The SOLCHECK project studied how fluctuations in the Sun’s energy output affect weather and climate. Strong solar storms deplete ozone and raise ultraviolet irradiance, the impact of the 11-year solar cycle depends on stratospheric dynamics, and long-term Grand Solar Minima leave fingerprints in past and future climate states. The large model ensemble explored in SOLCHECK helped to separate the various solar effects from human-driven change and improved our understanding of climate feedbacks.