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Corrosion is one of the main PV module failure mechanisms, as it can cause severe electrical performance degradation in PV modules exposed to hot and humid environments. Moisture penetrating a photovoltaic (PV) module may react with the metallic components causing corrosion. In addition, acetic acid which is produced by hydrolysis of ethylene vinyl acetate (EVA), the most common encapsulant, may further degrade metallic components. Corrosion is one of the main PV module failure mechanisms, as it can cause severe electrical performance degradation in PV modules exposed to hot and humid environments. The specific chemical reactions involved in the corrosion mechanisms for the different components are well understood. However, which of these causes the most serious degradation in the field, and therefore, most severe power loss is unknown. Moreover, the severity of corrosion in the absence of acetic acid is not yet well researched. This work distinguished between the front and rear side corrosion mechanisms and identified the different electrical signatures observed due to them. The experiment included damp-heat (DH) conditioning of single-cell mini-modules, containing passivated emitter and rear contact (PERC) solar cells, laminated with a polyethylene terephthalate (PET) based backsheet. Furthermore, half-encapsulated PERC PV cells were tested, with either the front or the rear side exposed. Electrical and material characterisation were conducted for the investigation of the sample degradation, and the performance decrease, related to the degradation of the rear surface passivation, was examined.

38th European Photovoltaic Solar Energy Conference and Exhibition; 1269-1274, Module temperature is one of the main factors that directly influence photovoltaic energy production, and therefore, its precise modelling is of foremost relevance. However, most of the temperature models in the literature fail to acknowledge the transient effect due to the heat capacity of the PV module, as they instead model the temperature based on the steady-state condition. This paper addresses these modeling weaknesses by comparing two wellestablished steady-state methods (the so-called Ross and Faiman models) with the Oh et al. model, which includes the transient effect of the heat capacity of PV modules in its calculations. Results show that the Oh et al. model provides more accurate results for high-resolution data when compared to steady-state models. The results are even more precise when using it to calculate the module temperature using the measurement from the previous time step, which indicates that the model could be used to forecast module temperature for a time step in the future. Across all models, climate is a major factor affecting model accuracy, what demonstrates the importance of the analysis of the impact of different site conditions on PV modeling and on the selection of models that are best matched to specific climates.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1065-1071, Photocurrent mapping can provide useful spatial information about the electrical and optical properties of a photovoltaic (PV) device under actual operating conditions. Although it is a well-established technique for PV cells, direct current mapping measurements of PV modules is impractical and time-consuming to be applied. One has to mechanically shade specific cells of the PV module or destructively access the cell to be measured. In this work, non-destructive, automated current mapping of encapsulated PV modules is demonstrated. A commercial Digital Light Processing (DLP) projector is utilised in order to apply compressive sampling for current mapping of PV modules. This method is non-destructive, cost effective and significantly fewer measurements are needed for acquiring a current map compared to raster scanning methods. When applying compressive sampling, a series of patterns is projected on the sample, the current response is measured for each pattern and the current map is acquired using an optimisation algorithm. Specific shading strategies, voltage bias settings and I-V curve details are investigated for optimised compressive sampling.

37th European Photovoltaic Solar Energy Conference and Exhibition; 1345-1351, Photovoltaic (PV) back-of- module (BoM) temperature measurements or estimations are key factors for the performance analysis and modeling of photovoltaic (PV) systems. Accurate module temperature estimation leads to more accurate energy yield predictions that are key determinants of investment value. Even though temperature prediction models have been investigated for decades, no studies analyzing the accuracy of different temperature estimation models across a wide range of climatic conditions have been identified prior to the work described here. This paper compares PV module temperature measurements and temperatures estimated through two methods (the so-called Ross’s and Faiman’s models) at multiple sites worldwide. Results showed that both models performed similarly at all sites and for different PV module technologies, with the exception of one test site in Germany, where the Faiman’s model outperformed the Ross model The test site in the United Kingdom presented the smallest differences between measured and estimated temperatures, possibly due to the fixation method of this site’s temperature sensor, that was cocooned with gas-flue silicone adhesive sealant on the back of the module. Results also showed that, for both models analyzed, all sites presented larger errors for higher irradiance levels, with the largest margin of error seen at the Brazilian test site.

37th European Photovoltaic Solar Energy Conference and Exhibition; 877-882, Bifacial Photovoltaic (PV) technology is expected to acquire an increased market share of the solar PV industry in the future, due to the ability of bifacial PV modules to collect light from both the front and rear side, increasing the energy yield for a specific available area for a PV system. Accurate measurement procedures for bifacial products result in more accurate energy yield estimates, consequently improving the bankability of bifacial PV technology. This work aims to evaluate the procedures for the measurement of electrical power and bifacial parameters of bifacial solar devices, concerning to their applicability in calibration laboratories and production line environments. An intercomparison for bifacial PV cells and modules is carried out between nine different test laboratories across Europe, as part of the PV-Enerate project. The measurement procedures as described in IEC TS 60904-1-2:2019 are followed among the different test laboratories, to evaluate the applicability of these procedures. Three different types of bifacial PV cells and three different types of bifacial PV modules are measured. The intercomparison involves measurements with systems using both single and double-sided illumination conditions. The uncertainty budgets and systematic differences that these procedures result in between different laboratories are determined and discussed. Specific common mistakes are reported and improvements to the IEC TS 60904-1-2:2019 are proposed as a result of this intercomparison activity.

36th European Photovoltaic Solar Energy Conference and Exhibition; 649-653, Within the European FP7 project CHEETAH, a thin-film tandem solar cell round-robin proficiency test was conducted between 13 testing laboratories, plus the European Solar Test Installation (ESTI) of the European Commission's Joint Research Centre as reference laboratory. The purpose of this RR was to compare testing facilities and procedures of the involved partners against the reference measurement by ESTI. In total, five cells were measured. Three tandem devices (a-Si:H/µc-Si) and a single-junction device representing the top (a-Si:H) and the bottom (µc-Si) cells, respectively, were provided by one partner. All cells (with active area of 1 cm2) were mounted in a standardised housing with connection sockets for I-V measurements and a Pt-100 temperature sensor. The cells were initially stabilised and calibrated at ESTI and afterwards circulated. The characterisation was done by I-V measurements at Standard Test Conditions and EQE measurements. ESTI checked and re-calibrated the cells at the end of the RR before and after further stabilization. Here we report on some preliminary I-V measurement results. A number of acquired or conversely still necessary improvements are discussed for the organisational point of view along with some measurement requirements that are still missing or that are not sufficient at many participating laboratories.

36th European Photovoltaic Solar Energy Conference and Exhibition; 1045-1049, This work demonstrates a novel method for the measurement of moisture ingress into PV laminates, by the use of humidity indicator cards encapsulated within the structure. The humidity indicator cards change colour due to moisture exposure, which is quantified by processing images of the samples taken with a camera. To allow the variance of colour to be matched to specific levels of humidity, a detailed calibration was first performed. To achieve this, laminates with the structure [EVA-humidity indicator card-EVA-glass] were stabilised in an environmental chamber at 85ºC at increasing levels of relative humidity. The colour change of the humidity indicator cards corresponding to the relative humidity inside the chamber was then plotted on RGB colour space diagrams. The purpose of this work is the development of a measurement method for the moisture that accumulates at the front side of PV cells, for the experimental verification of simulations of the moisture ingress into PV modules and the better understanding of degradation modes related to corrosion.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1034-1039, The aim of this work is to compare angle of incidence (AOI) measurement setups for solar cells between laboratories with such capability. For the first time, we compare relative light transmission measurements among eight laboratories, whose measurement techniques include indoor and outdoor methods. We present the relative transmission measurements on three 156 mm x 156 mm crystalline-Si (c-Si) samples with different surface textures. The measurements are compared using the expanded uncertainties provided by each laboratory. Five of the eight labs showed an agreement better than ±2% to the weighted mean between AOIs from -75° to 70°. At AOIs of ±80° and ±85°, the same five labs showed a worst case deviation to the weighted mean of -3% to 5% and 0% to 18%, respectively. When measurement uncertainty is considered, the results show that measurements at the highest incidence angle of ±85° are problematic, as measurements from four out of the six labs reporting uncertainty were found non-comparable within their stated uncertainties. At 85° AOI a high to low range of up to 75% was observed between all eight laboratories.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1076-1080, Damage accumulation of solder bonds in 6-cell photovoltaic (PV) mini modules is evaluated for 9 locations covering a variety of climate types. Finite-element methods are used to simulate the inelastic deformation of the solder bonds induced by changes in module temperature and mismatched thermal expansion coefficients between materials in the module. It is shown that accumulated damage is a function of mean daily maximum module temperature, temperature fluctuation frequency and mean daily maximum temperature change, with the latter showing the strongest correlation to accumulated damage and being the most influencing factor. Damage accumulation is also calculated for the standard thermal cycling protocol, TC200, as outlined in the IEC61215. The number of standard thermal cycles required to generate the same damage as one year in the field for each climate is then determined.

35th European Photovoltaic Solar Energy Conference and Exhibition; 114-121, This work presents the use of a combined measurement system for spectrally-resolved photoluminescence (PL), time-resolved photoluminescence (TRPL) and transient photocurrent decay (TPCD) to characterise the physical properties of solar cells and their materials. A physical model is proposed to quantify the localised carrier collection efficiency of solar cells from the measured localised minority carrier lifetime from TRPL measurements and the localised minority carrier diffusion time from TPCD measurements. A single excitation laser source is used to measure TRPL and TPCD at the same spot on the solar cell. Combined PL, TRPL and TPCD measurements are conducted on a CdS/CdTe and a CIGS sample. The resulting PL spectra for both samples show that the emission spectra can yield information on the material bandgap. TRPL and TPCD yield localised carrier lifetime and diffusion times of TRPL=3.91ns and TPCD=40.5ns respectively for the CdS/CdTe sample, and TRPL=2.45ns and TPCD=196.8ns respectively for the CIGS sample. The ratio between the TRPL and TPCD values is shown to be proportional to the localised carrier collection efficiency, yielding collection efficiencies of 21.97% and 7.93% for the CdS/CdTe and CIGS sample, respectively. The initial results show that the localised carrier collection efficiency may be affected by the sample’s metal contact configuration. In short, this combined measurement approach can offer a novel and useful method of characterising the material quality of solar cells and the localised carrier collection efficiency of finished PV devices.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1372-1375, The goal of this paper is to investigate the reactions responsible for the degradation of the front and rear side of c-Si solar cells that are immersed in acetic acid solutions. The types of degradation are characterised by electrical, optical and chemical methods. The identified degradation modes are compared to those observed in PV cells undergoing damp-heat aging. The degradation of the power output of a PV cell exposed under damp-heat conditions typically is observed after 3000-5000 hours of exposure. The purpose of this work is to research if acetic acid immersion of PV cells can result in the same types of degradation observed for damp-heat aging and how these degradation modes affect their power output. It is observed that acetic acid immersion and damp-heat exposure show a similar mechanism of degradation. This degradation is identified to occur because of reaction of acetic acid with lead, tin and aluminium. Lead and tin migration causes separation of the ribbons and the silver contacts from the cells. Aluminium corrodes severely because of presence of moisture, causing a series resistance increase of the cells.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1544-1547, Results from calibrations to determine the power conversion efficiency of photovoltaic (PV) devices can differ if they are obtained using different calibration methods or different facilities. However, every calibration value has a measurement uncertainty. The consistency of the calibration results around the world is a major task of metrology institutes and calibration laboratories and is ensured by regular comparisons. However, one important parameter of performance measurements of PV devices is the short-circuit current under standard test conditions ISTC. Therefore, the ISTC of an ensemble of reference solar cells were calibrated at the Joint Research Centre (JRC), at the Physikalisch-Technische Bundesanstalt (PTB) and at Centre for Renewable Energy Systems Technology (CREST) of Loughborough University (LU, United Kingdom). The determined ISTC of CREST and PTB are consistent within the uncertainties. Additionally, the spectral responsivities of the reference solar cells were determined at the facilities of JRC and PTB and the results discussed.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1795-1798, Ethylene vinyl-acetate (EVA) encapsulated crystalline silicon PV modules see encapsulant related degradation such as the hydrolysis of EVA which leads to generation of acetic acid that corrodes cells and cell metallisation. The formation and discharge of acetic acid in PV modules during an extended damp-heat test are studied in this work in dependence of the EVA crosslinking degree. To achieve different degrees of EVA encapsulation, mini-modules were laminated under different curing temperatures. The thermos-gravimetric analysis (TGA) is used to estimate the vinyl acetate (VA) content of the EVA before and after damp-heat ageing, from which the formation of acetic acid is evaluated. The net accumulation of acetic acid within modules is correlated to corrosion induced power losses. Results show mini-modules with highly cross-linked EVA form less acetic acid under damp-heat stresses, however, accumulated the highest amount of acetic acid leading to the most severe corrosion. Therefore, highly cross-linked EVA is not favoured in terms of long-term degradation due to DH stresses as it may trap the generated acetic acid within module.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1802-1807, A fast and effective model for the computation of solar energy potential in complex shading environments is presented. Accurate calculation and identification of solar energy potential profiles is demonstrated over large areas. Calculation time is exceptionally fast, even on an average specification PC (typically under 1 min per 1 km2). Problems with commonly used low-resolution sky domes that can lead to irradiance calculation errors of ~5% are identified. Ideal placements are easily visually identified from resultant irradiance/irradiation profile images. Image processing techniques for spatially distributed optimization problems are described and an example of energy value optimization is presented by means of individual dwelling demand separation & comparison.

Despite remarkable advances in antiarrhythmic drugs, ablation procedures, and stroke-prevention strategies, atrial fibrillation (AF) remains an important cause of death and disability in middle-aged and elderly individuals. Unstructured management of patients with AF sharply contrasts with our detailed, although incomplete, knowledge of the mechanisms that cause AF and its complications. Altered calcium homeostasis, atrial fibrosis and ageing, ion-channel dysfunction, autonomic imbalance, fat-cell infiltration, and oxidative stress, in addition to a susceptible genetic background, contribute to the promotion, maintenance, and progression of AF. However, clinical management of patients with AF is currently guided by stroke risk parameters, AF pattern, and symptoms. In response to this apparent disconnect between the known pathophysiology of AF and clinical management, we propose a roadmap to develop a set of clinical markers that reflect the major causes of AF in patients. Thereby, the insights into the mechanisms causing AF will be transformed into a format that can underpin future personalized strategies to prevent and treat AF, ultimately informing better patient care.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1854-1857, Whilst current photovoltaic (PV) module certification standards and procedures have been successful in reducing infant mortality, they do not reveal much information about the actual long-term durability of the modules in real outdoor conditions. In order to develop tests which provide more meaningful information about the longevity of a PV device, it is necessary to assess the real conditions to which they are exposed. With this in mind, high-resolution climate data has been collected for three case study sites within different climatic regions in order to assess the conditions which modules deployed in those sites would experience. The paper focusses on the thermal variation and thermally-induced stresses seen due to thermal cycling. It is shown that the module temperature profiles between different climatic regions vary significantly, with temperate climates often exhibiting frequent but small-magnitude temperature cycling whilst desert and tropical climates experience less frequent but large-magnitude cycles. Additionally, it is shown that ramping rates also vary between climates and are significantly less extreme than those outlined by the current standard test procedures. The conclusions drawn from the work illustrates the need to understand the impact of the different stress profile parameters, such as cycling frequency and ramping rates, on various failure mechanisms in order to develop meaningful tests which would allow for the prediction of actual degradation rates and lifetime in different climatic zones.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1748-1752, Electroluminescence (EL) images taken from on-field measurements often suffer from optical and perspective distortion affecting the interpretation and quantification of the images taken. Methods to correct these distortions are presented as well as a method to assess the associated uncertainties. This method uses the uncertainty of pixel position as intermediate step. The influence of pixel deflection, re-projection error and depth-of-field blur is evaluated. Three different camera systems are compared regarding tilt angle dependence. The re-projection error and the camera’s focal length are identified as major influence on the resulting uncertainty. It was shown that EL images with sufficient quality can be recovered, from images taken at high perspective misalignments with tilt angles of about 50°.

31st European Photovoltaic Solar Energy Conference and Exhibition; 29-34, Compressed sensing (CS) sampling theory is applied to the Light Beam Induced Current (LBIC) measurement technique in order to significantly reduce measurement time while maintaining or increasing accuracy. Using this method, a current map of the device can be reconstructed from far fewer measurements by means of an optimisation algorithm. Measurement simulations are implemented using a two dimensional photovoltaic (PV) device model to explore the capabilities and limitations of the method. A physical realisation of the technique is demonstrated. The raster scanning process of the LBIC system is replaced with a Digital Micro-mirror Device (DMD) pattern projection system. Measurement speed is also improved due to the response time of the DMD pattern generator, which is less than 20μs. An experimental CS-LBIC setup, alongside with initial experimental results that indicate the feasibility of the method are presented.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1594-1597, An analysis of PV system performance requires both meteorological and electrical data for the assessment period. However, actual in-field data acquisition is rarely 100%, often resulting in a significant amount of incomplete data sets for performance assessment. These gaps, if not taken into account, may add noticeable bias in yield assessment and thus estimations of the lacking data need to be made. An approach of back-filling the required data is given and validated here. Three different categories of data loss are identified and case-specific methods of synthesising missing data are developed. The integrity of the performance assessment process is assessed. The three cases of data loss are defined as: missing meteorological data only, missing electrical monitoring data only and missing both electrical and meteorological data. Case-specific methods are proposed and their performance against measured data is evaluated statistically by means of: root mean square error (RMSE), mean absolute error (MAE) and mean bias error (MBE). The inferred monthly performance ratio on two of the selected cases showed accurate agreement against measured data presenting significantly low MBE values, equal or less than -0.01.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1871-1876, The results of a measurement intercomparison between seven European laboratories characterising PV modules are reported. The purpose of the round-robin was to support the development of better measurement practices for thin-film devices, to assess the uncertainty analyses of the participating laboratories on thin-film modules and assess the variability of preconditioning techniques between partners. Alongside the STC measurements, measurements at 200 W/m2 and temperature coefficients (TC) measurements were performed. The benchmarking c- Si modules PMAX measurements were within ±1.9% and in agreement with stated uncertainties. The preconditioned PMAX measurements were within ±2.2 and -1.7% to +3.1% for the two CIGS types and in agreement with stated uncertainties. Both electrical biasing and light soaking increased the PMAX of the modules to a similar extent. The Tandem and CdTe preconditioned STC measurements were within -6% to +5.4% and -7.9% to +11.9% respectively. The measurement deviation of the out-of-the-box measurements of the Tandem and CdTe modules was in general smaller than the preconditioned ones emphasising the need of further investigation of preconditioning procedures for these type of devices. The measurement deviation at low-irradiance was larger than at STC as expected. The relative PMAX TC (%/°C) measurements were within -16.7% and +12.6%. with the exception of one CIGS module type where the deviation was as large as ±33%. This larger deviation is attributed to short timescale metastability effects.