Improvements in world-wide intercomparison of PV module calibration

Abstract

The calibration of the electrical performance of seven photovoltaic (PV) modules was compared between four reference laboratories on three continents. The devices included two samples in standard and two in high-efficiency crystalline silicon technology, two CI(G)S and one CdTe module. The reference value for each PV module parameter was calculated from the average of the results of all four laboratories, weighted by the respective measurement uncertainties. All single results were then analysed with respect to this reference value using the En number approach. For the four modules in crystalline silicon technology, the results agreed in general within ±0.5%, with all values within ±1% and all En numbers well within [−1, 1], indicating further scope for reducing quoted measurement uncertainty. Regarding the three thin-film modules, deviations were on average roughly twice as large, i.e. in general from ±1% to ±2%. A number of inconsistent results were observable, although within the 5% that can be statistically expected on the basis of the En number approach. Most inconsistencies can be traced to the preconditioning procedure of one participant, although contribution of other factors cannot be ruled out. After removing these obvious inconsistent results, only two real outliers remained, representing less than 2% of the total number of measurands. The results presented show improved agreement for the calibration of PV modules with respect to previous international exercises. For thin-film PV modules, the preconditioning of the devices prior to calibration measurements is the most critical factor for obtaining consistent results, while the measurement processes seem consistent and repeatable

Electrical characterization intercomparison of high‐efficiency c‐Si modules within Asian and European laboratories

“…The approach used in this work differs from that. Indeed, it considers as the reference value for each performance parameter the mean of all measurements weighted by the inverse square of the associated measurement uncertainty (from now on just referred to as “weighted mean”), as already applied to other intercomparisons . The chi‐square test was used to check the justification of using the weighted mean.…”

“…As already applied to other PV intercomparisons , a proficiency test based on E n number assessment was performed in order to verify the consistency of the participants' results within their stated UCs to a reference value, in accordance with the ISO/IEC 17043 . As ESTI was the only laboratory accredited for PV calibration according to ISO/IEC 17025, ESTI result for each measurand was taken as the reference value in the calculation of the E n numbers as where x i is a measurement of the i ‐th laboratory with expanded uncertainty ( k = 2) U 95 , and x ESTI is the result submitted by ESTI with expanded uncertainty U 95,ESTI .…”

A European proficiency test on thin‐film tandem photovoltaic devices

“…The RR was organised within the CHEETAH project 33 as a PT for 13 participating laboratories, also building on a failure analysis of the SOPHIA project's RR and on prior experience in interlaboratory comparisons. [21][22][23]25 The reference measurements were independently provided by ESTI, which calibrated all devices at the beginning of the PT (see Section 2.4). The devices were again shipped to ESTI at the end of the RR PT for a final verification and calibration.…”

“…The standard ISO/IEC 17043 34 was taken as guideline for the evaluation of the participants' results, as already done in previous similar exercises for PV. 23,25 As initiator of the RR within the CHEETAH project, Helmholtz-Zentrum Berlin (HZB) acted as the coordinator (but not as the official provider in the sense of ISO/IEC 17043 34 ) of the RR PT, although it was also a PT participant. This double role of one participant is usually avoided in PTs organised by official PT providers for testing laboratories, in order to assure unbiased results assessment.…”

“…In addition, as good practice for measurement and testing laboratories, and even required for calibration laboratories accredited to ISO/IEC 17025, 16 in the last 30 years several interlaboratory comparisons and round-robins have already been organised for SJ PV testing at STC. [17][18][19][20][21][22][23][24][25] The World Photovoltaic Scale (WPVS) itself, which nowadays has become a sort of alias to refer to a solar cell with some standardised package, was in fact established in 1999 as measurement scale for PV starting from a dedicated world-wide intercomparison on calibration of PV cells. [26][27][28] Similar measurement comparisons are less numerous and less geographically wide in the case of MJ PV devices.…”