Thermal Infrared Surveying of Photovoltaic Solar Installations

Utility-Scale, Commercial Ground-Mount, and Roof-Top

Thermal infrared surveying is a great way to commission solar installations in-situ. After analyzing and commissioning over four (4) gigawatts of solar panels in the past eight years, we have figured out what works and more importantly – what does not work.

Solar installations are not all the same. Before planning a site visit, we take into account the size and layout of the field, the types of panels, how the panels are wired, and then the best timing of the survey. Correct timing of the survey is the most important factor because the amount of solar insolation is critical to successful testing. To successfully accomplish the testing under good conditions, many factors need to be known or predicted with accuracy. These include the layout of the field, the ambient conditions (such as rain, sun, clouds, wind speed), and the angle of the Sun preceding and during the survey.

The ElectriSCAN division of Stockton Infrared Thermographic Services uses 4 different types of platforms to accomplish solar farm surveys:

  • On Ground
    • Driving
    • Walking
  • Elevated Vantage Point
  • Aerial
    • UAVs (rotor-wing / fixed-wing)
    • Helicopters (rotor-wing)
    • Airplanes (fixed-wing)

Factors Which Can Affect the Overall Performance and Efficiency of a PV Solar Plant

  1. Missing solar panels; never installed or removed without being replaced.
  2. Open strings of solar panels (open as result of multiple reasons including being electrically disconnected or resulting from open electrical circuits in the panels or the wiring which prevent continuity of current in the string).
  3. Hot / cracked / damaged panels – Panels that are significantly hotter than the operating temperature of the other panels in the solar plant, which may result from a variety of reasons including cracking of the panel, internal shunts which are shorting in the panel, and any other reason which is significant enough to prevent proper operation of the panel yet still able to provide electrical continuity in the string of the panel.
  4. Excessive heating of the panels closest to the ground (the lowest rank) as a result of a combination of (a) reflected solar irradiation and radiated heat from the ground reducing the differential temperature between the panels and the ground, and (b) variable airflow and environmental conditions associated with the lower ranks resulting in higher panel temperatures and lower PV panel operating efficiencies.
  5. Non-uniform temperatures caused by a variety of factors including, but not limited to, conduction and convection of the solar panels on a table which may cause meaningful variance in the output voltage from the panels on the table, and potential increase in the overall average operating temperature of the panels thus further reducing the efficiency of some of the panels.
  6. Variance in the output of the strings going to the combiners and the inverters, as well as variance in the operating temperature of the inverters which may cause operating efficiency variances among the combiner and inverter combinations of as much as 3% or more.
  7. Varying amounts of moisture can reduce the operating efficiency of the solar panels.
  8. Thermal and electrical effects of partial shading in monolithic thin-film photovoltaic modules.
  9. Less than optimal design of the solar plant layout may result in less than optimal convection and advection cooling, and may even result in a localized “heat island” effect which can cause a portion of the solar plant to run hotter than it should and operate at less than optimal operating efficiencies.

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A selected sample IR image of a solar farm with a productivity issue revealed by IR.