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Infrared image of a hot, defective PV cell in a solar panel

Infrared Solar Panel Inspection Detects Hot Cells in Photo Voltaic Arrays

Hot PV cells reduce efficiency and can cause panel failure

Infrared image of defective PV cell in a solar panel

This infrared image from an inspection of a solar PV panel shows a single defective cell, which is overheated. Defective cells like this will reduce the power output of the panel.  Bad cells can get hot enough to crack the glass cover allowing moisture in and can melt the solder connections resulting in the failure of the entire panel.  Infrared inspection finds defective cells and electrical components so they can be addressed thereby ensuring the efficient operation of the panel and long life of the array. 

Contact Us or call 845-641-5482 to schedule an inspection.

Thermal imaging locates efficiency robbing defects in PV Solar panels

To achieve the most benefit from your Solar Panel investment all panels should be producing their rated power output. Defects in Photovoltaic panels (PV panels) will reduce efficiency through reduced voltage and current output. Two issues, which are typically found on solar PV panels, are defective Photovoltaic cells and defective converter boxes. Defective cells may found individually or as a group, however defective convertor boxes are seen as a single hot spot, not usually fitting within the pattern layout of the individual PV cells on the panel.  To better understand the significance of having a single bad PV cell, please read the following section on how solar PV panels operate.

The first image shows several hot defective cells on several panels in this array. The second image shown the hot spot associated with a defective converter box.

Infrared image of several defective cells in a solar PV array
Infrared imaging detect overheated converter box on Solar Panel

Solar PV panel operational theory

A photovoltaic solar panel is made up of an array individual solar cell. A typical configuration may contain 36 cells in one panel. Each cell in a panel produces about 1 half of a volt (.5v) and the 36 cells are wired in series strings to produce 18V.  This voltage is selected so that when all the voltage losses due to the resistance in electrical connections, voltage drops across blocking diodes and the voltage drop across lengths of interconnecting wiring are taken into account, there is still enough voltage left to generate the approximately 14 volts needed to charge a 12V battery, or to be inverted to 110V AC.

When the sun shines on the panel, the energy in the sun’s photons knocks electrons free from the semiconductor material in each photovoltaic cell creating a flow of electrons, which is the "current" of electical power. The electrical current flows through each cell, positive to negative and through each of the cells in the string. When a cell in a string is defective, it blocks the current flow and voltage output produced by the good cells which proceed if in the string. If the first cell in the string is dewfective, not much power is lost. However, if the defective cell is near the end of the string it can eliminae the output of that entire string.

If there are enough good string cells preceding the defective cell, their voltage and current output can force the defective cell to operate in a “reverse bias” mode. The power from the proceeding cells forces the defective cell is forced to carry the current in the opposite direction to its semiconductor design and all the power produced by the good cells is dissipated as HEAT in the defective cell, like a toaster. Because all the power from the proceeding string cells is dissipated as heat in the bad cell, that power is not delivered to the string's output and therefore does not contribute to the overall power output of the panel, reducing the panel’s efficiency and power output.

Due to the excessive and highly localized heat created by the hot cell(s), secondary problems such as melted solder connections, cracking of the protective glass cover which allows moisture into the panel and the degradation of adjacent cells in the panel, can be caused by the overheating of a single PV cell.

Infrared inspection of solar panels works so well because the signature of a defective cell is heat, and that’s what thermal imagers are designed to detect. Infrared inspection of PV solar panels should be part of the quality acceptance procedures of any new installation and for the ongoing maintenance of established arrays. To find out more about how Infrared thermal imaging can help you maintain top performance of your solar PV array, please contact us at 845-641-5482

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