To view this page ensure that Adobe Flash Player version 11.1.0 or greater is installed.

COMMERCIAL FEATURE The right bill of materials for solar modules D uPont Photovoltaic Solutions has of the parks were showing signs of visual numerous types and styles of modules established an extensive fielded defects or changes. The size of the park is encapsulant yellowing; typically it is a module evaluation programme did not appear to matter as the trend was result of UV exposure. The encapsulant to develop the knowledge base which the same for both parks over 5.0 MWp is formulated with cross-linking agents, will enable a better understanding of and for smaller installations that were free radical scavengers and UV blockers how modules and materials age and less than 40 kWp. After totalling to prolong the life of the module, and degrade in the real world environment. the visual defects, 32 MWp out of the while the EVA can yellow on its own, As part of this work, solar field visits have 61 MWp were found to be showing visual these additives have also been known to been conducted on a global scale with signs of degradation or changes. Defects yellow. This yellowing phenomenon has over 60 fields inspected in the United such as Partially Induced Degradation been known to reduce transmission by States, Canada, India, China, Japan, (PID) or hot spots were not included in 5% directly impacting power. Europe, Turkey, and the Middle East. this survey. These degradation modes Out of the 32 MWp of modules These fields have ranged from newly are well documented and have led to with visual defects, backsheets defects commissioned to 30 years old. safety and performance issues. alone accounted for 42% of all defects. During field inspections, a Fourier Solar parks of all ages showed signs The backsheet is responsible for the transform infrared spectrometer (FTIR) of visual defects with an alarming trend of electrical insulation and protection of the was used to identify the chemical these defects occurring both on a large module. With the backsheet representing composition of the outer layer on scale in relatively young modules with such a large percentage of the defects the back of the module. This aids in less than six years in the field. A great observed, a very substantial risk exists determination of the type of backsheet deal of science and engineering go into in terms of safety and potential for long used by module manufacturers. The designing and producing a module that term power generation. The defects of inspections focus on checking for any will last 25 years in the environment, and the most concern for backsheets include visual changes in the module such as the current qualification standards are not cracking, yellowing, and delamination. yellowing, issues with the backsheet catching these early degradations. Modules containing backsheets that protection, snail trails, etc. Ribbon corrosion is any change in have cracked and delaminated represent Across Europe, Turkey and the colour that was noticed on the solder actual failures of the backsheets, but an Middle East, 22 crystalline-silicone solar ribbons. This darkening of the ribbon early potential predictor of backsheet parks were surveyed with a very wide surface can be due to darkening of failure is also yellowing of the backsheet. distribution of sizes from 1.4 kWp to UV-sensitive flux residues, which would Yellowing of the backsheet is typically 13.3 MWp for a total of about 61 MWp only impact the aesthetics of the module. associated with degradation of the of installations. The parks ranged in However, ribbon corrosion in extreme polymer, and degradation of the polymer age from two to 12 years. Only three cases can lead to backsheet degradation in severe cases can compromise the of the installations surveyed were by series resistive heating which will mechanical properties. After day- rooftop-based, the majority were ground- eventually affect the safety and power night thermal cycles of a mechanically mounted on a mixture of fixed structures, generation of the module. compromised backsheet, cracking or single axis trackers and double axis Along with ribbon corrosion and snail delamination of the backsheets can trackers. trails, a third defect that can be found in occur, resulting in loss of electrical During the field protection of the module. Tedlar inspections, the focus was on outer layer based backsheets the visual aspect of the solar had the lowest occurrence of panels, which can be an early these defects. and first indicator of failure This work reinforces that can lead to more serious that the best indicator of problems. The visual changes performance of materials is real and defects types looked for exposure to the environment, during inspections included and that many of these early ethylene-vinyl acetate (EVA) failures were not caught by yellowing, ribbon corrosion, current qualification testing. snail trails, backsheet cracking, Unfortunately, given the backsheet backside yellowing no-replacement policy of the and backsheet front side module makers for many of the yellowing. A reoccurring theme defects discussed, the best way found during the inspections forward is to select more proven Percentage of defects observed by type for all the parks combined (61 MWp). materials, like Tedlar TPT. ESI was that a sizable proportion 92 ESI AFRICA ISSUE 1 2014