Detection of the voltage distribution in photovoltaic modules by electroluminescence imaging

Abstract

We introduce an approach to determine the operating voltage of individual solar cells in photovoltaic (PV) modules by electroluminescence (EL) imaging. The highest EL signal of each solar cell is proportional to its operating voltage. Moreover the sum of all operating voltages equals the externally applied module voltage. Thus the operating voltage of individual solar cells is determined from the measured EL signal. The reliability of this relation is verified by measurements on specially prepared PV modules allowing us to measure the individual operating cell voltage. The experimentally measured cell voltages are deduced with an uncertainty of ±1% from an EL image. Moreover, the operating cell voltages determined from the EL image are used to calculate the module series resistance. Comparing experimentally determined values from the operating cell voltage and the total current flowing supplied to the module with calculated module series resistances using tabulated material and typical solar cell parameters, a very good correspondence is found. Copyright © 2010 John Wiley & Sons, Ltd.

Electroluminescence imaging of PV devices: Camera calibration and image correction

“…[7,13,[24][25][26] These background images are prone to noise and STE decreasing the quality of EL images after subtraction. For consistent light conditions, both problems can be significantly reduced by taking at least two background images for different exposure times as input to solve ( ) = • + .…”

“…Is was found suitable for qualitative analysis including identification of shunts, pre-breakdown sites, cracks, broken fingers and interconnectors. Quantitative analysis is also possible for effects such as diffusion length, local voltage and series resistance mapping for cells [2][3][4][5] as well as modules [6,7].…”

Mechanically stacked 4-terminal III-V/Si tandem solar cells

“…Yet, this approach idealizes the actual flat field and ignores the individual pixel deviation. Other methods image a 'homogenous' light source at short distance and out of focus of the camera [7,26]. It was reported that even a high resolution LCD flat panel emitting red light at 612 nm can be sufficient for measuring CdTe solar cells with a recombination peak at around 850 nm [28].…”

“…STE statistics and removal using a conditional minimum is detailed in [23]. [7,13,[24][25][26] As for EL images, these background images are prone to noise and STE decreasing the quality of EL images after subtraction. Both problems can be significantly reduced by taking at least two background images for different exposure times as input to solve ( ) = • + .…”

“…Is was found suitable for qualitative analysis (e.g. detection of shunts, pre-breakdown sites, cracks, broken fingers and interconnectors) as well as quantitative analysis (diffusion length, local voltage, series resistance mapping) for cells [2][3][4][5] as well as modules [6,7].…”