Optimising PCM thermal storage systems for maximum energy storage effectiveness

► PCM encapsulated in flats slabs was numerically investigated. ► Freezing and melting tests carried out on the PCM with a melting point of −27 °C. ► A new performance parameter for PCM thermal storage systems, the energy storage effectiveness, is defined. ► The parameter is used to optimise the useful energy that can be stored in the PCM thermal storage system. ► It is also used to compare the useable storage capacity of the PCM relative to a sensible energy storage system.