Early degradation of silicon PV modules and guaranty conditions

The fast growth of PV installed capacity in Spain has led to an increase in the demand for analysis of installed PV modules. One of the topics that manufacturers, promoters, and owners of the plants are more interested in is the possible degradation of PV modules. This paper presents some findings of PV plant evaluations carried out during last years. This evaluation usually consists of visual inspections, I-V curve field measurements (the whole plant or selected areas), thermal evaluations by IR imaging and, in some cases, measurements of the I-V characteristics and thermal behaviours of selected modules in the plant, chosen by the laboratory. Electroluminescence technique is also used as a method for detecting defects in PV modules. It must be noted that new defects that arise when the module is in operation may appear in modules initially defect-free (called hidden manufacturing defects). Some of these hidden defects that only appear in normal operation are rarely detected in reliability tests (IEC61215 or IEC61646) due to the different operational conditions of the module in the standard tests and in the field (serial-parallel connection of many PV modules, power inverter influence, overvoltage on wires, etc.).     

在户外条件下测量晶体硅组件最大功率的不确定度分析

依据地面用晶体硅光伏组件设计鉴定和定型标准(IEC61215-2005)的要求,在户外自然光条件下,对地面用晶体硅光伏组件的I-V特性进行了测量;依据光伏器件实测特性的温度和辐照度修正方法标准(IEC60891-2009)对测得的电压、电流及最大功率进行修正,使其结果能回推到标准测试条件(STC)下。分析了产生测量不确定度的因素。通过计算得出回推到标准测试条件下的电压、电流及最大功率的标准不确定度和扩展不确定度。     

Outdoor performance of amorphous silicon and polycrystalline silicon PV modules

The daily watt-hour efficiency (η_Wh) and daily integrated output power (P_Wh) of the a-Si and poly-Si module have been used to examine the performances of both modules on the basis of two years' data accumulated at outdoor conditions. Results from the analysis of experimental data taken under incident solar energy higher than 3.0 kWh/m² per day show that the annual average of η_Wh of the a-Si module is about 95% and 92.5% of its efficiency at STC condition at the first and second year, respectively, while the values are nearly unchanged at about 89% for the poly-Si module. During a one year period, the average P_Wh of the a-Si and poly-Si module was about 60% and 56%, respectively, of their calculated output power at STC condition, so that the P_Wh for each watt-peak (W_p) of the maximum power of a-Si module is about 11% higher than that of the poly-Si module.     

Characterization of thin film PV modules under standard test conditions: Results of indoor and outdoor measurements and the effects of sunlight exposure

Photovoltaic modules based on thin film technology are gaining importance in the photovoltaic market, and module installers and plant owners have increasingly begun to request methods of performing module quality control. These modules pose additional problems for measuring power under standard test conditions (STC), beyond problems caused by the temperature of the module and the ambient variables. The main difficulty is that the modules’ power rates may vary depending both on the amount of time they have been exposed to the sun during recent hours and on their history of sunlight exposure. In order to assess the current state of the module, it is necessary to know its sunlight exposure history. Thus, an easily accomplishable testing method that ensures the repeatability of the measurements of the power generated is needed.This paper examines different tests performed on commercial thin film PV modules of CIS, a-Si and CdTe technologies in order to find the best way to obtain measurements. A method for obtaining indoor measurements of these technologies that takes into account periods of sunlight exposure is proposed. Special attention is paid to CdTe as a fast growing technology in the market.     

Non-destructive degradation analysis of encapsulants in PV modules by Raman Spectroscopy

Raman Probe Spectroscopy as a powerful tool for analyzing the degradation behavior of encapsulants in c-Si based PV modules is reported. A non-destructive and quick testing method is needed in order to follow material changes during the aging of PV modules. Two types of c-Si PV modules with ethylene vinyl acetate (EVA) encapsulation have been aged indoors under damp-heat conditions (85% r.h./85 °C) and under combined UV/moisture conditions, respectively. The aged modules as well as a non-aged reference module for each type were analyzed by Raman Spectroscopy. The degradation of the encapsulant was observed, resulting in an increasing fluorescence background, as well as changing intensities of EVA Raman peaks. A lateral non-uniformity of the fluorescence intensity of and the EVA CH stretching vibration intensity ratios, depending on the position above the cell as well as from the aging condition, could be observed and it might be an indicator for the diffusion of water in the encapsulant.     

Evaluation of performance parameters of PV modules deployed outdoors

This paper evaluates the performance parameters of five photovoltaic (PV) modules comprising crystalline silicon, multi-crystalline silicon and edge-defined film-fed growth (EFG) silicon technologies. This evaluation was accomplished by measuring and analysing the modules' performances during initial, intermediate and final stages of a 17-month test period. The effect of temperature and irradiance on the performance parameters was investigated. Results obtained indicate that some modules exhibited shunting behaviour and that the EFG silicon module experienced moisture ingress, which in part, resulted in 14% performance degradation. An analysis of the results revealed that the moisture ingress effectively reduced the active module area, resulting in reduced photon absorption, consequently reducing the electron-hole generation as indicated by the reduced short-circuit current. In addition, the EFG-Si module's shunt resistance appeared to decrease over the test period. The rest of the modules showed relatively stable performance, information that is crucial to the system designer and consumer.     

Calculation of the PV modules angular losses under field conditions by means of an analytical model

Photovoltaic (PV) modules in real operation present angular losses in reference to their behaviour in standard test conditions, due to the angle of incidence of the incident radiation and the surface soil. Although these losses are not always negligible, they are commonly not taken into account when correcting the electrical characteristics of the PV module or estimating the energy production of PV systems. The main reason of this approximation is the lack of easy-to-use mathematical expressions for the angular losses calculation. This paper analyses these losses on PV modules and presents an analytical model based on theoretical and experimental results. The proposed model fits monocrystalline as well as polycrystalline and amorphous silicon PV modules, and contemplates the existence of superficial dust. With it angular losses integrated over time periods of interest can be easily calculated. Monthly and annual losses have been calculated for 10 different European sites, having diverse climates and latitudes (ranging from 32° to 52°), and considering different module tilt angles.     

Validation of the Sandia model with indoor and outdoor measurements for semi-transparent amorphous silicon PV modules

This paper presents a set of indoor and outdoor measurement methods and procedures to determine the empirical coefficients of the Sandia Array Performance Model (SAPM) for a semi-transparent amorphous silicon (a-Si) PV module. After determining and inputting the total 39 parameters into the SAPM, the dynamic power output of the a-Si PV module was predicted. In order to validate the accuracy of using SAPM for simulating the energy output of the a-Si PV module, a long-term outdoor testing campaign was conducted. The results indicated that the SAPM with indoor and outdoor measured coefficients could accurately simulate the energy output of the a-Si PV module on sunny days, but it didn't work well on overcast days due to the inappropriate spectral correction as well as the equipment measuring error caused by the intense fluctuation of solar irradiance on overcast days. Specifically, all the errors between the simulated daily energy output and the measured one were less than 4% on sunny days. In order to achieve a better prediction performance for a-Si PV technologies, the SAPM was suggested to incorporate a more comprehensive spectral correction function to correct the impact of solar spectrum on overcast days in future.     

Analysis and enhancement of PV efficiency with incremental conductance MPPT technique under non-linear loading conditions

This paper presents experimental evaluations for variation in the efficiency of energy extracted from a photovoltaic (PV) module (under non-linear loading) incorporated with an incremental conductance(IC) maximum power point tracking (MPPT) algorithm. The focus is on the evaluation of the PV panel under non-linear loading conditions using the experimental installation of a 100W_p photovoltaic array connected to a DC–DC converter and a KVA inverter feeding a non-linear load. Under the conditions of non-linear loading, both the simulation and experiment show that the MPPT technique fails to attain maximum power point due to the presence of ripples in the current leading eventually to a reduction in efficiency. In this paper, panel current is taken as a function of load impedance in the MPPT algorithm to eradicate power variation, as load impedance varies with supply voltage under non-linear conditions. The system is simulated for different non-linear loads using MATLAB-Simulink. A TMDSSOLAREXPKIT was used for MPPT control. In case 2, the inverter is connected to a single phase grid. When a voltage swell occurs in the grid, PV power drops. This power loss is reduced using the proposed MPPT method. The results of simulations and experimental measurements and cost efficiency calculations are presented.     

晶体硅光伏组件的检测

我国有丰富的太阳能资源，太阳能光伏发电已不再仅仅用于小功率电源系统，而且广泛用于通信、交通、石油、农村电气化、民用产品等各个领域。1998年我国生产的太阳能光伏发电系统的主要部件——光伏组件产量只有2MW。左右，仅相当于世界总产量的1．3％，到2002年产量已达到100MW。左右，截至到2003年底在我国使用光伏组件装机的太阳能电站达到55MWp。保证太阳能光伏发电系统的质量不仅取决于系统的设计，还取决于构成系统各部件产品的质量。光伏组件作为太阳能光伏发电系统的主要部件，其产品的质量就显得尤为重要。为保证该产品的质量，国家制定了相关的检测标准．本文就光伏组件产品质量的检测作一介绍．     

Evaluation of solar element and collector system efficiency under hot climate conditions

The performance of combined photo-heat-converter systems under hot climate conditions is considered. The parameters of the photo-heat-converter are obtained to reveal the potential for providing electric energy for domestic and household appliances and hot water for individual energy consumers living in areas far from the centralized power sources.     

Comparative study of performance degradation in poly- and mono-crystalline-Si solar PV modules deployed in different applications

Data on long-term performance and degradation of field-aged solar photovoltaic modules is widely recognized as necessary for continued technological improvement and market confidence. It is also important that such research should cover various geographical regions of the globe. This paper presents a study on twenty-nine (29) crystalline silicon modules deployed in grid-connected, battery-charging and water-pumping applications. The modules, installed at six different locations in Ghana were aged between 6 and 32 years. Peak power (P_max) losses ranged from 0.8%/year – 6.5%/year. The P_max losses were dominated by losses in fill factor (FF) and short-circuit current (I_sc). Visually observable defects are also reported.     

一种光伏组件寿命的测量方法

给出了组件日发电量和太阳日辐射量的测量方法,采用具有最大功率点跟踪的发电量测试仪测试被测组件和参考组件,通过比较它们日发电量之比与日期的关系,判断被测组件的稳定性,并评估组件的寿命。     

晶体硅光伏组件的检测

我国有丰富的太阳能资源，太阳能光伏发电已不再仅仅用于小功率电源系统，而且广泛用于通信、交通、石油、农村电气化、民用产品等各个领域。1998年我国生产的太阳能光伏发电系统的主要部件——光伏组件产量只有2MWp左右，仅相当于世界总产量的1．3％，到2002年产量已达到100MWp左右，截至到2003年底在我国使用光伏组件装机的太阳能电站达到55MWp。保证太阳能光伏发电系统的质量不仅取决于系统的设计，     

Theoretical analysis and experimental verification of PV modules

This paper introduces a theoretical analysis of the performance of photovoltaic modules under different meteorological conditions and design parameters. Based on the analysis, A FORTRAN computer sub-program has been constructed and connected to TRNSYS simulation program. The present sub-program is executed within the TRNSYS program to compute the different parameters of PV modules. These parameters include short circuit current, open circuit voltage, maximum output power, I-V and P-V characteristics, and efficiency. To verify the present sub-program, an experimental set up has been installed. It includes a group of identical PV modules mounted at different tilt angles and orientations, an electronic load, a weather station, a data acquisition system, and a computer. The comparison between the experimental and theoretical results shows good agreement at different meteorological conditions, tilt angles, and orientations.     

Characterisation of solar cells and modules under actual operating conditions

A PC-based measuring system is presented for outdoor testing of solar cells and modules under real operating conditions. It consists of a sun-tracked sample holder, different electronic loads (including control), digital multimeters, a PC and a laser printer. Insolation is measured and recorded with pyranometers, pyrheliometers and a reference cell. Current-voltage curves are acquired in the range of irradiance from 10 W/m² to over 1000 W/m². Small single cells of size down to 3 mm by 3 mm as well as large modules and laminates up to 1 m by 1.5 m can be tested. The measurement time for one test can be varied between 5 to 15 seconds. The maximum power point (mpp) is normally detected on-line. However, it can also be determined in a subsequent mathematical analysis, if more precise mpp data are required. The maximum relative uncertainty in the efficiency (determined from mpp data) has been estimated to be less than ± 1 %, depending on type and size of cell or module and on the constancy of the insolation during the testing time. Using a new dynamic method, the temperature coefficient of the efficiency can be determined within a relative uncertainty of about ± 3 %. The coefficient is used to derive standard test condition data. Results are given for two commercial modules.     

太阳能光伏发电系统光伏阵列保护用熔断器的选择分析

光伏发电系统是由能把太阳光能直接转换为电能的部件和子系统构成。其中的光伏阵列是将入射的太阳辐射能直接转换为直流电能的单元,太阳电池板组成的阵列与光伏阵列连接箱连接,电流经连接箱汇流后输出到逆变器或直接应用环节。太阳电池板组成的光伏阵列约占光伏发电系统总成本的70%,如何保护光伏阵列和充分提高     

Temperature and wind speed impact on the efficiency of PV installations. Experience obtained from outdoor measurements in Greece

Although efficiency of photovoltaic (PV) modules is usually specified under standard test conditions (STC), their operation under real field conditions is of great importance for obtaining accurate prediction of their efficiency and power output. The PV conversion process, on top of the instantaneous solar radiation, depends also on the modules' temperature. Module temperature is in turn influenced by climate conditions as well as by the technical characteristics of the PV panels. Taking into consideration the extended theoretical background in the field so far, the current study is focused on the investigation of the temperature variation effect on the operation of commercial PV applications based on in-situ measurements at varying weather conditions. Particularly, one year outdoor data for two existing commercial (m-Si) PV systems operated in South Greece, i.e. an unventilated building-integrated (81 kW_p) one and an open rack mounted (150 kW_p) one, were collected and evaluated. The examined PV systems were equipped with back surface temperature sensors in order to determine module and ambient temperatures, while real wind speed measurements were also obtained for assessing the dominant effect of local wind speed on the PVs' thermal loss mechanisms. According to the results obtained, the efficiency (or power) temperature coefficient has been found negative, taking absolute values between 0.30%/°C and 0.45%/°C, with the lower values corresponding to the ventilated free-standing frames.     

Scale-up issues of CIGS thin film PV modules

Photovoltaics cost has been declining following a 70% learning curve. Now the challenge is to bring down the cost of solar electricity to make it competitive with conventional sources within the next decade. In the long run, the module efficiencies tend to reach 80% of the champion cell efficiencies. Using a semiempirical methodology, it has been shown earlier that while the triple junction a-Si:H thin film technology is competitive, CIGS and CdTe thin film module technologies are highly competitive and presently offer the best approach for significantly exceeding the cost/performance levels of standard and non-standard crystalline Si PV technologies. Since 2006, the production of thin film solar cell in the U.S. has surpassed that of c-Si. At present, the production of CIGS PV modules lags considerably behind that of CdTe PV modules. This is mainly because of its complexity. Scale-up issues related to various CIGS preparation technologies such as co-evaporation, metallic precursor deposition by magnetron sputtering and non-vacuum techniques such as ink-jet printing, electroplating or doctor-blade technology followed by their selenization/sulfurization are discussed so as to assist the CIGS technology to attain its full potential. Besides the welcome announcements of large volume production, it is essential to achieve the production cost below $1/Wp in the near term and attain production speeds comparable to CdTe production speeds. Comparable production speeds are expected to be achieved within the next decade. This will enable reduction of CIGS module production costs to ∼65¢/Wp that would be comparable to the CdTe module projected production cost. Additionally CIGS will have a higher efficiency premium.     

Study of bypass diodes configuration on PV modules

A procedure of simulation and modelling solar cells and PV modules, working partially shadowed in Pspice environment, is presented. Simulation results have been contrasted with real measured data from a commercial PV module of 209 Wp from Siliken. Some cases of study are presented as application examples of this simulation methodology, showing its potential on the design of bypass diodes configuration to include in a PV module and also on the study of PV generators working in partial shading conditions.