Thermal Energy Storage

As latent heat accumulators, phase-change materials (PCM) increase the heat capacity of buildings and ensure a stable and pleasant indoor climate. In production, its operating temperature can be adjusted from -10°C to 80°C (14°F to 176°F). Of particular importance is the usage in lightweight construction, as they can be directly integrated in the plaster or dry construction panel in form of microcapsules. Besides buildings, PCM can also be used in any application where there is need for a high heat storage capacity in a small area, for example in heat exchangers or water heaters. Experts at Fraunhofer also work on pumpable high performance refrigerants like ice suspensions for use in process and transportation cooling or in the food industry. Absorption and adsorption processes also make heat and cold storage possible. This so-called sorptive or thermochemical heat storage provides the advantage of achieving a very high storage density and covering a wide range of temperatures. Moreover, thermal energy losses during the storage period are minimized.

Competencies of the Fraunhofer Energy Alliance in the Field of Thermal Energy Storage Systems

Sensitive Heat Storage

Sensible heat storage using water, thermal oil, rock, etc. is used in many applications from residential to industrial to power plants. The supply and withdrawal of thermal energy in these storage systems is expressed perceptibly (sensitively) by a change in temperature. Fraunhofer’s researchers are working on the efficient use of different storage types, geometries and materials. One aspect of this is the seasonal storage of heat and cold underground. In addition to classic closed geothermal heat exchanger systems, the focus is also on open systems in which heat or cold is stored by a circulation of formation water in suitable geological structures. In addition to natural hydrothermal reservoirs, artificial formations, such as mining infrastructures, are being examined. In order to increase the use of renewable energy, especially in the heating and cooling sector, the discrepancy between the availability of surplus (e.g. geothermal) heat in summer and the high energy demand in winter must be addressed efficiently. Underground thermal energy storage (UTES) systems could provide such a replicable and smart solution for balancing seasonal peaks in heating and cooling demand. Therefore, the integration of seasonal storage in suitable supply structures can make a significant contribution to achieving the targeted climate protection goals.




Heat storage for industry and power plants. In the TheMatIK project, metallic phase change materials (PCM) and metallic encapsulations were investigated for their suitability as heat storage materials. 



The use of Phase Change Materials (PCM) is a promising approach for storing heat in small temperature intervals ...



The MissElly is being carried out jointly between Fraunhofer IEG and Voltavision GmbH. The aim is to provide cold air to cool laboratories and test stations for performance electronics all year round. 

Latent Heat Storage

By using phase change materials (PCM), thermal energy can be stored in latent heat accumulators over a longer period of time. Experts of the Fraunhofer Energy Research are working to further develop the technology and integrate it into new contexts. This is done, for example, in the context of research into organic and aqueous PCM capsules, their integration into building materials, and mobile air conditioning using PCM. For applications in power plants and industrial parks, we are developing, among other things, high-temperature PCM in the form of metal alloys for storing heat >250°C, enabling direct evaporation and provision of process steam during extraction. In the field of refrigeration technology, water is used as a natural PCM in ice storage systems and its use in the coupling of the heating and cooling sectors and for making energy supply systems more flexible is being researched.




Emission-free heating of fully-electric vehicles is currently only possible with a significant reduction in range. In order to solve this problem, the Fraunhofer IVI developed a fast-charging latent heat storage system in the course of the Heat2Go project. 


High Temperature Heat Storage Systems

Heat storage units, in particular metal-based high-temperature storage units, can make the operation of industrial cogeneration plants more flexible by storing process heat and providing process steam. 


PCM Metro II

In the PCM-Metro II project, the objective is to create a basis for the development of accelerated aging tests specifically for the PCM material as well as measurement methods to determine the degradation parameters.

Thermochemical Heat Storage

Thermochemical storage systems are based on sorption processes in which heat is bound by endothermic reactions and released by exothermic reactions. An example of this is the hydration (accumulation of water) of salts such as CaCl2, MgCl2 or MgSO4. Thermochemical storage systems offer a virtually loss-free possibility to store heat - and this at comparatively high storage densities. In the field of thermochemical storage, for example, Fraunhofer’s researchers are developing new technologies for the hydrogenation and dehydrogenation of thermochemical storage materials, as well as working on the integration of these materials into storage systems. One technology of the future is metal hydroxides, which are characterized by high storage density and long-term stability. In addition to storing heat in selected operating states, this technology also allows thermal energy to be converted into electricity.



Seasonal Heat Storage System with Bodies formed out of Zeolites

Fraunhofer IKTS researchers systematically investigated the adsorption properties of binder-free zeolite granules and zeolite honeycombs in order to determine under which conditions they can be used as seasonal heat accumulators.