The thermal effect is a bothersome issue related to various types of photovoltaic (PV) panels in real working conditions. In this paper, we demonstrate a new and simple hydrogel cooling method that is inspired by marine mussels. We design an organic-inorganic hydrogel with all-weather adhesive and tunable cooling functions. Adhesion is achieved by the formation of amorphous calcium carbonate/polyacrylic acid hydrogel, and tunable cooling is achieved by the absorption of a phase change material into the hydrogel. Structural, thermal and electrical characterizations of this dual-function hydrogel are done. Reusability of the hydrogel by water swelling is also demonstrated. After optimization of the composition, applications of this hydrogel for backsheet and PV panel are evaluated, and according to our design, rough stable 70 Wm(-2) cooling power could be obtained using only 0.5 g optimized hydrogel on a standard six-inch PV panel without weakening the conversion efficiency, and consequential power output gain is also proved. Most importantly, this "plug-and-play" adhesive material simplifies the cooling process, adapts to dry or wet conditions, and reduces the fabrication cost significantly.