The sun shines, the wind blows briskly over Denmark – and green sustainable energy pours into our energy system. From here, it is led into our homes, factories, schools, hospitals and all of the other places in which our high standard of living is dependent on a stable supply of energy.

The ideal green transition – that is what we are striving for. However, a pivotal issue is yet to be solved: how do we store the green energy when grey clouds cover the sun, and the wind is insufficient to turn the rotor blades of the many wind turbines sprouting in the landscape and the seas around us?

A tough nut, which many strive to crack. Research has been directed at batteries, energy storage in chemicals such as hydrogen and ammonia – and at the energy and fibre-optic group SEAS-NVE, they are now ready to present a test setup viewed by the company as an environmentally friendly and inexpensive solution. The opening took place on 18 March when Minister for Higher Education and Science, Tommy Ahlers, turned on the new storage facility at DTU Risø CampusRisø. In this, stones are heated up to 600 degrees C using surplus electricity. When demand increases, heat is extracted from the hot stones to a generator, which produces electricity. Residual heat is supplied to homes in the area through district heating.

”I am excited that we have now come so far in our efforts that we are ready to unveil the facility and invite you inside,” says Jesper Hjulmand, CEO at SEAS-NVE.

He further explains that the company together with researchers from Technical University of Denmark (DTU) and Aarhus University and several other partners have worked intensely on the project since the summer of 2016:

”Geologists from Aarhus University have tested and found the ideal stones, and together with consultants from Niras and researchers from DTU, we have built the bowl-shaped energy storage model, which is partly dug into the ground. It’s a bit like a large kettle grill, into which you blow heat over a lot of stones, and later on, the heat in the stones can be extracted”.

As to the perspectives of a large-scale setup, Jesper Hjulmand states:

”Now, we will have to measure, and analyse these measurements, before we make any decision to proceed to larger test facilities. It’s immensely exciting, because in my best judgement, the vision of a 100 percent fossil-free energy supply cannot be obtained without energy storage solutions”.