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• Experimental shunt resistance increases for low irradiance levels on crystalline PV modules. • Experimental series resistance increases for low irradiance levels on crystalline PV modules. • Diode ideality factor does not present temperature or irradiance dependences. • Parasitic resistances do not present temperature dependence on the single-diode model. Five-parameter single diode models are the most used for photovoltaic modeling, and although they usually apply the same basic equation, there are several variations in terms of parameter dependences on irradiance and temperature. Different methods with variations on the resistances' values with the temperature or irradiance have been proposed, and there is also discussion on the treatment of the dark reverse saturation current with the temperature level. On experimental works, there is even more controversy. Several authors reach distinct conclusions about the behavior of almost every parameter of the single diode model when extracting them at each irradiance or temperature levels. For instance, in accordance to different publications, series resistance may either increase, decrease or remain constant under irradiance variations. In this paper, we review previous studies and their proposals, discussing also the possible influence of the extraction method on these results. Later, two experiments are performed in a solar simulator to extract all the parameters on a broad range of irradiance and temperature levels with an analytical extraction method for crystalline silicon modules. The results show that the thermal coefficient used to correct the open-circuit voltage for different temperatures may depend on the irradiance level, a finding that is not present in the single diode models found in the literature. The most common approaches for the diode ideality factor and the diode reverse current, constant ideality factor and a temperature variation for reverse saturation current are seen to fit with the experimental data, while the parasitic resistances both presented a significant increase for low irradiance levels and no significant dependence on the temperature. These experimental findings, reached using a set of 27 commercial PV modules, may help improve the development of methods for solving the single-diode model and improving its accuracy at different operating conditions. [ABSTRACT FROM AUTHOR]

• The mesh calibration achieved the required precision with minimal sample size. • The transmissivity of mesh screens was measured with <1 % error with 5–7 samples. • Layer arrangement in mesh screens affected their transmissivity by up to 0.3%. • The dependence between layers influenced mesh screen transmissivity by up to 1%. • Interlayer dependence and arrangement must be considered to achieve <2 % error. Mesh screens can be installed over a photovoltaic (PV) module to provide varying degrees of outdoor solar irradiance for I-V curve measurements. In such tests, it is often not possible to cover the PV module and the irradiance sensor with the mesh screen at the same time, requiring the transmissivity of the mesh to be accurately measured beforehand. This paper describes a measurement method and evaluates the uncertainty in determining the transmissivity of mesh screens used to attenuate solar radiation on PV modules. The method involves modeling the short-circuit current of the PV module as a function of irradiance and temperature indoors and measuring the transmissivity of mesh screens outdoors. Two mesh screens with nominal transmissivities of 50 % and 70% were assembled and used in single-layer and double-layer configurations, resulting in four different mesh filters. The transmissivity of each configuration was measured under four different conditions obtained by combining two angles of incidence for solar radiation – normal and 30° - and using two PV modules, one with monocrystalline and the other with polycrystalline silicon cells. The proposed measurement method succeeded in measuring the transmissivity and determining the optimal sample size for all mesh screen configurations, taking 5 to 7 measurements to obtain an uncertainty of less than 1%. The work highlights the importance of measuring the transmissivity of mesh screens and provides valuable results for future research using this method to study the performance of PV modules at low irradiance levels. [ABSTRACT FROM AUTHOR]

Abstract: An efficient and reliable characterization of PV devices is paramount for the establishment of new PV installations and for evaluation of the performance of the existent ones. In order to analyze the electrical performance of photovoltaic devices it is essential the determination of the characteristic current versus voltage (I–V) curve from which important information about several parameters of the PV generator can be obtained. The objective of this work is to present an accurate and reliable post-processing method for measured I–V curves (raw data) of photovoltaic devices. In order to implement this post-processing method in-house software (which is described in this work) was developed to post-process I–V curves of any PV device. This software allows the determination of several parameters from a measured I–V curve, as well as its translation to any irradiance and temperature conditions. The post-processing method has been tested in a wide range of raw data I–V curves related to modules based on different technologies. The results have shown a very good level of reliability and accuracy for traditional crystalline silicon and thin film devices. [Copyright &y& Elsevier]