Uncrewed Systems Technology 049 - April/May 2023

110 In operation | DroneWorks solar panel inspection detector with a pixel pitch of 17microns. In terms of sensitivity, it can resolve a noise-equivalent temperature difference of less than 50mK, at an aperture of f1.0, while in terms of dynamic range it can make accuratemeasurements of scenes simultaneously containing temperatures from-25 oC to +135 oCat its highest gain setting, and -40 to +550 oCat its lowest. The IR camera is paired with a colour camera operating in the visible spectrum. This is based on a 12 MP 1 x 1.7 in CMOS sensor and a prime lens, which is in focus from 8 mm to infinity. Both cameras also have a digital zoom. Mission planning involved a site visit to scope out the building and its PV array installation, along with anything that might affect flight safety and the ability to complete the job while complying with aviation authority rules. This, Hinsley explains, is mainly about ensuring safe distances from people not involved in the job and staying clear of restricted areas such as the airspace near airports. While operating in such areas is possible, the required planning and liaison with the airport is more involved. “Planning for Bleasdale was fairly straightforward due to the rural location,” he says. “The main consideration was the height of the roof and the direction and angle of the panels to ensure they were in direct sunlight during inspection.” This stipulation is included in the standards set out by the IEC and in the UK by BS EN/ISO 62446 for inspecting PV panels. “For thermography in particular, we need specific weather conditions,” Hinsley says. As well as being in direct sunlight, the panels must be subject to an irradiance level of greater than 600W/m 2 in lowwind speeds andminimal cloud, he adds. “Once on site, measurements of temperature, humidity, wind speed and irradiance are recorded and logged for use when processing the data. For PV panels in particular, we are looking for temperature anomalies at the cell and module levels. Certain faults will display a particular pattern, which helps to identify any issues causing the panels’ performance to be reduced.” Camera mutuality The cameras are used together so that each IR image has a corresponding visual image, while each IR picture is assessed in sequence to reveal thermal anomalies such as hotspots, dirt, damage, string errors, diode issues and faults in individual cells. The images are also paired in this way because it is quite easy to misinterpret an IR image, and the visible camera provides an alternative view that can be used for corroboration. “On the visual image we can also check for dirt, bird droppings, debris or physical damage,” Hinsley explains. “For example, the IR image might show a large hotspot that could be diagnosed as a cell fault, but the visual image might reveal that this is due to bird droppings, and the panel simply needs cleaning.” As it was relatively simple, the Bleasdale job was carried out by Hinsley alone, who operated both the UAV and the cameras. “We can have a second camera operator if required for a more complex environment,” he says. As the Bleasdale job was also small, Hinsley flew it manually. For more complex missions, such as surveys of large solar farms, the DJI Pilot 2 software in the Android-based hand controller provides a powerful planning function. “We can use Google Earth Pro to plan the flight and then import it into the controller,” he says “We tell the Pilot 2 software the camera we are using, the flight altitude and the level of detail we want to capture, and it can then plan the automated flight for us.” In addition to the UAV and its GCS, the operator brings a package of support equipment to the job site. “We carry spare batteries, a generator and charging equipment, spare propellers and basic tools, plus a laptop and various cables so we can deal with any technical issues if they arise – and they usually do,” Hinsley says. “In addition, we carry signs, cones, a fire extinguisher and a first aid kit, just in case.” At the hall, the owner granted DroneWorks access to the building, to enable it to check ancillary solar power systemcomponents such as themeter and the inverter. Readings from the latter showed that one string of PV panels was generatingmuch less power than the other, Hinsley says, and interpretation of the UAV’s imagery would help towork out why. Preparing the UAV for themission involved allowing it to warmup and run through its pre-flight checks, while Hinsley set up instruments to collect the essential temperature, irradiance, humidity and other environmental information. April/May 2023 | Uncrewed Systems Technology For more complex jobs, such as surveying large solar farms, DJI Pilot 2 software provides a powerful flight planning capability