Reversed polarity

Definition

A panel connected the wrong way round in a string works against the current produced by the rest of the string. Its bypass diodes then conduct continuously and the panel heats up without producing. A string connected the wrong way round in the combiner box can draw reverse current from the parallel strings.

Signs in the imagery

In the thermal image the reversed panel is warmer than its neighbours and its junction box area is clearly hot. Because the pattern resembles an offline panel, it is told apart by the shape of the heating and the panel's position in the string. In the RGB image the panel usually looks intact.

Possible causes

• Cable ends swapped during installation
• A wrong connection after a panel replacement or repair
• Mislabelled or unlabelled string cables
• A connector assembled the wrong way round in the field

Effect on production and safety

The reversed panel contributes nothing and lowers the string voltage. Continuous diode conduction overheats the junction box. If the reversal is at string level, reverse current puts stress on panels and cables. For this reason it is a serious safety issue even when the production loss is small.

Recommended action

Verify the polarity of the panel and the string by measurement in the field. Before correcting it, isolate the string using a safe procedure. After the correction, check the panel's diodes and junction box, because prolonged conduction may have damaged them.