The energy storage explained

The storage consists of a pile of insulated stones, heated to 600 degrees, powered by the surplus from wind turbines. After a couple of days, when energy is needed again, the heat is passed through a generator which generates electricity and the residual heat is fed to district heating.

energilager forklaring


A strong team: SEAS-NVE, DTU Energi, Aarhus University Geoscience, Dansk Energi,, Rockwool and EUDP


This is how the energy is saved

Renewable energy can be stored in several ways, with varying advantages and disadvantages. Here are the three main options.


TECHNOLOGY: Heat in liquids or solid material such as stone. There are no requirements regarding location.

ADVANTAGES: Great capacity. An environmentally friendly way of storing energy. Provides both electricity and district heating, for which there is growing demand. Easy to connect to an existing cogeneration plant. Inexpensive to operate and maintain.

DISADVANTAGES: Low temperature thermal storage of district heating is widespread, but high-temperature thermal storage is still under development.


TECHNOLOGY: Storage of water in reservoirs or compressed air underground for use in turbines.

ADVANTAGES: Reservoirs have no environmental impact. Compressed air has no environmental impact if gas is omitted as a supplement.

DISADVANTAGES: Traditional hydropower requires high standards and is less suitable for Denmark. Compressed air is of relatively low efficiency and is primarily undertaken in so-called salt domes (areas with high concentrations of salt in the subsoil, editor), which is only found in North Jutland in Denmark.



ADVANTAGES: Very efficient for storing electricity. No location requirements. The cost is constantly falling.

DISADVANTAGES: Limited capacity and longevity due to the gradual weakening of the battery. The least environmentally responsible method.

Detailed information

Learn more about the three energy storage methods


Project facts

Project name: High temperature thermal energy storage (HT-TES): The basic concept of the project is that cheap, non-degradable and environmentally friendly storage materials combined with known charging and discharging technology can reduce the cost and increase the efficiency of energy storage. EUDP has provided support for the project being able to run in a pilot phase for two and a half years until 2019. In the pilot phase, the energy storage facility is located at DTU Risø Campus. If the test results are positive, the project will enter a demonstration phase (from 2020 to 2024), where the project will be tested on a larger scale. It is not yet planned where the “real” full-scale warehouse will be located, but it is expected to be in Region Zealand if the market develops as expected The total budget for the pilot phase of the project is DKK 8.5 million.

The project’s aim is to ensure that it is financially viable to save energy in much larger quantities and over longer periods than previously. But the project is not just a technological project. It will also reveal the challenges and prerequisites for adding high-capacity energy storage to an existing grid, an existing market model and an existing tax system, thereby helping to pave the way for energy storage in a broader sense. The market potential for storage will be fully investigated during the project period, but it is expected to be achieved with a budget below DKK 100 million because the storage is so cheap to build. In addition, the project has the advantage that it can be connected to the existing district heating system in Denmark. The heat in the energy storage can be used to generate electricity for the electricity grid, but it can also be used for generating heat for the district heating system. This helps to ensure a high level of utilisation for the stored energy.

The concept is that we can save energy in a form so it can be used later than it is produced.

Energy production from renewable sources, such as solar and wind, is variable and does not always correspond to our energy consumption. If Denmark is to reach the goal of an energy supply totally independent of coal and oil by 2050, we must find new and better ways of storing energy.

  • Storage in the form of heating stones or water with electricity.
  • Large batteries.
  • Synthetic and sustainable fuels that can replace traditional fuels for cars and provide climate and environmentally friendly transport.

Background to the project

Read about the background to the project

Read about energy storage in english

Lesen Sie mehr über den Hintergrund des Projekts