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Drones and Solar Arrays: What Aerial Thermal Inspection Can Tell You

Writer: Jonathan G. Browning
Jonathan G. Browning
Oct 7
3 min read

Solar arrays sit on farms, rooftops, and open fields. Once installed, they are easy to forget. Panels do not make noise when they fail, and a bad connection or a damaged cell can drag down output without anyone noticing.

Aerial thermal imaging is one way to see the whole array at once and spot problems that are invisible to the eye.


What thermal imaging sees

A thermal camera records heat, not visible light. On a working solar array, modules should look fairly uniform. Faults tend to show up as warmer or cooler spots than their neighbors.

The industry guide Best Practices in Photovoltaic System Operations and Maintenance, 2nd Edition, published by the National Renewable Energy Laboratory with Sandia and the SunSpec Alliance (NREL/TP-7A40-67553, December 2016), describes aerial thermal imaging inspections as collecting and processing image data from aerial sensors to detect string, module, and sub-module faults. It explains that by detecting thermal variations between modules, critical defects reducing module efficiency can be found, along with proactive detection of hot spots and potential fire risks.

The guide also notes that these inspections can be performed instead of manual electrical testing as part of annual preventive maintenance, and can be used for system commissioning and end-of-warranty inspections. It says the work can be done with manned survey aircraft or unmanned aerial vehicles.


What makes the data good

Not every thermal flight produces useful results. The NREL guide says the quality of the assessment depends largely on the imaging and post-processing systems used, and lists recommended characteristics:

  • Thermal detector sensitivity of less than 0.02 °C and frame integration time under 2 ms.

  • Thermal ground resolution of 19 cm per pixel or better.

  • Visible ground resolution of 3 cm per pixel or better.

  • Irradiance of at least 600 W/m², with deviation under 100 W/m² and temperature deviation under 5 °C during the inspection.

The guide adds that imagery should be processed by a validated routine to correctly identify module defects and their specific location in the field.

The irradiance point matters for scheduling. A thermal flight on a cloudy morning is unlikely to meet that threshold. Panels need to be working under strong, steady sun for faults to stand out.


Lone high-voltage transmission tower standing in a grassy field

Timing the flight

Because irradiance drives the results, timing is part of the plan. The NOAA Solar Calculator gives sunrise, sunset, solar noon, and solar position for a location. Checking solar noon for the site, and the forecast for clear skies, helps you schedule the flight while the sun is high. Steady conditions matter too, since the guide recommends limited irradiance and temperature deviation during the inspection.


The flight rules still apply

An inspection flight is a commercial drone operation, so it falls under 14 CFR Part 107. Among the rules:

  • The drone must stay within visual line of sight of the pilot or visual observer, with unaided vision other than corrective lenses.

  • Altitude is limited to 400 feet above ground level, unless within 400 feet of a structure.

  • Flight visibility must be at least 3 statute miles, with 500 feet below and 2,000 feet horizontally from clouds.

  • Flights in Class B, C, or D airspace, or surface-area Class E airspace at an airport, need prior ATC authorization.

Larger arrays can stretch the limits of visual line of sight. That is part of planning the flight pattern, the launch points, and whether a visual observer is needed. For 48 Pegasus inspection work, flights are handled by licensed FAA Part 107 remote pilots.


Beyond solar

The same thinking applies to other infrastructure on rural properties. Visible and thermal imagery from above can help document roofs, outbuildings, and other assets that are hard to reach. The principle from the solar guide carries over: the value comes from good imaging, the right conditions, and careful processing, not just from putting a camera in the air.


Practical takeaways

  1. Aerial thermal imaging can detect string, module, and sub-module faults and hot spots on solar arrays.

  2. NREL guidance recommends specific thermal and visible resolution and at least 600 W/m² irradiance.

  3. Schedule flights for strong, steady sun. Use the NOAA Solar Calculator to plan.

  4. Images need validated processing to locate defects accurately.

  5. Part 107 rules, including line of sight and airspace, shape every inspection flight.

If you have a solar array or other infrastructure and want to talk about aerial documentation, contact 48 Pegasus, serving properties within 75 miles of Macon County, Tennessee, across Middle Tennessee and South Central Kentucky.


Sources

Photos: cover by Daniel Miksha / Unsplash; inline by Lee Milo / Unsplash. Free to use under the Unsplash License.

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