Multiple hot cells

Definition

In this class the heating is not confined to a single cell. It appears in several cells in different parts of the panel. The affected cells may be scattered, lined up along an edge or arranged in a pattern resembling a chessboard. The heating pattern is the most important indicator of the cause.

Signs in the imagery

In the thermal image the panel shows several hot cells, sometimes as a patchwork pattern. Heating concentrated in cells near the frame and repeated on panels at the same end of a string points to potential-induced degradation (PID). A scattered, irregular pattern is more often seen with cracked cells.

Possible causes

• Potential-induced degradation (PID)
• Multiple micro-cracks from hail, transport or installation
• Uneven ageing of the cells
• Unevenly distributed dirt on the panel surface

Effect on production and safety

Because several cells are weakened, the panel's output drops more than with a single hot cell. If PID is the cause, the loss spreads across many panels in the same string and grows over time. The heated cells can cause the bypass diodes to switch in frequently.

Recommended action

Examine the pattern of hot cells and whether it repeats on other panels in the same string. If it looks like PID, review the string and inverter grounding configuration. I-V curve measurement can be carried out by our solution partner as an option. Put crack-related panels on a watch list and plan the replacement of panels whose temperature difference grows.