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In this paper, a fundamental practical unit, namely the wedge-shaped enclosure, is proposed as a novel and efficient latent heat storage unit for thermal energy storage. The enthalpy-porosity method that treats the solid and liquid zones as a single domain is employed. Effect of the mushy zone constant C on melting is analyzed and a suitable value is obtained by comparing the numerical results with experimental data in the literature. A series of simulations are conducted to analyze the transient melting coupled with natural convection as well as the heat transfer process. Fourteen units those have different length ratios between top and bottom of the enclosures are investigated and compared by the analysis of transient temperature fields, vertical velocity distributions, and evolution of the melting fronts. It is found that the length ratio n dramatically affects the full melting time and heat transfer intensity. An enclosure of n = 5.5, which has the shortest completion time and the highest heat transfer intensity, is determined as the optimal unit. Compared with the base geometry ( n = 1), charging time of the optimal unit ( n = 5.5) decreased by 32.8 %, while the heat transfer intensity increased by 45.7 %. This is a significant improvement in the field of latent heat storage. [ABSTRACT FROM AUTHOR]