To use the renewable power sources such as solar, wind, biogas, and others is complicated because of their sporadic supply. Thus and so, energy accumulation makes the user independent on the operating mode of the power source.

Some of the heat accumulation methods can be realized with accumulators using phase transitions and based on the heat storage materials that change their state of aggregation during storage and rejection of thermal energy. In comparison with the gravel or liquid heat accumulators these devices are compact and provide high density of stored energy. To intensify heat exchange in such devices, are used highly heat-conductive metallic inсlusions of different shape, capsular laying or heat storage materials placed in the form of inserts, extended heat exchange surfaces, etc.

Heat transfer of accumulator using phase transitions is calculated through solving a nonlinear Stefan problem. For calculation, are, usually, used various sufficiently time-consuming methods.

The paper presents a heat transfer calculation when changing the aggregation state of substance. Its recommendation is to use the analytical dependences that allow calculation of heat exchange characteristics with charging phase transition accumulators of a capsular type in which a heat storage material is in cross-inserts.

It is assumed that heat transfer in the coolant flow is one-dimensional, thermal and physical properties of heat storage material and coolant are constant, and heat transfer in the accumulator using phase transitions is quasi-stationary.