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Photovoltaic power plants often have a planned lifetime of several decades. They are subjected to various aging processes, which can lead to local defects or even partial defects.
These defects are not always recognizable with the naked eye or electrically measurable. Thermal imaging cameras can however detect the smallest temperature differences in solar modules with minimum time.
In the following, you will find the practical application of a thermal imaging camera on a ground-mounted solar farm.
Thermal imaging cameras for detecting hot spots and local defects
Ground-mounted solar farms can be built in a variety of scales, which can make regular checks and troubleshooting complex. Thermography can significantly speed up routine checks or a targeted analysis, since infrared cameras can visually detect irregularities.
A prerequisite for this is that you have a thermal imaging camera with a relatively large field of view so that you can view large modules close up. You then go through the plant with the thermal imaging camera row by row having a constant look on the infrared image.
In order to be able to detect any problem at all, the individual modules and cells have to actively convert solar energy. Otherwise there will be no load-dependent heating and thus also no dependence of the IR image on the functional reliability of the solar cells. A good guideline is at least 50% of the nominal power.
Normally no irregularities should be visible in the IR image. Exceptions are, for example, points where the solar modules are attached to the structure and also switch boxes, which are often installed on the back of the modules.
These have an insulating or heat-conducting effect and thus alter the IR image. On the thermal image, however, these sites should appear regularly and can be ignored.
Here you see a video recording, where a complete carrier is inspected by means of a thermal imaging camera. No defect modules were found.
Failures and hotspots
Decisive for the ability to detect temperature differences is the so-called thermal sensitivity of the thermal imaging camera. A value smaller than 100 mK is sufficient for such applications.
Small differences in temperature indicate either small production deviations or, unfortunately, possibly looming failures. Larger thermal deviations of 2° K and more should be investigated more closely.
If local defects occur, in some cases the overall resistance of a cell increases. Since, however, the cells are usually operated in series configuration in order to supply a high voltage, all the same current flows through the same. In the cell with defects, the increased resistance leads to increased thermal emission. This is then also visible on the IR image.
Hot spots are locally very limited warmings and are recognizable as dots in the infrared image. There are point-like hot spots in the silicon semiconductor. Several hot spots often accumulate in a cell and lead to a “measles” pattern.
In order to detect the smallest hot spots, thermal imaging cameras with high sensor resolution are clearly advantageous. At least 300 x 200 pixels (better 640 x 480 pixels) are recommended here.
Conclusion – Use of thermal imaging cameras in photovoltaic plants
Thermal imaging cameras can be used for diagnostics on solar outdoor installations. With sufficiently high sensor resolution and low thermal sensitivity, smallest defects can be detected in a time-saving manner.
Suspicious cases can be investigated and documented immediately. Cables and switch boxes as well as inverters and transformers can, of course, also be thermally tested during the examination. The use of thermal imaging cameras is worth considering for operators of older plants in any case!