29th European Photovoltaic Solar Energy Conference and Exhibition UNMANNED AERIAL VEHICLES IN PHOTOVOLTAIC SYSTEMS MONITORING APPLICATIONS

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1 UNMANNED AERIAL VEHICLES IN PHOTOVOLTAIC SYSTEMS MONITORING APPLICATIONS 1 M. Aghaei, 2 P. Bellezza Quater, 1 F. Grimaccia, 1 S. Leva, 1 M. Mussetta 1 Department of Energy, Politecnico di Milano, Milano, Italy 2 Nimbus S.r.l, Lombardore (TO), Italy ABSTRACT: Over the past few decades, the world has seen a revolution in solar energy technology. Operation and maintenance of Photovoltaic (PV) systems is becoming very crucial and a high valuable activity to meet future energy efficiency requirements. Therefore, investigation on Photovoltaic (PV) system inspection must be developed to obtain appropriate and efficient methods. Current experimental research strives to find out possibility of Unmanned Aerial Vehicle (UAVs) or Systems (UASs) in monitoring application of Photovoltaic modules. For this purpose, a light Unmanned Aerial Vehicle (UAV) was employed to cooperate in Photovoltaic (PV) modules inspection by thermal imaging and visual cameras onboard in SolarTech laboratory and a real PV plant in Italy. However, the main scientific innovation of this experimental study is to propose a novel concept and method to contribute UAVs application in Photovoltaic (PV) systems inspection. The preliminary results show that Unmanned Aerial Vehicle (UAV) cooperation in Photovoltaic (PV) systems monitoring was effective to detect degradation and defects on Photovoltaic (PV) modules and it is much more reliable, fast and cost effective in comparison with traditional methods. Keywords: Unmanned Aerial Vehicle (UAVs)/Systems (UASs), Photovoltaic (PV) systems, Photovoltaic (PV) modules, Thermal imaging and visual cameras, operation and maintenance. 1 INTRODUCTION The past decade has witnessed a rapid development in monitoring methods. Regarding to the high concern of inspection concepts in operation and maintenance, various methods have been suggested to detect defects, failures, degradations. Typically, operation and maintenance are significant keys to guarantee system lifetime, safety, stability, energy efficiency, reliability and cost effectiveness. Regarding to the recent advances in photovoltaic energy, its start-up cost is decreasing hence investment on solar energy is more reasonable and reliable to meet the future energy requirement [1]. Initially, UAVs were introduced just for military purposes, but after Second World War, UAVs have been used in various monitoring applications such as civil monitoring, power transmission line inspection, gas and oil pipeline monitoring, pollution monitoring, port and off shoreline security and forest fire detection. The main part of any photovoltaic system comprises PV modules. During the sunlight conversion process to electrical energy, the PV modules maybe occurred to failures and defects. Thus, PV systems monitoring plays a crucial role to detect entire degradation on PV modules. Therefore, photovoltaic modules lifetime is very dependent on the appropriate inspection and monitoring methods. The UAVs have many advantages such as, cost effectiveness, safety, fast detection, light weight and the fact that large amount of data can be collected by various infrared and visual cameras. Accordingly, the UAVs are a proper choice for PV plants inspection [2], [3]. In current investigation, a light UAV platform has been employed from Nimbus Company to monitor PV modules degradations and defects in the SolarTech Lab of Politecnico di Milano university, as pilot by mounted infrared and visual cameras in UAV platform named PPL 610. The first experimental work has been carried out at SolarTech lab (Politecnico di Milano), and later on, the same experimental research has been done at a real PV plant in Piedmont region with a capacity of 200 KW. The main purpose of this research work is to propose a novel, reliable and cost efficient method to inspect the PV modules on PV plants in a minimum time. In fact, the proposed method can make the process of detection for the PV plants quite fast. Thus, it is very useful for large size PV field s arrays. Moreover, one of the significant approaches of this paper is to mix two different technologies meaning, various inspection instruments and the UAV, in order to set up a suitable method to scan PV modules failures. In this research, two thermal imaging and visual cameras were mounted on a light weight UAV (Nimbus PPL 610 UAV) platform to capture PV modules defects and degradation in the SolarTech Lab at Politecnico di Milano University and later on a real PV plant in Italy. 2 UNMANNED AERIAL VEHICLES (UAVS) OR SYSTEMS (UASS) Nowadays, UAVs or UASs are used mostly in various applications to inspect equipment in numerous fields such as civil application, environmental inspection, monitoring of disaster relief, wildlife, gas and oil pipe inspection, arctic ice, pollution monitoring, port and offshore line security, energy equipment monitoring, transmission line inspection and in other fields [4], [5]. UAVs have some special capabilities like light weight, low cost, large area coverage, rapid monitoring, high flexibility, their intrinsic safely, precise imagery and so on. In addition, UAVs can carry various cameras and sensors to detect failures and to collect precise data on targeted platform site [6], [7]. UAVs are designed based on the altitude, range, weight and size which is dependent on their area operation. However, UAVs can be classified by size (e.g. Micro, Mini), or for example range and endurance (e.g. Close Range (CR), Short Range (SR), Medium Range (MR), Medium Range Endurance (MRE), Low Altitude Deep Penetration (LADP), Low Altitude Long Endurance 2734

2 (LALE), Medium Altitude Long Endurance (MALE), High Altitude Long Endurance (HALE)), and use (e.g. Unmanned Combat Aerial Vehicle (UCAV), Lethal (LETH), Decoy (DEC), Stratospheric (STRATO), Exo- Stratospheric (EXO), Space (SPACE)) [8]. Nevertheless, the most important issue in monitoring process by UAVs is to obtain a permit to fly from the authorities in the considered country. In fact, there are many regulations for remotely piloted aerial vehicles in different countries. In visual inspection method, the most external stresses can be observed on the PV modules. However, both methods are useful for PV modules separate monitoring, but considering previous experiences, the visual inspection and thermal analysis can cover each other to provide precise, fast and reliable data. In thermography analysis, high resolution of IR detector can guarantee to capture accurate pictures of PV modules whereas, if picture of targeted PV module has insufficient amount of pixels, this impact lead to reduce the quality of temperature effect on measured PV modules [10]. Figure 1: Nimbus PPL 610 UAV platform In current research, PPL 610 UAV platform has been employed from Nimbus company, which has permit to fly certification in Italy to carry out the inspection on PV modules. Feature of Nimbus PPL 610 UAV is shown in Table 1 [9]. Table 1: Nimbus PPL 610 UAV features Items NIMBUS PPL -610 Cruise Speed 0-20 kts Operational range (0.25) Km (Regulation) Max Altitude (Regulation) 150 m (70 m) Flight Endurance h Weight 2.8 Kg Height 0.25 m Length (Ø) 0.98 m Propulsion Electric Power 3 THERMOVISION AND VISUAL INSPECTION There are various methods to inspect PV modules during the on line operation. The most popular methods are including visual inspection, infrared and thermal Cameras and PV systems parameters measurement. Inspection by sight is the first and easier evaluation method to detect macroscopic PV modules failures. Thermography analysis is the understanding of the temperature distribution over a photovoltaic module surface. In this regards, utilization of thermal cameras can be useful to find out defects on the modules. This inspection method is very fast and normally the measurement can be carried out during PV systems working period. Figure 2: Thermography analysis operations Obviously, thermovision and visual inspection processed by UAVs need to use high resolution cameras and it is fundamental to scan and capture precise pictures due to the different altitude of UAVs flight on targeted PV modules. Figure 2 illustrates the traditional thermovision inspection of PV modules without utilize any UAV cooperation. In this method, the inspector needs to displace many time the equipment to capture appropriate picture through different perspectives hence it may take long time to monitor all PV modules and it will represent a difficult and tedious activity for the inspectors especially in large size of PV plants. On the contrary thermography and visual inspection using UAVs is simpler than traditional capturing picture methods due to their coverage, speed and highly flexible capabilities. Thermography analysis can display temperature distribution on the PV modules surface and then shows on the screen of commercial thermocameras (Figure 3). Therefore, it is easier to collect right and proper pictures. Furthermore, thermography analysis process can be carried out without any disconnecting the PV systems. Typically, some defects such as micro-cracking, cell breakage, hot spot, snail trails and shading by using infrared and thermal cameras. Visual inspection presents an overview of PV systems situation and it can cover more monitoring areas. Moreover, some defects like discoloration, lamination, bubbles, cracking, yellowing, misalignment, oxidation and corrosion in connectors can be detected by visual monitoring [11]. 2735

3 In SolarTech Lab, PV modules are connected to the low-voltage distribution grid and whichever have separate micro-inverters hence operating condition can be measured for each PV module. Figure 3: Thermography analysis of PV modules However, visual and termography inspection methods are not sufficient to decide about kind of defects on monitored PV modules and to propose the right solution. The output of PV modules must be measured under standard test conditions (STC- Temperature: 25, Radiation: 1000 W/m^2, AM 1.5) to assure common reference criteria [12]. In this research, HD thermal (MicroCAM 640 unshuttered camera) and visual cameras (GoPro - HERO3+ Black Edition and BRAUN - Master) have been mounted on PPL- 610 UAV platform to carry out the experimental work in two different plants, SolarTech Lab and PV plant in Italy. 4 EXPERIMENTAL PROCETURE The first experimental study has been carried out in SolarTech Lab to estimate the possibility of using PPL 610 UAV platform in the PV modules inspection to detect degradation and defects. In this investigation, the high precision electro-optic sensors and high resolution infrared (MicroCAM 640 unshuttered camera) and visual cameras (GoPro - HERO3+ Black Edition and BRAUN - Master) have been used in a real PV plant as well. In addition, this PV plant has been located on the roof of a cars parking s canopy near to the Golf sport field in north of Italy. The SolarTech lab has been founded on the roof of the Department of Energy at Politecnico di Milano University in 2012 and its geographical coordinates are latitude N and longitude E shown in Figure 4 [13]. Moreover, 37 PV modules of different technologies have been installed in the SolarTech Lab and various manufacturers. 15 modules are from polycrystalline - silicon type, 6 modules are from monocrystalline - silicon type, 8 modules are from micro-crystalline and amorphous silicon film type, 6 modules are from PVthermal modules, and 2 modules from flexible PV panel without glass which is fabricated from innovative technology and furthermore, they have a higher efficiency and a weight of about one over eight compared to the traditional PV panels. In addition, all of the PV modules are in outdoor and they were faced to south and among of them, two of PV panels have tunable tilt angle and rest of them have been fixed in a tilt of 30. Figure 4: SolarTech lab facilities In the meteorological station of SolarTech Lab, there are various instruments to measure solar irradiance, humidity, temperature, speed and direction of wind. The meteorological station has been equipped from three different sensors for solar irradiance measurement including of a net radiometer measuring the direct normal irradiance (DNI) and two pyranometers that measure the global on horizontal plane and diffuse irradiance (See Figure 5). Figure 5: Meteorological station at SolarTech lab In the first experimental work, PPL 610 UAV platform has flew over the SolarTech Lab to monitor PV modules defects shown in Figure 6. Moreover, inspection duration just was took long around 5 minutes to monitor all of the PV modules due to small field size of SolarTech Lab. However, the monitoring process was repeated in order to prove the method robustness. 2736

4 Figure 6: PV modules monitoring by PPL 610 UAV platform at SolarTech Lab Next experimental work was carried out on a real PV plant. The PV plant has been located on roof of a cars parking s canopy in north of Italy. In addition, the PV plant was integrated with around 800 PV modules from polycrystalline and mono-crystalline silicon type and connected to the grid with output capacity up to 200 kw. Figure 8: Visual inspection of an amorphous silicon module affected by white spot As it is highlighted in Figure 8, a PV modules from amorphous type are affected by White Spot defect. In fact, when a cell or couple of cells shaded in a PV module, white spot phenomenon appears on the modules. Typically, shading causes the occurrence of hot spot on the PV module surface due to the cell is polarized as reverse and it leads to dissipate the energy as heat from the PV module. Figure 7: PV modules monitoring by PPL 610 UAV platform at the PV plant in Italy Figure 7 shows the PV modules inspection procedure by PPL 610 UAV platform at real PV plant in Italy. In this experimental work on PV plant, thermovision and visual inspection of the PV modules just were took time less than one hour by using of PPL 610 UAV platform which is too less in comparison with tradition method. 5 RESULTS AND DISCUSSION In this first experimental work, visual and thermal imaging cameras were mounted on PPL-610 UAV to capture the precise pictures and videos from PV modules in SolarTech lab. In present test, the visual camera has been employed to detect visual degradations and failures on the PV modules. Figure 8 shows visual picture of PV module from amorphous silicon type which has been taken by NIMBUS PPL-610 UAV. (a) Figure 9: (a) Thermography analysis of a polycrystalline module captured by Nimbus PPL 610 UAV (b) Picture captured by BRAUN - Master camera with a PV module affected by snail trails phenomena Figure 9 displays the thermal and visual pictures of PV modules captured by HD thermal camera (MicroCAM 640 unshuttered) mounted on UAV during flight over SolarTech lab. As it is observed in Figure 9 (a), thermography analysis has been carried out for a healthy polycrystalline module. Figure 9 (b) illustrates a visual analysis for other polycrystalline module which has been effected by snail trial phenomenon defect. (b) 2737

5 Figure 12 represents cell breakage defect on a monocrystalline PV modules. This defect was occurred on surface of the PV module due to the location of PV plant. The PV plant located in North of Italy was close to a golf sport field and PV modules have been installed on the roof of canopy. In fact, it can be occurred by Golf balls during Golf sport. 6 CONCLUSION Figure 10: Visual and thermography analysis of PV modules on the PV plant in Italy It is obvious in Figure 10 that PV modules inspection combining of the visual and the thermography analysis methods is to assure about correct recognition of degradation due to some of the defects such as microcracking, hot spot and shading are invisible and the cannot be detected by sight inspection. Thus, both of the methods are necessary to suggest right solution. In Figure 10 some polycrystalline PV modules defected by microcracking are shown. General overview of PV modules situation in the PV plant during the thermovision and visual inspection is shown in Figure 11. This study was undertaken to determine the possibility of UAVs application in the photovoltaic systems inspection. PV modules are the most important part of PV systems hence the inspection of PV modules is very necessary for the entire PV plant life. Light UAVs have many advantages in monitoring operations such as cost effectiveness, safety, light weight and the fact that large amount of data can be collected by various sensors and cameras at the same time. In present experimental study, a light UAV has been employed with different thermal and visual camera onboard to monitor PV modules performances in Solar Tech lab (small scale) and a real PV plant (large scale). However, the results of this experimental research have proven that there is a real contribution in this novel method to inspect PV modules defects by different sensors, visual and thermal cameras mounted onboard. The proposed method has several advantages like reliability, cost effectiveness, time saving and facility to monitor the PV system degradations and defects during grid connecting operation. REFERENCES Figure 11: General Visual and Thermography analysis of PV modules in the PV plant [1] M. Trancossi, "Testing Performance, Weathering and Aging of Photovoltaic Modules," in ASME th International Conference on Energy Sustainability, pp , [2] H. Eisenbeiss, A mini unmanned aerial vehicle (UAV): system overview and image acquisition, International Archives of Photogrammetry. Remote Sensing and Spatial Information Sciences, vol. 36, [3] K. Nonami, "Prospect and recent research & development for civil use autonomous unmanned aircraft as UAV and MAV," Journal of system Design and Dynamics, vol. 1, pp , [4] P. Bellezza Quater, F. Grimaccia, S. Leva, M. Mussetta, M. Aghaei, "Light Unmanned Aerial Vehicles (UAVs) for Cooperative Inspection of PV Plants", IEEE Journal of Photovoltaics, Vol. 4, n. 4, 2014, pp Figure 12: Visual analysis by GoPro - HERO3+ Black Edition camera for a PV module encountered to cell breakage [5] S. Montambault and N. Pouliot, "The HQ LineROVer: contributing to innovation in transmission line maintenance," in Transmission and Distribution Construction, Operation and Live- Line maintenance, IEEE ESMO IEEE 10th International Conference on, 2003, pp

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