Energy storage, big potential in little rocks

John Churchill
March 20, 2019

As the world continues shifting toward renewable energy, storing it remains a major challenge. In Denmark, ROCKWOOL is a partner in a project testing the potential of a lot of very hot rocks.

Danish energy company, SEAS-NVE, and the Technical University of Denmark (DTU) together with several partners including ROCKWOOL, recently unveiled an innovative energy storage test facility this week at DTU’s Risø campus in Denmark. 

The  facility, built by SEAS-NVE and DTU, is part of a project called “high-temperature thermal energy storage” (HT-TES), undertaken to address one of the biggest challenges with renewable sources of energy like wind and solar: storing it efficiently.

Rocks, not batteries

In this pilot phase, small stones, stored in what look like giant ball grills buried underground, are heated to 600°C by excess electricity from wind turbines and solar cells.

When demand for heat is high but renewable energy supply is unavailable because it’s cloudy or not windy, the heat (thermal energy) stored in the stones can be released to local power plants where it can be used to produce electricity and provide heat to homes. ROCKWOOL stone wool insulation is used on the pipes carrying the heat out to minimise heat loss. 

This is the second thermal energy project investigating the storage capabilities of stones that ROCKWOOL is involved in. The other, now reaching the commercial phase, is led by Siemens Gamesa in Germany. 

“The most sustainable energy is the one that is not used – it is one of the primary viewpoints of the ROCKWOOL Group when designing our solutions. High-temperature energy storage that stores excess energy is completely in line with this approach, and since the storage must be insulated as best as possible with insulation that can withstand high temperatures to function optimally, we naturally wanted to participate in this project,” says Frank Ove Larsen Managing Director, ROCKWOOL Technical Insulation.

From ball grills to large warehouses

While batteries are the most well-known form of storage (chemical), there are two other main types: mechanical and thermal. (Read about the advantages and disadvantages of all three at the SEAS-NVE project site). 

According to SEAS-NVE, some of the advantages of thermal energy, which is heat from liquids or solids like stone, include:

  • high storage capacity;
  • can be used to generate electricity and heating
  • is easy to connect to existing power supply systems
  • is environmentally friendly and
  • easy to operate and maintain.  

During the next six months, the test facility will be looking at a lot of different factors like the best type of rock to use in order to determine how the project should proceed. If the test results are positive, the project will be tested on a larger scale with a warehouse full of stones dug into the ground. 

“The last 4 years have been the warmest in a man's memory, and that worries me. I have gone into politics to create change, and it can succeed with projects like this,” said Danish Minister of Education and Research, Tommy Ahlers, who was in attendance at the official opening of the facility. “Here, universities, businesses and energy companies have joined forces. This is high-class entrepreneurship, and the solution has potential far beyond Denmark's borders.”