Now that we locally generate and use more and more renewable energy, chances are that green power is produced in such large amounts, that a surplus arises at certain times during the day. When we switch to 100% sustainable production, that temporary surplus will only become larger. To prevent that we need to turn off wind turbines and solar farms in order to anticipate such a production peak, we, among other things, look for other types of long-term storage.
By now, we as consumers are fairly familiar with batteries that can temporarily store and discharge power. Examples of these are the powerful batteries in your smartphone and laptop and those in electric vehicles like Tesla’s. All the same, storage in batteries is still quite expensive and mainly suitable for quick charge and discharge.
Large-scale seasonal underground storage
Another, fairly cheap, way of storing energy is thermal storage in water. When there is a lot of electricity, you can change it into heat and store it in water. This may offer a good solution for new housing districts and for the transition into natural gas free housing districts.
Ecovat in Veghel has developed a storage tank in which a large quantity of heat is stored underground in water. This heat can be stored with a 95% efficiency for more than 6 months. That is a unique feature of this Dutch technology! One of those ‘Ecovats’ has been installed and is operational in Uden. This thermal tank has a 13 meter diameter and a 16 meter depth.
Practical tests
Enexis Netbeheer and Ecovat, together with VITO (Flemish Institute for Techological Research), are investigating whether thermal seasonal storage can contribute to a local heat grid and how the system can be of aid regarding the storage of surplus renewable energy. The functioning of the Ecovat can be practically tested with the help of a contribution by the European Horizon 2020 subsidy fund. Enexis Netbeheer, as a partner, provides contribution to the project by making the connection to the local grid. It also provides detailed information about the local grid throughout the study. In cooperation with VITO, Enexis Netbeheer will study what thermal storage may imply, by simulating various scenarios on the local distribution grid.
Grid balancing through local storage
The pilot serves as a first underground seasonal thermal energy storage demo project. A surplus of energy that is generated in summer, e.g. via solar panels, can be stored by means of thermal storage for long periods. In winter the stored energy can still be used, for instance for heating housing districts, office buildings or utility buildings. By storing heat in times of surplus and using it when there is a shortage, we flexibly deal with energy and we ensure balance on the power grid. When there is an energy surplus, the energy is not returned to the grid, but stored locally.