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Akuo wanted a method that would reduce the amount of time and money spent on inspection, in addition to increasing detection of damage and hotspots in its panels. It benchmarked several UAV-inspection companies for the job, but noted that most only had a small amount of knowledge in thermographic inspection of solar plants. It ended up selecting an aerial surveillance company called Air-Marine to evaluate the efficiency of its fields. Air-Marine had previous experience in UAV and IR inspection and was flexible in developing new processes to fit Akuoâs needs in follow-up thermographic inspections. â©
This relatively new method of solar field inspection has a workflow that includes the use of UAVs, an integrated visual and thermal sensor solution, and photogrammetric software. Akuo chose one of its solar farms in France to be the first it tested with Air-Marineâs workflow. This particular farm stretches over 30 hectares of land, with an installed power capacity of 24MW produced by more than 75,000 solar modules. Regularly inspecting these solar field panels is in the ownerâs best interest: ensuring that any defects, or potential defects, that could cause a reduction in solar power yield are quickly found and repaired. â©
For an inspection over a large surface area like this solar field, a UAV needs to be able to fly relatively long periods of time without stopping or running out of battery. It also needs to be very reliable, in order to fly over highly valued assets such as solar panels, and capable of completing very precise flight plans. â©
The MD4-1000, a vertical takeoff and landing Microdrones UAV was chosen as it is capable of flying up to 88 minutes non-stop and can carry a payload of 1.2kg. Â â©
Data acquisition and processingâ©
During the second flight, the thermal channel was transmitted to the ground and displayed in Panoptesâ Solar Inspector software. When a hot spot was detected, the drone operator bookmarked the corresponding video frame to analyse later during post-processing.â©
After data acquisition, post processing began. The 370 still images acquired by the Sony Alpha 7 and the ground control points (GCPs) were processed in Pix4Dmapper Pro in order to create a georeferenced true orthomosaic of the field with 3cm GSD accuracy. Akuo Energy fixed five GCPs at 2cm accuracy over the PV field area and entered them into the Pix4Dmapper software, which helped to improve the absolute accuracy of both the orthomosaic and final reporting.â©
The orthomosaic was then digitised using a GIS to create georeferenced vector drawings (shapefiles) of the solar panels, to be used as a base map for the final reporting. The georeferenced thermal and RGB-integrated videos were analysed in Solar Inspector software. When playing videos, the operator could switch between the thermal and RGB captures at any time, detecting hotspots and creating text or image annotations in the software. After the video review, the annotation set was ready and could be used to generate the final inspection report. â©
Reportingâ©
Captured thermal data enables hotspots of all sizes to be recognised, whether they be in cells or entire solar arrays. These hotspots are the main indicator of malfunctions and failures in PV panels, and if the user knows the temperature measurement of a hotspot, it can determine criticality levels and prioritise its maintenance planning. The RGB data provides ancillary information on dirty modules, cracks and so on, and can be used to detect the origin of any possible shadowing on the panels. â©
Air-Marine also provided a final turnkey report with a map of all the hotspots. Each hotspot had a dedicated file that included position, characterisation, temperature and a final recommendation for Akuo personnel, who could go right to the spot among the 75,000 solar panels and check for potential malfunctioning. â©
End resultsâ©
The UAV inspection was carried out in two days, with two operators in the field and one geomatics expert doing post-processing. In comparison to the previous methods of inspecting that Akuo had used, UAV inspection enabled a 50% reduction in time spent on site by field technicians and a 30% reduction in time spent post-processing the IR images.â©
In the end, having lower inspection costs enable a company to increase the effectiveness and number of yearly inspections, which could be especially relevant in the cases of operation and maintenance contracts linked to plant efficiency. â©
âUAV inspection in the solar industry is just starting,â says Vincent Fournier, chief operations officer for Air-Marine, âbut potential customers are more and more aware of solutions for inspecting their facilities.ââ©
Both UAV and software technology are advancing quickly, developing more capabilities, such as the ability of Pix4Dmapper to process video natively (Pix4Dmapper 2.0) or upcoming advancements to Panoptes thermal sensors (temperature measurement) and software (feature extraction). These changes will decrease the number of flights needed from two to just one, and create further reductions in time and cost. â©
Jobard is optimistic about the future. âI would expect that all solar fields will be inspected by UAVs within the next five years.â â©
I would expect that all solar fields will be inspected by UAVs within the next five yearsâ©
Krista Montgomery is a writer for Pix4D (www.pix4d.com), Romain Jallat is operations and maintenance manager for Akuo Energy (www.akuoenergy.com), Yoann Jobard is business developer for Air-Marine (www.air-marine.fr) and Antonio DâArgenio is CEO of Panoptes (www.panoptesuav.com)
