Experiments are performed on the effect of percussion vibration on triggering solidification of supercooled sodium acetate (CH3COONa) salt solution in the rounded - rectangular thermal storage unit. To provide quantitative analysis, the steel ball freely falling down to the surface of PCM (phase change material) unit is applied for percussion vibration with parameters of percussion number and crystallization induction time. Factors such as the steel ball diameter and falling height, as well as the percussion position on the PCM unit are examined about their effects on the crystallization induction. The results show that it is favorable to activate solidification of supercooled sodium acetate solution with larger percussion momentum (larger ball diameter and higher falling height), percussion near the cover lid and edges of unit. A term named percussion effectiveness is also introduced for evaluation of percussion effect on solidification activation. The results in this paper are useful for seasonal thermal storage of solar energy within supercooled inorganic PCMs and control of discharging the stored energy for space heating. (C) 2018 Elsevier Ltd. All rights reserved.