Latest research on the application, improvement and impact of HT-ATES systems presented at the 4th NCB

KWR was well represented at the conference. Martin Bloemendal was involved in the organisation and chaired the Underground Thermal Energy Storage session. In this session, Stijn Beernink, Niels Hartog and Gilian Schout contributed by presenting their latest research on the functioning and impact of aquifer thermal energy storage (ATES) systems.

Determining HT-ATES suitability based on subsurface conditions

Aquifer Thermal Energy Storage (ATES) is a proven technique, with more than 3000 systems applied in the Netherlands. Recently, the interest for ATES at high temperatures between 50 and 100 °C (HT-ATES) is growing, as this shows high potential for utilisation of renewable heat sources like geothermal, waste-heat and solar in district heating networks. For efficient and sustainable use of HT-ATES local subsurface conditions need to be known in detail. Important aspects are, among others, the aquifer thickness and hydraulic conductivity and the presence of a sealing top and bottom layer (aquitard) around the aquifer. Determining these properties is not straightforward as the layers of interest for HT-ATES are often (but not always) relatively deep and thus far unexplored. Stijn Beernink showed in his talk that innovative methods were applied at multiple pilot locations to investigate this in the WarmingUP and Ultimate project. Currently, the results of these pilot drillings are used to determine local subsurface conditions and the optimal design of the HT-ATES systems at these locations. All the data and samples collected from these locations are used in Beernink’s PhD study to determine the applicability of new techniques and workflows.

Even if local subsurface conditions are available that are suitable for HT-ATES from an operational perspective, concerns about the thermal, chemical and microbiological impacts on groundwater quality have led to strict permitting conditions, which have thus far prevented the large-scale implementation of HT-ATES. In his presentation, Gilian Schout outlined the state-of-the-art knowledge of these effects and the research scope that is still required to determine the conditions under which HT-ATES can be safely applied.

Slide from Stijns’ presentations, showing the effect of the prescience of confining layers on the heat distribution and recovery efficiency of a HT-ATES system.

Significant CO2 emission reduction potential with new ATES concept: ATES Triplet

Over the past decades, the use of low-temperature ATES systems to reduce the CO2 emissions for the heating and cooling of a building has become common practice in the Netherlands. However, unless heat is stored at temperatures sufficiently high to allow direct heating, heat pumps on the demand side will continue to require significant amounts of imported electricity in a quantitative and temporal mismatch with the availability of green electricity. Therefore, Niels focused his presentation mainly on the recent research on the development of the ATES triplet.

Slide from Niels’ presentation, showing the potential for greenhouse gas emission reductions with ATES-TRIPLET.

This new ATES concept is operated using three storage volumes at 1) direct use temperatures together with 2) an intermediate buffer and 3) cold storage. It was shown that the ATES Triplet concept could significantly reduce the use of grey electricity and maximise the local harvest and utilisation of green heating and cooling potential, e.g. by storing heat at temperature levels suitable for direct heating (e.g. by solar collectors, power-2-heat). Whenever the return temperatures from the building systems do not conform with either of the hot or cold wells, the buffer well is used to store at the return temperature. In times of abundant heat (or cold) harvesting potential, the buffer volume temperatures can be upgraded to the hot (or cold) storage volume. Simulations and an economic evaluation show significant potential for triplet ATES with economic performance better than conventional ATES while the CO2 emissions are reduced by a factor of ten. As the temperature differences are larger, the volume of groundwater required to be pumped is considerably lowered, causing an additional energy saving. Overall, there is good potential to significantly improve the CO2-emission reduction of ATES systems with respect to their current common use. The concept is currently being further developed in collaboration with TU Delft, TU Delft and other partners.