An unique experiment is currently underway in Seelisberg: A construction physicist from Lucerne had Empa researchers install six cubic meters of special concrete in the garage of his vacation home. The concrete stores heat during the summer and releases it in the winter as and when needed. The system enables the house to be heated for weeks – sustainably and ecologically. Read the whole story (pdf). Pictures can be downloaded here.

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Update (2021)
The prototype built in Seelisberg in 2015 has been dismantled in 2019. The project will not be continued at Empa. Unfortunately, the prototype had not generated enough heat during test runs in 2016 and 2017, and a technical retrofit in 2017 did not improve the situation either. Then in 2018, it was discovered that many of the concrete heating modules showed severe cracking. A scientific publication by Empa researchers reports in detail on the technical specifications of the storage unit and the experience gained during operation: J Kaufmann, F Winnefeld; Seasonal heat storage in calcium sulfoaluminate based hardened cement pastes – experiences with different prototypes; Journal of Energy Storage (2019); doi: 10.1016/j.est.2019.100850