# Strategy Based on Two Stages for IR Thermographic Inspections of Photovoltaic Plants
## 4 Discussion  
IR thermographic inspection was conducted with clear skies (okta level 0) and the absence of wind (<1 m/s), which are highly favourable weather conditions for inspection. In general, the PV installation has maintenance deficiencies that affect its performance. The comments below merit mention with regard to two-stage thermographic inspection:  
* For one-off incidents due to hotspots, spatial resolution may be insufficient with aerial IR thermography. Ground-level IR thermography enables greater precision for determining thermal behaviour.
* Heat incidents from shading may be totally or partially concealed by the item causing the shadow (vegetation or post) with aerial IR thermography. Ground-level IR thermography prevents any possible blocking.
* PV modules with technology different from m-Si reveal an irregular temperature pattern. This pattern is characteristic of a module in a short circuit. For this reason, all m-Si type PV modules are operating in a state close to a short circuit as a consequence of the intensity values produced by the p-Si type PV modules, which are series connected within each string. This incident is seen indistinctly by both thermography types, although at ground level the behaviour is viewed with greater sharpness and definition.
* For PV modules in open circuit, the thermal behaviour is some 5 to 7 \({}^{\circ}\)C higher than temperatures in operational modules. These modules do not produce power. This incident does not depend on the thermography type.  
Figure 12: Thermographic analysis with an incident of PV modules with open-circuit substrings: (**a**) aerial IR inspection, and (**b**) ground-level IR inspection.  
Figure 13: Thermographic analysis (**a**) and image (**b**) with an incident of PV modules with solar reflection.  
* For PV modules with open-circuit substrings, thermal behaviour is some 5 to 7 \({}^{\circ}\)C higher than operational substrings. These PV modules' power production at the PV plant is very limited. This incident is observed interchangeably in both thermography types.
* In the stage one of the thermographic inspection, it is necessary to determine the specific location of the PV modules with faults and to identify them correctly. This is essential for the success of the stage two and for the documentation of the final report.
* The stage two of thermographic inspection can also be performed aerially, but at a reduced distance to allow for the necessary thermal resolution. This may require the scheduling of two flight plans. The second flight plan would be conditioned by the results of the first flight plan. This will simplify the thermographic equipment to be used and the subsequent analysis. This may be the subject of future research.  
Figure 14 summarises the incidents detected after a two-stage thermographic inspection and their locations for the PV plant inspected, considering the identification matrix by module.  
The Table 1 summarises the incidents detected during inspection, where the temperature value is extrapolated at STC (1000 W/m\({}^{2}\)) conditions and calculated according to IEC-62446-3, with a com  
Figure 14: Location and types of incidents in the PV plant after thermographic inspection, considering the identification matrix of Figure 4a.