Under standard conditions, panels for output of 500kW can be imaged by one flight of a drone. One flight takes 10 minutes, including the time for takeoff and landing, and about 8,000m2 of area can be imaged during that time. The time is longer at 18 minutes for the electronic helicopter, making it possible to image a wider area.
By replacing the batteries, the drone can be flown up to four times a day (Fig. 7). It takes just one day to image the panels at a 2MW output mega solar power plant that has numerous solar panels.
Fig. 7: The helicopter can image panels for 500kW output per flight and panels for 2MW output per day. If the batteries are replaced, it can fly up to four times a day. (source: Hokkaido Electrical Safety Services Foundation)
If the flight route is ineffective because of the panel layout or the shape of the site, panels for 500kW output, in some cases, cannot be imaged by one flight.
The flying height is basically set at 50 to 100m. If the height is lower than 50m, the drone will be affected by wind and the flight will become unstable. If the height is higher than 100m, the resolution of shot images will become low (Fig. 8) while the risk to flight safety will be higher. The flying height is set at about 80m for shooting by the infrared camera. To obtain clear thermal images by the 320 x 240 pixel infrared camera mounted on the drone, 80m is the upper limit, according to the foundation.
Fig. 8: Balance between flying height and resolution of shot images is also important. The height is set at 80m or lower for shooting by the infrared camera and 100m or lower for shooting by the digital still camera. (source: Hokkaido Electrical Safety Services Foundation)
The drone shoots images by flying at a height above 100m and below 250m, which is allowed under the Civil Aeronautics Act, in special cases, when a picture showing the entire view of a power plant is requested.
The lowest flying height is set at 50m because strong upward airflow is generated due to the sharp inclination of solar panels and also because the drone is significantly affected by windbreak forests.
There are many windbreak forests in Hokkaido, and the majority of them are roughly 30m in height. Air turbulence is often observed around windbreak forests. According to the foundation, the drone could be caught in the turbulence if it flies near windbreak forests, resulting in a crash. Such effect is avoided if the flying height is set at 50m or above.
If images are shot from this height, a temperature difference of about 2°C on solar panels can be detected (Fig. 9). It is also possible to detect states such where “power generation is reduced due to shade caused by weeds ” and “there are areas where power is not generated and bypass diodes are activated,” in addition to excessive heating due to some other problem.