Short answer: a good solar thermography report lists every defect with its type, exact location (block, string, module), temperature difference and severity, backed by a thermal and a visual image of each one, a plant map, and a record of the conditions during the flight. The widely used standard for aerial thermography of PV plants is IEC TS 62446-3.
Flight conditions that matter
Thermal images only show faults clearly when the modules are working hard and conditions are stable. IEC TS 62446-3 sets a minimum irradiance of 600 W/m² in the plane of the modules, with clear sky and stable conditions. In practice this means flying around the middle of the day on clear days with the plant running normally.
- Use a radiometric thermal camera, which records a temperature for every pixel.
- Record irradiance, ambient temperature, wind and cloud cover during the flight.
- Fly at a height and angle that give enough thermal resolution on each module and avoid sun reflections.
Common defects found
| Defect | How it looks in thermal | Typical cause |
|---|---|---|
| Single-cell hot spot | One cell much hotter than its neighbours | Cell crack, damage or local shading |
| Multi-cell or patchwork heating | Several warm cells in a pattern | Cell degradation, potential-induced degradation (PID) |
| Substring hot | One third of the module uniformly warmer | Bypass diode active or failed |
| Whole module warm | Entire module warmer than others | Module disconnected or open circuit |
| String off | A whole row of modules warmer | String fault, fuse or connector failure |
| Junction box or connector heating | Small, very hot point at the box or cable | Loose or corroded connection |
| Soiling and shading | Irregular warm areas | Dust, bird droppings, vegetation, structures |
Checklist: what the report should contain
- Plant details, date, time and the weather and irradiance during the flight.
- Equipment used, including the thermal camera and whether it is radiometric.
- A plant map or orthomosaic with every defect marked.
- For each defect: type, location (block, inverter, string, module), temperature difference against normal modules, and severity.
- A thermal image and a matching visual image of each defect.
- A summary table by defect type and severity, with recommended action.
- Data files your O&M team can use, such as a spreadsheet and GIS layers.
What the report is used for
Owners and O&M teams use the report to prioritise repairs, support warranty claims with module makers, plan cleaning and vegetation control, and compare plant health year on year. A repeat flight after repairs confirms the faults are fixed.
See our drone thermal survey and power sector services.