Seasonal storage of solar energy


The volatility (fluctuations) of renewable energies results in a high demand for energy storage. This is the only way to ensure a secure supply even at times of low energy production. In the future, heat storage systems will therefore play an important role in the integration of renewables and waste heat into energy systems. Their considerable flexibility and compensation potential make them particularly well suited for this. It ensures that the storage system can absorb excess energy from renewable heat and electricity sources and release it again in times of high heat demand. This balances out load peaks in renewable energy production and consumption and relieves the network.

The aim of the FlexModul project is the development and demonstration of an innovative, modular and compact sorption storage system; a so-called thermochemical storage. This technology is characterized above all by its high energy storage density and flexibility, low losses and simple, safe handling for building applications. Investment costs should be reduced to a minimum and the applicability of the concept should be maximized. Due to its modular structure, a sorption storage system is easily scalable and adaptable to various applications in the heating and electricity sector. The enormous potential of thermal storage as a cross-sectional technology becomes clear: the flexibility of the entire energy system is increased significantly, and CO2 emissions are significantly reduced. Long-term storage is possible with almost no loss.

The project examines the diverse possible uses of sorption storage and demonstrates two use cases. One use case is the seasonal storage of solar energy for a single family home. The excess solar thermal energy or the PV electricity is stored from summer to winter, which enables up to 100% supply by solar energy. The second application demonstrates a so-called Power-to-Heat (P2H) storage system, which is integrated into a larger building and is used for smoothing load peaks (peak-shaving, short-term storage).

Technological pioneering role

The thermochemical storage systems mentioned have the potential to achieve three to four times higher energy densities compared to water storage systems. Energy is also efficiently stored over a long storage period (seasonal). So far, neither national nor international developments have been able to be launched on the market in this area. The technology used in the FlexModul project has already been successfully tested in previous projects. The project now combines numerous technological improvements at various levels in order to successfully complete the last development work up to the market launch and thus take on a technological pioneering role nationally and internationally.


Franz Hengel

Project key facts

01.05.2021 - 30.04.2024

funding program
Flagship Region Energy

Project type
Cooperation project experimental development

Project budget
1.510.629 €

Project management

AEE - Institut für Nachhaltige Technologien

The following model solutions are being developed in the FlexModul project: