The green transition is well under way, and increasingly larger energy volumes are produced from renewable energy sources such as wind and solar. Many expect that in just 10 years our electricity will be fully based on renewable energy sources. But when the sun does not shine, the wind does not blow and the traditional power plants are no longer in operation, what do we do, then? That is one of the great challenges in the green transition and to this end, pumped thermal electricity storage is a strong option.


The energy storage reservoir that the partners are working on comprises crushed stones the size of peas stored in insulated steel tanks. When there is excess supply of electricity in the electricity grid, the storage is charged using a specially designed heat pump system which moves heat energy from one set of tanks to another. The stones get colder in the tanks from which the energy is taken, while they get a lot hotter in the tanks that receive the heat, up to a temperature of approx. 600 degrees C.

The heat can be stored in the stones for many days, and when electricity is needed in the grid the heat energy is returned from the hot tanks to the cold tanks using a kind of gas turbine which produces the electricity. This is a highly efficient solution due to a low loss of energy. In serial production the round trip efficiency is expected to be 55-60%. The size of the storage facility can be scaled up simply by adding more tanks containing stones. The technology will both be suitable for storage in the 8-18 hour 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.

Project Deliverables:

The aim in the project is to optimize a full-scale design of the GridScale storage technology for the Danish and European energy system. Based on the GridScale technology, two energy system analyses will be carried out: one focusing on Lolland and one focusing on Europe.

Based on these, the optimal requirement specification for a full-scale plant will be developed for various applications, including energy islands.

A charge/discharge decision model will be developed. Turbomachinery tailored for charging and discharging the system will be optimized with consideration to both performance and cost by use of advanced models. Detailed numerical models for the storage units will be developed to optimize their design. The aim is to obtain a significant specific cost reduction for the whole system. Development work will, when possible, be validated on a pilot plant under construction in parallel with the EUDP project. The output of the project will be one or more optimized full-scale designs, ready for construction on the energy islands and in many other locations where energy storage is required.

Problem owners

Problem solvers

Project timeline

PHASE 1: Conceptualisation
PHASE 2: Development and testing
PHASE 3: Demonstration and validation
PHASE 4: Commercialisation

Financed by


Start: January 2021
End: December 2023
EUDP funding: DKK 21 million
Budget in total: DKK 35 million

Contact person

Christian Munk Jensen

Christian Munk Jensen
Project Manager
Tlf: +45 5055 2606