Thursday 23 Feb 17

Using hot stones and steam turbines, DTU researchers seek new solutions for storing green surplus energy.

Every once in a while, significant scientific breakthroughs appear almost shockingly simple when viewed in retrospect. Even laymen may, from time to time, think ‘I could’ve invented that if I’d only come up with the idea’. The trick then is simply getting the idea.

The energy storage project—currently in its early start-up phase at the Risø Campus near Roskilde Fjord—is an excellent example of this. Costing in excess of DKK 8 million (EUR 1,1 million), it is essentially a wilderness trick as old as the hills that now will be rolled out and tested.

That said, it has the potential to solve one of green energy’s biggest problems: the storage of surplus energy from, among other things, wind turbines.

The idea is to develop the old trick of laying stones in the campfire during the day in order to provide heat in the cabin at night—just on a bigger scale.

We cannot tell the wind to blow or the waves to roar—the energy is there when it is there, and we must adapt accordingly. And the hot stones in Roskilde may perhaps solve the problem of storing energy in a very simple way without either the cost or energy loss rendering the project economically unviable.

Wind energy into heat

The idea is to convert the surplus wind energy into heat by means of an old-fashioned filament blow heater. The heat is then channelled through a lot of stones to reach a temperature of approx. 600 degrees. At the other end, the heat can be used for district heating and driving a steam turbine that generates electricity for Danish homes—even when the wind is not blowing.

Development Manager Ole Alm, SEAS/NVE "It represents a potential revolution as it means we can store energy—and draw power—on an industrial scale. "

The filament. Hot stones. Steam turbine. These are not exactly new technologies being employed at Roskilde, which begs the question why energy storage in the green sector has not previously gone down this road. However, Head of Section Allan Schrøder Pedersen from DTU Energy has a ready answer:

“Most researchers in their respective field prefer to focus on new technologies. It probably hasn’t been… sexy enough to warrant further investigation,” he says, pointing out that there has been a great deal of research into energy storage using large batteries, chemical storage, and the production of green synthetic fuels—something which he stresses there will be a continued need for, even if storing energy in stones proves viable.

The cheapest solution

The difference between these technologies and the stone energy storage project at Risø is that the stones are cheap—and in principle have been tested since the first Inuits found their way to Greenland.

And price is precisely where Allan Schrøder Pedersen and his people believe they can make a difference.

“We will still need other energy storage methods, but this will probably be the cheapest solution to the problem,” he says. Following DTU’s final testing at the research facility at Risø, the task of building a full-scale solution will fall to the energy company SEAS/NVE headed by development manager Ole Alm. And he is not modest in his enthusiasm for the project:

“It represents a potential revolution as it means we can store energy—and draw power—on an industrial scale. As things stands, this isn’t possible—so this is a very, very important step on the road to making us fossil fuel independent,” he says.

Viable solutions on industrial scale

The energy industry is also keenly interested in any project that can help to resolve the age-old storage problem associated with green energy:

“Denmark is at the forefront of developing smart grid solutions, and we therefore have a great potential for sharing our energy in an efficient manner. But storage is one of the key challenges to overcome, so we’re looking very carefully at all the options. It will be really interesting when we have developed a method that can operate on an industrial scale without the heavy energy losses we see today,” says Mikkel Hedegaard, Head of Validation and Quality at Siemens Wind Power.

For the moment, Allan Schrøder Pedersen’s chief concern is initiating tests at Risø:

“Our main focus is to determine how we can best design stone energy storage to minimize heat loss. In the next year and a half to two years, we will have a small functioning plant that can pave the way for a full-scale facility,” he says.