• Energy Research

Abstract Mismatch between photovoltaic (PV) devices connected in series, caused by degradation or partial shading, may result in the significant power loss of a PV system. Therefore, smart PV (SPV) modules, integrated with power-optimization converters at the submodule level, have been used to overcome this problem. Due to the complex circuit topology of the integrated converters, the current-voltage (I-V) characteristics of most SPV modules cannot be tested directly using the routine method. This study aims to develop an I-V measurement procedure for SPV modules in the laboratory. The characteristic of the SPV module was investigated through theoretical and experimental analysis. The noise generated from the optimizer circuit was considered as the major hindrance in the I-V measurement for SPV modules, which was tested and then analyzed using Fourier analysis. Then, a filter corresponding to the noise characteristics was applied in the measurements to eliminate the noise. The measured result corresponded with the theoretical analysis; furthermore, the power linearity with irradiance and the field test verified the reasonableness of our method. The proposed method is applicable in the laboratory measurement of SPV modules within a few hundred milliseconds, which may be applied in relevant power sorting and measurements in production line.

In high-efficiency crystalline silicon photovoltaic (PV) modules, the internal capacitance may lead to a strong hysteresis effect in current–voltage ( I–V ) measurements. This hysteresis introduces a significant error in measurement results. This work investigates the nature of the hysteresis error ( ϵ ) variation caused by different measurement parameters in the I–V measurement. The effects of the I–V measurement parameters on the hysteresis error of a silicon heterojunction PV module were investigated through some comparative tests. Among all the parameters, the number of sweep points ( N ) and the voltage hold time ( Th ) of each sweep point are the most important factors affecting the value of the hysteresis error in I–V measurements. With the same total Th , the ϵ variation can be expressed as a single-peak curve with the increase of N . With the same Th for each point, ϵ increases in proportion to the reciprocal of N . To explain the origin of the theoretical relation among ϵ , Th , and N , an analytical equation was derived according to the diode model circuit and first-order circuit analysis method. Based on the derived equation, a parameter-setting optimization method for high-capacitance PV module measurements is proposed to precisely control the hysteresis error through certain simple pretests.

AbstractThis work presents the comparison of measurement results for four types of encapsulated high‐efficiency c‐Si solar cells measured by 10 laboratories based in Asia, Europe and North America utilizing a wide range of voltage sweeping methods, which include well‐established procedures that represent good industry practice, as well as recently introduced ones that have not been verified yet. The aim of the round‐robin interlaboratory comparison was to examine the measurement comparability of different laboratories with respect to their measurement methods of high‐efficiency solar cells. A proficiency test was employed to examine the consistency of results and their corresponding uncertainties. The short‐circuit current (ISC) under STC measured by four accredited laboratories was firstly compared. In order to investigate the consistency related to the high device capacitance, the value of the ISC was fixed for all 10 participants. The results of all participant laboratories—compared via En number analysis—generally remained well within [−1; 1], thus indicating consistency between the measured values and the reference values within stated measurement uncertainties. The differences remained within ±1.15% in PMAX and within ±0.35% in VOC for all participants and methods applied. Correlations were observed among the PMAX, VOC, and FF differences from their weighted mean. An analysis of the effects of transient current (dQ/dt) at maximum power point caused by hysteresis effect on the measurement error of PMAX showed a significant linear correlation between error of maximum power and junction voltage sweep rate for heterojunction (HJT) solar cells. This work forms the basis to validate all applied methods and their stated measurement uncertainties.

The equivalent single-side illumination method was proposed as the possible way to measure the bifacial photovoltaic devices. To verify the equivalent single-side illumination method, we compared the current–voltage ( I–V ) characteristic measurement of bifacial single-cell laminates under double-side and equivalent single-side illumination conditions. The results showed that the short-circuit current ( $I_{{\text{sc}}}$ ) and the open-circuit voltage ( $V_{{\text{oc}}}$ ) of each method were almost consistent, whereas the maximum power ( $P_{{{\max}}}$ ) of the double-side illumination method was higher than that of the single-side method under a range of different combinations of front and rear irradiation. To analyze the reason for this difference, we applied the penalty-based differential evolution method to further extract the one-diode model parameters of bifacial single-cell laminates. Among all the parameters, it was found that the series resistance ( $R_{s}$ ) measured with both methods was obviously different. As a result, an $R_{s}$ -correction model was accordingly proposed to correct the $P_{{{\max}}}$ measured with the equivalent single-side illumination method.