Second law analysis has been applied to an industrial refrigeration phase-change energy storage which consists in the use of a cylindrical tank filled with encapsulated phase-change materials. The paper focuses on the charge mode and more precisely on the effect of undercooling on the entropy production during crystallization. This numerical study is conducted to identify and minimise the thermodynamics losses of the storage process. The dependence of the second law efficiency of the system on various parameters is investigated and discussed.