High-Temperature BTES Facility

High-Temperature Borehole Thermal Energy Storage (HT-BTES) systems use the subsoil as a heat-exchanger to both store and recover heat depending on the season, using the ground as a thermal battery. They allow storing the excess of energy captured during the summer months deep in the subsurface, which is then available again for extraction in the winter months, reducing the dependency on non-renewable energy sources for heating purposes. Typical heat sources include the excess of energy from solar or wind plants, and the waste heat generated from waste incineration plants and cooling systems.

HT-BTES systems are characterized by being closed-loop systems, meaning that no direct exchange of water with the underground takes place. Instead, the system is based on an array of boreholes, each one equipped with an independent loop of pipes used to circulate water and exchange heat with the surrounding ground. At the new Empa research campus, an HT-BTES facility was recently built and is operated by the Energy Hub team. It consists of a total of 144 boreholes of 100 m depth each, arranged in a circular array and located in the vicinity of the new parking building. It has the capacity to inject up to 65 ºC in the underlying aquifer, leading to expected changes in the aquifer temperature of around 50 ºC.

Given the high density of geothermal installations in Switzerland, most of which are employed exclusively for energy extraction in the winter months, the creation of HT-BTES facilities is met with high expectations given its large potential towards the development of cleaner and more sustainable energy sources. The use of renewable energy sources, such as solar or wind energy, depends directly on the existence of optimal natural conditions, which leads to periods of both abundance and insufficiency in the energy production in relation to the energy demands. Additionally, water energy from waste treatment plants or from cooling installations is commonly not repurposed. HT-BTES facilities can contribute to overcome these limitations, since they can be integrated to renewable energy sources to store the excess of energy generated with these techniques and make it available again in periods where the energy demands cannot be met. This is for instance achieved at the Empa campus by storing waste heat from the cooling systems and/or the excess heat obtained from solar panels during summer for its future use in the winter months. In this way, HT-BTES facilities can contribute to reduce our dependency on non-renewable energy sources.