The results of the second World Photovoltaic Scale recalibration

The World Photovoltaic Scale (WPVS) is used as a worldwide reference value for terrestrial PV performance measurements of I_STC, the short-circuit current under standard test conditions. The WPVS has already been established in 1997 based on an international comparison where a set of 20 transfer/travelling standards were circulated between 11 national laboratories. After the first recalibration carried out at NREL in 1999, the PTB acted as pilot laboratory for the second recalibration, i.e. the 2003/04 intercomparison. It was performed as an international star-like comparison with 43 reference solar cells as reference standards, where 25 reference solar cells were made in accordance with the WPVS reference cell package design. Nine institutes have participated: AIST (Japan), BGNSEC (Israel), CIEMAT (Spain), ESTI (EU), Fraunhofer ISE (Germany), NREL (USA), PTB (Germany), Sandia (USA), TIPS (China). The measurements of the pilot laboratory were carried out between August 2003 and January 2004. Summarizing the main result of the comparison, the deviations of the calibration values obtained by the pilot laboratory and by the participants are, in general, within ±2%. In addition to the results of the comparison, typical stability and linearity test results of some reference cells as well as reproducibility of the DSR calibration facility of the pilot laboratory are described and discussed. Finally, the recommendations of a working group concerning the future development of the WPVS are presented.