Do you think the cheapest way to store energy is a traditional battery like the one you have in your car? Well, there are other ways – with a fraction of the cost. With the increased share of renewable energy sources such as wind and solar, there will be more variances in availability of energy. And sometimes energy will be really cheap – the ones that are capable of buying energy at these times could save a lot of money if they can store it for days with less sun or wind.

Sebastian Spaun, manager of the Austrian Cement Industry Association, has tested this in real conditions. In a typical two story house, they installed water pipes in the concrete slabs. They could then heat up the “battery” – the concrete slabs – with cheap energy from the local wind turbines.

“Concrete has very good heat conductive properties,” explains Sebastian Spaun. “We wanted to test how it works to get heat from the ceiling. Will it be comfortable? Yes, it is. We warm up the ceiling with 3-4 degrees more than the room temperature. The temperature difference from the ceiling to the floor is less than one degree. 90 % of the heat is directed downwards in the room. So, it feels comfortable!”

When you “charge” up the ceiling with heated water, one cubic meter of concrete can store 2.67 kWh when heated 4 degrees. This means up to 140 hours of heating of the room, compared to 47 hours when conventional convection heating is used. The house has now two years of use, and the results show that it works as expected. 90 % of the energy use comes from the cheap excess energy.

“This battery has no self-discharge and endless cycle stability, we have a huge potential in energy savings. And it cost nearly nothing!”