Analysis of failures and degradation modes of small scale domestic/farm protovoltaic power plants in rural communities of the Atacama Desert

Abstract

The present work is the result of a detailed analysis of the occurrence of failure/degradation modes found in 95 solar photovoltaic modules operating in the Atacama Desert. The data was collected using an IDCTool (Inspection Data Collection Tool) designed for desert climate applicability. This tool gathers visual inspection, thermal imaging and the electrical measurements of each module. Additionally, statistical data derived from a previous field testing campaign is used as well, and results are supplemented with a theoretical analysis based on the fundamental materials properties and interactions, from a physics perspective. With this five dimensional approach (visual, thermal, electrical, statistical, materials), failure/degradation modes and possible mechanisms characterization was enabled, regarding three solar module components: front cover glass, EVA encapsulant and solar cells. As a result, seven different abnormalities were detected and analyzed: Soiling, discoloration of front cover glass, delamination of EVA encapsulant, hotspots, partial shading, cell fracture and defective soldering. The last two failures were inferred from thermal profiles and described on a qualitative basis - given it is not feasible to check these failures without a further, and more detailed visual inspection - giving cause to discussion for future works and more indepth inspections. The most common issue detected was soiling; in different intensities and deposition patterns, showing a correlation between dust deposition and modules geographical location. Regarding electrical measurements, the relationship between the short circuit current and maximum power drops due to soiling becomes patent; and, for severely soiled modules voltage is also affected. However, both soiling and partial shading (i.e. bird drops, localized mud or dirt) cannot be correlated to excessive heating. Hotspots are also a common issue, being present in more than 50 percent of the total sample. Severe temperature rising in cells may relate to loss of glass transmittance, but also to internal cell failures such as shunt paths or reduced parallel resistance. Chemical interactions between environmental agents such as moisture, atmospheric particles or pollutants and modules can also be inferred, given that permanent changes in front cover composition have been observed. Finally, although there is not statistical evidence, the data analyzed in this and previous work suggest that the excess of UV radiation, typical of desert regions does not seem to play a primary role in modules degradation, however, it may contribute as a catalyst in presence of other environmental agents.