Results of an International Comparison of Indoor Photovoltaic Measurements Among Seven Metrological Institutes

This study presents results of an intercomparison of indoor photovoltaics (PVs) among seven metrological institutes. Three types of solar cells were measured; organic and amorphous silicon cells representing current indoor products in the market and a reference solar cell. Three different light sources—AM1.5G, International Commission of Illumination Standard Illuminant A, and light-emitting diodes (LED) L41—were used at illuminance levels 100–2000 lx. Each laboratory reported short-circuit current as mandatory. Open-circuit voltage, maximum power, and differential spectral responsivity were reported where possible. Measurements revealed notable discrepancies. At the 1000 lx level, best agreement of 7% as standard deviation was achieved for the amorphous silicon cell using Standard Illuminant A. Similarly, the worst agreement of 37% was found for the reference cell using AM1.5G. Measurement methods varied across the laboratories. Some participants used lamps for Standard Illuminant A and LED L41. These measurements were generally in agreement but deviated from measurements with LED-based solar simulators, due to differences in measurement geometry, spectral properties, and treatment of infrared. Different illuminance measurement approaches, using either calibrated reference cells or luxmeters, further impacted consistency. This study highlights need for harmonized procedures to support reliable performance assessment of indoor PVs and gives recommendations to account for in standards.