High-Temperature Aquifer Thermal Energy Storage (HT-ATES) for short, is a technology that can help bridge the gap between energy supply and energy demand, which is particularly interesting to use in combination with renewable energy sources. The impact of subsurface heterogeneity on energy efficiency and thermal plume extent is not yet fully understood. In this paper, subsurface heterogeneity is linked to energy efficiency and thermal plume extent. A case study at the TU-Delft is considered, in which the Pleistocene deltaic deposits of the Maassluis formation have been characterized. Insights are gained from performing well correlations with high-resolution Gamma-Ray logs, which translates to an increase in understanding the possible architecture of the deposit and which adds a level of heterogeneity to current subsurface models that depict the Maassluis formation as a homogeneous medium. Stochastic and process-based geomodels have been constructed to represent the subsurface, using sequential indicator simulation with sequential Gaussian simulation and PyBarSimPseudo3D, respectively. Due to the difference in the underlying principles of the geomodeling techniques, the created geomodels show contrasting distributions in hydraulic properties. HT-ATES simulations have been performed with these heterogeneous geomodels using open-DARTS (Delft Advanced Research Terra Simulator). The results of the simulations show that heterogeneity has a negative impact on energy efficiency. The negative impact varies between 0.4 and 9.5 percent in the final cycle of simulation. The thermal plume distortion as a result of subsurface heterogeneity and potential for buoyancy flow to develop show to be the controlling mechanisms for the long term efficiency. The impact of heterogeneity also decreases over time as the thermal plume distortion is reduced as a result of conduction. The thermal plume extend, becomes highly unpredictable when aquifers have a low net-to-gross ratios. For stratified and high net-to-gross aquifers, the predictability is higher, as the thermal plume is more circular.

Solar panel adoption increases in residential areas, so electricity grids face growing pressure from peak feed-in, especially during hours with high radiation during summer months. In this thesis, the potential of a Smart Heat Transfer Station (SHTS) to alleviate these challenges by converting surplus solar-generated electricity into usable heat for district heating networks (DHN) is investigated. The SHTS aims to improve local energy system performance by enhancing flexibility, reducing grid feed-in congestion, and increasing renewable self-consumption.

A Python-based simulation model is developed to evaluate the technical and economic performance of the SHTS under realistic conditions. The model integrates solar panels, a heat pump, an electric boiler, and a tank thermal energy storage system (TTES).

The strategy proved robust enough to perform effectively under varying solar radiation and thermal demand conditions. Simulation results show that the SHTS can significantly reduce electricity feed-in, by using up to 86\% of generated solar electricity internally, and lower $CO_2$ emissions by replacing district heating demand with local heat production. Optimal configurations depend on a trade-off between system efficiency, emissions, and cost. High solar availability, a well-sized TTES, and a balanced combination of heat pump and electric boiler capacities are found to be critical for the performance of the SHTS.


Despite spatial constraints and regulatory uncertainties, the SHTS presents a promising, scalable solution for energy systems with high solar panel integration. It offers grid operators relief from feed-in congestion without reinforcements in the electricity grid and behavioral change from end users. Additionally, this allows heat providers to increase the share of renewable heat in their supply, while ensuring the service remains both affordable and reliable for end users.


This study presents a practical, simulation-based framework with rule-based control for evaluating and optimizing innovative systems, such as the SHTS, providing insights into how SHTSs can enhance the utilization of locally generated energy. By identifying the key technical and economic conditions for successful implementation, it lays the groundwork for real-world deployment. Future research should focus on integrating predictive control algorithms, which can improve system responsiveness by anticipating solar availability and demand patterns. Additionally, future work should examine regulatory and spatial constraints and analyze the aggregated behavior of multiple SHTS units.

Climate change is an urgent global challenge. Buildings significantly contribute to energy consumption and CO2 emissions. To accelerate decarbonization, ATES systems, integrated with 5GDHC networks, offer a sustainable approach. These systems enable seasonal thermal energy storage and bidirectional energy exchange. However, designing these complex combined systems in urban areas poses significant challenges, including integrating dispersed ATES wells, managing phased construction, and navigating dense underground infrastructure. This study investigated a biologically inspired approach, utilizing the network optimization capabilities of slime mould (Physarum polycephalum). A simulation model was developed and verified, incorporating key slime mould behaviours like efficient pathfinding, to generate optimal thermal network configurations. Using the TU Delft Campus as a case study, this research explored the model's capacity to streamline the design of sustainable and efficient heat distribution systems. Key findings indicate that the visual differences in layout between the best results and all results are minimal. In conclusion, this research successfully developed and applied a slime mould growth model for optimal thermal network design, specifically for district heating systems combined with ATES in an urban environment. The model proved effective in generating a network designs that minimize CapEx.

As Amsterdam moves toward its 2040 carbon-neutral and 2050 renewable-heating targets, infrastructure must increasingly support the city’s energy transition. The Oostbrug, a planned cycling and pedestrian bridge across the IJ River, provides an opportunity to demonstrate an energy-autonomous bridge concept. Its combined electrical and thermal loads for lighting, operation, and winter de-icing are traditionally supplied by grid electricity and salt spreading. Integrating renewable energy sources with hydronic bridge-deck heating can reduce grid dependence, eliminate salt use, and enhance the bridge’s sustainability.
This thesis investigates the feasibility of a self-sufficient bridge energy system combining solar, wind, and thermal sources with on-site battery storage. Five configurations were modeled: three direct heating systems using energy piles or aquathermal heat pumps, and two indirect systems with Aquifer Thermal Energy Storage (ATES). A MATLAB-based hourly simulation using KNMI 2024 weather data and modeled IJ-water temperatures evaluated energy and peak coverage, embodied CO2, and battery requirements.
Among the direct systems, only the aquathermal heat-pump configuration (System 3) meets both annual and peak de-icing demands, though it requires substantial battery capacity and is sensitive to cold conditions. ATES-based systems (Systems 4 and 5) achieve full annual coverage with strong winter resilience. System 4, combining aquathermal recharge with ATES, provides the highest energy surplus of 2373 MWh yr−1 but with greater complexity and embodied emissions, while System 5, using bridgedeck regeneration, offers a simpler, more material-efficient solution with 1048 MWh yr−1 surplus and higher robustness. Both storage-led systems eliminate salt-based de-icing, avoiding 7.9 t CO2 yr−1 , salinization in the IJ river, and deterioration of the bridge construction. System 5 is identified as the preferred option for full-deck, energy-autonomous operation. The Oostbrug demonstrates how bridges can serve as energy-positive infrastructure, integrating structural, thermal, and electrical systems. Future work should extend model validation across multiple climate years and explore integration with Amsterdam’s district heating network.

The transition to renewable energy in the heating sector faces significant challenges, particularly the mismatch between the availability of renewable thermal energy sources and fluctuating demand. High Temperature Aquifer Thermal Energy Storage (HT-ATES) systems offer a promising solution to mitigate this mismatch and further decarbonize heating systems by bridging the gap between supply and demand.

This thesis explores the integration of HT-ATES into the heating system at TU Delft, which is transitioning from gas-fired boilers and a combined heat and power plant to a geothermal well-based thermal energy system. During periods of low demand in summer, excess geothermal energy will be stored in the HT-ATES system, to be utilized during high-demand periods in winter when the geothermal well's capacity is exceeded. The objective is to meet 85% of the annual heating demand through sustainable thermal energy sources.

In this study, two design options for integrating the HT-ATES into the heating system are analyzed. Besides the geothermal well and the HT-ATES, the heating system also comprises a heat pump to reach the required supply temperatures. One option is to locate the HT-ATES behind the evaporator of the heat pump and therefore use the previously cooled down temperature to extract thermal energy from the HT-ATES. In the second option, the HT-ATES is located directly behind the heat sink in the system, using the return temperature of the consumers to discharge the HT-ATES.

An energy system model is set up using TESPy and coupled to a numerical model to simulate temperature changes in the HT-ATES. With the results of the model, the influence of the integration concept on the system performance is explained. Furthermore, the effect of varying input parameters such as supply and return temperatures as well as overall demands in the system are examined.

The results indicate that, when comparing the two design options with HT-ATES, locating the HT-ATES behind the evaporator yields the better results across all evaluated performance indicators – mainly a reduction of GHG emissions, an improved system SCOP and a better thermal recovery efficiency of the HT-ATES. However, compared to a base design without HT-ATES, the integration of a HT-ATES leads to additional financial costs and a substantial intervention into the subsurface. Due to its lowest electricity consumption, the base design also shows the best system SCOP.

District heating networks (DHN) in the Netherlands have the potential to supply sustainable heat but are currently designed to deliver around 80 \% of the heat from a sustainable source. The peak demand is delivered with a gas boiler because of flexibility and costs. With the share of DHNs increasing in the Netherlands and the goal to be CO$_2$ neutral by 2050, a replacement for gas boilers in DHNs has to be found. This research evaluates the potential of seasonable thermal energy storage to supply the peak load in small-size DHNs in the Netherlands.

The research consists of 3 steps. First, the key performance indicators (KPIs) of the implementation of STES in DHNs are determined and the technologies with the most potential per seasonal thermal energy storage (STES) category (sensible heat storage (SHS), latent heat storage (LHS) and thermo-chemical energy storage (TCES)) are determined. Then a Matlab model is developed to determine the volume, storage losses and total efficiency of the three selected technologies. Multiple scenarios are defined to evaluate the technical and financial potential of STES in different situations and configurations. Lastly, the STES are assessed on their potential to be integrated into a DHN to supply peak demand by analyzing investment costs, operating costs, volume, storage losses, and total efficiency. Throughout the research, a gas boiler is used as the reference scenario.

The models developed in the research are validated and can be used in specific case studies to determine the necessary volume of the STES, temperature profile throughout the year in the STES, mass flows and temperature of the supply HTF to the DHN, and the total losses of the STES, using the heat demand of the DHN, the HTF, the PCM, the reactant, the shape of the tank, the insulation thickness an material and the heat supply of the source.
With the outputs of the developed models, the costs can be calculated. The output of the model and the costs can be used to select the optimal STES to be implemented in the DHN of that specific case study.

This research shows that SHS is most feasible to be integrated into a small-size district heating network to deliver winter peak load in the existing built environment regarding volume, CO2 emissions, and costs.\\
A buried tank with water as the storage medium and heat transfer fluid (HTF) is selected as the technology with the most potential within SHS. For LHS, Paraffin is selected as phase change material (PCM) and water as HTF. For TCES, potassium carbonate is selected as the reactant.

This research is aimed at creating a generic design method for infiltration drywells on sandy soils by acquiring knowledge on the functioning of these wells. Infiltration drywells are vertical infiltration pipes that are installed above the groundwater table and through which stormwater is drained to the subsurface. Infiltration drywells can have a prominent place in urban water management since they mimic processes that occur under natural conditions. In urban areas the hydrological cycle is altered due to impermeable surfaces. Utilization of infiltration reduces the effects of the alteration on the hydrological cycle. Hereby, reducing the risk on urban flooding and surface water contamination. Furthermore, urban heat stress is reduced by enabling more drought resilient vegetation through groundwater replenishment. Especially considering that climate change will result in more extreme weather conditions, infiltration facilities can aid in creating more resilient urban areas. Until now, there are no design rules for these wells which hinders the implementation in urban areas that are fit for infiltration facilities. In this research a design method for sandy soils in the Netherlands is created and set forth.

The theoretical and practical performance of infiltration drywells is analysed by conducting experiments with Hydrus 3-dimensional geohydrological model simulations, as well as in the field and laboratory. In the field falling head tests were performed with existing infiltration drywells to determine the functioning while soil samples were analysed in the laboratory to determine the hydraulic conductivity. The model simulations also exist of falling head tests and are compared to the experiments in practice. It was found that the most important parameters on functioning of infiltration drywells are the soil hydraulic conductivity and well dimensions. When comparing the simulated falling head tests to field tests and laboratory tests at the same location, discrepancies were discovered. This can be clarified by simplifications that were made like homogeneity and isotropy of the soil in the model. Furthermore, the absence of wall resistance of the well in the model and the method that was used for the calculation of hydraulic conductivity using in practice falling head test data could be the cause.

To this end the generic design method is based on the Hydrus 3D model. This design method consists of empirical contour plots that give the necessary number of wells based on multiple input parameters, including a design storm of 21 mm in 10 min, which has a statistical return period of 25 years in the Netherlands. Due to discrepancies in the research, the design method is used to test the viability of a plan to implement infiltration drywells. Afterwards, a detailed design procedure is still necessary. Overall, the research resulted in a generic design method and shows the advantages of using infiltration drywells, which could be an essential part of urban water management in the Netherlands in the future.

Currently, a large part of the energy used to provide heat to heating network comes from gas boilers, a combustion process where 2.2kg of CO2 is emitted for every m^3 of gas. Deep geothermal energy is implemented more in The Netherlands over the last couple of years as a substitute to the conventional boilers and this is a technique that is proven to be working. However, one problem with geothermal energy is the fact that only base load extraction is possible, whereas the heating demand varies throughout the year. During winter there is an energy shortage while during summer there is a surplus. Hence, seasonal heat storage is seen as a promising technique to increase the portion of green energy in heating networks.

High-Temperature Aquifer Thermal Energy Storage (HT-ATES) can bridge the gap between the supply and demand, storing excess produced heat during summer and supplying during the winter months. This research focuses on both the technical aspects as well as the business case of the implementation of such a system in a heating network. Technical simulations are performed where the fluid transport and heat loss processes are modelled. The output of these simulations is used to compare the business cases of a heating network with and without HT-ATES implementation, based on the Levelized Cost Of Heat (LCOH) and total annual CO2 emissions in an economics tool developed in Python. All simulations are based on the situation at the TU Delft Campus, where plans are made for a HT-ATES in the Maassluis formation.

The base case shows a thermal recovery efficiency of 0.75 in cycle four. The LCOH for a project with a lifetime of 30 years is 52 €/MWh (14 €/GJ) when HT-ATES is implemented, compared to 61 €/MWh (17 €/GJ) in the case where only geothermal energy and gas boilers are used to supply the heat. Total CO2 emission reductions are 31%. Based on these values, one can conclude that the situation where HT-ATES is included is the economic scenario.

On top of the case study, a parameter sensitivity study is performed. The results show that storage volume, storage reservoir permeability and temperature differences between the wells are the key geological and operational parameters when assessing the project feasibility. Economic parameters such as the discount rate and gas prices also have a considerable impact on the economic results. The results of the sensitivity analysis shows that the project in Delft is feasible as long as the future average gas price remains above 21 €/MWh and the discount rate does not exceed 18.3%, while keeping the other variables constant.

Research towards aquathermal energy solutions is still in a pioneering phase. Especially in urban environments, these solutions could potentially form the missing connection between heating supply and demand. This study focuses on the application of these solutions in the city canal waters in the largest city of the Netherlands, Amsterdam . Currently, these so-called Surface Water Heat (SWH) systems have not been implemented at all in the inner city canals of Amsterdam. One of the reasons for this can be found in a lack of knowledge about natural water temperature variations in these types of waters and the unknown thermal effects related to SWH systems. This study is an answer to this knowledge gap and an attempt is made to provide insight in the thermal effects of SWH on a city canal. The Amsterdam city canals form a unique water system in open connection with larger waterways and they are part of a hydrodynamically complex interaction between sea and the river Rhine. Until date, such a study towards SWH system effects, not being restricted to the boundaries of the respective water body, is scarce or even non-existent.\\ The case study location is situated at the Jacob van Lennepkanaal in Amsterdam, where a collective of civilians has recently started the exploratory phase for installation of the first SWH city canal system for heating of their own district. To respond to this societal development, this specific case study location was chosen. To be able to model the SWH system for this neighborhood, the first part of this thesis focuses on system layout and related system characteristics. It was found that open-loop SWH systems are often applied at district level. Secondly, a reference surface water temperature model without SWH systems was built and validated upon meteorological forcing with local water temperature measurements. The third part of the followed method was to apply the modelled SWH system to this validated three-dimensional thermodynamic model. For this purpose, the Delft3D model was chosen, which computes the RANS equations under the hydrostatic assumption. Several scenarios were calculated with varying temperature difference through the SWH heat exchanger and varying distance between system intake and outfall. The modelling results for the Jacob van Lennepkanaal case show that SWH systems used for heating purposes, thereby cooling the surface water, produce a negatively buoyant flow, causing the discharged cold water plume to sink to the bottom. Existing thermal stratification in the city canals is enhanced and hydrodynamic mixing processes are not strong enough to disturb this stratification built-up. Further away along the plume, in the far-field, a combination of buoyant spreading and the process of passive diffusion mix the water column and the temperature decrease, induced by the SWH system, becomes uniformly spread over the entire water column. Currently, steady state one-dimensional models are often used for assessment of SWH thermal effects. It was demonstrated that these models are useful and accurate, provided that the right heat exchange coefficient is used and near-field mixing at the outfall is represented correctly. These models can be used to study for example the time-averaged extent of the cold water plume, but fail to provide insight in time-varying and spatial characteristics of the canal. Local changes in bed level height, attraction of ambient water by the intake and intersections with lateral canals also influence the thermal profile. For a study towards these effects in greater detail, three-dimensional modelling or 2DV-modelling are preferred. Also, in case of a study towards application of multiple systems, these are the models of choice.

Projections show that urban areas are growing at an increasing rate and produce 60% of the global greenhouse gas emissions (United Nations, n.d.). In Europe, the thermal energy sector consumes about half of the energy resources, of which 85% is produced by fossil fuel-based energy systems (Drijver, Bakema, & Oerlemans, 2019). As a result of this, district heating companies have set climate targets to
lower the harmful emissions produced by the thermal energy sector. This can only be done by replacing fossil fuel-based energy systems by sustainable energy systems. One of the promising sustainable energy systems is the high
temperature aquifer thermal energy storage (HT-ATES) system. HT-ATES
is a buffer system used to store waste heat from industrial processes in a suitable aquifer and transfers this heat to buildings to heat them up in the winter and cool them down in the summer. However, this system is very complex in use and carries many risks. Due to the HT-ATES being a buffer system, complex in use and carrying many risks there are not many running projects incorporating this system. This makes the revenue model and possible exploitation for commercial use very unclear. Therefor, the goal of this thesis is to develop a business case for the commercial use of HT-ATES systems and to assess the business case sensitivity to the thermal energy demand. The research goal will be achieved
by performing a literature study. Assessing the business case viability against other geothermal energy systems will not be in the scope of this thesis. This thesis is merely meant to gain insight on the business case of HT-ATES systems.

The findings of the research show that a project is solely profitable when the benefit outweighs the cost. The total business expenditure of a 30-year lifecycle HT-ATES project with 3,000 households will be fixed upfront expense of EUR 1,236,991 and an additional yearly expense of EUR 695,795. The benefit of the project is strongly dependent on the thermal energy demand. The revenue model of this project consists of a heating price model and government provided subsidy. This business model assumes a heat price of EUR 3.89 per kWh and a subsidy of EUR 2.73 per kWh thermal energy produced. Assuming the annual thermal energy demand is 12.66 kWh per household, the 30-year HTATES project with a district heating network of 3,000 households will have a payback time of 8.4 years. This means that the project will be profitable after 8.4 years. A sensitivity analysis on the thermal energy demand proved that a HT-ATES will be more profitable if the thermal energy demand is higher. This sensitivity analysis also shows that the project will need to have a minimum of 1,300 households in the network in order to be financially feasible, as the payback time of less households will not be within the project lifecycle. A district heating network with a 30-year lifecycle HT-ATES system will have a payback time of 22 year. When this same network where to incorporate 4,000 households the payback
time will be reduced by a factor of 4.

In the winter of 2014 upon 2015 the Hondsbossche dike, between Petten and Camperduin in the Netherlands, has been transformed into a dune area through sand replenishment at the seaside of the dike. The area inland has been appointed as a Natura-2000 area because of the highly appreciated ecological value. A reduction of saltwater seepage would cause potential harm to the flora and fauna which is undesired. Two sectional models of the density dependent groundwater flow have been developed to map out the growth of a freshwater bubble forming beneath the Hondsbossche dunes and the corresponding decline of saltwater seepage to the polders inland. The two sections chosen are a section perpendicular to the coastline through the middle of a small lake De Putten and a section perpendicular to the coastline just south of a small lake Abtskolk. Both sectional models have been tested through a calibration process for the measurement data considering the freshwater head and geophysical properties of the groundwater. From the models the development of the groundwater regime for the coming 95 years has been calculated (100 years in total and 5 years until the present situation). Besides this the development of the groundwater regime in several sectional variations to the developed sectional models have been investigated. This has been done to investigate the impact of certain assumptions in the layout of the sectional models. These variations to the sectional models also are an indication of the range of possible changes to the groundwater regime for the whole area because elsewhere in the area these resulting sections could be present. Looking at the results of both sectional models and all model variations the conclusion can be drawn that the biggest reduction of saltwater seepage takes place in the years 2026 till 2056. Therefore it is advised to take action against the reduction of saltwater seepage before 2031. A sensible way of doing this is to firstly identify the most critical sections perpendicular to the sea in the area of interest. A good first step would be to identify the most permeable spots in the clay layer beneath the dunes. The results show that in these spots a faster spread of the freshwater bubble is expected. Besides this it has become apparent from the model results that the small lake De Putten attracts a bigger fraction of the seepage currents in comparison to the surrounding area. It would be a good idea to investigate where other hotspots for seepage are present in the area. In these areas the reduction of saltwater seepage would most likely be more intense. The identified critical sections would be the best places to start implementing measures against the decline of saltwater seepage. When actions are taken timely and precisely it is expected that the decline of saltwater seepage will remain small and the ecological value of the polders will remain.

Aquifer thermal energy storage (ATES) is an energy efficient technology to temporarily store groundwater of different temperatures in an aquifer. The basic idea behind ATES is to store thermal energy in warm and cold wells so that the energy can be used for heating and cooling of buildings in the next season. Design and planning of ATES systems requires numerical simulation tools such as SEA- WAT, COMSOL, and FEFLOW. COMSOL and FEFLOW are expensive commercial products. SEAWAT is a free computer program based on MODFLOW and MT3DMS. The flow field is modelled with the finite difference method while there are several methods to simulate the heat transport including the finite difference (FD) method and the total variation diminishing (TVD) method. OpenGeoSys (OGS) is an open-source alternative based on the finite element method which is able to simulate groundwater flow and heat transport processes and can potentially be used for design and planning of ATES systems. There are very few applications of OGS to simulate ATES systems. The main goal of this research is to assess the usability of OpenGeoSys in the simulation of ATES sys- tems. The numerical solutions of OGS and SEAWAT (both the TVD scheme and FD scheme) are compared to the analytical solutions for a single well that injects water with a constant flow rate of water and constant temperature. For a doublet with a cold well and a warm well, the OGS solution is compared to the SEAWAT solution for both a sin- gle cycle system and a multiple cycles system with constant flow rates and temperatures. Finally, a field case of a doublet with varying flow rates and injection temperatures is studied to compare the performance of OGS to SEAWAT. The main findings of this study are as follows. Both OGS and SEAWAT can reproduce the heat transport process of the analytical solutions for a single well injecting warm or cold water. There are some deviations between the temperature distributions computed by the numerical models and the analytical solutions which are primarily caused by nu- merical dispersion. The TVD scheme results in the smallest numerical dispersion while OGS shows slightly more numerical dispersion when applying the same number of cell- s/nodes. Numerical dispersion can be reduced by application of finer spatial resolution for the SEAWAT since the time step is adjusted automatically. For OGS, the time step must be reduced manually when the grid is refined. Both OGS and SEAWAT show energy balance errors smaller than 1%. Numerical dis- persion has an effect similar to physical dispersion so that the thermal radius increases when the numerical dispersion is larger. The interaction between the warm well and cold well of a doublet increases when the thermal radius increases, which may result in an increase of the energy balance error. According to the analytical solution for the model where the heat transport between the aquifer and aquitards is included, OGS shows the smallest overestimation of thermal energy that remains in the aquifer part compared to the two solution schemes of SEA- WAT. The vertical temperature distribution in aquitards simulated with OGS is closer to that of the analytical solution compared to SEAWAT. Both numerical dispersion and the overestimation of thermal energy in the aquifer have an influence on thermal recovery efficiency of an ATES system. Larger numerical dis- persion indicates a longer heat transport distance, resulting in more time needed for thermal energy to transport back to the wells during the extraction period. Similarly, the overestimation of the thermal energy in the aquifer provides more thermal energy dur- ing the extraction period. There are some overshoots/undershoots when simulating an ATES system with varying flow rates and injection temperatures by the TVD scheme. This can be eliminated by refining the spatial resolution. It is more complicated to simulate an ATES system with OGS than SEAWAT. The com- putational time is much longer for OGS compared with SEAWAT by a factor of around 10 for the same number of cells/nodes. Despite these drawbacks, OGS is suitable for the simulation of ATES systems as the simulated temperature distribution in both the aquifer and aquitards compares well to the analytical solution, and there are no prob- lems of overshoots/undershoots in the simulation of varying flow rates and injection temperatures.

Aquifer Thermal Energy Storage (ATES) is a geothermal technique that is an important component in the transition towards renewable energy in the heating and cooling industry, which accounts for half of the world's energy consumption. However, the technology has not yet been implemented in many countries. The main reason is that extensive preparation and site-specific analysis are required for the implementation of ATES systems and many stakeholders need to be involved. These stakeholders are typically unfamiliar with the technology and unaware of the potential applicability. To stimulate stakeholders and the decision-making process within the ATES sector, several studies emphasise the necessity of examining the potential of ATES technology on a local level. Such potential studies support ATES decision-makers as they evaluate the technology, potential scale and its commercial viability.

The objective of this research is therefore to develop a methodology to determine the technical and commercial potential of ATES while incorporating local characteristics. Until now, ATES feasibility studies have mainly been focused on large-scale ATES suitability. For generating more representative results, however, this new methodology also incorporates local geohydrological conditions and the interests of and restrictions imposed by its local ATES stakeholders. The methodology can be applied globally to every region that has available aquifers and moderate climate conditions. The developed methodology in this study is applied to the region of New York State (NYS). High expected energy savings and promising geothermal trends are among the main reasons for this geographic selection. Moreover, no commercial ATES project is yet in operation in the US, a country of which the potential energy savings are expected to be highest in the world. A successful introduction of the technology in NYS could therefore function as a valuable use-case for many other states in the US and also for other countries.

Firstly, the stakeholders in NYS are identified and analysed in this study. They are assessed based on their level of influence, attitude and their ability to solve current barriers that are preventing ATES from being adopted. This analysis indicated that geothermal architects are the most influential stakeholders and are therefore essential to engage for the successful implementation of ATES in NYS.

Secondly, the technical and commercial ATES potential is examined by analysing local geohydrological conditions, building characteristics and the identified requirements from geothermal architects. It is concluded that over 99\% of all buildings in Nassau County (around 400,000) could technically receive the required amount of heat and cold if an ATES system was installed for those buildings. Moreover, it is found that for buildings with ATES systems, heating is twice as efficient as conventional methods in Nassau County and cooling is even 10-30 times more efficient, depending on ATES design parameters. Furthermore, it is concluded that ATES is already a commercially attractive solution for 385 separate buildings in Nassau County, accounting for an estimated 10\% of the total heating and cooling demand of buildings in the county. This number is expected to increase significantly when multiple buildings are connected to a single ATES system.

This research shows that ATES is a technically and commercially viable geothermal solution for buildings in NYS. Therefore, it is critical that ATES is included in the existing evaluation tools developed and currently used by the city and state authorities of New York. The methodology developed in this study is characterised by the inclusion of local characteristics such as the interests and requirements of a region's key stakeholders and local geohydrological conditions, which are found to be essential to generate realistic and accurate insights into the technical and commercial potential of ATES. The model that has been developed is scalable and can be applied to other regions and the accuracy of the model can be increased further by also incorporating groundwater models in the analysis. All in all, the methodology developed in this study offers valuable support for local decision-makers and is an effective resource to increase the adoption of ATES technology worldwide.

Underground thermal energy storage (UTES) is an efficient technique to fulfill the heating and cooling demand of buildings. UTES uses stable subsurface temperatures store and extract energy. This study covers two types of UTES systems: aquifer thermal energy systems (ATES) and borehole heat exchangers (BHE). UTES systems in the Netherlands have seen a significant growth over the past years (Bloemendal, 2018) and are expected to contribute up to 20% of the heating and cooling demand of buildings by 2050 (Naber et al., 2016). As more UTES systems are installed, the risk of unwanted interaction between different system increases. However, ATES-BHE interaction is largely unknown.
The objective of this study is to gather more insight in the interaction of ATES system on the efficiency of BHE systems. A numerical model is used to simulate an ATES well near a BHE system using SEAWAT (Langevin et al., 2008). The model is used to run different simulations, from which the efficiency of a BHE system is computed under different circumstances over a five year period. Four conclusions are drawn from the results. First, groundwater and temperature interference from ATES systems affect the efficiency of a BHE system differently. Simulations show that the effect of groundwater flow induced by an ATES system always has a positive effect on the efficiency of a BHE system. The effect of temperature interference is dependent on the temperature of the ATES well. Groundwater was also found to interfere at larger distances between both systems compared to temperature. Second, the degree of interference is related to the distance between the ATES and BHE system. For distances smaller than 0.5 times the thermal radius of the ATES system, interference from temperature was found to be dominant in the simulations. For distances larger than 0.5 times the thermal radius of the ATES system, groundwater interference was found to be the dominant factor. The third conclusion is that the depth placement of the ATES well screen has little to no effect on the amount of interference on the BHE system. Fourth, it is important to realize that no energy is spontaneously generated or lost as BHE efficiencies increase or decrease respectively. Energy is simply exchanged between the ATES and BHE system through the subsurface. Whether that is disadvantageous depends on the energy demands of both systems. Most energy demands are imbalanced, meaning either cooling or heating demand is larger than the other. It is recommended to consider UTES system installations from a holistic point of view.

Hydraulic properties of aquifer systems are usually estimated by conducting field experiments, which are called aquifer tests. Different approaches have been applied to simulate the drawdown data, such as graphical type curves, analytical solutions, and grid-based models. Since the type of groundwater system varies greatly from location to location, only a few general solutions have been developed. Computation of hydraulic properties are limited by the size and time step of grid-based model. Determining the boundary conditions is also difficult in actual groundwater system. Thus, in order to better simulate various aquifer systems, semi-analytic approaches have been promoted and used in aquifer test analysis. In this report, three different softwares aiming at aquifer tests simulation are presented. Both MLU and TTim are based on semi-analytical solutions and need users to build their own aquifer models, while AQTESOLV provides a base model for adding a variety of data and a stack of choices containing both analytical and semi-analytic solutions. Some benchmark analyses have been performed to assess the performance of TTim with limited types of aquifer systems. This research focuses on the application of TTim to different aquifer systems and the investigation of TTim's performance compared to the other two softwares. In this study, fifteen aquifer tests have been simulated with TTim. Test 0 uses hypothetical data to verify TTim's capabilities of retrieving specified parameters and reporting accurate confidence interval. Test 1 through Test 10 are pumping tests which are taken from reported field experiments and are grouped as confined systems, leaky systems, and unconfined systems. Test 11 through Test 14 present four slug tests with different top boundaries and well construction. The values and confidence intervals of the calibrated parameters are compared to the results of AQTESOLV and MLU. Improvement of conceptual models is carried out by model structure adjustments and parameters set adjustments. Different models' performance are assessed by root-mean-squared-error and AKAIKE Information Criterion (AIC). Most of the pumping tests and slug tests can be conceptualized using either ModelMaq and Model3D within TTim. Model3D is recommended when conceptualizing unconfined systems. The top boundary needs to be specified as `confined', and an additional thin aquifer needs to be added to simulate the specific yield, which is calibrated separately. The performance of TTim is similar, in general, to AQTESOLV and MLU. Well construction parameters cannot be calibrated with AQTESOLV, and only one aquifer system is available. TTim is more flexible and accurate than AQTESOLV when the groundwater system has information of multi aquifers and well construction. Modifications of parameters to be calibrated and model structure have been carried out to improve TTim's performance. It is concluded that aquifers with multi subdivided layers perform better when the well is partially penetrating or the observation wells have different depths. Calibration of well construction parameters may also contributes to a better simulation, but they are usually sensitive to the initial values. It is important to note that adding parameters may give better results, but whether this is significant needs to be tested by the AIC criterion.

High Temperature – Aquifer Thermal Energy Storage (HT-ATES) is a way to efficiently store heat with use of the subsurface. Region Holland-Rijnland has the vision to be free of the use of natural gas in 2050. A proposed high temperature heating network from the port of Rotterdam to the households of Leiden, combined with the use of an HT-ATES system as a buffer, could be the next step to achieve the laid-out vision. This research is a first step in the possibility of placing an HT-ATES system near Leiden. An interpretation of the subsurface near Leiden is done based on information from DINOloket to find potential formations and aquifers. Then, combined with different scenarios for the heat demand from the proposed heat network, a preliminary design of an HT-ATES system is made to test the viability of the potential aquifers. The most suitable aquifer is found in the Maassluis formation at a depth of 230 meters. Per scenario, this aquifer needs the least number of wells for the desired pumping rate. Depending on the scenario, the aquifer has a thermal recovery efficiency ratio between 0,16 – 0,26 and an area – to – volume ratio between 0,051 – 0,056. Other suitable aquifers can be found in the Maassluis formation at a depth of 170 meters and in the Oosterhout formation at a depth of 320 meters. The subsurface near Leiden is suitable for an HT-ATES system, but more research needs to be done on the conflict between heat supply from the port of Rotterdam and heat demand from the proposed network in order for an HT-ATES system to fully supply the seasonal heat demands.

In 2020 TU Delft will build a geothermal well producing enough energy to power all its faculties and a number of buildings surrounding the campus. This is done to meet the climate goals the TU set itself: an energy neutral campus by 2040. Geothermal plants are designed to produce for 30 years. After this period, by 2050, the TU has to be energy-neutral without the geothermal heat flowing from deep underground. To prevent falling back to fossil fuels there is need for a new energy source. In this feasibility study one of the options is investigated, low temperature aquifer thermal energy storage (LT-ATES). This technology stores heat-energy produced during summertime in aquifers, during wintertime this water is used to heat the faculties. It was found that a LT-ATES system is viable. A 19 MW ATES system containing 23 cold and 23 warm wells to a depth of 180 meters is needed. Cooling during summertime is not sufficient to charge the system to meet the winter heating demand; therefore an additional solar thermal collector field of 35.000 m2 is needed. Designing a strategy for 2050 means that there is a considerable amount of assumptions to be made. To optimize the LT-ATES-system, a more in-depth study should be performed.

High Temperature Aquifer Thermal Energy Storage (HT-ATES) is a technique for storing large amounts of residual heat in the subsurface. In this report, the thermal deformation resulting from the temperature change in the subsurface is investigated and the resulting risks for buildings are assessed. To do this a case study is done on the TU Delft campus subsurface. It has been determined that the thermal deformation due to HT-ATES systems is small with a maximal deformation of 14 cm. It has also been determined that the stability risks for buildings that are constructed in the vicinity of a HT-ATES system are very low.

The thermal recovery efficiency of High Temperature Aquifer Thermal Energy Storage (HT-ATES) systems can be limited due to the effect of buoyancy flow of the injected hot water. This thesis has researched the application of a Multiple Partially Penetrating Wells (MPPWs) as a well design method to counteract the effect of buoyancy flow and improve the performance of HT-ATES systems (>60°C). A MPPW is a well with more than one screen that allows injection and extraction of water at different depths in the aquifer.This method to counteract the effect of buoyancy flow was tested through numerical modelling with SEAWATv4. The modelled HT-ATES systems were running for four recovery cycles each including injection-storage-extraction-rest phases. The thermal recovery efficiency was determined over these cycles for 7 different scenarios and four different cases: a) A regular HT-ATES system with a fully penetrating screen, b) a regular HT-ATES system where buoyancy flow is neglected, c) an HT-ATES system with a MPPW with two screens, d) an HT-ATES system with four screens. The latter case was tested for three different control approaches based on data from four different locations in the aquifer.For the reference scenario where 90°C water was injected, a regular HT-ATES system had a thermal recovery efficiency of 0.61. With the application of MPPWs for both two or four screens this was 0.81 in the fourth recovery cycle, which approaches the case without buoyancy which had a thermal recovery efficiency of 0.88. The application of two or four screens did not show significant difference in thermal recovery efficiency after the first recovery cycle.A sensitivity analysis showed that the absolute increase in thermal recovery efficiency of an HT-ATES system with a MPPW compared to a regular HT-ATES is higher for larger buoyancy flow (i.e, high injection temperature and high (vertical) hydraulic conductivity), smaller injection volume and larger aquifer thickness. An applicability analysis showed that application of MPPWs is beneficial if the buoyancy flow (which is defined as the vertical hydraulic conductivity times the density ratio of the ambient groundwater and injected water) is greater than 0.1 meters per day.

Aquifer thermal energy storage (ATES) is a sustainable technology that provides thermal energy to buildings in temperate climates. The principle of ATES is to temporary store thermal energy in aquifers in a warm and cold well in order to use this thermal energy for heating and cooling in the next season. Because the available subsurface space is limited, congestion problems can occur in areas with high ATES density. In these areas a conflict of interests exists between private parties who want to achieve maximum efficiency by avoiding negative influence of other systems (leading to large buffers between wells), and the public interest to maximize the amount of thermal energy stored in the aquifer. One solution to this problem is to reduce the distance between wells of the same temperature, creating one large thermal zone around the wells. The main goal of this research is to quantify the change in performance of ATES systems when their thermal zones are connected. The results of this research are as follows. Connecting the thermal zones of wells of the same temperature increases the thermal recovery efficiency of individual systems. This increase is between 8-15% for an average ATES system with a storage volume of 250.000 m³. It is even higher for smaller systems, 15-40% for a system with a storage volume of 50.000 m³. This is crease in efficiency is due to lower losses to the surroundings due to a lower area of the thermal zone compared to the volume of the thermal zone. The reduced distance between wells leads to an increase in pumping energy. Therefore an optimal distance between wells of the same temperature of 0.5 times the thermal radius is found. The distance between wells of opposite temperature should be larger than 3 times the thermal radius.