In this paper we investigate defects in photovoltaic modules which cause variations in output performances. Here, we concentrate on two possible ways to verify potential output power levels. Firstly, we characterise the output behaviour by measuring the amount of current at different voltage levels to obtain the I–V (Current-Voltage) and P-V (Power-Voltage) curves. Secondly, we measured the infrared (IR) emissions of photovoltaic modules by the use of synchronized thermography. From those measurements, temperature maps can be derived which indicate that the temperature rises differently in photovoltaic modules due to defects. As a result, we are able to establish quantitative and qualitative verifications of photovoltaic modules.