Identifying Issues On Installed PV Systems: A Thermal Imaging Guide for Solar Professionals

Originally adapted from a technical paper titled “Identifying Issues on Installed Photovoltaic Systems Using Thermal Imagery” with permission from Infrared Training Center

As solar professionals, regular maintenance is crucial for keeping photovoltaic systems operating at peak performance. But how do you spot problems that aren’t visible to the naked eye? The answer lies in thermal imaging – a powerful diagnostic tool that can reveal issues before they become costly failures or safety hazards.

As with any thermal imaging tool you need to understand what you are looking at and should have a working knowledge of the equipment to understand the measurements. The thermal scanning that is conducted does not just look at the installed photovoltaic panels but also the other electrical equipment associated with the photovoltaic panels. There are certain elements that need to be taken into consideration when conducting the thermal scan on the installed photovoltaic (PV) system. The use of the thermal imagery with the other data collected on a site is an invaluable tool to determine the health of the installed photovoltaic system.

We will answer the following questions:

What are we able to see?
How can we tell if this is a real issue or not?
What are some of the causes for the issues we can find?
What can be done with some of the issues when found?
What are the conditions for conducting a proper thermal scan with true results?

What Are We Able to See?

When conducting a thermal scan of the panels you are able to identify hot spots on cells of a panel, notice if a diode has failed, or is working depending on the condition, or if there is major dirt or staining on a panel. You can see the junction boxes on the panels and know they are working as they have a higher heat signature. Inside of the combiner boxes you are able to see if there is a hot string entering the combiner box or if there is a dead string. This can indicate either the line is not torqued properly or if there is a production issue. The inside of system disconnects this is the main system knife edge disconnects for electrical equipment where you can see if a line is overheating. On the inverter you are able to see if you have proper ventilation occurring, you can also tell if an inverter is not producing what it should be in comparison with the other inverters in the area.

Showing hot spots on a solar panel with no visual indicators on the panels

Figure 3 – Hot spot in the thermal camera | Figure 4 – Visible marking on the panel

Figure 5 & 6 – The cell has failed to the point that there is a full visible crack inside the wafer of the cell – this is near burn out. The hottest area in the figure above is 94.6 degrees C. We are 5.4 degrees away from boiling point.

Figure 7 – Working diodes from a shadowing effect | Figure 8 – Panel with failed diodes

Figure 9 – Working diodes from the minor shading on the panel as seen in Figure 10 | Figure 10 – Minor shading on the panel

Figure 11 – A hot spot anomaly, but looked at from the visual point, you see the vent pipe casting a shadow in Figure 12, having an effect on the panels and forcing the diodes to work. These are normal working diodes in a panel. This is not a true hot spot.

Figure 13 – Hot spots on the panels that are coming from the junction boxes in the back of the panels | Figure 14 – Visual of the panel

Figure 15 – Even heat distribution and all inverters appear normal. | Figure 16 – An anomaly, and we found all inverters operating but the top right inverter was having a minor issue which would trip off line for a couple of minutes then run for a few minutes then shut down. This was an underperforming unit but all light indicators stated it was operating.

These are some of the basic items we are able to find easily with the thermal camera helping to determine the health of a PV system.

How Can We Tell If This Is a Real Issue or Not?

When we are conducting our thermal scans of the system the beginning part of the scan is a preliminary analysis to see if there are any anomalies. The reason being there are some items that are truly not issues that come up as thermal scan hot spots. When determining the authenticity of a hot spot a more in depth analysis needs to be conducted. One of the quickest hot spots that comes up that is not a true issue are from nature (bird droppings, trees sap, dirt, etc.)

Figure 17 – Bird droppings in IR show up hot, with a different heat signature from true problems | Figure 18 – Bird droppings as they look visually

Figure 19 & 20 – Not all blemishes on a panel will create a thermal issue – this is what is known from the panel manufacturers as a cometic blemish and does not affect panel performance

With all thermal imagery work you are aware of your surroundings and shadowing so you always want to take a couple of images from different angles to see if it is truly an anomaly. When thermal scanning any of the equipment you need to note your irradiance at the time of the scan. On a solar panel you will need to shoot the panel hot cell and surrounding cell to find the differential temperature (Δt) as this is going to let you know if it is a serious issue or not. Here are some of the basic guidelines from our experiences:

Solar Panels:

Under a 5°C Δt not a major issue
5-10˚C Δt note it and see if there is anything that might be causing this issue
Greater than a 10˚C Δt is an indication of a problem and further actions need to be taken

Inside of a combiner box and a service disconnect:

Under a 2˚ C Δt is not a real issue
Above 2˚ C Δt needs to be addressed

Inverters are a bit different as the thermal scans are comparative with side by side inverters to ensure the proper cooling is taking place on the equipment or if one unit is not working. You are doing the thermal scan on these units as if looking for a leak and making sure the heat is being dissipated properly.

What Are Some of the Causes of the Issues We Have Found?

Some of the causes of hot spot issues:

PV panels:

External damage (golf balls, baseballs, tree limbs etc.)
Shading issues
Diode failure
Catastrophic failure the panels sometimes just shatter and the jury is out to what caused these issues.

With a PV panel with a catastrophic failure it is really important to get as much information as possible on the site location, site conditions, location in a string and all the electrical information you can about the panel.

Figure 21 – Hot spot but see the comments on Figure 22 | Figure 22 – All the glass is spider-webbed and there were no impact marks; this panel is a catastrophic failure

Figures 23 & 24 show the back of the panel of Figure 21 & 22 – Although this panel was still producing power, the hot spot is not where there is a visible burn mark, but the backing was slightly discolored. The burn marks were not highly visible from the front. Catastrophic failure.

Combiner boxes:

Torque specification has not properly met
The string is a higher performing string and can cause heat
The string has failed and is no longer producing (this is when we would see a cold line) – this can be caused by a string being disconnected. Blown fuse in the combiner box.

Inverters:

Inverter ventilation covers not properly sealed
Unit is not operating
Poor ventilation (externally or internally such as the intake screens or blocked or a failed fan)
Unit has a problem with the PV system not performing as designed and is under producing.

What Can Be Done With Some of the Issues When Found?

Always perform a full visual inspection and document what is seen. Then continue on with the further testing.

PV panels:

Map out the location and identify the string number it is associated with (do this with all hot spots found even if they are not at the major issue phase)

Identify what might have caused the hot spot

These next steps are if the panel is a major issue:

Take a minimum of 3 thermal images from various angles and be sure to have irradiance readings
If there is a replacement panel change that panel out of the system
If no replacement is available start the warranty claim process with the panel manufacturer
Always inform the customer of the situation and if there are no spare panels available let them know that it is recommended that the string be shut down until a replacement panel is available
If there are obvious burn marks it is recommended to immediately shut down the system.

Combiner box:

Note the string and what system it is on
Visibly inspect the area to ensure the wires are not damaged or there are no obvious issues in the box
Test the fuse and ensure the fuse has not blown
Perform system checks on the string, this would be the voltage and current checks and ensure to have the irradiance at the time of the check. This will be a good comparative analysis with like strings under the same condition going to the combiner box. Some strings will have a greater current and that can be the reason for the hotter temperature.

If none of these are the items continue to the next steps:

Perform a torque check on all the strings and ensure they meet the torque specifications on the box.
Upon completing these steps turn the system back on, let the system run for at least 15 minutes – perform a new the thermal scan to see if this has cleared the anomaly if it was not torqued properly

If this has not corrected the anomaly further investigation and testing will be required. This work falls under PV testing and maintenance.

Inverters:

Check to ensure the unit is running
See if there are any physical items blocking it
Verify the strings and system energy going to that inverter

With all the items, good documentation is the key element. If it is a major issue, be sure and contact the manufacturer with:

State that you are a certified thermographer and found an anomaly on a PV system and found an issue
Site name
Site address
Contact information
Serial number
What exactly was found (if there is a large Δt, burn mark, no visible signs, or any significant items)

What Are the Conditions for Conducting a Proper Thermal Scan With True Results?

The ideal conditions for conducting a PV system thermal scan are:

The system needs to be operating with no fault conditions
Irradiance is greater than 600 w/m²
Weather condition is stable
Full knowledge of the installed PV system
Have the system layout and mapping preset to do the thermal inspection.

Panels are tested under certain test conditions 25°C, at 1.5 Atmosphere condition (which you will not have any control of) and at 1000 w/m². Since the atmosphere condition is going to be a constant at your location and you are going to be doing a comparative analysis its critical to get the temperature and the irradiance at the time of the reading since you can calculate a proper answer.

You are able to find thermal anomalies in low light conditions, we have found anomalies on systems with irradiance as low as 100 w/m² coming to the panels, but with higher irradiance we have found better results.

Summary

PV systems have a lot of areas that can be thermally scanned to find out the proper system health. There are items to check to ensure there are no true issues in the system. A proper system commissioning done using the thermal imager and documented at the start of the systems life as well as an annual system inspection with the use of a thermal camera that will ensure the solar investment is at its peak performance. Whenever there is a loss to heat that is a loss of energy which is a loss of money. Scan the photovoltaic systems at least once a year and keep good documentation from year to year, equipment fails, thermal imaging can find those failures.

Interested in learning more about solar and PV O&M? Check out our Solar PV and BESS Operations and Maintenance Tech 1 Training and NFPA 70B: A New Standard for Electrical Equipment Maintenance.