Life Cycle Assessment of an Aquifer Thermal Energy Storage System - Exploring the environmental performance of shallow subsurface space development

Abstract

Thermal energy storage systems can have a significant positive contribution to the mitigation of climate change and facilitate sustainable development. For this purpose exploiting the subsurface is increasingly looked into due to the ground’s inherent properties that make it a medium suitable for thermal energy storage. A number of different technologies are commercially available and widely implemented nowadays and are considered environmentally friendly solutions, especially when compared to conventional heating and cooling systems. Systems that make use of aquifers for thermal energy storage (ATES) are presently one of the most common thermal energy storage options. However, an ATES system still creates environmental impacts during its construction, use and end-of-life phases. Therefore, this report adopts a cradle-to-grave approach aiming to assess the potential life cycle environmental impacts of a combined heat and cold, shallow ATES system. To fulfil this aim the life cycle assessment (LCA) methodology as defined by the ISO standard is utilized. Given the increasing number of installed systems in the Netherlands this becomes especially relevant research and so data for this LCA was drawn from the ATES system that serves the heating and cooling demands of the Tetra building in Deltares in Delft. Using the ReCiPe Midpoint impact assessment method the first result of this study confirms the outcome of previous research, namely that the electricity consumed during the use phase of the ATES system has the largest influence in the majority of the environmental impact categories. This is mainly due to the fossil fuels used in power plants and so switching to a renewable electricity source can reduce these impacts considerably. An additional, original finding of this research regards the preventive maintenance of the well screens of ATES systems. A certain amount of aquifer groundwater is extracted annually and used to “flush” the wells in order to prevent clogging of the well screens. Dutch legislation allows the owners of ATES systems to choose between draining this groundwater to nearby surface water or in the sewage. This study shows that the second option can incur considerable environmental impacts which in some impact categories are even larger than those of electricity use. Lastly, it is shown than when looking only from an energy perspective the use phase of an ATES system performs significantly better than a conventional heating and cooling system. However, when compared at midpoint level and accounting for more impact categories it is unclear which system is more preferable in environmental terms as their impacts appear evenly-matched. The general conclusion that can be drawn is that, at this point and taking into account the specific assumptions and characteristics of this research, ATES systems appear to still have room for the optimization of their environmental performance and to successfully exploit their vast potential towards the transition to sustainable development.