Predictive Maintenance in Solar PV Industry

Saksham Bhutani

Saksham Bhutani , Marketing Head at Indshine

April 15, 2020


Table of Contents

  1. Need for predictive O&M in solar photovoltaic industry
  2. Technology currently used for O&M
  3. Causes for reduced production in solar power plant
  4. Classification of defects observed through Thermal Imaging
  5. Process followed for Aerial Thermal Inspection
  6. Minimum requirements for Aerial Thermal Imaging
  7. Interactive RGB and Thermal maps of solar power plant
  8. How will the Aerial Thermal Imaging help?
  9. Commonly available sensors for Aerial Thermal Imaging
  10. Conclusion

Need for Operation and Maintenance (O&M) in Solar PV industry

In the wake of the current environmental concerns, it is necessary to focus on renewable energy resources. Solar energy is becoming a favorite choice among many industries and thus there is a rise in the installation of solar plants across the country.

With a rise in demand for any commodity, begins a race for manufacturing and offering the same at the lowest possible prices for gaining business share. The same is the state of the current solar plant industry as well. With more and more entities entering the market, the competition is rising, and the plant owners are forced to keep their prices to the minimum to win the bids.

While lowering the prices is helping the solar plant owners gain business, their need to keep the plant up and running optimally at every point of time is surmounting. The solar plant which could earlier provide ROI in 10 years, needs almost double the time to give ROI.

A solar plant usually has a lifespan of 18 years. So, you can well imagine the difficult situation the plant owners are in. They cannot afford to lose production from even the smallest unit even for a minute as that small pitfall could lead to big losses at the current prices offered.

Losses have always been a menace but with less profitability, the need for immediate action becomes all the more pertinent. Failure-free operation of the solar panels is a prerequisite for efficient power generation, long life, and a high return on investment.

This is analogous to roof damages are required to be inspected regularly for insurance claims. A detailed case study on roof inspection has been covered in Digital Revolution in Roof Inspection.

Technology currently used for Operations and Maintenance

SCADA systems are used to measure voltage and current. While they have been used for inspection of solar plants for long, they are unable to give minute level results. For instance, if a plant has 40,000 solar panels, usually one SCADA system is used to monitor about 1000 panels. This wide range is often unable to pick up the exact point of fault. A discrepancy will tell you something is wrong but not exactly where. The detection of the exact point of a fault will take time and this will delay production and thus lead to losses.

Using Unmanned Aerial Vehicles, on the other hand, minute level inspection becomes possible. Aerial Thermal Imaging will sense a rise in temperature and aid you to detect the faulty panel quickly, thus leading to quicker solutions. Although aerial mapping have various other commercial applications, which can be referred in ABC of Aerial Mapping and Surveying!!

It is also important to note that while SCADA systems help in real-time monitoring drones can help in predictive maintenance. The main aim of a thermographic inspection is to detect errors before yield reduction or serious material damage will occur. Because outlined damages often have not developed yet, the objective interpretation of thermographic scans is not trivial. Furthermore, defects found during a thermographic investigation do not inevitably lead to performance degradation.

However, these defects have the potential to cause power degradations in subsequent years. Hot spots with strong local heat gradients can affect the performance of the PV modules significantly and even, in extreme cases, lead to smoldering fires.

  • Natural Degradation:

    Natural degradation cannot be prevented but must be taken into account in the planning process. Usually, manufacturing companies that produce solar modules offer warranties if the degradation rate exceeds certain amounts(0.6-0.8%).

  • Grounding and Lightning Protection:

    The first level of such protection is the ground mount system itself, whereby the grounding system redirects the energy from the lightning into the ground and away from the panels.

Even after the lightning energy has been discharged into the ground, it can still cause a power surge within the solar panels array, which is why a surge protection equipment is required.

  • Component Failures (panels, inverters, trackers)

    • Panel cracking

      The micro-cracks are not always obvious, and that’s why the new panels must be inspected and a warranty must be secured.

    • Visual discolouration.

      The visual discolouration is another common defect that reduces the amount of sunlight that penetrates into a solar cell. As a result, solar cells are less exposed to solar irradiation and generate less energy.

    • Hotspots

      Hot spots occur when a panel is shaded, damaged, or electrically mismatched and decrease power output. Since solar cells are attached in strings, just one hot spot can lead to multiple cells functioning poorly.

    • Inverters failure

    • Trackers and Panel Orientation

    • Structural Integrity

  • Weather Conditions (snow, wind, soiling)

    Finally, depending on the environmental conditions, the panels must be protected from wind, snow, and soiling (in dusty areas). Regular cleaning and maintenance will be enough in these cases.

  • Other issues

    Other common unscheduled maintenance requirements include but are not limited to:

    • Tightening cable connections that have loosened
    • Replacing blown fuses
    • Repairing lightning damage
    • Repairing equipment damaged by intruders or during module cleaning
    • Rectifying SCADA faults
    • Repairing mounting structure faults
    • Rectifying tracking system faults

Classification of defects observed through Thermal Imaging

Thankfully, with times, there have been technological advancements that can significantly aid in operation and maintenance (O & M) of solar plants. Thermal sensors mounted on drones are equipped to sense faults in solar panels which help solar plant owners and managers take corrective measures on an immediate basis. Thermal sensors record the temperature values of the panels and analyse any discrepancies in temperature. A discrepancy may mean malfunction, which must get corrected immediately so as to avoid losses in production. Finding defects manually, whether they occur at the time or post-installation are very much time and money consuming which results in an uneconomic installation for the plant owners. The best way to prove that the solar panel installation is free from defects or the pre-installed panels are low on losses is by thermal imaging analysis of the site. The defects, recognised using thermal images can be classified into three categories called CoA (Class of Abnormalities) on the basis of urgency of the action taken. CoA is allocated by comparing the specific pattern and measured temperatures with examples of thermographic images and differences in temperature shown in Annex C. The three classes are:

  • Class 1 : No imminent action required.
  • Class 2 : Checking the cause and if necessary rectification should be don in reasonable period.
  • Class 3 : Current operation should be interrupted. The cause should be checked and rectified on immediate basis as it can hamper with the safety of product and personnel.

The table below explains some common defects examined by Thermal Drones along with their category, CoA, temperature difference to the temperature of the normal operating device, thermal pattern, and call to action.

Drones in the Solar PV Industry

Drones in the Solar PV Industry

Drones in the Solar PV Industry

Drones in the Solar PV Industry

Source : Research

Process followed for Aerial Thermal Inspection

There are 3 main steps involved in Thermal Inspection process:

  • Preparation:

    This is the initial stage used to gather all technical information and confirm suitable environment and experimental conditions before flight.

  • On-site:

    In this stage a site visit is arranged.

  • Post analysis:

    This stage is used to analyse and validate the data collected from thermal sensors.

Drones in the Solar PV Industry

It is important to understand that while thermal images are captured, there is a need to capture the RGB images for localisation of defects. RGB images are used to create orthomosaics on which cells are numbered and defects are marked subsequently.

Minimum requirements for Aerial Thermal Imaging

Aerial Thermal Imaging requires some minimum specifications of sensors, consistent environmental conditions and a precise way of execution. To observe the best result, the inspection is conducted between 11:00 am to 3:00 pm when the irradiation level is more than 600 W/m2. The drone needs to fly at an altitude of 25m-35m, so as to capture only one row of panels at a time. Sequential thermal images are to be captured of the solar assets with a side overlap of 25% and a front overlap of 80%. The camera angle needs to be within 20 degrees of perpendicular to the solar panels. Infrared cameras need to possess a thermal resolution of at least 320 x 240 pixels and thermal sensitivity of least 0.1 K.

Minimum requirements for Aerial Thermal Imaging

Key Points to remember :

  • Fly UAV at slow speed to avoid blurry images.
  • Orthomosaic is often blended at the edges, thus orthomosaic is not ideally suited for getting true temperature values.
  • Don’t fly too close since shadow from UAV will change reflectance value thus thermal reading.

Interactive RGB and Thermal maps of solar power plant

  • Commercial Plant

  • Rooftop Plant

Credits to WeDoSky Team for above datasets. For more open datasets, refer to Indshine project library.

How will the Aerial Thermal Inspection help?

A Drone Inspection can aid the operation & maintenance of a solar plant in the following major ways:

  • Report Generation

    Aerial Thermal Imaging provides detailed reports to solar asset owners and maintainers to enable quick decision making, repair crews and plan their assignments.

  • High-level summary

    A summary of defect types and a number of defects allows O&M providers to prioritise which arrays need immediate attention.

  • Localisation

    Crews need to know exactly which string or module they need to fix. Your report should save them time and allow them to do their job better.

  • Data Reduction

    The report should be reduced to the images that highlight specific faults. Most inspections will produce well over 1,000 images. The important ones will be segregated.

  • As-Built Drawings

    As-built typically contain a designation number for each string, and these numbers are incremented in a logical manner. The as-built drawings are georeferenced and the defects are annotated directly on the document so that solar O&M providers can direct their crews to the specific location of the issue. This also helps keep track of changes in the asset over time.

  • Return on Investment

    The reports generated through Thermal Drone Image Capturing is of immense importance to the solar plant owner as these can help in savings of about 35k euros per year for 12 MW solar plant.

How will the Aerial Thermal Inspection help?

The sum of money is in Euros. This table is from the reference of ABJ drones case study.

Commonly available sensors for Aerial Thermal Imaging

Thermal drones work on the principle of heat differentiation. “Thermal Imaging Drones” are being used for firefighting, search and rescue, building inspections, industrial inspections, and agriculture. Here's a quick description of common sensors available.

Commonly available sensors for Aerial Thermal Imaging

  • Radiometric Thermal Cameras:

    Cameras labeled "R" are radiometrically calibrated. Using such cameras enables the capture of absolute temperature in every pixel of an image. FLIR Vue Pro R and Zenmuse XTR are both radiometric versions that do record absolute temperature. They save their images in RJPG (radiometric JPG) format.

  • Non-Radiometric Thermal Cameras:

    Some Non-Radiometric Thermal Cameras also offer absolute temperature values of each pixel but there is generally a formula/mapping which is needed to be applied at the raw image in order to get the absolute temperature values.

For more details, this blog can be referred: or here is the detailed FLIR specifications sheet for reference.


In today’s highly competitive scenario, Thermal Drone surveys are a necessity for solar plants. These surveys can significantly help:

  • In reducing inspection time by 50% and post-processing time by up to 40% which results in time-saving and faster actions in case of solar plants.
  • In lowering the inspection cost which enables a company to increase the effectiveness and number of yearly inspections.
  • It could be relevant in the cases of operation and maintenance contracts linked to plant efficiency.
  • Hot spot identification showing defective cells/ geotagged images.
  • Diagnostic purpose that is the planning of panel placement.
  • Keep the solar farm running at peak efficiency as inspection of panels by thermal camera can be done without disturbing plant functioning.
  • On time detection of defects, so they can be replaced by the manufacturer while they are in the warranty period.
  • Safety of personnel is improved as there is less need for personnel to ascend to height for inspections in the case of elevated arrays.
  • Localisation of faults as exactly which string or module need to be fixed as the images taken are geotagged, making it more specific and time-saving.
  • Some systems use high voltage wiring, but thermal inspections are done from a distance and never come in contact with live wiring yet are still able to pinpoint overloads and short circuits by their thermal signature characteristics.

Referred Sources

  1. Scopito
  2. Solar Power Europe
  3. Semanti Scholar
  5. Green Deal Flow

Contributors : Shimonti Paul; Deepali Joshi and Shashank Tewari

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