Photovoltaic Modules by Karl-Anders Weiß

Author:Karl-Anders Weiß
Language: eng
Format: epub
Publisher: De Gruyter
Published: 2021-02-02T05:13:10.888000+00:00

Atomic force microscopy (AFM) to analyze the surface properties

Contact angle measurements by optical tensiometer to analyze the wettability of the surface, especially if functional coatings have been applied

Due to the specific properties of glazing materials, they can usually be tested independently; since there is no relevant degradation inducing interaction with other components expected. The different functionalities and the specific position of the glazing as outer layer make special tests essential for the reliability assessment. On the one hand, condensation testing directly addresses the reliability of the surface, and is therefore of special importance for coated glazing materials. Another relevant test addressing the stability of the surface is humidity freeze testing, which can show effects on porous materials. Also high humidity at high temperatures, with damp heat testing, can discover surface degradation effects. All tests can invstigate possible glass corrosion. Glass corrosion is caused by the leaching of oxides. A formation of a brittle white layer on the surface makes the glass opaque and can cause small cracks. To avoid this fatal failure it is recommended to perform reliability testing of glazing materials, including all typical PV module tests plus the special tests as described in this chapter.

Degradation is usually determined by analyzing the surface conditions and the transmission of the glass. On the other hand, there are tests addressing abrasive and soiling loads, which are typically only applied to glazing materials. As described in Section 4.1, these loads are very location dependent and therefore the testing has to be adapted to the specific requirements of the planned site. Since the relevant equipment is only necessary for glazing testing, it is also described briefly in this chapter.

Experimental investigation of soiling effects is made with different custom-made setups at different institutions, since there is no standardized approach available, yet. Available “dusting devices” for standardized dust testing as in the IP tests so far aim at bringing large quantities of dust into an (electrical) system without a qualitative distribution pattern. The new soiling tests are to be seen as a functionality tests detecting, for example, performance and/or degradation of functional surfaces. Hence, soiling testing itself is not a reliability test. Most soiling tests are done with dry dust. The goal is to quantify the soiling losses related to a reproducible and defined soiling load. In comparison to abrasion testing is homogeneous dust deposition onto surfces, such as anti-soiling (AS) coatings on solar glass simulated. Soiled samples are subsequently analyzed with optical and gravimentrical tools.

There are approaches to combine soiling testing directly with artificial weathering, such as light, temperature, or humidity exposure. If such artificial weathering is used to create soiling patterns and the exposure is for sure not degrading the samples surfaces a fast, reliable, and reproducible soiling method can be defined. The assessment of soiling effects is done by transmittance measured via FT-IR spectroscopy before and after artificially soiling the sample surfaces. In parallel are the deposited amounts of dust weighted. Plotting the deposition in gram per square meter of the transmittance loss, a dust-specific graph with usually linear relationship is found.

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