Degradation and partial shading impact the long-term reliability and power production of photovoltaic (PV) modules and power plants. Time-series power (P-mp) and current-voltage (I -V) curve datastreams from PV modules enable a remote diagnostic approach to quantify active degradation mechanisms and identify partial shading. We study three to nine years of these datastreams, including 3.6 million I -V curves and 36 million P-mp values, from eight PV modules, four each of double-glass and glass-backsheet module architectures, located in three distinctly different Koppen-Geiger climate zones, to determine the module's performance loss rates (PLR), identify active degradation mechanisms and power loss modes, along with partial shading by local objects. Considering both module architectures, PLR results indicate that the BSh climate zone is the most aggressive for module degradation, while the Alpine ET zone is the mildest climate. PLR of double-glass modules located in BWh and BSh climate zones are different due to the significantly greater uniform current loss (Delta P-Isc) for double glass modules in BSh, at a 5% significance level. Power loss for four out of five modules located in the BWh and BSh climates are dominated by uniform current degradation. Statistical analysis of multistep I -V curves detects partial shading experienced by three studied modules with details of the shading profile, the shading Poynting vector diagram for the obstacle's relative position, shading scenarios, and duration. This work demonstrates how remote monitoring and diagnosis of P-mp & I -V time-series of modules can provide quantitative operations and maintenance insights into system performance, degradation mechanisms, and shading.

This work deals with the simulation of water vapor ingress into wafer-based PV-modules for long-term exposure under different climatic conditions. Measured material parameters together with climatic data sets from four test sites (tropic, moderate, alpine, and arid) were used to calculate the water concentration inside of the encapsulant between solar cell and glass for a lifetime of 20 years. Two back-sheet materials (PET-based and PA-based) combined with EVA as encapsulant were used in respect to their influence on water ingress. The results show faster water ingress for warmer regions, but the highest concentrations were found for the moderate test site. The water ingress was additionally influenced by the used encapsulant and back-sheet combination. In particular the temperature dependency of the mass transfer, which differs from material to material, was the focus of this investigation.

Here we report about the use of spatially resolved fluorescence spectroscopy for non-destructive analysis of encapsulants in outdoor weathered commercial PV modules. Photovoltaic modules with crystalline Si-cells of seven German manufacturers were analyzed after 2 years outdoor weathering in four different climates. For the first time spatially resolved images of the polymer fluorescence for complete photovoltaic modules are reported.The presented results show that the fluorescence intensity and distribution is inhomogeneous within any module. The fluorescence intensity and its spatial distribution depend on the climate, particularly the weathering site. Diffusive processes in the polymer layer between glass and silicon cell can be evaluated with this method. Cracks in the wafer, visible with electroluminescence, show up in spatially resolved fluorescence images as well. The diffusion through the cracks influences the spatial distribution of the fluorescence intensity.Compared to averaging methods, detailed information about the impact of the different degradation factors like UV-irradiation and moisture ingress on the degradation processes can only be obtained using spatially resolved fluorescence measurements. For PV-modules investigated in this study areas can be identified and compared where similar degradation parameters can be assumed. This will allow improving to quantitatively interpret measurement results. (C) 2012 Elsevier B.V. All rights reserved.

The reliability of photovoltaic modules is highly influenced by the material properties of the backsheet and encapsulation material. Currently, little attention is paid to the permeation properties of the back-sheet material or to its impact on encapsulation degradation and module reliability. We investigated the interaction of different types of solar encapsulation and back-sheet materials. Therefore, various laminates were made to examine the environmental impact on such materials during the aging processes. One focus of our study lies in oxygen and water vapor permeability of the back-sheet materials. The encapsulants used were an ethylene vinyl acetate (EVA), a TPSE (thermoplastic silicone elastomer), an ionomer, and a PVB (polyvinyl butyral). Back-sheet materials were a TPT (Tedlar-PET-Tedlar) foil, a polyamide (PA) sheet and a polyethylene terephthalate (PET) composite film. Raman spectroscopic and FT-IR/vis-reflectance measurements were carried out before and after different accelerated aging procedures. The water vapor and oxygen permeation properties were measured. A clear correlation between the permeation properties and the observed aging behavior was found. The degradation, especially of the encapsulant, resulted in increased fluorescence background in the Raman spectra. It could be shown that the encapsulation-cell-backsheet system should be optimized in order to minimize the stress on the PV-module components.

The interaction of different types of new encapsulation and back sheet materials for PV modules was investigated. Therefore, various types of laminates were made in order to examine the environmental impact on such materials during the materials aging process with special attention to the permeability of the back sheet. The laminates were characterized by Raman Spectroscopy, FT-IR/VIS reflectance measurements before and after different accelerated aging procedures. The water vapor and oxygen permeation properties were measured. A clear correlation between the permeation properties and the observed aging behavior was found. The degradation, especially of the encapsulant, resulted in increasing background fluorescence in the Raman Spectra and in a change of transmittance of the encapsulants which is also known as yellowing. It could be shown that the encapsulation/cell/back-sheet system should be optimized in order to minimize the stress on the PV-module components.

Polymeric films are commonly used as water-vapor barriers, or as substrate materials for barrier coatings in food packaging, photovoltaic devices, organic light emitting diodes (OLEDs), and vacuum isolation materials. The permeation properties of these films determine the level of water in the polymers and inside the devices. The water can cause corrosion and/or degradation of functional properties of the devices. The temperature of solar devices and the ambient water vapor concentration vary over time according, to the solar radiation and the ambient climate. Temperature-dependent permeation and diffusion properties are needed for modeling the water concentration over time in order predict the long-term behavior and the service life of such devices. This chapter describes the measurement of the temperature-dependent permeation coefficient for polymer films different laminates of polymer films, and first results of modeling the processes integrating time series of condition experienced during outdoor exposure.

Flat collectors are usually not air or water tight. Therefore, they can exchange air and moisture with the environment. Moisture can accumulate in the collector, especially when the thermal insulation material acts as a storage for moisture (for example mineral wool). The moisture can increase the corrosivity of the micro-climate in the collector. An optimised ventilation rate, which is a measure of the air exchange between the collector and the environment, with respect to the moisture absorption properties of the thermal insulation materials helps to keep the collector dry. Optimum might be a relatively high ventilation if the collector case is not designed to be completely tight.

Humidity inside the collectors is one factor that can be minimised to keep the most favourable microclimatic condition for the internal materials of the collector. This microclimate inside the collector is an important factor in determining the service lifetime of an absorber coating. During the design of the collector, the location and size of ventilation holes, properties of the insulation materials and dimension of the solar collector box are parameters that have to be taken into account for the optimisation in order to achieve the most favourable microclimate to prevent corrosion.

Solar absorber coatings are exposed to stresses, which are - depending on the collector and the local climate - temperature, humidity and moisture, solar irradiation and pollutants. The investigation of the durability of the coatings against these stresses requires accelerated short-term tests. Reproducible indoor tests, in which the loads are applied separately, allow a direct and quick comparison of the respective stability of different coatings and the identification of specific sensitivities to single loads. Constant temperature tests in air as well as humidity and condensation tests were carried out with six commercially available absorber coatings (black chrome, black nickel, coloured stainless steel and nickel-pigmented anodized aluminium). They showed great differences in the stability of the optical properties of the coatings. The degradation data obtained from these tests are contributions to a data base for service lifetime prediction models to be developed in the framework of the Task X of the IEA-programme “Solar Heating and Cooling”.