Meeting the requirements of IEC TS 60904-1-2 for single light source bifacial photovoltaic characterisation: evaluation of different back panel materials

Abstract

The International Electrotechnical Commission (IEC) published a technical specification, TS60904-1-2 in 2019 to standardize both indoor and outdoor characterisation ofbifacial PV cells and modules. The indoor electrical characterisation can be performed with a single or double light source. Given the linear relationship between irradiance and short-circuit current, the effect of stray light on the non-irradiated side could generate measurement artefacts in the single light source characterisation. Hence, the technical specification mentions several procedures to carefully control the unwanted irradiance below 3 W m−2. This paper describes an approach for systematic analysis of the back panel materials through experiment and simulation to meet IEC TS 60904-1-2 requirements. First, optical properties (specular and diffuse reflection) of four different backpanel materials are evaluated. Next, using different back panel materials, the irradiance on the non-irradiated side of a bifacial module is spatially mapped out using low-noise response silicon photodiode. The average irradiance on the non-irradiated side for the existing solar simulator configuration is measured to be 5.7 W/m2, failing to meet the standard requirements. The low-reflection coating (LRC) material with mask achieves the lowest average irradiance of 0.9 W m−2 on the non-irradiated side and reduces the irradiance from existing configuration by 84 %. Lastly, ray-tracing simulation is used to plot the irradiance profile on the non-irradiated side, to compensate for the low-resolution irradiance map constructed using experimental measurements with the photodiode. The simulation results also show that when a flash chamber is long, similar to a black tunnel of rectangular tube, the back panel is not required to fulfil the requirements of technical specification for single light source characterisation.