Hot rock energy storage

News

The Danish company Stiesdal is now developing the first commercial demonstration energy storage system based on heating rocks in big tanks on the island of Lolland.

When the wind blows and the sun shines, the facility will store electricity from renewables for later use. The new storage system, called GridScale, stores energy in large tanks filled with crushed stone.

Location

Renewable energy production is so large at Lolland that sometimes you must shut off the energy-producing facilities as consumption does not match production. Extensive investments in the electrical infrastructure are needed to transfer the abundance of energy from Lolland.

That is why Stiesdal selected the island for placing GridScale.

Technology

Stones can withstand repeated heating, that it is possible to re-extract the energy from the storage at a constant temperature. 

The energy storage contains pea-sized crushed stones stored in insulated steel tanks. When there is an excess electricity supply in the grid, it charges the storage using a specially designed heat pump system, which moves heat energy from one set of tanks to the other.

When you take energy from the tank, the stones there get colder. While they get a lot hotter in the tanks that receive the heat, as hot as approx. 600 degrees C.

Stones can store the heat for many days. When you need more electricity in the grid, the heat energy is returned from the hot tanks to the cold tanks using a turbine, which produces the electricity. It is a highly efficient solution due to a low loss of energy.

Both the number of sets of storage tanks and the number of turbine units may vary. It depends on the length of the discharge cycle and the electrical power wanted.

Future

As per the CEO of Stiesdal Storage Technologies, Peder Riis Nickelsenstorage, "our technology can make a difference and contribute to a far more extensive integration of power from sun and wind than what has been feasible up till now. The market for storing electricity from renewables is huge, and we expect that GridScale’s combination of a long discharge cycle and low cost will attract international interest."

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.

Tech for Good

💡 Article on Cleantechnica

🌐 Stiesdal website