An ice storage system has a higher energy storage capacity than a chilled water storage system due to the latent heat of fusion of water. The latent heat of fusion is the energy required to change the state of water from solid (ice) to liquid (water) or vice versa. This means that an ice storage system can store more thermal energy per unit mass of storage medium than a chilled water storage system. As a result, ice storage systems are often more compact and require less storage volume than chilled water storage systems.