• Energy Research

Bifacial c-Si photovoltaic (PV) modules can increase the performance of traditional PV modules because both sides of the cells, front and rear, absorb solar radiation. The knowledge of the temperature coefficients (TCs) is relevant to compare indoor and on-field performance of PV devices. In this paper, the TCs of c-Si bifacial PV modules from five different manufacturers were measured under natural sunlight and simulated indoor condition with a large-area steady-state solar simulator and the data were compared with the datasheet values. The effects on the TCs of an opaque and a reflective rear cover were also analyzed. There were no relevant differences between indoor and outdoor and for front and rear side TCs (within the measurement uncertainty). Slight differences with respect to the datasheet values were found for most of the modules under test for the TC for current α and for maximum power δ coefficients. However, since the manufacturers do not declare the TC uncertainty, a definitive statement cannot be made.

Performing measurements and compiling a power matrix (IEC 61853-1) is a useful tool for illustrating the energy production of a PV module at different levels of irradiance and temperature. At the European Solar Test Installation (ESTI) a steady-state solar simulator can be used to determine these matrices. The steady-state solar simulator irradiates the PV module from the front side, which heats the module to the desired temperature. However, this causes a temperature difference between the front surface of the module and the rear, where the temperature sensor is attached. This temperature difference, between the measured module temperature (Tm) and the temperature of the cell junction, gives rise to errors. In this paper, a correction procedure according to the determination of the equivalent cell temperature (ECT) of photovoltaic devices by the open-circuit voltage method in IEC 60904-5 is proposed and evaluated. In this study the difference between the Tm and the ECT was determined to about 1 °C to 3 °C, resulting in a deviation of the Pmax value in the power matrix up to about 1.5%, for a monocrystalline PV module.

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.

AbstractToday's variety of photovoltaic (PV) technologies imposes new challenges to laboratories and industries to precisely measure the performance of devices and, consequently, to accurately estimate the energy yield once installed in a specific location. Spectroradiometry has become a key discipline for metrology applied to PV: Spectral irradiance is one of the three parameters according to which solar simulators are classified according to IEC 60904‐9; precise spectrum measurements are a key factor in the spectral mismatch calculation. Finally, energy rating calculations according to IEC 61853 involve spectral irradiance conditions different than the AM1.5G standard spectrum. To tackle these issues, since 2011, the International Spectroradiometer Interlaboratory Comparison (ISRC) takes place annually in different locations of Europe with the participation of laboratories, research institutes, and industry partners to assess spectral measurement capabilities and share good measurement practices and protocols. In this paper, several results of the 9th ISRC 2019 are presented, looking in particular at the impact on characterization of new technologies like organic devices (OPV), dye‐sensitized (DSSC), and perovskites.

AbstractThis work presents the results of a high‐efficiency (HE) photovoltaic (PV) module round‐robin intercomparison between five Asian and European ISO/IEC 17025 accredited laboratories and one industrial laboratory based in Europe. The scope of the round‐robin was to examine the measurements comparability for this PV technology with respect to ISO/IEC 17025 laboratory conformity assessment and also to examine the accuracy of step‐like methods towards transient errors against already validated methods. The devices under test were four types of HE c‐Si PV modules with efficiencies varying between 16.5% and 19.0%. The results indicate that a satisfactory agreement was achieved with maximum deviations of 1.59% in Pmax, 1.13% in Isc, and 0.64% in Voc for all devices under test. The weighted standard deviations in Pmax per device type, which can be seen as a conservative estimate of interlaboratory agreement for HE c‐Si PV, ranged within 0.82% to 2.23% (k = 2). The accuracy of step‐like methods towards transient errors was evaluated by comparing a second series of results at fixed Isc for each module under test, eliminating the influence of the effective irradiance measurement. This work suggests that the contribution of capacitive errors was in the range (0.47 ± 0.19) % (k = 2). A spectral mismatch sensitivity analysis showed that an accurate measurement of the spectral irradiance and of the involved spectral responsivities together with the punctual correction for the spectral mismatch can reduce the error in the measurement of PV modules performance of about 2% even in the case of c‐Si against c‐Si and class AAA solar simulators.

This study focuses on the fill factor (FF) measurement uncertainty contributing to the uncertainty in the labeling of the nominal maximum power (Pmax) of photovoltaic modules, which is determined under Standard Test Conditions (STC). Given that the price of these modules is tied to their Pmax, accurately quantifying the uncertainty of this measurement is crucial for ISO/IEC 17025 accredited laboratories. Adhering to the “Guide to the expression of uncertainty in measurement”, this work evaluates the uncertainty contribution of the Fill Factor (FF), a key parameter linking Pmax, the open-circuit voltage (Voc), and the short-circuit current (Isc). The analysis is based on data from three reference modules measured at the European Solar Test Installation (ESTI), part of the Joint Research Centre of the European Commission, since 1996. This data shows a reduction in FF uncertainty from approximately 0.6% to 0.3%, attributed to advancements in measurement technologies and techniques. Considering the goal of top calibration laboratories to measure Pmax with the lowest possible uncertainty, the improvement in FF uncertainty measurement is significant, ensuring more accurate labeling of photovoltaic modules.