A thermal drone inspection uses an infrared camera to measure surface temperatures from the air, so faults that show up as heat, such as loose electrical connections, failing solar cells, wet roof insulation and heat loss from buildings, can be found without shutting equipment down or sending people to height. The key is comparison: a component that runs hotter than identical neighbours under the same load is a warning sign. For electrical equipment, the widely used ANSI/NETA maintenance testing guidance treats a difference of more than 15°C between similar components as a major discrepancy that needs immediate repair. Results depend on the right conditions, such as load on electrical equipment, strong sunshine for solar, and a cool clear evening for roofs.
This guide covers what thermal drones find, how an inspection is flown, the conditions for each asset type, how to read severity, the limits of thermography and how to choose a provider.
Table of contents
What thermal drone inspections find
| Asset | What heat reveals | Guide |
|---|---|---|
| Power lines | Hot joints, clamps, connectors and damaged conductors | Powerline inspection |
| Substations | Overheating transformers, bushings, breakers and connections | Reading severity |
| Solar plants and rooftop PV | Hot cells, failed bypass diodes, disconnected modules and strings | Drone solar panel inspection |
| Flat roofs | Wet insulation beneath the membrane | Drone roof inspections |
| Buildings and facades | Heat loss, missing insulation, thermal bridges and air leaks | Facade inspections |
| Wind turbines | Hot spots in nacelles and some blade defects | Wind turbine inspection |
| District heating and pipelines | Leaks and insulation damage on buried or exposed pipes | Conditions |
| Geothermal and industrial plant | Overheating motors, bearings, conveyors, pipework and electrical cabinets | Drones for mining |
On construction sites, thermal surveys at handover can catch missing insulation and air leaks while the contractor is still responsible; see our guide to drones in construction. Thermal cameras are also used for search and rescue and security at night; see our guide to drones for search and rescue.
How a thermal drone inspection works
Plan for the conditions. Choose the time of day and weather that make faults visible for that asset type.
Set the camera. Use a radiometric thermal camera that records a temperature for every pixel, and set emissivity, distance and reflected temperature for the materials being inspected.
Fly close enough. Resolution must be fine enough to see the smallest fault in scope. For solar thermography, IEC TS 62446-3 calls for 3 cm per pixel or better.
Capture visual images too. A visual image of the same spot helps identify components and rule out reflections.
Analyse. Compare similar components, classify each anomaly and estimate its severity.
Report and confirm. Deliver findings with locations, thermal and visual images and conditions, and confirm critical findings on the ground.
Conditions for accurate results
| Asset | Best conditions |
|---|---|
| Electrical equipment | Under significant load, ideally at peak demand; little wind, no rain |
| Solar PV | Strong, steady sunshine of at least 600 W/m² under IEC TS 62446-3, usually around midday |
| Flat roofs | A clear, calm evening after a sunny day, with a dry roof free of snow and debris |
| Buildings | A large temperature difference between inside and outside, typically on cold mornings before sunrise |
| District heating | Cold, dry conditions when the network is running hot |
Wind cools surfaces and hides faults, rain and wet surfaces distort readings, and sunshine can heat surfaces unevenly. In the Nordics, timing matters even more because of short winter days and low summer temperature differences. See our guide to drone weather limits.
Reading severity
For electrical equipment, ANSI/NETA guidance compares a component with a similar component under similar load:
| Temperature difference between similar components | Suggested action |
|---|---|
| 1 to 3°C | Possible deficiency; investigate and recheck at the next survey |
| 4 to 15°C | Probable deficiency; repair as time permits |
| Above 15°C | Major discrepancy; repair immediately |
A separate scale applies to temperatures compared with the surrounding air, so the two should not be mixed. Solar plants and roofs use their own classifications, based on the type and pattern of the anomaly.
Limits of thermal imaging
Surfaces only. Thermal cameras see surface temperatures, not inside equipment or behind cladding.
Shiny surfaces. Bare metal and glass reflect heat from the sky and surroundings, which can hide or fake hot spots.
Distance and angle. Small components seen from far away or at steep angles read inaccurately.
Load and conditions. Faults may not show if equipment is lightly loaded or conditions are wrong.
Interpretation. Readings need a trained thermographer, and important findings need confirming on the ground.
Rules and safety
Many thermal inspections take place near live electrical equipment, in towns or at night, so they often need the specific category and an operational authorisation. Keep safe distances from energised equipment and coordinate with the asset owner. See our SORA guide, our guide to EU drone regulations and our no-fly zone guide.
Choosing a thermal inspection provider
Radiometric cameras. Temperature data for every pixel, not just a coloured picture.
Qualified thermographers. People trained to interpret thermal data for your asset type.
Standards. A method based on the relevant standards, such as IEC TS 62446-3 for solar. See our guide to drone inspection standards.
Clear reports. Locations, thermal and visual images, temperatures, severity and conditions.
Flyby Guys provides thermal inspections with high-resolution thermal cameras, including solar farms.
Frequently asked questions
What is a thermal drone inspection?
An inspection that uses an infrared camera on a drone to measure surface temperatures and find faults that show up as heat, such as electrical hot spots, solar cell defects and wet roof insulation.
What temperature difference indicates a problem?
For electrical equipment, ANSI/NETA guidance treats more than 15°C between similar components under similar load as a major discrepancy needing immediate repair, and 4 to 15°C as a probable deficiency.
When is the best time for a thermal inspection?
It depends on the asset: under load for electrical equipment, in strong sunshine for solar, on a clear evening after a sunny day for roofs, and on cold mornings for buildings.
Can thermal drones see through walls?
No. They measure surface temperatures. Problems inside a wall only show if they change the surface temperature.
Can thermal drones find building defects?
Yes, defects that change surface temperatures, such as missing insulation, thermal bridges, air leaks and wet roof insulation. Surveys work best when inside and outside temperatures differ strongly.
Do thermal inspections need equipment to be switched off?
No. Most faults only show when equipment is running, so inspections are usually carried out under normal operation.
