Pulsed Solar Simulator Research Articles

Characterization, traceability, and uncertainty estimation of reference solar panel module measurements using pulsed solar simulators and reference solar cells

This paper presents the design, characterization, and traceability of reference solar panel modules for determining the performance of photovoltaic (PV) modules at standard test conditions (STC). The research introduces an advanced experimental system based on a class AAA pulsed solar simulator to measure the radiometric, electrical performances, and efficiency of PV modules. I-V/P characteristics of three PV modules at different STCs and the associated uncertainty budget of the system were estimated. I-V characteristic and associated parameters including Isc, Voc, Pmax, FF, and efficiency were measured. The radiometric and electrical traceability were discussed, and the relative expanded combined uncertainties were concluded to be 1.62 % (Isc), 0.42 % (Voc), 2.05 % (Pmax), and 2.5% (η), with a coverage factor k = 2. Reference solar panel modules were also used on-site to test the performance of large PV panels, and the results are reported.

Characterization of dual‐junction III‐V on Si tandem solar cells with 23.7% efficiency under low concentration

AbstractMonolithic two‐terminal III‐V on Si dual‐junction solar cells, designed for low concentration applications, were fabricated by means of surface‐activated direct wafer bonding. The III‐V top cell is a heterojunction formed by an n‐Ga0.5In0.5P emitter and a p‐Al0.2Ga0.8As base. An efficiency of 21.1 ± 1.5% at one sun and 23.7 ± 1.7% at 10 suns is demonstrated, which to our knowledge is the best dual‐junction two‐terminal III‐V on Si tandem cell efficiency reported to date under verified reference conditions. The I‐V characterization of these 1‐cm2 tandem cells under concentration required the development of a new method using a single‐source multiflash solar simulator and not perfectly matched component cells, also known as pseudo‐isotypes, formed by Si single‐junction cells and optical filters. In addition, the spectrum of the pulsed solar simulator was measured using a high‐speed CMOS spectrometer, allowing the calculation of the spectral mismatch correction factor. Merging these two techniques results in the hybrid corrected pseudo‐isotype (HCPI) characterization method, which shows a fast and accurate performance with a simplified procedure based on a single‐source solar simulator. Pseudo‐isotypes are easily adaptable to new cell designs by simply using a different filter, hence allowing the characterization of new multijunction solar cell architectures.

Refractory In$_{x}$ Ga1−$_{x}$ N Solar Cells for High-Temperature Applications

In $_{x}$ Ga1− $_{x}$ N solar cells are ideal for use in extreme temperature applications due to their wide band gap and chemical stability. In this paper, the details are given for the growth, fabrication, and characterization of In $_{x}$ Ga1− $_{x}$ N multiple quantum well solar cells designed for high temperatures. Materials characterization confirms basic optical and physical properties of the layers. External quantum efficiency, dark current–voltage, 1-sun current–voltage, and 300-sun high intensity pulsed solar simulator current–voltage measurements were taken at varied temperatures. Correlations are made between different characterization methods to draw conclusions about device behavior. Photovoltaic performance for $V_{{\rm{OC}}}$ , $W_{{\rm{OC}}}$ , $J_{{\rm{SC}}}$ , and fill factor is given at multiple temperatures from 25 °C to 600 °C.

Assessment of PV modules shunt resistance dependence on solar irradiance

Modeling and simulation of photovoltaic systems, further than aiding on the project design phase, can be used to emulate the system performance in real time, therefore helping to identify any malfunction that may occur. Among the available performance models for photovoltaic systems, the single diode model is preferred by many authors, since it combines relative simplicity and accuracy. Previous works reported that this model has some limitations on describing the photovoltaic system I–V curves under low irradiances, indicating that the variation of the shunt resistance parameter with the irradiance level can be adopted to minimize this drawback. This paper aims to study the shunt resistance dependence on the irradiance level in order to evaluate some of the usual expressions proposed on the literature. A large area pulsed solar simulator model PASAN SunSim 3C was used to acquire the I–V characteristics of several photovoltaic modules of different brands and technologies under 20 distinct irradiance levels ranging from 75W/m2 to 1000W/m2. The shunt resistance parameter was calculated as the inverse slope of the I–V curve in the short circuit region, and fitting equations were derived for each photovoltaic technology. The results in general agreed with previous published works, showing the tendency of an increase of the shunt resistance on lower irradiance levels. Some empirical models tested did not present satisfactory accuracy to reproduce the experimental data. Although simpler, an inverse dependence of the shunt resistance on the irradiance using the measured value at STC as a reference was seen to describe adequately the experimental data. A preliminary study showed that the inclusion of this dependence on the single-diode model indeed increases the model accuracy, reducing the average error on the performed tests by more than half comparing to the original model.

Statistical analysis of I–V curve parameters from photovoltaic modules

The performance of a photovoltaic (PV) system depends on several factors, such as the solar radiation availability and its spectral distribution, the PV module temperature, soiling, cable losses, PV power degradation over time and so forth. An important factor that also affects the PV array power is the mismatch loss due to the differences between single modules, since is inherent to the manufacturing process certain variability in the I–V curve parameters. The manufacturing technology of PV modules has improved considerably, resulting in higher efficiencies and better quality control process, which enabled a lower maximum power tolerance range of PV modules available in the market. The actual shape of the statistical distribution of the main electrical parameters is necessary to evaluate the mismatch losses using simulation software, and also to verify if a new selection of PV modules besides the one performed by the manufacturer is relevant. In order to analyze these topics, a statistical study was carried out based on data obtained from I–V curve measurements of 105 multicrystalline PV modules with the same nominal characteristics. The measurements were performed in a pulsed solar simulator in standard test conditions. The descriptive statistics were obtained for each main electrical parameter and the best probability density function that describes the parameters dispersion was determined. The results show that the maximum power, the maximum power voltage and the open circuit voltage are preferably represented by a Burr probability density function, however a normal distribution is adequate as well. The short circuit current, the maximum power current and the fill factor are actually described by a two parameter Weibull distribution. In order to analyze the effects of the mismatch losses in arrays, several I–V curves of strings with 10 PV modules randomly selected from the sample were synthesized and compared to strings of modules sorted by the maximum power current value. The advantage of performing a new selection of PV modules with better current match was not relevant in comparison to random strings. The selection performed at the factory for a PV module with the same nominal power is sufficient to prevent considerably mismatch losses considering that the PV modules were sorted using standard procedures.

High-Current ESD Test of Advanced Triple Junction Solar Array Coupon

Testing was conducted on an advanced triple junction (ATJ) coupon that was part of a risk reduction effort in the development of a high-powered solar array design by Space Systems/Loral, LLC (SSL). The ATJ coupon was a small, four-cell, two-string configuration that has served as the basic test coupon design used in previous SSL environmental aging campaigns. The coupon has many attributes of the flight design; e.g., substrate structure with graphite face sheets, integrated by-pass diodes, cell interconnects, room-temperature vulcanizing grout, and wire routing. The objective of this test was to evaluate the performance of the coupon after it is subjected to secondary arc testing at two string voltages (100 and 150 V) and four array currents (1.650, 2.000, 2.475, and 3.300 A). An external test circuit, unique to SSL solar array design, was built that simulates the effect of missing cells and strings in a full solar panel with special primary arc (PA) flashover circuitry. A total of 73 PAs were obtained that included seven temporary sustained arcs (TSAs) events. The durations of the TSAs ranged from $50~\mu \text{s}$ to 2.75 ms. All TSAs occurred at a string voltage of 150 V. Post-test large area pulsed solar simulator, Dark $I$ – $V$ , and by-pass diode tests showed that no degradation occurred due to the TSA events. In addition, the post-test insulation resistance measured was $>50~\text{G}\Omega $ between cells and substrate. These test results point toward a robust design for application to a high-current, high-power mission.

Nonstationary Effects at Photovoltaic Module Characterization Using Pulsed Solar Simulator

This paper presents the dynamic characteristic of a tandem silicon/amorphous silicon (a-Si:H/a-Si:H) photovoltaic (PV) module measured in the nonstationary regime. The current-voltage (I–V) characteristics of the PV module are generally measured by using a pulsed solar simulator. Distortions of the I–V curves can often be observed when measurements are done under the solar simulator with different pulse durations or different sweeping rates of the curve tracing, a direction of the curve tracing from short circuit to open circuit (SCOC), or from open circuit to short circuit (OCSC). In this paper, the measurements were made on the a-Si:H/a-Si:H tandem PV module consisting of 40 cells in series connection. The PV module area is 0.78 m2. Dissimilarities of the I–V curves of the PV modules can be observed by the deviation of power at maximum point (Pm) and fill factor (FF). From the experimental results, it is found that the largest deviation of Pm is 6.12% for 1 ms sweeping duration with OCSC direction of the curve tracing. Dissimilarities of the I–V curves can be explained by charging and discharging capacitive currents due to a voltage dependence of solar cell parameters. Moreover, the capacitance effects can be described by a dynamic impedance measurement of the PV module in the dark with forward and reverse biasing. The voltage and time-dependent parameters are the diffusion capacitance (CD), transient or junction capacitance (CT), series resistance (Rs), and shunt resistance (Rsh),which can be revealed by an impedance plot.

Luminescent emission of multi-junction InGaP/InGaAs/Ge PV cells under high intensity irradiation

Combined electroluminescence (EL) and photoluminescence (PL) measurements were conducted in order to investigate the presence of luminescent emission of InGaP/InGaAs/Ge at different operating conditions of the tandem. Luminescent emission from cell samples was observed at different sun concentrations, voltage biases and temperatures. A high intensity pulsed solar simulator was used to photoexcite the device which exhibited strong radiative recombination from both the top InGaP and middle InGaAs junctions. Luminescent emission from the device was investigated under a range of voltage biases and was clearly observed at the maximum power point voltage of the sample under test indicating its presence during typical operating conditions of the solar cells. Investigation of the emission was also performed at relatively high temperatures (up to 60°C) in order to mimic the outdoor operating conditions of a solar cell device. Luminescence was detected at high temperatures indicating that significant radiative recombination is present at even higher temperatures. Outdoor measurements under actual solar spectrum demonstrated the presence of luminescent emission in agreement with indoor testing. The significant amount of radiative recombination at the band-gap edges of the top junctions observed in our measurements gives evidence that optical coupling to the lower ones may occur. Finally, excitation power dependent PL was performed using monochromatic laser sources in order to investigate the impact of externally induced photocurrents of different intensity upon the radiative signal of each junction.

Estimate of the Expanded Uncertainty in the Result of Measuring the Short Circuit Current of Thin-Film Photovoltaic Modules

The sources of uncertainty in measurements of the short circuit current of thin film photovoltaic modules are analyzed. An Ishikawa diagram is developed to represent the main sources of uncertainty when a pulsed solar radiation simulator is used. The expanded combined uncertainty in the result of measuring the short circuit current is calculated taking these sources into account.

Standardization of the energy performance of photovoltaic modules in real operating conditions

The performance of a PV module at STC (1) is a useful indicator for comparing the peak performance of different module types, but on its own is not sufficient to accurately predict how much energy a module will deliver in the field when subjected to a wide range of real operating conditions (2). An Energy Rating approach has to be preferred for that aim. It is currently under development the standard series IEC 61853 on Energy Rating, for which only part 1 (3) has been issued. It describes methods to characterize the module performance as a function of irradiance and temperature. The reproducibility of the power matrix measurements obtained by the three different methods specified in the standard, namely: under natural sunlight using a tracking system; under natural sunlight without tracker; and a large area pulsed solar simulator of Class AAA were evaluated and discussed (4, 5). The work here presented is focused on the second method listed above, which explores the real working conditions for a PV device and therefore it represents the situation where Energy Rating procedures are expected to give the largest deviations from the STC predictions. The system for continuous monitoring of module performances, already implemented at ESTI, has been recently replaced with a new system having a number of improvements described in the following. The two system results have been compared showing a discrete compatibility. The two power matrices are then merged together using a weighted average and compared to those acquired with the other two remaining ideal systems. An interesting tendency seems to come up from this comparison, making the power rating under real operating conditions an essential procedure for energy rating purposes.

Fast and accurate methods for the performance testing of highly-efficient c-Si photovoltaic modules using a 10 ms single-pulse solar simulator and customized voltage profiles

Performance testing of highly efficient, highly capacitive c-Si modules with pulsed solar simulators requires particular care. These devices in fact usually require a steady-state solar simulator or pulse durations longer than 100–200 ms in order to avoid measurement artifacts. The aim of this work was to validate an alternative method for the testing of highly capacitive c-Si modules using a 10 ms single pulse solar simulator. Our approach attempts to reconstruct a quasi-steady-state I–V (current–voltage) curve of a highly capacitive device during one single 10 ms flash by applying customized voltage profiles–-in place of a conventional V ramp—to the terminals of the device under test. The most promising results were obtained by using V profiles which we name ‘dragon-back’ (DB) profiles. When compared to the reference I–V measurement (obtained by using a multi-flash approach with approximately 20 flashes), the DB V profile method provides excellent results with differences in the estimation of Pmax (as well as of Isc, Voc and FF) below ±0.5%. For the testing of highly capacitive devices the method is accurate, fast (two flashes—possibly one—required), cost-effective and has proven its validity with several technologies making it particularly interesting for in-line testing.

Reflection-type single long-pulse solar simulator for high-efficiency crystalline silicon photovoltaic modules

Photovoltaic module measurements are predominantly taken by using pulsed solar simulators. However, significant errors can be generated when the existing simulators are applied to current high-efficiency crystalline silicon photovoltaic modules. This paper presents the design and implementation of a novel solar simulator featuring reflection-type light source and single long-pulse flash. The analysis and experimental study of the capacitance effect and the technical details of the simulator including reflection-type lamp house, xenon flash lamp power supply, and source-measure unit are introduced. The results show that the complete system achieves Class AAA performance in accordance with the international standard. The proposed simulator outperforms other similar products on the market and has been adopted by some well-known photovoltaic module manufacturers. The practical application demonstrates that this high-performance and cost-effective simulator is quite suitable for photovoltaic module production line.

Characterization of high‐efficiency c‐Si CPV cells

AbstractConcentrating photovoltaics (CPV) represent an emerging market at its early stage for terrestrial application with large growth expectation and considerable research activity on new cell production has been conducting recently. In response to a fast growing demand for traceable and independent measurements on CPV cells and systems the European Solar Test Installation (ESTI) has started a research program on indoor/outdoor devices characterization. This paper focuses on two essential components of device calibration. Calibration requires traceable calibrated reference devices: for this purpose reference c‐Si cells equipped with neutral density filters of various optical densities have been used at ESTI for checking device linearity at different concentration ratios. Also essential is the implementation of common procedures and intercomparison of test results at different test laboratories. Procedures and experimental setups for concentrating c‐Si cell characterization at both ESTI and at the UTTP FOTO Laboratory of ENEA are described and results of an intercomparison are presented and discussed. Electrical performance measurements have been performed at high intensities on three different setups: a recently developed 1500× pulsed solar simulator at ESTI and two modified solar simulators capable of achieving up to 250× concentration at ENEA. Reported results show agreement within measurement uncertainties of the electrical parameters. Copyright © 2011 John Wiley & Sons, Ltd.

Comparison of indoor and outdoor performance measurements of recent commercially available solar modules

AbstractThe strong growth of the PV market is accompanied by an increasing number of “new” PV technologies and concepts now mature for commercialization. A correct calibration of these devices is in some cases very difficult, because indoor and outdoor performance measurements often lead to different results. In this paper we compare the indoor and outdoor performance measurements of a set of recent commercially available PV modules (conventional and high‐efficiency c‐Si, single‐, double‐, and triple‐junction thin film (TF) technologies) and we observe that the maximum power Pmax of some devices measured indoors using our large area pulsed solar simulator is usually lower than the power measured outdoors under natural sunlight. The major effects which lead to these discrepancies are identified, as follows: (a) spectral mismatch errors, very significant for CdTe, and all a‐Si TF technologies; (b) measurement‐related sweep‐time effects, which seem to strongly influence the performance of high efficiency c‐Si devices and to a lesser extend of all a‐Si TF technologies; and (c) short‐time light‐soaking effects, which influence the performance of CIS and to a lesser extent CdTe. Copyright © 2010 John Wiley & Sons, Ltd.

Characterization of a pulsed solar simulator for concentrator photovoltaic cell calibration

The upgrade of a large area xenon lamp pulsed solar simulator to a 1500X pulsed solar simulator is presented in detail. Spectral match, spatial non-uniformity and temporal instability are analyzed according to the existing international standards, resulting in a Class CAA solar simulator: ongoing improvements to meet Class AAA requirements are discussed. The procedure for the calibration of a set of c-Si reference cells equipped with neutral density filters for calibrated measurements at high intensity is also presented. The paper finally highlights the importance of the spectral match to the standard AM1.5d (direct beam) spectrum over a wider range than described in the available standards for solar simulator classification.

Seasonal variations on energy yield of a‐Si, hybrid, and crystalline Si PV modules

AbstractThis paper presents a study of long‐term outdoor performance of a‐Si and hybrid modules mounted in the same location over several years. The modules were also characterized indoors using standard measurement methods employing pulsed solar simulators at the European Solar Test Installation (ESTI). The present study is intended to contribute to future standards on energy rating by presenting a common procedure for correcting the outdoor performance measurements to standard test conditions and comparing the resulting module performance at real and laboratory conditions. A seasonal variation in output, higher in the summer and lower in the winter, suggests that the module performance improves due to annealing when the module temperature is higher. The total output energy per month for these two technologies and a reference c‐Si technology is also presented. Copyright © 2010 John Wiley & Sons, Ltd.

A simple method for quantifying spectral impacts on multi-junction solar cells

A method to quantify spectral effects on the electric parameters of multi-junction solar cells is presented. The method is based on measuring the short circuit current of at least two monitor cells. Ideally these monitor cells have the same spectral responses as the subcells in the investigated multi-junction solar cell. In contrast to the subcells, the current of the individual monitor cells can be measured separately. This allows conclusions to be drawn about the spectral impact on the current mismatch of the multi-junction solar cell. A spectrometric evaluation method is then applied. The method has been tested experimentally with three concentrator modules using III–V triple-junction solar cells. These modules were measured outdoors for several months under variable solar spectral conditions. In parallel, the IV curves of the modules and the current of two component cells were measured. A spectral parameter Z was derived from the monitor cell current signals, which was correlated to the short circuit current and the fill factor of the modules. A linear correlation was found between Z and the normalized short circuit current of the concentrator modules. Translation equations were derived from the linear correlation. These enable the calculation of a module’s short circuit current under any spectral conditions. In particular, the short circuit currents of the modules were derived for direct normal irradiance of 850 W/m 2 and spectral conditions corresponding to the AM1.5d low AOD spectrum. This is an important step towards comparing the performance of modules which show strong spectral sensitivity. Future rating methods can benefit from the presented simple method for quantifying spectral impacts on multi-junction solar cells. Furthermore, the method can be of interest for tuning the spectrum of pulsed solar simulators.

Double-cavity radiometer for high-flux density solar radiation measurements

A radiometric method has been developed, suitable for both total power and flux density profile measurement of concentrated solar radiation. The high-flux density radiation is collected by a first optical cavity, integrated, and driven to a second optical cavity, where, attenuated, it is measured by a conventional radiometer operating under a stationary irradiation regime. The attenuation factor is regulated by properly selecting the aperture areas in the two cavities. The radiometer has been calibrated by a pulsed solar simulator at concentration levels of hundreds of suns. An optical model and a ray-tracing study have also been developed and validated, by which the potentialities of the radiometer have been largely explored.

The Impact of Mechanical Defects on the Reliability of Solar Cells in Aerospace Applications

A stable supply of electrical power is crucial for the success of space missions. Photovoltaic arrays are the most common means of in-orbit energy generation. Mechanical solar cell defects have the potential to impact their reliability considerably. In order to address this question, the environmental loads encountered in space were simulated experimentally. Five miniature solar arrays, featuring a total of ap200 cells with representative mechanical defects, were built and subjected up to 12 000 simulated eclipse phases. ap400 cell cracks on actual flight panels were monitored throughout sine vibration and acoustic noise testing to cover the mechanical loads during launch of a solar array. Electroluminescence imaging and pulsed solar simulator measurements were used to record crack patterns, to track their evolution and to quantify their electrical impact. The original size of the crack and the number of thermal cycles were identified as the main factors that determine crack growth. The number of crack growth events (CGE) per cycle was found to follow a power law dependence with an exponent of -0.85 on the number of thermal cycles and the total number of CGE accumulated over 2000 cycles showed a linear dependence on the size of the crack. A preferential crack growth direction along the short cell edge was found and attributed to the particular coupling between the cells and their carbon fiber support structure. Sine vibration and acoustic-noise testing did not result in any crack propagation. The electrical impact of mechanical defects originated predominantly from the interruption of the contact network on the cell front side. Cell area is electrically isolated either by a propagating crack that separates the singular electrical connection of a particular area, or along the original path of the crack. The quantitative laws derived allow to predict the propagation and the electrical impact of a given mechanical defect during 15 years in a geostationary-orbit environment

Infrared enhanced pulsed solar simulator

Infrared enhanced pulsed solar simulator