The BILS Idea

Seasonal heat storage using hot water is probably the easiest storage technology that is not adding load to the electric grid: The larger the storage volume, the less the thermal losses and the lower the costs.

Large-scale pit storages or underground thermal energy storages are known in different variants and very high seasonal storage efficiencies exceeding 90% have been reported. However, the space required is considerable, and this space is usually not available close to urban locations. 

Bubble in the lake storages (BILS) offer a solution.

The Project

The BILS project aims at developing large sensible heat storages in lakes for seasonal heat storage and for short term storage. The main idea consist in building large seasonal heat storages by using flexible skins (e.g. plastics, textiles and similar) to enclose a hot liquid (e.g. water) in waters (e.g. lakes), submerged and surface floating. The project includes the development of strategies to manage the heat in(side) the storage, namely reducing thermal losses, charging and discharging, active and passive stratification.  

The Potential

The potential of BILS in district heating systems is huge: In theory only 2% of the Lake Zurich would be sufficient to cover the heat demand of the city of Zurich. Many smaller cities with a roughly estimated number of 1.5 - 2 Mio inhabitants are located ashore of similar or much bigger Swiss lakes.

The Potential

The potential of BILS in district heating systems is huge: In theory only 2% of the Lake Zurich would be sufficient to cover the heat demand of the city of Zurich. Many smaller cities with a roughly estimated number of 1.5 - 2 Mio inhabitants are located ashore of similar or much bigger Swiss lakes.

The Partners

BILS Is co-financed by the Swiss Federal office of energy (SOUR Call). 

Experts from the SPF Institute for Solar technology and from the company Luft und Laune work on the project. 

If you have good ideas to share, please let us know.