Oblivion Aerials SA. assisted clients to resolve issues for their solar panel system. Based on the temperature difference in the thermal map, created using a FLIR Vue Pro thermal camera and Pix4Dmapper, exact problems and locations were noticed…

Project Description

When a well-known company noticed the solar panel systems on the roof of one of their properties were not producing the expected energy amount, they contacted drone service company Oblivion Aerial SA to investigate. In order to detect the problematic modules, Oblivion Aerial immediately started the first inspection (October 12 (12:35), 2016), mapping the solar panels to get a general view of the plant.



Pix4Dmapper-generated thermal map using non-adjusted and adjusted images 


From the first inspection, two issues were found. A large region of the southern part of the rooftop evidently has a higher temperature, which indicates possible connection issues for the inverter. Upon receiving this information, the client decided to shut down the power supply for the detected region and recheck the connectors. This issue normally happens when connectors are oxidized, due to high humidity and low-PH weather conditions. The other problem is a hot spot on the north-west region.
Thermal maps are very useful tools for the company to estimate hot spot causes. For example, a large temperature difference between a hot spot and surrounded modules (32 degrees Celsius for this project) normally indicates a broken module, while a smaller difference can simply be dirt or soil coverage on a module.



Dirt cleaning process of the solar panel


After the first check, a second mapping was conducted while the installations were connected to the inverters. There was clearly a misconnection between multiple groups of modules appearing. The issue was resolved by replacing the connectors. Other scheduled minor repairs are still going on.


Data Acquisition

A quadcopter multi-rotor drone equipped with a FLIR Vue Pro (640) camera, 9 mm for focal length, was flown manually to acquire NADIR* images, which were triggered every second.


The first inspection includes 211 images with a rough resolution of 10 centimeters, and the second inspection includes only 11 images, which took less than 5 minutes to process while giving the client sufficient information for the quick examination after the replacement work.


Achieved Results

From the first inspection result, we can see some dark regions, which were affected by the camera calibration during the flight. We used (software) from FLIR to manually adjust each image for constant reflectance values. Along with some on-site temperature sampling, a high accuracy thermal map was created in Pix4Dmapper.


Inconsistency in values on thermal images due to camera drifting and re-calibration during the flight


For this project, some issues were found apart from the major connection problem. An overheated cell indicates a possible damage on the north-west, and some scattered dirt coverage which resulted in minor temperature rise.


(Left) A hotspot found on thermal images, the cells appear overheated and cracked; (Right) A visual inspection will confirm the physical breakdown of the module



South side of the rooftop, a small hot spot due to shading from stock dirt


This gives information on location and condition of solar modules. The output can be overlaid with other existing building data for further analysis, and archived for repetitive monitoring.


Advantages of This New Technology

The most obvious advantages of thermal mapping for this project are the speed and flexibility of response, such as hot spot detection, and hot spot type estimation, based on the information thermal images provide. This information cannot be gleaned from color images. The ease of locating problematic modules over a huge area is an obvious benefit, over a large area of modules that look exactly the same. Thanks to the Pix4D’s mapping technique, it is now easy to orientate through an entire installation without the risk of having the wrong location of malfunctioning modules or problematic components.




* Nadir images are especially recommended for these type of projects. They are optimal for mapping purposes in general, with valid reflectance and thus temperature values. 


Incorrect reflectance and temperature values for facade on oblique image



Author: Damiano Maeder

Website: www.oblivion-aerial.ch