The profitability of photovoltaic systems depends on proper installation and maintenance.
Over the last five years, the use of solar radiation to generate electricity through photovoltaic systems has developed spectacularly, addressing the growing demand for renewable energy sources. However, given the amortisation period of photovoltaic plants (six to ten years), it is essential to ensure optimal performance so that its profitability can be guaranteed.
According to Comtest, thermography is an essential tool for analysing the operation and efficiency of the different elements that make up the installation: photovoltaic modules, connections, motors, transformers, inverters and more.
Temperature is a decisive variable in the correct operation of the equipment. For example, an increase of 10°C above the recommended operating temperature could lead to a 50% reduction in its useful life and since solar panels incorporate many semiconductor cells, the heat generated in a defective cell could lead to a deterioration of the neighbouring cells, making the problem worse over time.
Another very important aspect is the success of the installation during the start-up process. In this case, a thermal imager is a very valuable tool as it allows the plant manager to detect photovoltaic panels with manufacturing defects and to refer to the relevant guarantees.
A photovoltaic system consists of panels that contain cells that are sensitive to solar radiation and generate the DC voltage. These cells are grouped together in one or several parallel series to achieve the desired power. Depending on the structure of the photovoltaic panel and given that the cells are connected in a series, a fault in one of the cells could lead to total or partial loss of power in a panel.
Under normal operating conditions, each photovoltaic cell, when it receives solar radiation, generates voltage which, when added to the rest of the cells in the series, provides the output voltage for the panel and feeds the inverter to generate the alternating output voltage.
When a cell is not working or not generating energy because it is not receiving solar radiation, it may be inversely polarised. It will then behave as a charge instead of a generator, which may result in a high dissipation of heat. This situation is easily detectable by a Fluke thermal imager with IR-Fusion® technology.
The most favourable conditions for detecting this type of problem are when the panel is providing the most power, normally in the middle of a clear day.
Capturing thermal images
The imager captures a radiometric thermal image together with a visible light image, superimposing them pixel-for-pixel with different degrees of translucency that indicates surface temperatures. This allows for hot points on panels to be identified quickly and from a distance.
In order to try to avoid the problems associated with the inverse polarisation of cells, photovoltaic modules may include protection diodes, which will dissipate more power with a greater number of defective cells. This heating could also be detected by examining the panel from the side of the connections.
When scanning the installation, particular attention should be paid to shadows on the photovoltaic panels that may cause seemingly irregular thermal areas and the wind factor, as it will reduce the temperature of hot points through convection, which could both lead to a false interpretation.
Other areas that can be examined with a thermal imager are motors, inverters and medium-voltage transformers.
Thermography can also assist in preventative maintenance through the inspection of connection points, which may become loose over time, leading to operational problems and unnecessary breaks, especially given that a photovoltaic plant may have a large number of both DC and AC connections and electric panels.
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