Danish Company is Storing Renewable Energy in Stones

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Danish Company is Storing Renewable Energy in Stones

The technology, which stores electrical energy as heat in stones, is called GridScale, and could become a cheap and efficient alternative to storing power from solar and wind in lithium-based batteries. It is developed by the Danish company Stiesdal Storage Technologies (SST), and the GridScale demonstration plant will be the largest electric storage facility in Denmark with a capacity of 10 MWh. Read more about the Danish company which is storing renewable energy in stones.

The GridScale storage system is an industrialized and scalable technology for cost-effective thermal storage of electric energy. GridScale uses crushed rock as a low-cost storage medium and offers high round-trip efficiency with no geological or topological constraints. Following an investment by Danish power and fiber-optic group Andel of some DKr75m ($12m), the ‘hot rocks’ energy storage system design is heading for prototyping in the front-running long-duration thermal concept.

Danish Company is Storing Renewable Energy in Stones
Stiesdal hot rock energy storage technology

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GridScale is built for modular adaptation to local demands
Pea sized crushed stones heated to 600C in large, insulated steel tanks using an innovative pump-based system and releases the stored energy via a turbine to produce electricity are at the heart of a new innovation project aiming to make a breakthrough in the storage of intermittent wind and solar electricity. GridScale is built for modular adaptation to local demands. The storage duration is adjusted with the number of storage tanks.

The technology has undergone tests at the Technical University of Denmark (DTU), but will now be trialed at a solar array in the Zealand region on the Baltic Sea, as well being incorporated in a Danish Energy Agency ‘GridScale’ project.

Danish Company is Storing Renewable Energy in Stones
SST industrial factory

While lithium batteries are only cost-effective for the supply of energy for short periods of up to four hours, a GridScale electricity storage system will cost effectively support electricity supply for longer periods – up to about a week.

However, the GridScale range covers both the 12-18 h duration required for day-to-day smoothing of solar PV, and the 3 to 7 days duration required for smoothing of wind power over gaps caused by low wind periods.

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Danish Company is Storing Renewable Energy in Stones
“SST represents a very special technological competence. We must now jointly complete a prototype, which can subsequently be tested and displayed,” says Andel CEO Jesper Hjulmand

Stone is an inexpensive and sustainable material
“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,” says 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.”

“The only real challenge with establishing 100 per cent renewable electricity supply is that we can’t save the electricity generated during windy and sunny weather for use at a later time. Demand and production do not follow the same pattern. There are not yet commercial solutions to this problem, but we hope to be able to deliver this with our GridScale energy storage system,” says Henrik Stiesdal, founder of the climate technology company Stiesdal Storage Technologies.

Danish Company is Storing Renewable Energy in Stones
Henrik Stiesdal, founder of the climate technology company Stiesdal Storage Technologies. Press image 2012

Stores large amounts of energy in small spaces
The hot storage reservoir material is crushed basalt rock. Basalt is formed by the cooling of lava, and due to its volcanic origin, it is very resistant to rapid heating and cooling. Basalt is abundant and easily accessible, and it is readily available in large volumes all over the world.

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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.”

“Basalt is a cheap and sustainable material that can store large amounts of energy in small spaces, and that can withstand countless charges and discharges of the storage facility. We are now developing a prototype for the storage technology to demonstrate the way forward in solving the problem of storing renewable energy – one of the biggest challenges to the development of sustainable energy worldwide,” says Ole Alm.

Danish Company is Storing Renewable Energy in Stones
A typical lithium ion battery system. NPS

A very inexpensive storage medium
The total specific cost of the thermal storage materials, including storage tanks, insulation, etc. is expected to be less than 10 EUR per kWh for serial production systems. In comparison, conventional battery storage systems typically have storage capacity costs in the range of 200 EUR per kWh.

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 GridScale prototype will be the largest storage facility in the Danish electricity system, and a major challenge will be to make the storage flexibility available on the electricity markets in a way that provides the best possible value. Consequently, this will also be part of the project.

Since 2019, the GridScale concept and technology has been validated through a wide range of tests using a combination of standard industrialized components and proprietary technology.

In 2022, the first full scale demonstration project will be installed. It comprises a 1-2 MW, 24 h capacity unit to be installed at a decentral heat and power plant in Denmark.

The demo plant will operate commercially.

Danish Company is Storing Renewable Energy in Stones, written by Tor Kjolberg

Feature image (on top) Andel CEO Ole Alm.

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