Multiple diodes

Definition

In this class several of the panel's bypass diodes are conducting continuously, or several substrings cannot produce current. The panel has lost most of its power and is close to the condition of a fully offline panel. When several diodes are affected at once, there is often a common cause.

Signs in the imagery

In the thermal image two or more lengthwise bands of the panel are uniformly warm. A band at normal temperature may remain between them. The junction box area is often clearly warm. If neighbouring panels show the same pattern, look for the cause at string level.

Possible causes

• Several diodes shorted after lightning or an overvoltage
• Thermal damage or moisture ingress in the junction box
• A break affecting several substrings of the panel
• Diodes conducting continuously because of a reversed connection

Effect on production and safety

Most of the panel's output is lost. Diodes carrying current continuously heat the junction box, which can develop into junction box damage over time. If the same pattern appears on neighbouring panels, the loss is not limited to one panel.

Recommended action

Raise a priority work order and check the junction box, diodes and cables in the field. If similar panels sit in the same string, also inspect the string box and the overvoltage protection. Replace the damaged panel and confirm the close-out at the next flight.