81 RCI 0614

RCI June 2014

SAFETY, ACCESS & TOOLS Thermal imaging, the perfect technology for solar panel inspection RCIMAG.COM JUNE 2014 081 By Andrew Baker, FLIR UK and Ireland sales manager With the UK’s commitment to reducing its greenhouse gas emissions by 80% by 2050, it stands to reason that renewable energy systems will increasingly feature in our built environment. Solar power is one of several technologies that will help meet this goal and despite its chequered take-up in the UK, an upward trend has been established. Indeed in 2012, the government estimated that 4 million homes will be solar powered by 2020, representing an installed solar power capacity of 22,000 MW. Solar farms are also becoming relatively common in the landscape and growth in the commercial and industrial markets have been stimulated too. So there is no doubt that the maintenance of these installations will soon become standard practice for future generations of building services and environmental engineers. Fast and effective defect detection For maximum power generation, system life and best return on investment, every solar cell on a solar panel must be working. To provide this assurance, those involved in maintaining these installations are increasingly employing thermal imaging as their preferred method for locating defects. Thermal imaging allows anomalies to be seen clearly and, unlike other methods, can be used to scan installed solar panels during normal operation. It is also a highly time efficient process as a large area can be scanned in minutes. If a solar cell produces less electricity it usually generates more heat than other cells and that difference is easy to spot with thermal imaging. The cause of this inefficiency commonly lies in the uniformity, or lack of it, in the silicon wafer used. Often the source of the problem can be traced back to the production stage so thermal imaging is also a vital verification tool for post-installation inspection. Cell defects can render the entire solar panel useless as a critical threshold needs to be reached by the combined performance of the cells to allow direct current from the sun to be converted to alternating current. And the loss of one complete panel in the installation for any length of time can be the difference between asset and liability. However there are many other possible causes for a solar panel’s poor performance; broken cells, broken glass, water leakage, damaged solder, defective sub-strings and bypass diodes, delamination of the semiconductor material and poor connections, to name but a few. By scanning the panel with a thermal imaging camera the effect of these problems can be clearly seen. Importantly it also shows the precise location of the fault. And by using a camera with a high resolution it is even possible to identify the cause. Choosing the right camera Handheld thermal imaging cameras typically have an uncooled detector that is sensitive in the 8 – 14μm waveband. However, glass is not transparent in this region. So when solar cells are inspected from the front, a thermal imaging camera sees the heat distribution on the glass surface but only indirectly, the performance of the underlying cells. As a result, the temperature differences that can be measured and seen on the solar panel’s glass surface are small. In order for these differences to be visible, the thermal imaging camera chosen needs a thermal sensitivity of <80mK. It should also allow manual adjustment of the level and span function to optimise visual contrast. New technology from FLIR is also helpful in this regard. Our multispectral image enhancement (MSX) feature produces a detailed and texture rich image. Unlike traditional thermal fusion that inserts a thermal image into a visible light picture, this patent pending technology embeds a digital camera image onto thermal video and stills. The result is superb image quality that allows not only the location of the fault to be determined but also its nature. Onsite considerations The emissivity of any material is the relative ability of its surface to emit energy by radiation. It is therefore vital that this value is factored in to any thermal measurement and professional thermal imaging cameras will allow this to be preprogrammed. As with all highly reflective material, the glass on a solar panel requires particular attention as any thermal image of its surface will also pick up the radiated temperature of surrounding objects as well as the sun itself. In the worst case, this results in false hotspots and measurement errors. Choosing the best viewing is therefore essential. Pointing the thermal imaging camera at the solar panel perpendicularly provides the best result as the emissivity value is at its highest. However this angle runs the risk of radiated temperature from the camera and its operator skewing results. A view angle of 5º to 60º is therefore considered to be the best compromise. An even better way is to avoid Above: With thermal imaging, complete panels can be inspected in one view Pic: FLIR T640 thermal imaging camera is the perfect tool for solar panel inspections


RCI June 2014
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