Future energy systems with a large share of fluctuating renewable energies demand thermal energy storages that are flexible and reliable. Sodium acetate trihydrate (SAT) has been investigated for many years as heat storage materials but the focus of the investigations were mostly on short-term applications. SAT has a high energy storage density and a large supercooling degree which make it an ideal flexible heat storage material. Heat storages utilizing stable supercooling of SAT can store heat almost heat loss free in both short-term and long-term, which offers great benefits for the energy system. A review of SAT heat storages is presented in this article. The investigations show that flexible heat storages using SAT have clear advantages over a traditional water based heat storage in both short-term and long-term heat storage. Significant decrease of the storage size (at least 60%) is considered a merit for applications in single family houses where there is a spatial constrain. Moreover, the SAT heat storages offers flexibility in system operation, which is considered beneficial for renewable energy such as solar heating systems. The main challenges for the heat storages, for instance, low heat exchange capacity rate, phase separation and spontaneous crystallization, are addressed. Remedies to overcome the challenges are discussed. The paper will also investigate stability of supercooling and reliability of triggering methods for controllable release of the latent heat stored in supercooled sodium acetate trihydrate. Recommendations for further investigations are proposed.