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I can see a lot of silver lines in a panel, how are they important in determining the quality of a panel?

Solar cells within solar panels are interconnected using a flat, conductive ribbon in series and parallel connection. Most use a tin coated copper ribbon although the number of connections, width and thickness varies by manufacturer.

An issue increasingly well understood by quality manufacturers is how these interconnectors are connected (soldered) to the silicon solar cell and how the connection method maximizes conductivity without placing undue stress on the solar cell. In cheaper panels these solders are often undertaken by hand via manual labour. Therefore the consistency of the soldering varies. In automated manufacturing the solders connectors are uniform. LG’s panels are made with very low tolerances, meaning each panel must match each other to a fraction of a mm.

Poor hand soldered interconnections can cause micro cracking in the solar cells through thermal expansion and contraction stress or the interconnector can break. In the worst case, a poor solder connection which opens and closes with thermal movement can cause an arc and potentially damage the panels.

For example, some manufacturers solder the entire length of the interconnector, and some only solder every few millimetres, theoretically reducing stress caused by thermal expansion and contraction. Some use thinner interconnectors which may stretch more, avoiding stress.

When you are assessing a solar panel, observe the neatness, alignment, size and quantity of the interconnectors.