Is your solar power plant producing less than expected, or less than in previous years? A drop in photovoltaic production is never insignificant: every kilowatt-hour lost translates directly into lost revenue. In this article, Solphenix, a photovoltaic operation and maintenance (O&M) company based in Pérols (Hérault), reviews the most frequent causes of underperformance and concrete ways to identify and correct them.