With a growing share of discontinuous renewables on the electricity grid, such as wind and solar, needed to meet international decarbonization targets, it is becoming increasingly difficult to balance supply and demand, ensure grid stability and avoid distortions in electricity markets, so there is a need for increased research and development of energy storage and system flexibility.
Hybrid energy storage, therefore, using heat together with other forms of energy storage, can provide significant help, especially by system integration aims. Applications span residential heating/cooling, industrial waste heat utilization, Concentrated Solar Thermal/Power (CST/CSP), and Carnot batteries (CBs), which convert electricity to heat, store it, and reconvert it to electricity.
Kinds of thermal storage that can be coupled include: Sensible (SHTES), which stores heat via temperature changes in a medium (e.g., water, rock, concrete), having low-cost but low specific energy (10-50 Wh/kg) and requiring large storage volumes; Latent (LHTES), that utilizes phase change materials (PCMs) for high specific energy (50-150 Wh/kg) and temperature stabilization needs; Thermochemical (TCES), able to accumulate energy through reversible chemical reactions, offering a very high energy density. In these sections some studies on materials and application related to these technologies will be discussed.

The activity is funded by the Program Agreements between ENEA and the Italian Ministry of the Environment and Energy Security (MASE), Project 1.2 “Technologies for electrochemical and thermal storage” (PTR 2025-2027, CUP I53C24003300001).