The world is on a mission to decarbonise. In 2019 the UK Government was the world’s first major economy to cast a its pledge to end its contribution to climate change by 2050 into law. While much progress has been made on decarbonising the UK’s electricity sector in recent years, the built environment is and remains a major challenge. A core vector for the decarbonisation of heat will be electrification, bringing with it challenges around the balancing of supply and demand that need to be addressed by increasing amounts of energy storage. Thermal storage has been a segment of the HVAC market that has seen little innovation over the decades. This presentation will discuss how the use of phase-change material based heat batteries will contribute to meeting the decarbonisation challenge in the built environment by providing the necessary flexibility in a future energy system. It will detail the functional principles of heat batteries, their theoretical applications as well as real world case-studies for their use in today’s projects.