Drone attached thermal imaging cameras with high thermal sensitivity are being used for monitoring photovoltaic cells in solar energy generating installations.
Over the last decade, the market for photovoltaic systems has grown tremendously. In Germany alone, about 1.5 million photovoltaic systems were installed at the end of 2014. Considering the necessary maintenance of such a high number of modules, there is a need for efficient quality assessment tools.
It is the surveillance of solar panels, which is of high importance to guarantee a disturbance-free operation of the modules, which is the basic requirement for efficient electricity generation, long period of operation and fast amortisation of the assets.
The use of thermal imaging cameras provides several advantages: the most important are for example: anomalies can be seen very clearly on a thermal image and – in contrast to other methods – thermal imaging cameras can be used to monitor solar modules, while they are mounted and operating.
In research and development, thermal cameras are already an established tool for monitoring solar cells and modules. But nowadays those cameras are not only used under laboratory conditions, but uncooled thermal imaging cameras support more and more the quality control of solar modules before mounting and for the routine control during the preventive maintenance.
But not every camera is suitable for that purpose. Here are mentioned some rules for thermal imaging for photovoltaic modules with crystalline cells or for thin-film cells, as both are based on the same principles.
For example to get sufficient thermal contrast for the inspection of solar cells on-site, an incident solar radiation of 500 W/m² and more is necessary and about 700 W/m² would be preferable. Influencing factors also are the location and the local weather conditions, as low outside temperatures can increase the thermal contrast.
So which camera should you use?
Portable thermal imaging cameras are usually equipped with an uncooled microbolometer-detector, which works in a wave range of 8 – 14 µm. But in this spectral range, glass is not transparent. This means that, as the thermal camera captures the heat distribution directly on the glass surface, the heat distribution on the cells below is only measured indirectly. The differences can be small, but to make them visible, the suitable thermal imaging cameras need a thermal sensitivity of ≤ 0.08 K.
EVT offers with its EyeCheck Thermo an intelligent smart camera for thermal imaging, which can be used for fixed thermal inspections or for mounting onto a drone to fly over the solar panels for thermal inspection. Especially as it does not need a PC, it can be used for portable applications such as flying over a field of solar panels. Also there is the EyeVision software included in the EyeCheck Thermo, which means the system is ready-to-use right after setup. The EyeVision software will handle the temperature monitoring. The software allows the user to set a threshold temperature value that corresponds to when their system is developing a fault. The software will alarm the user with an error message if any temperatures above this threshold occurs, allowing them to deal with the issue immediately.