Detecting Solar Panel Hot Spots with Thermal Cameras

What a 'Hot Spot' Really Is

A solar panel hot spot is a localised over-temperature region on an operating PV module. The cause is almost always reverse-biased current flowing through a shaded, cracked, or defective cell — turning that cell from a generator into a load. Left unfixed, the cell exceeds 150 °C, the encapsulant browns, and within months the module is permanently damaged.

1. Camera Specifications That Matter

For PV thermography, three specs decide success:

• NETD ≤ 50 mK — small temperature differences against bright sky.
• Resolution ≥ 256×192 — covers a whole module from drone altitude.
• Radiometric file output — every pixel temperature exportable for analysis.

2. Inspect Under Load and Sun

Hot spots only appear when current flows. Inspect at ≥ 70 % of rated irradiance, with the inverter operating at MPPT, not in clipping. Cloudy days produce ghost hotspots from shadow movement and waste the survey.

3. Hand-Held vs Drone

For arrays under 100 kWp, a pole-mounted hand-held thermal camera is fastest. Above 100 kWp the drone wins on time and operator safety. A 384×288 thermal payload at 30 m altitude resolves individual cells; 25 mm focal length is the sweet spot.

4. Classifying What You See

1. Single-cell hot spot — temperature delta > 20 °C: cracked cell or shaded cell with bypass diode failed open.
2. Sub-string hot block — three or more cells at > 10 °C delta: bypass diode shorted, sub-string is now a load.
3. Whole-module hot: junction-box fault or module disconnected from string.
4. Diagonal hot stripe: PID (potential-induced degradation) — usually transformerless inverters with floating array.

5. False Positives to Discard

Adjacent obstructions, soiling streaks, and reflective glare from racking can all mimic hot spots. Always compare with a visible-light image of the same module before raising a maintenance ticket. EK PV thermography reports automatically pair every IR frame with a visible image.

6. From Image to Action

Each confirmed hot spot deserves a follow-up: a string IV trace to confirm electrical impact, then either bypass-diode replacement, junction-box repair, or full module swap. Trend the count of hot spots year-on-year — a rising number indicates wider system issues, not isolated faults.