Abstract. The effect of contrails on global short-wave radiation (sum of direct and downward diffuse solar radiation) and on solar energy gain was investigated. The study was performed during days with high contrail persistence and focused on situations where the contrails were obstructing the sun. Measurements of cloudiness using a fish-eye camera, diffuse and direct short-wave measurements and measurements of the short circuit current of three different types of photovoltaic (PV) modules were performed at the Kanzelhöhe Observatory (1540 m a.s.l.) with a time resolution of 1 min over a period of 1 year. The results show that contrails moving between sun and observer/sensor may reduce the global radiation by up to 72%. An analysis of contrail persistence and the influence of contrails on global irradiance and solar energy gain is presented. The losses in solar energy gain that were recorded may be critical under specific circumstances.