A new in-situ moisture monitoring technique for photovoltaic (PV) modules is proposed using miniature digital humidity and temperature sensors. The sensors were embedded in three different ethylene-vinyl-acetate (EVA) stacks and proved to be resistant to lamination conditions. The fact that they are in direct contact to EVA does not affect their performance, since their saturated relative humidity (RH) reading is proportional to the external RH in the air. By exposing the sensors to elevated temperature and RH conditions, water vapor transmission rate of the backsheet and diffusion coefficient of the EVA can be determined. Obtained coefficients agree with reference values within their measurement uncertainties. Besides determining material moisture ingress properties, this monitoring technique is also applicable for long-term outdoor PV module monitoring. It shall provide valuable location and installation specific information of RH and temperature stress conditions, especially as feedback information to manufacturers of materials and PV modules.
COBISS.SI-ID: 11601748
Extremely bright electroluminescence (EL) inhomogeneities are observed in cadmium telluride (CdTe) photovoltaic (PV) devices. Small circular laboratory CdTe cells and commercially available CdTe PV modules are inspected with EL at different temperatures. The phenomenon appears as bright ring around the cells, and as bright lines along and bright dots at the end of the monolithic contacts of the modules. The areas of the devices that exhibit the phenomenon correspond to the areas where the local applied voltage is the highest. The exact shape of the phenomenon appears grainy and may be defined by the grainy structure of the CdTe. The effect is present on devices when the temperature of the devices is below a certain threshold (around 30 °C in our case), and when the applied forward bias is high enough (around one half of the short circuit current). The results suggest that the phenomenon may be correlated with either temperature or voltage break down of the back contact barrier which exists between the CdTe and the metal back contact.
COBISS.SI-ID: 11472468
A unique non-destructive characterization method for apparent bandgap imaging in photovoltaic (PV) devices based on acquisition of two electroluminescence (EL) images in different spectral ranges is presented. The method consists of a calibration procedure and a bandgap imaging procedure. Calibration has to be performed once per module type and EL imaging setup, and must provide a relation between the bandgap and the ratio between two spectrally independent EL images. After calibration, bandgap imaging only requires acquisition of two spectrally independent EL images followed by image processing, making the method very fast and suitable for in-line PV module characterization with regard to spatial (in)homogeneity and production process stability. The method is demonstrated on a commercial state-of-the-art Cu(In,Ga) Se2 PV module where apparent bandgap fluctuations between 1.07 and 1.15 eV are detected.
COBISS.SI-ID: 11645780