much power is generated under standard test conditions (STC). This is due to the fact that the modules´ power rates could vary depending both on the amount of time they have been exposed to the sun and on their history of sunlight exposure. So it is necessary to know the previous periods of sunlight exposure in order to know the current state of the module. It is necessary to determine an easily accomplishable testing method that ensures the repeatability of the measurements of the power generated. This is essential because in order to have a reliable sample of the PV module population of a large PV plant, a huge number of modules must be measured. This paper shows different tests performed on different commercial thin film PV modules in order to find the best way to obtain measurements. A correlation was tested between sun exposure and power measured. A method for obtaining indoor measurements of these technologies that takes periods of sunlight exposure into account is proposed. Additionally, temperature and irradiance coefficients were also determined for different technologies in order to obtain accurate measurements.