AbstractThe evidence of the cycle stability of a latent heat storage unit is an important requirement of its technical application. In this paper an apparatus for investigation of Galisol (GLS) latent heat storage substance combinations is described. The stored heat and the heat transfer power are determined with an uncertainty of ± 5 per cent by means of the applied calibration. The results of the cycle stability of the Glauber salt in its substance combination confirm the stability behaviour of this salt hydrate under the dynamic conditions of the GLS storage unit