Not every loss of generation is soiling or shade. Two silent faults degrade modules from the inside: the PID effect and hot spots. Those who can identify them early protect the customer's generation, trigger warranty claims in time and even avoid fire risk. It is technical knowledge that sets an installer apart in O&M.
What the PID effect is
PID (potential-induced degradation) occurs when leakage currents flow between the cells and the grounded frame or glass, driven by the system's high voltage combined with humidity and heat. The result is a progressive loss of power that can reach double-digit percentages. It usually affects the modules at the start of the string most (greatest potential difference to ground). In many cases PID is partially reversible with specific (anti-PID) equipment, but prevention is best.
What hot spots are
Hot spots are localised overheating in a cell. They happen when a cell is shaded, dirty or damaged and starts to consume instead of generate, dissipating energy as heat. Besides reducing generation, a hot spot degrades the encapsulation and, in extreme cases, is a fire risk. Micro-cracks (from transport or installation), bird droppings and recurring shade are frequent causes.
How to identify and prevent them
The key tool is thermography (a thermal camera), ideally drone-mounted on solar farms: hot spots show up as hot patches and PID as a heating pattern along the string. Combine it with monitoring (performance drop per string). To prevent: choose modules with low PID susceptibility, ensure correct grounding, avoid shade in the design, handle modules carefully (micro-cracks) and keep cleaning up to date.
PID vs hot spot: telling them apart
| Aspect | PID effect | Hot spot |
|---|---|---|
| Cause | Leakage current + voltage/humidity | Shaded/dirty/damaged cell |
| Extent | Several modules (start of string) | Localised in a cell/module |
| Detection | Thermography + string curve | Thermography (hot patch) |
| Risk | Progressive power loss | Degradation and fire risk |
| Reversible? | Sometimes (anti-PID) | No — requires replacement |