Electricity and Control November 2022

PLANT MAINTENANCE, TEST + MEASUREMENT

Inspecting solar panels to maintain optimum performance In South Africa, solar energy is being used increasingly in commercial and industrial applications by organisations looking to supplement grid supply from the national electricity utility, to transition to cleaner energy and, particularly in industry, to reduce carbon emissions and potential carbon tax liabilities. Obviously, contracted suppliers and the users of solar energy installations look for optimum performance from the system.

G errit Barnard – Comtest Fluke Product Manager advises that, to support this objective, solar panels should be inspected regularly and defective pan els repaired or replaced as necessary. Here Barnard points to some of the problems maintenance teams should look out for. Solar panels are made up of cells joined together in se ries, and their combined energy is relayed to a control box. Of course, when connected in series, the panel is only as good as the weakest cell. If one of the cells fails, it affects the overall performance of the whole panel. The case of a rooftop installation on the Old Mutual building in central Johannesburg illustrates this vulnerability and other indica tors of below par performance.

The image below left, shows how one block is heating up relative to the rest of the cells. This indicates a faulty panel and that one of the cells, which are connected in se ries, has failed, reducing the performance of the panel. This panel needs to be replaced.

This image clearly shows that it is the corner cell in this panel that has failed.

In this rooftop panel installation on the Old Mutual build ing in central Johannesburg, an initial inspection shows where the hotspots are. Using a Fluke TiS60+ thermal imag er, the technician identifies and pinpoints a number of faulty panels. The ideal thermal imager presents a high resolution image (minimum 320 x 240) and must have good thermal sensitivity in order to detect and highlight sometimes small differences in the cells.

It can happen that two or more cells at different points in the panel fail. A thermal imager is particularly useful to identify and pinpoint those faulty cells in a solar panel quickly. Keeping in mind that all the strings are connected in series, if this one has two cells that are faulty, overall performance is lost on the panel. The screen of the thermal imager shows that one cell is running at 53°C relative to the high marker – the centre point is the general temperature of the panel – here, at 29°C, it shows a significant (23°C) difference in temperature. This panel has performance problems and is not delivering the full output expected. In this view of another panel (opposite page, above), hotspots show up in different places. The image clearly demonstrates the advantages of a thermal imager. Looking at the panels with the naked eye, one would not pick up any

24 Electricity + Control NOVEMBER 2022