Long‐term performance degradation of various kinds of photovoltaic modules under moderate climatic conditions

Various kinds of photovoltaic (PV) modules have been developed and practically operated as PV systems up to present. Investigation of the long‐term reliability of PV modules is indispensable for the use of PV systems as reliable energy sources. In this study, we show the results of outdoor exposure test in which the performance of 14 PV modules composed of five different kinds made by six different PV manufacturers have been measured since July 2004. The average performance is calculated in each year from 2005 to 2008, and the performance degradation is quantitatively evaluated. The results are that the magnitude of the performance degradation can be clearly classified by the kinds of the PV modules. The performance difference of the single‐crystalline silicon (sc‐Si) modules between 2005 and 2008 is from 1.9% to 2.8%. Polycrystalline silicon (pc‐Si) modules show performance degradation from 0.7% to 1.4%. The performance of an amorphous silicon/crystalline silicon (a‐Si:H/c‐Si) decreased by 0.7%. Although a pair of a‐Si modules had been already exposed to sunlight for about 6 months, the pair of modules show 4.4% of performance degradation. More than half of the performance degradation happened during the initial period from 2005 to 2006. This indicates that it takes about 2 years until the performance of a‐Si modules is stable. The performance is quite stable after 2006. Interestingly, the performance of the cupper indium gallium diselenide modules in 2008 is about 0.8% higher than that in 2005. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of shadowing on photovoltaic module performance

A procedure of simulation and modelling PV modules' performance, working partially shadowed, is presented. Several shadow rates have been tested on a single cell forming part of a PV module having 36 solar cells serially connected, and the influence of shadow rate in most of the important PV module characteristic parameters has been evaluated.The correlation between PV module output lowering due to shadowing and the variation of resistive losses is also reported. Copyright © 2007 John Wiley & Sons, Ltd.     

Compendium of photovoltaic degradation rates

Published data on photovoltaic (PV) degradation measurements were aggregated and re‐examined. The subject has seen an increased interest in recent years resulting in more than 11 000 degradation rates in almost 200 studies from 40 different countries. As studies have grown in number and size, we found an impact from sampling bias attributable to size and accuracy. Because of the correlational nature of this study we examined the data in several ways to minimize this bias. We found median degradation for x‐Si technologies in the 0.5–0.6%/year range with the mean in the 0.8–0.9%/year range. Hetero‐interface technology (HIT) and microcrystalline silicon (µc‐Si) technologies, although not as plentiful, exhibit degradation around 1%/year and resemble thin‐film products more closely than x‐Si. Several studies showing low degradation for copper indium gallium selenide (CIGS) have emerged. Higher degradation for cadmium telluride (CdTe) has been reported, but these findings could reflect a convolution of less accurate studies and longer stabilization periods for some products. Significant deviations for beginning‐of‐life measurements with respect to nameplate rating have been documented over the last 35 years. Therefore, degradation rates that use nameplate rating as reference may be significantly impacted. Studies that used nameplate rating as reference but used solar simulators showed less variation than similar studies using outdoor measurements, even when accounting for different climates. This could be associated with confounding effects of measurement uncertainty and soiling that take place outdoors. Hotter climates and mounting configurations that lead to sustained higher temperatures may lead to higher degradation in some, but not all, products. Wear‐out non‐linearities for the worst performing modules have been documented in a few select studies that took multiple measurements of an ensemble of modules during the lifetime of the system. However, the majority of these modules exhibit a fairly linear decline. Modeling these non‐linearities, whether they occur at the beginning‐of‐life or end‐of‐life in the PV life cycle, has an important impact on the levelized cost of energy. Copyright © 2016 John Wiley & Sons, Ltd.     

The results of performance measurements of field‐aged crystalline silicon photovoltaic modules

This paper presents the results of electrical performance measurements of 204 crystalline silicon‐wafer based photovoltaic modules following long‐term continuous outdoor exposure. The modules comprise a set of 53 module types originating from 20 different producers, all of which were originally characterized at the European Solar Test Installation (ESTI), over the period 1982–1986. The modules represent diverse generations of PV technologies, different encapsulation and substrate materials. The modules electrical performance was determined according to the standards IEC 60891 and the IEC 60904 series, electrical insulation tests were performed according to the recent IEC 61215 edition 2. Many manufacturers currently give a double power warranty for their products, typically 90% of the initial maximum power after 10 years and 80% of the original maximum power after 25 years. Applying the same criteria (taking into account modules electrical performance only and assuming 2·5% measurement uncertainty of a testing lab) only 17·6% of modules failed (35 modules out of 204 tested). Remarkably even if we consider the initial warranty period i.e. 10% of P_max after 10 years, more than 65·7% of modules exposed for 20 years exceed this criteria. The definition of life time is a difficult task as there does not yet appear to be a fixed catastrophic failure point in module ageing but more of a gradual degradation. Therefore, if a system continues to produce energy which satisfies the user need it has not yet reached its end of life. If we consider this level arbitrarily to be the 80% of initial power then all indications from the measurements and observations made in this paper are that the useful lifetime of solar modules is not limited to the commonly assumed 20 year. Copyright © 2008 John Wiley & Sons, Ltd.     

Effects of solar spectrum and module temperature on outdoor performance of photovoltaic modules in round‐robin measurements in Japan

The performance of six photovoltaic (PV) modules composed of polycrystalline silicon (pc‐Si), amorphous silicon (a‐Si), and hydrogenated amorphous silicon/crystalline silicon (a‐Si:H/c‐Si) modules was investigated at eight locations in Japan from August 2007 to December 2008. In addition, solar irradiance, solar spectrum, and module temperature were simultaneously measured in these round‐robin measurements. In this study, we evaluate quantitatively the effects of module temperature and solar spectrum on the performance of the PV modules as thermal factor (TF) and spectral factor (SF), respectively. Furthermore, we investigate the variation in module performance, which is converted into module performance under standard test conditions (STC) using the TF and SF. In the case of the pc‐Si modules, the variations in performance ratio under STC (PR_STC) for these modules range from 0.056 to 0.074 through the round‐robin measurements. The TF indicates that the contribution of module temperature to the variation in performance is large, between about 15 and 20%. However, the SF suggests that the contribution of solar spectrum is quite small, less than 3%. In the case of the a‐Si modules, the contribution of module temperature is about 8%. The performance is largely influenced by solar spectrum, more than 12% at its maximum. Consequently, the variations in the corrected PR_STC of the a‐Si modules are between 0.117 and 0.141. These large variations may result from the effects of thermal annealing and light soaking. The variation in PR_STC of the a‐Si:H/c‐Si module is similar to that of the pc‐Si modules. Copyright © 2010 John Wiley & Sons, Ltd.     

Accelerated irradiance and temperature cycle test for amorphous silicon photovoltaic devices

An accelerated irradiance and temperature cycle test (AITCT) has been developed as a method to evaluate the long‐term performance stability of amorphous silicon (a‐Si) photovoltaic (PV) devices. The AITCT simulates the daily light–dark cycle in 6 min (0.1 h). It also simulates the annual temperature cycle while controlling the temperature at 45 °C above the average monthly outdoor ambient temperature. This allows the influence of the day–night cycle and seasonal variation to be included in the acceleration factor for single‐junction a‐Si PV devices. The initial degradation and seasonal variation of performance of a‐Si PV devices simulated by the AITCT agreed well with experimental results of 4‐year outdoor exposure. Subsequent tests with the AITCT equivalent of 30‐year outdoor exposure revealed that rapid degradation in the efficiency of a‐Si PV devices would not occur by repeating the cyclic changes corresponding to seasonal variations following the initial degradation. The AITCT is able to accelerate further recovery in addition to light‐induced degradation. Furthermore, the AITCT is applicable to other PV devices with light‐intensity dependencies related to light‐induced degradation as well as thermal recovery dependencies, such as multi‐junction PV devices consisting of a‐Si layers and other materials. This point will be discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Evaluation of high‐temperature exposure of photovoltaic modules

Photovoltaic (PV) modules operate at temperatures above ambient owing to the thermal energy of sunlight. The operating temperature primarily depends on the ambient temperature, incident sunlight, mounting configuration, packaging configuration, and wind speed. In this paper, the cumulative thermal degradation is modeled to follow Arrhenius behavior. The data are analyzed to determine the constant temperature that would give average aging equivalent to the variable temperatures observed in the field. These equivalent temperatures are calculated for various locations using six configurations, providing a technical basis for defining accelerated thermal‐endurance and ‐degradation testing. This data may also be useful as a starting point for studies of the combined effects of elevated temperature and other factors such as UV, moisture, and mechanical stress. Copyright © 2011 John Wiley & Sons, Ltd.     

Characterisation of charge voltage of lead‐acid batteries: application to the charge control strategy in photovoltaic systems

In stand‐alone photovoltaic (PV) systems, charge controllers prevent excessive battery overcharge by interrupting or limiting the current flow from the PV array to the battery when the battery becomes fully charged. Charge regulation is most often accomplished by limiting the battery voltage to a predetermined value or cut‐off voltage, higher than the gassing voltage. These regulation voltages are dependent on the temperature and battery charge current. An adequate selection of overcharge cut‐off voltage for each battery type and operating conditions would maintain the highest battery state of charge without causing significant overcharge thus improving battery performance and reliability. To perform this work, a sample of nine different lead‐acid batteries, typically used in stand‐alone PV systems including vented and sealed batteries with 2 V cells and monoblock configurations have been selected. This paper presents simple mathematical expressions fitting two charge characteristic voltages: the gassing voltage (V_g) and the end‐of charge voltage (V_fc) as function of charge current and temperature for the tested batteries. With these expressions, we have calculated V_g and V_fc at different current rates. An analysis of the different values obtained is presented here focusing in the implication in control strategies of batteries in stand‐alone PV systems. Copyright © 2006 John Wiley & Sons, Ltd.     

Validation of energy prediction method for a concentrator photovoltaic module in Toyohashi Japan

III–V concentrator photovoltaic systems attain high efficiency through the use of series connected multi‐junction solar cells. As these solar cells absorb over distinct bands over the solar spectrum, they have a more complex response to real illumination conditions than conventional silicon solar cells. Estimates for annual energy yield made assuming fixed reference spectra can vary by up to 15% depending on the assumptions made. Using a detailed computer simulation, the behaviour of a 20‐cell InGaP/In_0.01GaAs/Ge multi‐junction concentrator system was simulated in 5‐min intervals over an entire year, accounting for changes in direct normal irradiance, humidity, temperature and aerosol optical depth. The simulation was compared with concentrator system monitoring data taken over the same period and excellent agreement (within 2%) in the annual energy yield was obtained. Air mass, aerosol optical depth and precipitable water have been identified as atmospheric parameters with the largest impact on system efficiency. Copyright © 2012 John Wiley & Sons, Ltd.     

A novel analytical model for determining the maximum power point of thin film photovoltaic module

Achieving the maximum power output from photovoltaic (PV) modules is indispensable for the operation of grid‐connected PV power systems under varied atmospheric conditions. In recent years, the study of PV energy for different applications has attracted more and more attention because solar energy is clean and renewable. We propose an efficient direct‐prediction method to enhance the utilization efficiency of thin film PV modules by tackling the problem of tracking time and overcoming the difficulty of calculation. The proposed method is based on the p–n junction recombination mechanism and can be applied to all kinds of PV modules. Its performance is not influenced by weather conditions such as illumination or temperature. The experimental results show that the proposed method provides high‐accuracy estimation of the maximum power point (MPP) for thin film PV modules with an average error of 1.68% and 1.65% under various irradiation intensities and temperatures, respectively. The experimental results confirm that the proposed method can simply and accurately estimate the MPP for thin film PV modules under various irradiation intensities and temperatures. In future, the proposed method will be used to shed light on the optimization of the MPP tracking control model in PV systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Operational performance of grid‐connected PV systems on buildings in Germany

This paper presents operational performance results of grid‐connected PV systems in Germany, as collected and elaborated for the Photovoltaic Power Systems Programme (PVPS) of the International Energy Agency (IEA). Performance ratios obtained from 235 PV installations in Germany and from 133 PV plants in other countries are compared and discussed. For Germany, a significant rise in PV system performance and reliability was observed for new PV installations due to higher component efficiencies (e.g., inverter) and increased availabilities. There is a lack of long‐term experience in performance and reliability of PV systems, owing to the absence of monitoring programmes. As an outcome of IEA PVPS collaborative work, Task 2 provides reliable and worldwide monitoring performance data and results (www.task2.org). Technical and operational data is available for system planning and comparison, for teaching and training purposes as well as for future developments of financing schemes (e.g., feed‐in‐tariffs) in order to stimulate the PV market. Copyright © 2004 John Wiley & Sons, Ltd.     

Innovation and fabrication of 5.5 generation image‐patterned translucent photovoltaic module by using laser scribing technology

The building‐integrated photovoltaic (PV) technology is one of the most promising applications for amorphous silicon (a‐Si) thin film solar cells. It is necessary to develop more various building‐integrated PV modules, which will provide architects and industries more options for the PV installation to their buildings or construction bodies. In this paper, a new type of a‐Si PV module, called image‐patterned translucent a‐Si PV module, is developed. Any required image can be displayed on the module by using laser processes. In the present result, a 5.5 generation (1100 × 1400 mm) image‐patterned translucent PV module with 10% transmittance exhibits the stabilized maximum power output (P_max) of 92.5 W, which can be further improved by optimizing the laser parameters. The remarkable features of our module such as the image displaying, natural light transmission, and heat reduction create entirely new applications including windows and logos and provide an option that adds personal style and unique design to the building interiors. Copyright © 2011 John Wiley & Sons, Ltd.     

An analysis of reliability in the early stages of photovoltaic systems in Japan

In order to disseminate Photovoltaic (PV) technologies into the energy network, the cost down is not only important, but also improving the performance of the PV system is significant issues. Long‐term reliability is one of the most important issues in terms of PV system performance. Previous researches were mainly focused on the reliability of PV modules, but the PV system is composed of a power conditioner, wiring, junction box, and so on. To improve the reliability of PV systems, it is important to accumulate trouble cases focused on all components of PV system. In this paper, we aim at evaluation of the reliability for the PV system on the early stages of PV system's lifetime by using large number of Japanese PV systems' data from the field Test in Japan. New Energy and Industrial Technology Development Organization has been running the “Field test project in Japan” from 1992. In this project, PV system users have cooperated with the collection of monitoring data and reported on the information of maintenance and certain failures of PV systems for 4 years after installation of PV system. Using those reports each year of installation, we evaluated reliability of PV systems by means of parameters such as Mean Time Between Failure, Mean Time To Repair, and the suspension time of PV system. As a result, the main trouble of PV systems was related power conditioner, and a few trouble of PV module was caused by typhoon. Moreover, the trend of the failure rate before FY 2000 of installation was demonstrated as the trend of initial failure in “bathtub curve;” however, the trend of its after FY 2001 of installation was indicated as the accidental failure in “bathtub curve.” Further, the operator simply forgot to restart the power conditioner after maintenance or suspensions of PV system in many trouble cases, and the user did not notice that it had been suspended for a while. These trouble cases can be avoidable easily through the effective alarm such as error message of power conditioner systems with monitoring systems. Thereby, monitoring with the evaluation method of PV systems is one of the important technologies due to the long‐term reliability and stable operation. Copyright © 2010 John Wiley & Sons, Ltd.     

Enhanced photovoltaic performance of cross‐linked ruthenium dye with functional cross‐linkers for dye‐sensitized solar cell

Photovoltaic performance of cross‐linkable Ru(2,2′‐bipyridine‐4,4′‐bicarboxylic acid)(4,4′‐bis((4‐vinyl benzyloxy)methyl)‐2,2′‐bipyridine)(NCS)₂ (denoted as RuS dye) adsorbing on TiO₂ mesoporous film was enhanced by polymerizing with either ionic liquid monomer, 1‐(2‐acryloyloxy‐ethyl)‐3‐methyl‐imidazol‐1‐ium iodide (AMImI), to form RuS‐cross‐AMImI or di‐functional acrylic monomer with ether linkage, triethyleneglycodimethacrylate (TGDMA), to form RuS‐cross‐TGDMA. Their cross‐linking properties were investigated by UV–vis spectroscopy by rinsing with 0.1 N NaOH aqueous solution. The power conversion efficiencies (PCEs) of dye‐sensitized solar cells (DSSCs) with RuS‐cross‐AMImI and RuS‐cross‐TGDMA both reached over 8% under standard global air mass 1.5 full sunlight. The increased PCE for DSSCs with RuS‐cross‐AMImI comparing with cross‐linked RuS was attributed to the I⁻ counterion of AMImI increasing the charge regeneration rate of RuS dye, whereas that with RuS‐cross‐TGDMA was attributed to the Li⁺ coordination property of TGDMA. The photovoltaic performance of RuS‐cross‐TGDMA was also slightly better than that of RuS‐cross‐AMImI because of higher open‐circuit photovoltage (V_oc) and short‐circuit photocurrent (J_sc). Its higher V_oc was supported by the Bode plot of impedance under illumination and Nyquist plots at dark, whereas higher J_sc was supported by the incident monochromatic photon‐to‐current conversion efficiency spectra and charge extraction experiments. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance stability of photovoltaic modules in different climates

The current–voltage ( I‐V) characteristics of 15 different photovoltaic modules are monitored during more than 2 years of operation at four locations (Germany, Italy, India and Arizona) corresponding to four different climate zones. The electrical stability of the photovoltaic modules during the time of outdoor exposure is investigated in terms of measured I‐V curve translated to standard test conditions. This translation compensates the influence of module temperature, irradiance, spectral effects and soiling on the I‐V curves. The changes of output power after these corrections are attributed to initial consolidation phases, to long‐term degradation of the electrical properties and to seasonal cycles associated with metastabilities. Modules made from crystalline Si turn out to show no or only minor effects. Thin‐Film modules (CdTe, Cu(In,Ga)Se₂ and thin‐film Si) exhibit a wide spread of metastable behaviour with consistent patterns for identical modules in different climates but with significant differences amongst different manufacturers of the same thin‐film technology. We show further that this metastable behaviour influences the energy yield of the modules. Copyright © 2017 John Wiley & Sons, Ltd.     

Developing a method and simulation model for evaluating the overall energy performance of a ventilated semi‐transparent photovoltaic double‐skin facade

A comprehensive simulation model has been developed in this paper to simulate the overall energy performance of an amorphous silicon (a‐Si) based photovoltaic double‐skin facade (PV‐DSF). The methodology and the model simulation procedure are presented in detail. To simulate the overall energy performance, the airflow network model, daylighting model, and the Sandia Array Performance Model in the EnergyPlus software were adopted to simultaneously simulate the thermal, daylighting, and dynamic power output performances of the PV‐DSF. The interaction effects between thermal, daylighting, and the power output performances of the PV‐DSF were reasonably well modeled by coupling the energy generation, heat‐transfer, and optical models. Simulation results were compared with measured data from an outdoor test facility in Hong Kong in which the PV‐DSF performance was measured. The model validation work showed that most of the simulated results agreed very well with the measured data except for a modest overestimation of heat gains in the afternoons. In particular, the root‐mean‐square error between the simulated monthly AC energy output and the measured quantity was only 2.47%. The validation results indicate that the simulation model developed in this study can accurately simulate the overall energy performance of the semi‐transparent PV‐DSF. This model can, therefore, be an effective tool for carrying out optimum design and sensitivity analyses for PV‐DSFs in different climate zones. The methodology developed in this paper also provides a useful reference and starting point for the modeling of other kinds of semi‐transparent thin‐film PV windows or facades. Copyright © 2015 John Wiley & Sons, Ltd.     

Dark I–V curve measurement of single cells in a photovoltaic module

A simple method of obtaining single cell dark I–V curves in a photovoltaic module was developed. The method does not require disassembling the module and was verified experimentally. From the dark I–V curves, the cell characteristic parameters were obtained. By following the time evolution of the characteristic parameters it is possible to determine the main degradation mechanisms and predict the mean life time of the module before failure. Copyright © 2005 John Wiley & Sons, Ltd.     

SFP光模块PCB制作工艺研究

在SFP光模块PCB高速/高频信号传输存在趋肤效应的条件下,分析了“镀水金+镀厚金”常规工艺信号传输线镀覆镍金对信号传输的影响,研究出“镀厚金+沉金”工艺,实现了信号传输线无镀覆镍金,有利于信号完整性控制,并保证了PCB长短金手指完整性良好(无残缺、无残留镀金导线头、无尖角等异常).     

Impact of photovoltaic orientation on its relative economic value in wholesale energy markets

Most calculations of optimum photovoltaic (PV) performance focus on maximizing annual energy production. However, given the seasonally and daily time varying electricity demand and resulting variation in price, the PV orientation resulting in maximum energy yield may not yield the maximum economic benefit. With the use of historical solar irradiance and wholesale market prices for several locations in the USA, we evaluate the benefits of a variety of orientations for fixed and tracking PV arrays. We find that orienting fixed arrays slightly to the west of due south generally increases their economic value in the simulated systems because the reduced generation on an annual basis is more than offset by increased generation in high‐value hours in late summer afternoons. However, this effect is small, typically providing an increase in value from 1% to 5%. The economic value of adjusting the orientation semi‐annually (May 1st and September 1st) and monthly shows a modest increase in value from 3% to 5%. Several other implications of this analysis are also discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

System memory effects in the sizing of stand‐alone PV systems

Models based on daily energy balance (or long‐term models) have been widely used as a tool in the stand‐alone photovoltaic (PV) system sizing, mainly with the purpose of obtaining analytical expressions of the relation between the generator size and the storage capacity of the battery. The system can then be designed to meet the reliability requirements of the specific case. However, such models represent the complex operation of a stand‐alone system in an oversimplified way. There is little research so far on the reliability and improvement of such models. Validation and possible modification of a long‐term system model requires comparison of the simulated state of charge (SOC) of the battery with that obtained from an experimental system. In this work, experimental data from a 6‐month operation of a basic stand‐alone PV system have been analysed and compared with modelling results. One obvious improvement that could be applied to the long‐term system model is to account for a charging efficiency of the battery, and this possibility is examined in the present work. However, comparison with the modelling results shows that the data cannot be fitted by simply taking into account battery inefficiency. A method to account for system memory effects in the increase of the battery SOC, imposed by the operation of the regulator, is necessary to accurately model the macroscopic diurnal charging/discharging process. Copyright © 2012 John Wiley & Sons, Ltd.