Photovoltaic energy is the renewable energy with the greatest growth and use. The tendency of the last years is directed towards the formation of increasingly larger plants, which implies that optimizing their maintenance is becoming extremely important. Aerial thermography has become a convenient quality assessment tool for photovoltaic power plants, being reliable, cost-effective and time-saving. However, it is essential to be aware of its strengths and limitations in order to apply and interpret the results correctly. This paper presents a study about the influence of Spatial Resolution of thermographic images on the severity of failures, evaluating the results obtained in a set of experimental aerial and manual inspections performed in a 3 MW PV plant in Spain. The research analyzes how aerial thermography should be arranged as a function of the thermographic camera and lens used with the aim of satisfying the resolution requirements. Indications about the correct procedure to perform aerial thermographic inspections are also provided.