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THERMAL CLASSIFICATION MODELLING AND ENERGY YIELD PERFORMANCE OF DIFFERENT CRYSTALLINE SILICON PHOTOVOLTAIC MODULES WITH INNOVATIVE PACKAGING COMPONENTS
Abstract
The packaging materials (especially the backsheet) directly affect the performance and reliability of photovoltaic (PV) modules, especially when exposed to locations with prolonged elevated temperatures. The scope of this work is to analyse the thermal behaviour of different crystalline silicon (c-Si) PV modules manufactured with innovative packaging components capable of reducing the operating cell temperatures and in parallel, to assess their energy yield under warm outdoor climatic conditions. In particular, the outdoor evaluation was performed with different backsheet material modules installed side by side as grid-connected systems and monitored at the PV Technology Laboratory, University of Cyprus (UCY), in Cyprus. The thermal operation comparative analysis for each system, based on acquired cell temperature measurements over a three-year period, verified that backsheets can be designed in order to keep PV modules operating at cooler temperatures, in some cases, by up to 10 °C during clear sky days. Finally, the annual energy yield results showed clearly that the systems equipped with the white control and black color thermal management backsheet systematically produced the highest annual energy yield.
The composition, properties and construction of a backsheet have a direct bearing on its functional performance in a photovoltaic module. Typically, the performance properties are examined under fixed stress conditions and the performance and stability of backsheets to these stress conditions are studied. But exposure to the outdoor environment involves stresses acting sequentially and simultaneously. The effect of these stresses should be applied to modules as well as components to adequately assess their impact on performance and durability.
To better understand the expected performance in the field, we have examined established and new backsheet constructions and characterized their initial properties and durability under the usual accelerated test stressors (heat, humidity, UV, temperature cycling) and under conditions where these stressors are applied sequentially or simultaneously. We have also investigated performance of materials under new stress conditions designed to better simulate the operation of a PV module in the outdoor environment. We have applied weathering conditions based on the expected life of the product under various climates to temperature and UV exposure using albedo exposure from the back of the module and using transmitted UV light through the package.
The performance and durability of modules from the field after long outdoor exposure are further examined by non-destructive and destructive analysis. Backsheet constructions are identified and module performance is assessed using IV, EL, insulation, color, visual assessment, and ATR-IR spectroscopy. Further assessment employing sampling techniques and a wide range of analytical methods to better understand chemical and physical changes is also described.
A number of candidate alternative encapsulant and soft backsheet materials have been evaluated in terms of their suitability for photovoltaic (PV) module packaging applications. Relevant properties, including interfacial adhesion and moisture transport, have been measured as a function of damp-heat (85°C / 85% relative humidity) exposure. Based on these tests, promising new encapsulants with improved properties have been identified. Backsheets prepared by industry and at NREL have been found to provide varying levels of moisture ingress protection. To achieve significantly improved products, further development of these candidates is ongoing. The relative effectiveness of various packaging strategies to protect PV devices has also been investigated.
Mathematical, empirical, and electrical models have long been implemented and used to predict the energy yield of many photovoltaic (PV) technologies. The purpose of this paper is to compare the annual DC energy yield prediction errors of four models namely the single-point efficiency, single-point efficiency with temperature correction, the Photovoltaic for Utility-Scale Applications (PVUSA), and the one-diode model, against outdoor measurements for different grid-connected PV systems in Cyprus over a 4-year evaluation period. The different models showed a wide variation of prediction errors, demonstrating a strong dependence between model performance and the different technologies. In particular, it was clearly shown that the application of temperature loss correction based on the manufacturer's temperature coefficients of power at maximum power point assisted in improving the energy yield prediction significantly especially for the crystalline silicon (c-Si) technologies. In most cases, the best agreement between the modeled results and outdoor-measured annual DC energy yield for mono-crystalline silicon (mono-c-Si) and multi-crystalline silicon (multi-c-Si) technologies was obtained using the one-diode model. The energy yield for the thin-film technologies was more accurately predicted using the PVUSA model with the exception of the copper-indium-gallium-diselenide (CIGS) technology, which was best predicted using the single-point efficiency with temperature correction and one-diode models, thus demonstrating similar physical properties to c-Si technologies. The paper further quantifies the combined uncertainties associated with the predicted energy yield as a function of the input parameters for the single-point efficiency, single-point efficiency with temperature correction, and the PVUSA models. Copyright © 2011 John Wiley & Sons, Ltd.
It is well-known that the maximum power output of photovoltaic devices changes with temperature. Therefore, the temperature coefficients of the basic device performance parameters (open-circuit voltage, short-circuit current, fill factor, and efficiency) are important factors which must be taken into account in the design of a photovoltaic power system, where temperature changes occur throughout the day and year. This paper reports results of experimental temperature coefficient measurements obtained on a wide variety of different photovoltaic devices, many of which have not had temperature coefficient data published previously.
As photovoltaic penetration of the power grid increases, accurate predictions of return on investment require accurate prediction of decreased power output over time. Degradation rates must be known in order to predict power delivery. This article reviews degradation rates of flat-plate terrestrial modules and systems reported in published literature from field testing throughout the last 40 years. Nearly 2000 degradation rates, measured on individual modules or entire systems, have been assembled from the literature, showing a median value of 0.5%/year. The review consists of three parts: a brief historical outline, an analytical summary of degradation rates, and a detailed bibliography partitioned by technology.
The energy produced by different photovoltaic (PV) systems depends to a great extent on the inverter and photovoltaic module outdoor efficiency which in turn vary according to the irradiance and temperature of the field conditions. The objective of this paper is to describe the investigations performed to evaluate the outdoor efficiencies of thirteen (13) different types of PV modules which have been exposed to real conditions in Stuttgart, Germany and Nicosia, Cyprus. The inverter and PV array efficiencies have been evaluated by using direct outdoor measurements and data analysis on the measured metereological and operational data collected by the installed sensors present at the two test sites. The measured efficiency of the PV modules has been further evaluated on a seasonal basis reflecting the obvious effects of the seasonal variations of incident irradiation, operating temperature and seasonal spectral shift on the outdoor operating efficiency. The average annual inverter efficiency measured in Stuttgart was 89.8 % while the corresponding inverter efficiency in Nicosia was 90.9 % for the same period and for identical inverters that are rated at a European Efficiency of 91.6 %.