An innovative ‘hot rocks’ energy storage system design being developed by Stiesdal Storage Technologies (SST) is heading for prototyping following an investment by Danish power and fibre-optic group Andel of some DKr75m ($12m) in the front-running long-duration thermal concept.

Green is the new black. Subscribe to Accelerate

Get the market insight you need into the global oil & gas industry's energy transition – from the new newsletter from Upstream and Recharge. Sign up here

The technology — which heats up pea-sized crushed stones in insulated steel tanks using an innovative pump-based system and releases the stored energy via a turbine to produce electricity – has undergone tests at the Technical University of Denmark (DTU), but will now be trialled at a solar array in the Zealand region on the Baltic Sea, as well being incorporated in a Danish Energy Agency ‘GridScale’ project.

“Stone is an inexpensive and sustainable material, which can store large volumes of energy taking up only a little space, and it can withstand innumerable rounds of charging and discharging of the storage,” said Ole Alm, Andel’s head of development. “We know this from our tests at the Risø [DTU] facility. We must now create units that are flexible and relatively easy to handle.

“They can be placed at solar farms and offshore wind farms, at substations and industrial facilities, and perhaps on the future wind energy islands. For this, we need an industrial partner like SST so that together we can create functional large-scale solutions”.

SST founder Henrik Stiesdal said: “The only really big challenge to an electricity supply that is 100% green is that we cannot store the electricity from the time when the wind blows and the sun shines until its subsequent use. Production and consumption are simply not in balance. So far, there are no commercial solutions to this problem. But we hope to be able to provide that with our ‘GridScale’ energy storage system.

“Technological development and sophisticated equipment are not enough, we also need collaboration with an experienced operator that has extensive knowledge about the electricity grid and can make production, storage and consumption interact in practice. On this, Andel is a strong and ambitious partner, which can test the technology and perform large-scale rollout.”

Andel CEO Jesper Hjulmand said: “[SST] represents a very special technological competence. We must now jointly complete a prototype, which can subsequently be tested and displayed.

“It is a strategic match for Andel that we strengthen our focus on energy storage. That is the way forward if we want to achieve full integration of renewable energy and the electrification of society.”

SST CEO Peder Riis Nickelsen, spotlighted that “commercially sustainable” storage of large volumes of energy would need “a very inexpensive storage medium and that the supplementary equipment can be mass produced – GridScale technology fulfils both of these criteria”.

“The cost of crushed stone is at a totally different level per unit of energy than practically any other material for energy storage. Besides, our charging and discharging system can utilise well-known technologies that have been applied for a century within other industries and are well-suited for mass production.”

Along with Andel and SST, the GridScale project, which has been backed by DKr35m from the Danish government, includes Aarhus University, DTU, Welcon, BWSC, Energi Danmark and Energy Cluster Denmark.