Audits and diagnostics using thermal imaging

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Thermal imaging cameras are primarily used to efficiently locate defects and flaws, photovoltaic panels that are a common part of photovoltaic installations. With a thermal imaging camera, potential problems can be effectively avoided.

Examples of thermal imaging reports made with our partner PRAGMASOFT:

How does it work and what purpose does thermal imaging serve?

Thermal imaging cameras are primarily used to locate defects. Classification and evaluation of detected anomalies requires a thorough understanding of photovoltaic technology, knowledge of the photovoltaic system/photovoltaic farm under inspection, and additional electrical measurements. Proper documentation is, of course, a must and should include all inspection conditions, additional measurements and other relevant information.

Thermal imaging camera inspections of photovoltaic panels/photovoltaic farms – starting with quality control at the installation phase and followed by regular inspections – allow full and simple monitoring of the condition of a photovoltaic installation and its individual photovoltaic panels. This will help preserve the functionality of all photovoltaic modules and extend their life. The use of thermal imaging cameras to inspect photovoltaic panels will therefore drastically improve the return on investment in photovoltaics for the investor.

In the field of photovoltaic system testing and diagnostics, thermal imaging cameras are an established tool for evaluating silicon cells and photovoltaic panels. However, using thermal imaging cameras to evaluate photovoltaic panels has a wide range of other benefits and advantages.

With a thermal imaging camera, potential problem areas can be detected and repaired before real problems or failures occur with the use of the entire plant or photovoltaic farm. However, not every thermal imaging camera is suitable for inspection of silicon cells and photovoltaic panels.

There are certain rules and guidelines that must be followed in order to conduct effective inspections and be sure to draw the correct conclusions. Wanting to achieve sufficient thermal contrast when inspecting photovoltaic panels in the field, asolar irradiance of 500 W/m2 or higher isneeded. However, if you are aiming for maximum accurate measurement results, an insolation of 700 W/m2 is advisable.

What problems do we encounter when testing photovoltaic farm installations by thermography?

Solar irradiance describes the instantaneous power incident on a surface in units of kW/m2, which can be measured with a pyrometer(for global solar irradiance) or a pyrheliometer (for direct solar irradiance). Heavily dependent on location and local weather. Low outside temperatures can also increase thermal contrast.

Although the emissivity of glass is 0.85-0.90 in the 8-14 μm wavelength band, thermal measurements on glass surfaces of photovoltaic panels are not easy to make. The reflections of the glass are specular, which means that surrounding objects of different temperatures are clearly visible in the thermal image. In the worst case, this leads to misinterpretations (false “hot spots” on the PV panel) and measurement errors! Often the thermal image shows large areas of elevated temperature, and without additional information it is not obvious whether these are thermal anomalies or shadows/reflections that occur quite frequently on PV installations and farms.

To avoid reflection of the thermal imaging camera and the operator in the glass of the photovoltaic panel, the camera should not be positioned perpendicular to the module to be inspected. However, emissivity is highest when the camera is perpendicular and decreases as the angle increases. A good compromise is a viewing angle of 5-60° (where 0° is perpendicular).

What are the takeaways from drones equipped with sensitive thermal imaging cameras?

At Lighthief, we mainly use thermal imaging cameras mounted on drones, because in cases of inspecting larger PV installations on rooftops or PV farms (i.e., large areas), a greater distance from the PV panels will be beneficial. The timing of the diagnostic service is also important, and with a camera mounted on a remote-controlled drone, a larger area can be seen and examined more quickly in one pass/shot. To ensure the quality of thermal imaging at longer distances, use a thermal camera with an image resolution of at least 320 × 240 pixels, preferably 640 × 480 pixels.

The camera should also have an interchangeable lens so that the operator can switch to a telephoto lens for long-distance observation. However, it is advisable to use telephoto lenses only with thermal imaging cameras that have high image resolution. Low-resolution thermal imaging cameras will not be able to pick up the fine thermal details that indicate solar panel failures when measuring over long distances with a telephoto lens.

What are the ideal conditions for a thermal imaging camera audit from a drone?

When performing thermographic inspections on photovoltaic installations and farms, the sky should be clear, as clouds reduce solar irradiance and also cause interference through reflections. However, informative images can be obtained even under overcast skies, provided the thermal imaging camera used is sensitive enough. Quiet conditions are desirable, since any air flow on the surface of the photovoltaic panel will cause convective cooling and thus reduce the thermal gradient. The lower the air temperature, the higher the potential thermal contrast. It is possible to perform thermographic studies early in the morning.

Another way to increase the thermal contrast on the tested installation or photovoltaic farm , is to disconnect the cells from the load to prevent current flow, allowing only solar radiation to heat up. The load is then connected, and the cells are observed during the heating phase.

How do we examine photovoltaic installations and farms with a thermal imaging camera? What problems do we see?

Under normal conditions, the installation of photovoltaic panels should be checked under standard operating conditions, namely under load. Depending on the type of cell and the type of damage or failure, measurements under no-load or short-circuit conditions can provide additional information.

If parts of the photovoltaic panel are hotter than others, the warm areas will be clearly visible on the thermal image. Depending on their shape and location, these hot spots and areas can indicate several different faults. If the entire photovoltaic module is warmer than usual, this may indicate problems with the connections.

Shadows and cracks in the cells are visible on the thermal image as hot spots or polygonal patches. An increase in the temperature of a cell or part of a cell indicates a defective cell or shading.

If in doubt, compare thermal images obtained under loaded, unloaded and short-circuit conditions. Comparing thermal images of the front and rear surfaces of the module can also provide valuable information.

Thermal imaging inspection of photovoltaic systems can quickly locate potential defects at the cell and module level and detect possible problems with electrical connections. Inspections are carried out under normal operating conditions and do not require shutting down the system.

Check also:
Other services
Authorized representative for sellers of photovoltaic panels
Inspections of photovoltaic and wind farms from a drone
Investor audit due diligence- photovoltaic farms
Research projects
Reporting to BDO
Service of photovoltaic installations

Lighthief

Lighthief is innovation, technology and science in the service of recycling photovoltaic panels and wind farms. The company's topics of interest touch on recovery and recycling in the broadest sense, mainly in the field of RES, or renewable energy sources.

Contact

St. Kazimierza 2B, 42-226 Częstochowa, Poland

biuro@lighthief.com

+ 48 797 897 895

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