Uncertainty in Photovoltaic performance parameters – dependence on location and material

When considering the system yield, one needs to know the uncertainty in key parameters for the annual yield in order to determine the confidence limit. This requires a consideration not only of the instrumentation but also of the operating environment. The importance of this is demonstrated by carrying out an uncertainty analysis for different locations, technologies and instrumentations. The accuracy of the key parameters is determined with regards to whether the uncertainty margins allow meeting contractual obligations for guarantees of results. It is shown that different operating environments have different boundaries. The main uncertainty is in the irradiance which ranges from 0.6-1.5% and filters into the PR with up to 6% for northern Europe (Site 1)

Accuracy of energy prediction methodologies

In the current market, the specific annual energy yield (kWh/kWp) of a PV system is gaining in importance due to its direct link to the financial returns for possible investors who typically demand an accuracy of 5% in this prediction. This paper focuses on the energy prediction of photovoltaic modules themselves, as there have been significant advances achieved with module technologies which affect the device physics in a way that might force the revisiting of device modelling. The paper reports the results of a round robin based evaluation of European modelling methodologies. The results indicate that the error in predicting energy yield for the same module at different locations was within 5% for most of the methodologies. However, this error increased significantly if the nominal nameplate rating is used in the characterization stage. For similar modules at the same location the uncertainties were much larger due to module-module variations

Photovoltaic performance measurements in Europe: PV-catapult round robin tests

Two sets of modules have been sent around to different testing installations across Europe, one set to laboratories performing indoor calibrations and one set to laboratories performing outdoor power and energy ratings. The results show that for crystalline and polycrystalline devices, a very good agreement between laboratories has been achieved. A lower agreement between laboratories has been achieved for thin film devices and further need for research is identified

Accuracy of Energy Prediction Methodologies

In the current market, the specific annual energy yield (kWh/kWp) of a PV system is gaining in importance due to its direct link to the financial returns for possible investors who typically demand an accuracy of 5% in this prediction. This paper focuses on the energy prediction of photovoltaic modules themselves, as there have been significant advances achieved with module technologies which affect the device physics in a way that might force the revisiting of device modelling. The paper reports the results of a round robin based evaluation of European modelling methodologies. The results indicate that the error in predicting energy yield for the same module at different locations was within 5% for most of the methodologies. However, this error increased significantly if the nominal nameplate rating is used in the characterization stage. For similar modules at the same location the uncertainties were much larger due to module-module variations

Results of the Sophia module intercomparison part-1: stc, low irradiance conditions and temperature coefficients measurements of C-Si technologies

The results of a measurement intercomparison between eleven European laboratories measuring PV energy relevant parameters are reported. The purpose of the round-robin was to assess the uncertainty analyses of the participating laboratories on c-Si modules and to establish a baseline for the following thin-film round-robin. Alongside the STC measurements, low irradiance conditions (200W/m2) and temperature coefficients measurements were performed. The largest measurement deviation from the median at STC was for HIT modules from -3.6% to +2.7% in PMAX, but in agreement with the stated uncertainties of the participants. This was not the case for low irradiance conditions and temperature coefficients measurements with some partners underestimating their uncertainties. Larger deviations from the median from -5% to +3% in PMAX at low irradiance conditions and -6.6% to +18.3% for the PMAX temperature coefficient were observed. The main sources of uncertainties contributing to the spread in measurements were the RC calibration, mismatch factor and capacitive effects at STC and low irradiance conditions as well as the additional light inhomogeneity for the latter. The uncertainty in the junction temperature and the temperature deviation across the module were the major contributors for temperature coefficients measurements

Uncertainty in energy yield estimation based on C-Si module roundrobin results.

Results of the European FP7 Sophia project roundrobin of c-Si module power measurements at STC and low irradiance and temperature coefficients were used to calculate annual energy yield at four sites. The deviation in the estimates solely due to the different measurement results is reported, neglecting the uncertainty in the meteorological data and losses unrelated to the performed measurements. While minimising the deviation in Pmax measurements remains the key challenge, the low irradiance and temperature coefficient contributions are shown to be significant. Propagating the measurement deviation in c-Si module measurements would suggest that expanded uncertainty in energy yield due to module characterization alone can be as high as ±3-4%

Are the spectroradiometers used by the PV community ready to accurately measure the classification of solar simulators in a broader wavelength range?

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35 years of photovoltaics: Analysis of the TISO-10-kW solar plant, lessons learnt in safety and performance-Part 2

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

Analysis of Non-Linear Long-Term Degradation of PV Systems

The current work presents the degradation evaluation of different PV systems under the weather conditions prevailed in the Swiss midlands, Jura and Alps. The purpose of this paper is to analyze degradation rates and change of degradation rates over time. The analysis is done for the degradation rates of three 25-30 years old PV systems in Switzerland, one of which is the oldest grid connected PV system in Europe of its size (30-year-old 555 kW PV system Mont-Soleil). The two other PV systems are located on Jungfraujoch and in Burgdorf. The examined degradation metric in this study is the performance ratio (PR) which is normalized energy yield with received insolation. The focus of this study is to examine the linear degradation rate of the PV plants and find the best non-linear fitting functions to the degradation. It is found that the annual degradation differs between the systems although they have identical PV modules. The highest linear degradation was found for Tiergarten East system with 0.6 %, 0.5 % for Tiergarten West, 0.3 % for Mont-Soleil and 0.02 %, for the Junfraujoch system. For non-linear degradation, 2nd order polynomial and breakpoint functions were used. The performance of both functions varies depending on to the PV system, and it is found that breakpoint function provided the best results and fit better than polynomial function

35 years of photovoltaics: Analysis of the TISO‐10‐kW solar plant, lessons learnt in safety and performance—Part 1

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.JRC.C.2-Energy Efficiency and Renewable