This Swiss technique will make it possible to better store energy

Energy storage is the key to the energy shift away from oil and gas. The prestigious Watt d’Or has just rewarded a project which uses solar energy stored in winter and produced in summer, thanks to inexpensive long-term storage technology.

Bruno Knellwolf / ch media

An unpleasant smell floats around the new animal carcass processing facility in Frauenfeld (TG). Benjamin Fumey from the University of Lucerne (HSLU) stands in front of the door behind which is the first long-term energy storage demonstration plant that he developed. With its industrial partner Matica, received the prestigious Watt d’Or from the Federal Office of Energy (Ofen) in the “Energy Technologies” category in Bern.

For a long time now, research is looking at ways of long-term storage. Indeed, the development of renewable energies leads to seasonal fluctuations in electricity production – too much in summer, not enough in winter. In addition, due to the numerous heat pumps installed in homes, electricity consumption for heating is increasing sharply.

A storage medium long lasting cheap

Caustic soda is Benjamin Fumey’s answer. This liquid, sodium hydroxide dissolved in water, stores energy like oil, but it takes millions of years. With caustic soda, it goes much faster.

Excess renewable energy produced by photovoltaic panels, solar thermal installations or wind energy in summer is stored there. After 20 years of research, the idea has now reached its first objective. Marc Lüthi from Matica explains:

A third will be built in a housing development in Germany.

In the demonstration facility, funded by BGE in the deadstock building, there are eight tanks filled with either caustic soda or water. Next to it, a mass and heat exchanger, called SeasON, which manages energy flows.

From April to October, caustic soda is charged with renewable energy. This means that the water in the caustic soda evaporates and a more concentrated caustic soda is left. “This concentrated soda stores the potential to provide heat later”explains Benjamin Fumey. The higher the concentration of caustic soda, the greater the energy stored.

In winter, this energy is taken from the concentrated caustic soda, which is thus discharged. The following summer, the caustic soda is charged again with solar electricity from the roof of the animal carcass processing facility. A closed circuit. The heat pump is powered by chemical means and not electricity like common air-water heat pumps.

Benjamin Fumey explains:

This is precisely the case with caustic soda, because it is a waste from plastic production. The storage volume can also be easily increased. “Just add more tanks of caustic soda”explains the energy researcher. If the home or business lacks heating energy in winter, it is additionally possible to recharge with concentrated caustic soda.

Each cubic meter of caustic soda stores approximately 200 to 350 kilowatt hours of heat. This storage density of caustic soda is therefore six times greater than that of a hot water tank. For a single-family house, you need approximately 8 to 10 cubic meters of caustic soda for one winter, depending on the standard of the house and its location.

From idea to marketable product

“Caustic soda is very stable, there are no losses in the closed system and it does not decompose», explains Benjamin Fumey. It is simply a loading-unloading process that oscillates between concentrated and diluted caustic soda. Caustic soda is therefore not consumed. The researcher continues:

Benjamin Fumey first explored the idea with Robert Weber for 14 years as part of a European project at Empa. He then took this research to Lucerne three years ago. From now on, it is no longer a question of building a bridge between fundamental research and applied research. This idea now needs to become a marketable product. “Today, it is clear that it is working”concludes Benjamin Fumey.

(Translated and adapted by Chiara Lecca)