The transition from a fossil to a sustainable energy supply requires large-scale storage of energy. Heat demand in the Netherlands is very dependent on the season: high demand in winter and lower demand in summer. The challenge is to optimally match the demand for heat and its supply with climate-friendly heat sources without the costs of the energy system becoming too high.

Seasonal underground storage of heat can play an important role in this. TNO supports innovation that enables the large-scale application of climate-friendly heat sources with heat storage in smart grids and thus makes an important contribution to a cost-effective heat transition.


Heat storage is already widely used in households (e.g. boilers), but also in heat networks that supply heat to homes, buildings and businesses. In heat networks, for example, there are often above-ground buffers for heat storage. They can then store the heat for a few hours. Seasonal storage of heat in heat grids is a technology that is not yet widely used. The challenge now is to store heat on a large scale in a way that is safe, large-scale and affordable.


Heat storage will become even more effective in combination with the further development of sustainable heat sources and the construction of smart heat grids. These are no longer fed by gas-fired heat, but by climate-friendly heat sources such as geothermal heat, solar heat, industrial waste heat and heat pumps. Then sustainable energy generation, smart users, infrastructure and seasonal storage will form an ideal interplay in the energy transition.


In European and national projects, we are working on heat storage systems that are able not only to bridge seasons but also be applied on a large scale, with up to thousands of households or hectares of horticulture receiving their heat from storage in the winter months. No particularly complex technology needs to be used to make underground heat storage possible on a large scale.


It is particularly important to determine precisely where the subsurface is suitable for heat storage and where it can best be combined with the above-ground infrastructure. Linking existing technologies and knowledge already seems to yield a lot. TNO has unique knowledge of the subsurface and wants to take this further by demonstrating even more accurately where the layers in the subsurface are sufficiently suitable for large-scale storage. TNO also has key expertise in the field of relevant heat sources such as geothermal energy, heat pumps and heat grids. This allows us to assess where and how seasonal storage can best be integrated into the heat infrastructure.


Drs. ing. Maurice Hanegraaf