MATERIALS I TESTING
for specific uses. Testing during the product development cycle supports the development of process improvements and may contribute to a reduction in manufacturing cost.
Various mechanical tests are employed to determine the suitability and durability of the materials including strength tests on the glass, plastic or metal backing materials and wafer strength tests. Multi-layer composites require adhesion, peel and shear tests. Assessments of tear strength of the ribbon busbar joint and other mechanical joints are also commonly applied.
Testing of solar cells during production is performed primarily for quality control purposes. Testing routines must be developed for each step of the process with close attention paid to temperatures, contact pressures, dwell times, joining forces and tightening torques for fasteners.
Some tests are destructive in nature. At the change of product or material batch, components are removed on an individual basis and tested to destruction. An example of a destructive test is the removal of a string as part of a “tear test” to check the soldering process.
Non-destructive tests are also used including optical inspection of the wafer for breaks and optical tests on the soldered ribbons to ensure the soldering process was performed correctly. Laminate testing is performed optically to ascertain whether the lamination is free of bubbles. A check of the module is performed visually to make sure none of the components has been damaged. Finally, electrical tests check the performance of the cells.
IEC, EN test standards A variety of international standards have been created to support the testing process. IEC or EN 61215 is utilized for thick layer modules and IEC or EN 61646 for thin layer modules. These standards describe a wide variety of climate and mechanical tests.
A puncture testing setup includes a collection tray to capture broken glass
The module is said to have passed the test if no major visible damage is apparent and the performance output and insulation properties have not changed significantly from the beginning of the test. The 61215 and 61646 standards are considered a mark of quality for crystalline PV modules and are required by most international funding authorities.
The 61215 test is designed to be rigorous, as solar modules must withstand up to 25 years outdoors in varying geographic regions throughout the world. This particular test can take up to five months to complete. The batch of modules must pass environmental tests involving UV radiation and prolonged exposure to high temperatures and humidity. Mechanical loading and torsion tests simulate hail and stone impact. The 61646 standard is also wide ranging, involving sunlight (UV), climate extremes and mechanical loading factors that simulate hail, snow and wind suction.
Various tests based on EN 1288 are focused on determining flexural strength of glass in buildings. The addition of supplementary standardized testing equipment can be used to make the testing process faster and remove outside influences.
Solution based Zwick offers a four-point flexure kit for testing wafers, individual chips or components. The kit contains two bending beams with adjustable compression dies and can be utilized with a load cell (Fmax 10N). The anvils and bending rollers can be rotated freely. Rubber overlay strips are provided for placement between the specimen and anvil.
Also available is a kit to support double ring flexure tests on flat specimens. The kit includes support and loading rings, a collection tray and safety panel for protection from glass splinters. Centering strips are also provided to assure accurate positioning of specimens.
Tests on performance of high strength adhesives used in production of PV modules include ISO 614 non-destructive test for shipbuilding and marine structures and EN 1464 and 1465. The tests support the determination of the mechanical characteristics of different silicone bonding materials.
“Silicone adhesions should remain absolutely reliable even with high temperature fluctuation and strong light irradiation,” said Volz.
Mechanical joints such as the ribbon busbar must be tested to determine tear strength of the individual soldered connections. A specialized peel test kit from Zwick is designed to support the testing of solar modules, enabling both 90° and 180° peel tests. The kit includes a linear unit and support table with laterally adjustable clamping strips. A cable pulley guide system for the support table ensures that the pull-off position is always exactly in line with the tensile axis of the testing machine. The support table with clamping strips can be moved to a vertical position via an integrated 20mm connection.
Mechanical test equipment The base testing platforms must be able to measure small forces necessary to test lightweight materials such as plastic
Issue V 2014 I
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