The Ultimate Guide to Aerial Thermographic Inspections for Solar Plants
14/09/2023
Aerial thermographic inspection is a powerful way to capture and analyze thermal images by using drones. This works by equipping drones with thermal imaging cameras, offering quick, comprehensive, and non-invasive inspections across large areas.
It’s a method that’s actually been around the solar industry since 2015.
As a result, aerial thermographic inspection has established itself as a standard procedure and is recognized as best practice by leading solar industry associations, including Solar Power Europe.
This has inspired us to create a concise overview of the topic, highlighting its functionality, benefits, and how it’s impacting solar plant management.
Are aerial thermographic inspections performed by drones or planes?
Although aerial thermography can be performed in a variety of different ways, such as helicopters and airplanes, this blog will focus on drone-based inspections using thermal imaging cameras.
Inspections carried out by planes can cover large areas with great efficiency. However, quality usually suffers with this approach making results less useful. This in turn creates issues for technicians who must work with the data onsite.
To best illustrate the potential of aerial infrared thermography inspection for solar, our focus will be specifically on the capabilities of drone technology.
What is an aerial thermographic inspection for solar?
Both Operations and Maintenance (O&M) personnel and Technical Assistants (TA) have used thermography within the solar industry for the detection of defects and root cause analysis.
The method was useful but always limited to spot analysis because it was limited by the distance a human could cover. However, the combination of drones equipped to detect heat signatures and AI-driven data analysis has made it possible to inspect 100% of a solar plant in a short time span, providing a comprehensive overview of module conditions.
This has made it the most efficient and reliable method to get a thorough and complete overview of module condition.
Many O&M contracts used to include a partial thermographic module inspection of 10% a year. Over the course of 10 years, this approach was able to achieve 100% module inspection.
However, due to technological advances and market adaptation, drone thermography has become a superior solution in terms of cost and quality.
Most asset owners recognize the benefit of inspecting 100% of modules every year as opposed to 100% in ten years.
For more information on best practices, we recommend the Solar Power Europe best practice mark or download the comprehensive checklist.
What does thermographic imagery show?
Thermography is like having an X-ray at the doctors. To the naked eye, you might only notice the blue color of the modules and obvious problems like damage. However, using thermal scanners, thermography not only measures temperature differences but shows distinct anomaly patterns which support issue identification.
This technology reveals various module conditions, highlighting distinct thermal patterns that indicate specific anomalies such as heated junction boxes or suspicion of PID.
While the terms used can vary, here is a list of common anomalies found during drone thermographic inspections. It is important to note that thermography should go hand in hand with an RGB (regular visual) image analysis.
The reason is that regular visual imagery often provides information regarding the root causes of anomalies. It’s critical to know if hotspots are caused by soiling or if actual module quality issues exist on-site.
With a thermal scanner, the anomalies detected by thermography in solar modules include:
Why is root cause analysis essential?
While this list shows the main thermographic anomalies identified, there is a lot more information to infer from the data. Visual imagery as well as frequency of anomalies give further information leading to identification of root causes. To give you an example, let’s look at potential root causes of “heated modules”:
Individual module heating
No identifiable cause on RGB, may be
‘Open circuit’ module
Junction box issue
Activation of all three diodes
Damaged module (may be visible in RGB)
String Heating – a chain of heated modules corresponding to a string
String heating – no identifiable cause (typically “open circuit” string).
String heating – secondary to arboreal shading.
String heating – secondary to permanent shading.
String heating – secondary to damaged module (a single damaged module in a string can cause the whole string to heat).
String heating – secondary to missing module (a missing module can cause the whole string to heat if the string has not been reconnected correctly).
Inverter-level anomaly – a large group of heated modules corresponding to an inverter area.
An inverter fault is causing a large area of modules to heat.
Understanding the cause of a module’s heating—whether it’s for instance from shading or an unidentified issue—significantly impacts the interventions required. Moreover, the depth of the data enhances the quality of the information available.
How to make use of this information
Thermographic data feeds into your regular condition management process. Depending on the results, site technicians either
act to resolve the issue,
replace modules,
monitor progression closely,
dig further into root cause analysis
prepare a warranty claim.
On the one side, initial defects might be present at setup, and on the other further degradation typically happens under operational conditions. Without regular aerial thermographic inspection, these issues can go unnoticed until they have significantly progressed and negatively impact power production. .
This underscores the importance of routine module condition monitoring, especially for large solar farms where manual inspections are too costly and time-consuming. Aerial thermographic inspections present a fast, cost-efficient, and reliable method for carrying out a health check on solar assets.
What Are the Industry Standards for Aerial Thermographic Inspections?
The most commonly used industry standard is IEC TS 62446-3:2017.
The International Electrotechnical Commission (IEC) sets international standards for all electrical and electronic technologies, including energy production and distribution. The IEC TS 62446-3:2017 details how to perform thermographic inspection on modules outside, meaning not in lab conditions. It sets clear guidelines which should be adhered to. The standard from 2017 does not yet include drones, but the next version certainly will adapt to this. The relevant guidelines for thermography are:
environmental conditions and
geometric resolution of the imagery
Environmental conditions refer to:
Irradiance levels: Minimum of 600 W/m2
Cloud coverage of maximum 2/8 of the sky
Wind speed max of 28km/h
Soiling – no or low
The other parameter, geometric resolution, outlines the requirements for image quality. This parameter has a direct bearing on the accuracy of the temperature measurements made from the inspection data. Geometric resolution is a function of the drone height above the module, the sensor angle, the lens, and the camera resolution. Deviation from this part of the standard will have a direct impact on the credibility and quality of the data and the accuracy of the measurements being made. The standard states 5 x 5 pixels per 6-inch cell is sufficient.
If you want to know more about the details of IEC 62446:3-2017 in relation to drone thermography, then download the following paper.
The IEC Quandary: Exploring Your Certification Options
When contemplating an inspection, it’s important to determine whether you prefer adherence to IEC standards. Many providers offer various inspection tiers, with lower-quality options typically being less expensive.
Be aware that small discrepancies in image resolution, as little as a few centimeters, can significantly impact data usability. This is particularly true for detecting subtle anomalies like PID, where temperature variations can be as minor as 0.1 degrees Celsius.
Collecting data that complies with IEC standards is essential to identify subtle discrepancies. The initial step for module manufacturers is to examine the image resolution. Should your data fall short of IEC norms, it may weaken your warranty claim right from the beginning.
Closing Thoughts
Thermographic inspection is a dynamic field that adapts as module technologies and thermal anomalies evolve. Bifacial modules, thin-film modules, and half-cut cell modules each display unique thermal patterns and behaviors. This variability implies that the list of anomalies provided is not exhaustive and underscores the importance of a provider’s solar expertise in their selection process.
Secondly, it might seem that our focus on European best practices is not directly applicable to your region. However, understanding European standards is crucial as developments in the solar sector there often predict global trends by about five years.
The early surge in solar infrastructure development in Europe has led to widespread repowering and revamping projects to address numerous module malfunctions and accelerated degradation.
As a consequence, there is a significant demand for high-quality thermographic data, module serial number scanning, and sophisticated software for managing plant conditions—a trend we anticipate will soon be global.