Mounting structure defect

A mounting structure defect is a racking or frame that is unsuitable for the site or has been damaged. It shows as cracking, bending, or corrosion of the frame or mounting holes that can be seen on the structure. Typical causes are a structure not designed for the local wind or snow loads, weak anchoring to the ground or roof, corrosive or poorly galvanised materials, and installation errors such as missing parts or screws tightened too much or too little. A defective structure puts extra stress on the modules. This can break the front glass and is also linked to cell cracks, backsheet damage, and damaged or detached junction boxes. On single-axis trackers, bent torque tubes, loose clamps, failed hardware or foundation settlement can twist a row. The twisted row then suffers cosine loss, row-to-row shading and electrical mismatch. In the worst case, single modules or the whole structure can come loose from the roof or ground, or the roof can collapse, which puts people and nearby property at serious risk. Galvanic corrosion often starts around fastening screws where two different metals touch, such as an aluminium frame on a steel structure, especially in humid or coastal areas. Insulating the two metals from each other is required there. Rust has been seen on a mounting structure that had been in operation for about one year at a desert site. To reduce exposure, use only compatible structures, follow the manufacturer's mounting instructions, check local wind and snow loads, and inspect the system regularly. Repair or replace any structure that poses a direct safety risk.

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• sentence 3: support check: partial - Glass breakage from extra stress due to a mounting defect is stated (u6), but cell cracks, backsheet damage and junction box damage are only listed as module-level damage consequences, and the 'extra stress on the modules' mechanism is stated only for glass.
• sentence 4: support check: partial - Evidence supports twist causing cosine loss, shading and mismatch, and lists bent tubes, loose clamps, settlement and failed hardware, but only as producing similar production signatures or inspection items, not explicitly as causes of twist; mismatch is said to cascade on long rows only.
• sentence 6: support check: partial - The passages state galvanic corrosion frequently happens around fastening screws with two different metals, especially in humid or coastal areas, and that insulation is required, but 'often starts' and 'insulating each from the other' are slight paraphrase shifts; the core is stated. -->