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Thermal Imaging - a very powerful tool to find defects in solar power plants
Thermal imaging allows a very efficient check of solar power plants and finds quickly failures in modules and other devices.
Thermal imaging in photovoltaics
Some characteristics of photovoltaic technology support the analyze with thermal imaging.
DC-current
Photovoltaic Power Plant are working with relatively high DC currents. As string has typically a max. current of 8 A, the main cables a multiple of it. DC currents tend to overheat internal resistance. Some example of internal resistancesGleich:
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connectors
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junction boxes of the modules
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string connection boxes, especially fuses and clamps
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internal soldering in modules
Some explanations on these "hot spots":
- DC has no Zero Point, ther is no self-extinction of electrical arcs.
- Visually you can not see anything until you have a damage.
- Depending on the construction situation a thermal damage can have severe consequences
Thermal imaging helps to find this type of problem immediately.
Examples of overheating
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cold soldering in a module
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overheated clamp
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cold solderin in the cell
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bad contact in the junction box
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Solar Cells are sensitive to mismatch in the cell string. This means different electrical characteristics of cells within on
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| Hot spot close to the point where EVA gets damaged. |
The same module in normal vision |
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Challenges for thermal imaging in photovoltaics
- A solar power plant is a mix of various materials with different emissivity rates. The pictures contain sometimes wrong temperatures, especially in metal parts.
- Glass is a mirror for thermal radiation. Very oftehn you see something different, for example clouds or your own mirror image. Or you see the sun instead of a hotspot.
- You should take pictures in a right angle to the surface. Sometimes it's difficult or impossible, you shade the modules, cut the current and influence the thing you want to find.
- Very often the place is not accessible with normal means, for example on roofs.
Thermal imaging needs to be done with special care and the knowledge of potential mistakes. On the other hand the temperatures that indicate mistakes are usually high enough that you easily find the hot spots. Thermally it's not a precision measurement.
News tools for thermal imaging
Drones are a efficient help for thermal imaging. Jendra Power has now a drone with a thermographic camera to check power plants from the air.
modules with PID-defects, nicely visible from the air
one defect module and a part out of service
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