Sustainable energy management with sorption heat storage
Switzerland's second SeasOn demonstration plant is currently being put into operation in the new Swiss Post delivery center in Kaltenbach, Thurgau. It will provide further insights for the market launch of the long-term storage system, which stores surplus solar energy and waste heat in summer without loss using a thermochemical process based on caustic soda.
The flat roof of the Swiss Post delivery point (ZS) in Kaltenbach TG, which will open in spring 2025, is equipped with a photovoltaic system of 1000m2 and has an annual output of 215 kilowatt peak (kWp). Its output is therefore around six times greater than that of the first system at the animal carcass collection point in Frauenfeld TG, which has been in operation since the end of 2024 (see image above).
Milestone for further market launch
The The second SeasON demonstration system, which is installed in a new industrial building, saves 33 tons of CO2 per year. As a tenant of the building, Swiss Post is thus ensuring CO2-neutral energy production, storage and use at the site and contributing to achieving its Scope 3 net-zero target (eliminating and neutralizing indirect greenhouse gas emissions in its value chain), which it aims to achieve by 2040.
"For us and the team at Lucerne University of Applied Sciences and Arts, the implementation of the project in Kaltenbach is another important milestone on the way to the market launch of our innovative over-seasonal energy storage system SeasON," emphasizes Marc Lüthi, CEO of Matica AG. He adds: "The experience gained from the construction of the system, its installation and the analysis of the operating phase are essential for the efficient further development of our pioneering solution. The fact that we were able to win Swiss Post as a partner for this project demonstrates the market's great interest in innovative long-term energy storage options."
Award-winning collaboration between science and industry
The Lucerne University of Applied Sciences and Arts (HSLU) and its industrial partner Matica, which has been manufacturing high-quality water heaters and heat and cold storage tanks for over 50 years, have joined forces for SeasON. "In the development of SeasON, we are mutually dependent and at the same time create a win-win situation between research and practice," emphasizes Marc Lüthi, CEO of Matica.
Matica AG and HSLU received the prestigious Prix Watt d'Or in the Energy Technologies category for their innovative solution at the beginning of 2025. At the end of September, they will present SeasON at the Swiss-Japan Energy Days 2025 of Swissnex Japan as part of the Expo in Osaka/Japan and are among the finalists for the Swiss Technology Award 2025 in the "Industry Innovation" category. The Frauenfeld engineering firm novus engineering supported the planning of the demonstration plant for Swiss Post's ZS in Kaltenbach TG. As funding partners, the EKT Energy Foundation, the Swiss Climate Foundation and Swiss Post made the realization of the project possible.
How the SeasON long-term energy storage system works
SeasON uses caustic soda as a storage medium. In summer, it is charged with surplus electricity from the PV system by extracting the water. The concentrated caustic soda and the separated water can each be stored in separate tanks at room temperature until winter. In winter, the concentrated caustic solution is diluted again with the separated water. Specifically, the lye absorbs the water, which is evaporated in the closed system using low-temperature heat. The thermochemical process releases both the condensation heat of the water vapor and the mixing heat at a higher temperature. The mass and heat exchanger therefore works as a sorption storage heat pump (SSWP) and provides heating energy with practically no additional electrical energy. The storage tank efficiency is up to 95 percent.
"SeasON solves several challenges of the energy transition at once and promotes sustainable, efficient energy management," emphasizes Benjamin Fumey, Head of the CC Thermal Energy Systems and Process Engineering research group at the Institute of Mechanical and Energy Engineering at the Lucerne School of Engineering and Architecture. From the plant operator's point of view, the system increases the PV plant's degree of self-utilization, dampens energy price fluctuations and reduces CO2 emissions. In addition, as a long-term energy storage system, SeasON smoothes out seasonal fluctuations in the power grid (peek shaving), relieves the power grid accordingly and does not require any grid expansion.
In addition to surplus summer electricity, SeasON can also store waste heat from industrial processes and data centers without loss and use it to heat buildings in winter. Depending on the operating temperatures, SeasON achieves an energy density of around 300 kWh/m3 and therefore up to six times the capacity of a hot water storage tank.
Source and further information: https://www.season-swiss.ch/. See also our report (for a fee) here: https://www.organisator.ch/de/sustainability/2025-08-26/energie-nachhaltig-speichern/
