By Chris Rowe
Updated Mar 24, 2022
The transition between a material’s solid, liquid, and gaseous phases involves large amounts of energy. This energy requirement is known as latent heat transfer. Researchers in the alternative energy field are exploring ways to harness latent heat for energy storage, such as using molten salt in concentrated solar power systems, as investigated in a recent Department of Energy (DOE) study.
Sensible heat transfer occurs when two substances at different temperatures come into contact, and heat flows from the warmer to the cooler substance. For instance, after sunset the ground, which remains warmer, transfers heat to the cooler air, causing the ground to cool and the air to warm.
When a substance is about to change its phase—solid to liquid, liquid to gas, or vice versa—heat can be absorbed or released without any change in temperature. This phenomenon, in which heat is transferred without a temperature shift, is called latent heat transfer.
The amount of heat required to convert a liquid into a gas is the latent heat of vaporization, while the heat needed to melt a solid into a liquid is the latent heat of fusion. These values are typically far greater than the energy needed to raise a gram of the same substance by one degree Celsius, which is referred to as its specific heat. For example, water’s specific heat is 1 cal g⁻¹ °C⁻¹, whereas its latent heat of fusion is 79.7 cal g⁻¹.
No energy is lost during latent heat transfer. Melting ice absorbs latent heat, while freezing water releases it. Similarly, evaporation absorbs energy, and condensation releases it.
Because many renewable sources, such as solar and wind, produce power intermittently, efficient storage is critical. Latent heat thermal energy storage (LHTES) systems can absorb large amounts of energy as materials melt and later release it when they solidify, offering a promising low‑cost solution for balancing supply and demand. Continued research is essential to identify materials with optimal properties for use in everything from electric vehicles to industrial processes.
