Abstract A numerical study is performed on the effects of surface waviness and nanoparticle dispersion on solidification of Cu–water nanofluid inside a vertical enclosure for different Grashof numbers. A geometry with sinusoidally curved wavy surface can be used to enhance heat transfer performance if it is carried out in an appropriate way. Therefore, the enclosure has wavy surfaces on right side with higher temperature and left side with lower temperature, while the top and bottom walls are both flats with insulated condition. Computations are conducted for the surface waviness ranging from 0 to 0.4, Grashof number from 104 to 106 and nanoparticle dispersion from 0 to 0.1. An enthalpy porosity technique is used to trace the solid and liquid interface inside the enclosure. To validate the results, the numerical solutions for special cases in a rectangular cavity were compared with previously published works which are in good overall agreement with those results. The numerical results show that for surface waviness of 0.25 and 0.4, a maximum of 60% decrease in solidification time for Gr = 106 is observed in comparison with Gr = 105 which indicates the increasing effects of natural convection on solidification due to distortion on surface. Therefore, surface waviness can be used to control the solidification time based on enhancing different mechanism of solidification.