  Since photovoltaic (PV) plants require periodic maintenance, using Unmanned
Aerial Vehicles (UAV) for inspections can help reduce costs. The thermal and
visual inspection of PV installations is currently based on UAV photogrammetry.
A UAV equipped with a Global Positioning System (GPS) receiver is assigned a
flight zone: the UAV will cover it back and forth to collect images to be later
composed in an orthomosaic. The UAV typically flies at a height above the
ground that is appropriate to ensure that images overlap even in the presence
of GPS positioning errors. However, this approach has two limitations. Firstly,
it requires to cover the whole flight zone, including "empty" areas between PV
module rows. Secondly, flying high above the ground limits the resolution of
the images to be later inspected. The article proposes a novel approach using
an autonomous UAV equipped with an RGB and a thermal camera for PV module
tracking. The UAV moves along PV module rows at a lower height than usual and
inspects them back and forth in a boustrophedon way by ignoring "empty" areas
with no PV modules. Experimental tests performed in simulation and an actual PV
plant are reported.
