The TISO‐10‐kW solar plant, connected to the grid in 1982, is the oldest installation of this kind in Europe. Its history is well documented, and the full set of modules has been tested indoors at regular intervals over the years. After 35 years of operation, we observe an increase in the degradation rates and that the distributions of modules' performances are drastically changing compared with previous years. Two groups of modules can be observed: (a) group 1: 21.5% of the modules show a very modest degradation, described by a Gaussian distribution with mean yearly power degradation of only −0.2%/y. (b) Group 2: 72.9% of the modules form a negatively skewed distribution with a long tail described by mode (−0.54%/y), median (−0.62%/y), and mean (−0.69%/y) values. In earlier years, decreases in performances could strongly be correlated to losses in fill factor (FF). After 35 years, the situation changes and, for a subset of modules, losses in the current (Isc) are superimposed to losses in FF. The reasons for this will become clearer in part 2, where we will present results of a detailed visual inspection on the whole set of modules and will focus on safety aspect too. We conclude that, after 35 years of operation in a temperate climate, approximately 60% (~70% if considering a ± 3% measurement uncertainty) of the modules would still satisfy a warranty criteria that module manufacturers are presently considering to apply to the technology of tomorrow: 35 years of operation with a performance threshold set at 80% of the initial value.
The TISO‐10‐kW plant, installed in Lugano (Switzerland) in 1982, is the first grid‐connected PV plant in Europe. In a joint publication (part 1), we presented the results of the electrical characterization performed in 2017—after 35 years of operation—of the 288 Arco Solar modules constituting the plant. Power degradation rates were different among modules and two groups could clearly be distinguished: group 1, with a remarkably low mean degradation rate of −0.2% per year, and group 2, with a mean degradation of −0.69% per year. After 35 in a temperate climate, approximately 70% of the modules (considering a ±3% measurement uncertainty) still exhibit a performance higher than 80% of their initial value. In this paper, when possible, we attempt at correlating module performance losses to specific failure mechanisms. For this sake, an extensive characterization of the modules was performed using visual inspection, IV curve measurements, electroluminescence, and infrared imaging. We remarkably find that module degradation rates are highly correlated to the aging pattern of the encapsulants used in module manufacturing. In particular, a specific formulation of the encapsulant (PVB), which was used only in a minority of the modules (approximately 10%), leads to degradation rates of −0.2% per year, which corresponds to a loss in performance below 10% over 35 years. Potential safety threats are also investigated, by measuring the frame continuity, the functionality of the bypass diodes, and the module insulation. Finally, we discuss how the analysis of a 35‐year‐old PV module technology could benefit the industry in order to target PV module lifetimes of 40+ years.
This paper reports the results of an international interlaboratory comparison study on light‐ and elevated temperature‐induced degradation (LETID) on crystalline silicon photovoltaic (PV) modules. A large global network of PV module manufacturers and PV testing laboratories collaborated to design a protocol for LETID detection and screen a large and diverse set of prototype modules for LETID. Results across labs indicate the reproducibility of LETID testing is likely within ±1% of maximum power (PMP). In intentionally engineered LETID‐sensitive modules, mean degradation after the prescribed detection stress is roughly 6% PMP. In other module types the LETID sensitivity is smaller, and in some we observe essentially negligible degradation attributable to LETID. In LETID‐sensitive modules, both open‐circuit voltage (VOC) and short‐circuit current (ISC) degrade by a roughly similar magnitude. We observe, as do previous studies, that LETID affects each cell in a module differently. An investigation of the potential mismatch losses caused by nonuniform LETID degradation found that mismatch loss is insignificant compared to the estimated loss of cell ISC, which drives loss of module ISC. Overall, this work has helped inform the creation of a forthcoming standard technical specification for LETID testing of PV modules, IEC TS 63342 ED1, and should aid in the interpretation of results from that and other LETID tests.
This paper presents the results from an extensive interlaboratory comparison of angular‐dependent measurements on encapsulated photovoltaic (PV) cells. Twelve international laboratories measure the incident angle modifier of two unique PV devices. The absolute measurement agreement is ±2.0% to the weighted mean for angles of incidence (AOI) ≤ 65°, but from 70° to 85°, the range of measurement deviations increases rapidly from 2.5% to 23%. The proficiency of the measurements is analysed using the expanded uncertainties published by seven of the laboratories, and it is found that most of the angular‐dependent measurements are reproducible for AOI ≤ 80°. However, at 85°, one laboratory's measurement do not agree to the weighted mean within the stated uncertainty, and measurement uncertainty as high as 16% is needed for the laboratories without uncertainty to be comparable. The poor agreement obtained at 85° indicates that the PV community should place minimal reliance on angular‐dependent measurements made at this extreme angle until improvements can be demonstrated. The cloud‐based Daidalos ray tracing model is used to simulate the angular‐dependent losses of the mono‐Si device, and it is found that the simulation agrees to the median measurement within 0.6% for AOI ≤ 70° and within 1.4% for AOI ≤ 80°. Finally, the impact that the angular‐dependent measurement deviations have on climate specific energy rating (CSER) is evaluated for the six climates described in the IEC 61853‐4 standard. When one outlier measurement is excluded, the angular‐dependent measurements reported in this work cause a 1.0%–1.8% range in CSER and a 1.0%–1.5% range in annual energy yield, depending on the climate.
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