Aquifer Thermal Energy Storage Systems Research Articles

Life Cycle Assessment of an Aquifer Thermal Energy Storage System: Influence of design parameters and comparison with conventional systems

This paper presents a Life Cycle Assessment (LCA) of a low-power capacity Aquifer Thermal Energy Storage (ATES) system supplying a building on Bordeaux INP’s university campus, powered by the French low-carbon electricity mix. It compares environmental impacts with alternative thermal energy supply solutions, analyzing various scenarios including design choices, construction methods, equipment lifespan, and failures.Results show that the operational phase contributes 60% to the total environmental impact, mainly from electricity consumption by the heat pump and pumping wells. The ATES operational phase has a climate change impact of 37 gCO2eq kWhth−1, lower than reported in existing literature, but borehole construction, particularly chromium steel production for the casing, poses environmental burdens. The comparative assessment of the different scenarios underlines the pivotal influence of energy delivery optimization, borehole casing material choice, and heat pump performance coefficient on LCA outcomes.Comparative analyses demonstrate that ATES outperforms conventional natural gas or biomass heating and vapor compressor chillers for cooling, but slightly trails air or ground-source heat pumps. Despite high construction phase impacts, mitigation occurs relatively quickly, except for human health concerns.The study underscores the potential of low-power ATES systems with low-carbon electricity to replace fossil fuel or biomass-based heating, reducing environmental footprints. The choice between ATES and other heat pumps depends on the electricity mix, performance factors, and delivered energy.

Thermal performance of an aquifer thermal energy storage system: Insights from novel multilateral wells

Aquifer thermal energy storage (ATES) is an effective time-shifting thermal energy storage technology. Considering the enormous technical and economic input of the well pattern layout, the storage volume of a single well needs to be improved. This study proposes a novel aquifer thermal energy storage system in which several multilateral wells are side-tracked from the vertical well in the aquifer. Radial branches can enhance the connectivity of the wellbore to the aquifer. The research creates an unsteady-state 3D model to analyze the novel ATES system's fluid flow and heat transfer performance. The model is verified using experimental data. The temperature and pressure fields of the multilateral-well ATES are analyzed. Additionally, the effects of injection rate, radial branch length, number of radial branches, aquifer temperature, and aquifer thickness on system performance are studied. According to the research results, compared with the vertical wells, the performance coefficients of the multilateral hot well and cold well increase by 113.06 and 39.25, respectively, and the economic efficiency increases by 14.19% and 23.87%, respectively. The findings can provide a crucial reference for scientific research and the application of aquifer thermal energy storage systems with multilateral wells.

Coupled thermo-hydro-mechanical modeling on geothermal doublet subject to seasonal exploitation and storage

Combining the conventional high-temperature aquifer thermal energy storage system with the common geothermal reservoir development system is a potential alternative to increase energy access, but effects of natural parameters like fracture aperture and reservoir permeability and development parameters like flow rate and injection temperature on the efficiency of energy exploitation and storage have seldomly been investigated. In this study, three assessment parameters and three evaluation criteria were defined to evaluate the sustainability and efficiency of deep geothermal reservoirs with seasonal energy exploitation and storage, and a robust approach of optimizing the development parameters was proposed by combining numerical reservoir model, experimental design and surrogate model, and multiple response optimization method. Based on a case study of the geothermal doublet in Tsinghua University, China, the robustness and reasonability of the developed optimization method were demonstrated. The results show that the optimal development parameters can not only maximize the total recoverable energy and effective recovery efficiency, but also satisfy the requirements of sustainably developing deep geothermal reservoirs. The recoverable heat energy can increase about 20% by adding artificial thermal storage into geothermal reservoir development. Therefore, it is strongly recommended to add energy storage into the future geothermal reservoir development system.

The Influence of Regional Groundwater Flow and a Neighbouring River on the Behaviour of an Aquifer Thermal Energy Storage System

One promising solution for mitigating CO2 emissions in arid regions is to use Aquifer Thermal Energy Storage (ATES) systems in cooling and heating systems. However, ATES systems need to be subjected to geohydrological investigations before their installation to ensure high performance. Two geohydrological properties are considered: regional groundwater flow and the influence of neighbouring rivers. This study considers a hypothetical ATES system within the city of Hilla, Iraq. MODFLOW 6.1 software was used to simulate the influence of the two properties. The simulation tested two locations situated at 75 m and 300 m from the river. Each location was explored using three flow rates: 10 m3/d, 50 m3/d, and 100 m3/d. The results indicate that the temperature change in the warm and cold wells increases proportionally with time of operation and rate of flow. For example, the temperature of the middle layer (for 10 m3/d operation) changes from 29 °C (after one year) to 34 °C (after twenty years operation), while it changes from 34 °C (one year) to 35 °C (twenty years) under 100 m3/d operation. Another result is that the available regional groundwater flow has a negligible influence on the storage system, while the neighbouring river has a high influence on the stored energy when the distance between them is 75 m or less. The paper recommends the installation of ATES systems at least 300 m from the bank of a river.

Risk of surface movements and reservoir deformation for high-temperature aquifer thermal energy storage (HT-ATES)

High-temperature aquifer thermal energy storage (HT-ATES) systems are designed for seasonal storage of large amounts of thermal energy to meet the demand of industrial processes or district heating systems at high temperatures (> 100 °C). The resulting high injection temperatures or pressures induce thermo- and poroelastic stress changes around the injection well. This study estimates the impact of stress changes in the reservoir on ground surface deformation and evaluates the corresponding risk. Using a simplified coupled thermo-hydraulic-mechanical (THM) model of the planned DeepStor demonstrator in the depleted Leopoldshafen oil field (Upper Rhine Graben, Germany), we show that reservoir heating is associated with stress changes of up to 6 MPa, which can cause vertical displacements at reservoir depth in the order of 10–3 m in the immediate vicinity of the hot injection well. Both the stress changes and the resulting displacements in the reservoir are dominated by thermoelasticity, which is responsible for up to 90% of the latter. Uplift at the surface, on the contrary, is primarily controlled by poroelasticity with by two orders of magnitude attenuated displacements of << 10–3 m. Our calculations further show that the reservoir depth, elastic modulus, and injection/production rates are the dominant controlling parameters for the uplift, showing variations of up to two order of magnitudes between shallower reservoirs with low elastic moduli and deeper and more competent reservoirs. In addition, our findings demonstrate that the cyclic operation of HT-ATES systems reduces the potential for uplift compared to the continuous injection and production of conventional geothermal doublets, hydrocarbon production, or CO2 storage. Consequently, at realistic production and injection rates and targeting reservoirs at depths of at least several hundred meters, the risk of ground surface movement associated with HT-ATES operations in depleted oil fields in, e.g., the Upper Rhine Graben is negligible.

City-scale heating and cooling with aquifer thermal energy storage (ATES)

Sustainable and climate-friendly space heating and cooling is of great importance for the energy transition. Compared to conventional energy sources, Aquifer Thermal Energy Storage (ATES) systems can significantly reduce greenhouse gas emissions from space heating and cooling. Hence, the objective of this study is to quantify the technical potential of shallow low-temperature ATES systems in terms of reclaimable energy in the city of Freiburg im Breisgau, Germany. Based on 3D heat transport modeling, heating and cooling power densities are determined for different ATES configurations located in an unconsolidated gravel aquifer of varying hydrogeological subsurface characteristics. High groundwater flow velocities of up to 13 m d−1 cause high storage energy loss and thus limit power densities to a maximum of 3.2 W m−2. Nevertheless, comparison of these power densities with the existing thermal energy demands shows that ATES systems can achieve substantial heating and cooling supply rates. This is especially true for the cooling demand, for which a full supply by ATES is determined for 92% of all residential buildings in the study area. For ATES heating alone, potential greenhouse gas emission savings of up to about 70,000 tCO2eq a−1 are calculated, which equals about 40% of the current greenhouse gas emissions caused by space and water heating in the study areas’ residential building stock. The modeling approach proposed in this study can also be applied in other regions with similar hydrogeological conditions to obtain estimations of local ATES supply rates and support city-scale energy planning.

Heat losses in ATES systems: The impact of processes, storage geometry and temperature

The technical and economic success of an Aquifer Thermal Energy Storage (ATES) system depends strongly on its thermal recovery efficiency, i.e. the ratio of the amount of energy that is recovered to the energy that was injected. Typically, conduction most strongly determines the thermal recovery efficiency of ATES systems at low storage temperatures (<25 °C), while the impact of buoyancy-driven flow can lead to high additional heat losses at high storage temperatures (>50 °C). To date, however, it is unclear how the relative contribution of these processes and mechanical dispersion to heat losses across a broad temperature range is affected by their interaction for the wide range of storage conditions that can be encountered in practice. Since such process-based insights are important to predict ATES performance and support the design phase, numerical thermo-hydraulic ATES simulations were conducted for a wide range of realistic operational storage conditions ([15–90 °C], [50,000–1,000,000 m3/year]) and hydrogeological conditions (aquifer thickness, horizontal hydraulic conductivity, anisotropy). The simulated heat loss fractions of all scenarios were evaluated with respect to analytical solutions to assess the contribution of the individual heat loss processes. Results show that the wide range of heat losses (10–80 % in the 5th year) is the result of varying contributions of conduction, dispersion and buoyancy-driven flow, which are largely determined by the geometry of the storage volume (ratio of screen length / thermal radius, L/Rth) and the potential for buoyancy-driven flow (q0) as affected by the storage temperature and hydraulic conductivity of the aquifer. For ATES systems where conduction dominates the heat losses, a L/Rth ratio of 2 minimizes the thermal area over volume ratio (A/V) and resulting heat losses for a given storage volume. In contrast however, the impact of dispersion decreases with L/Rth and particularly for ATES systems with a high potential for buoyancy-driven flow (q0 > 0.05 m/d), increasingly smaller L/Rth ratios (<1) strongly reduce the heat losses due to tilting. Overall, the results of this study support the assessment of thermal recovery efficiencies for particular aquifer and storage conditions, thereby aiding the optimization of initial ATES designs.

Prediction of Dynamic Temperature and Thermal Front in a Multi-Aquifer Thermal Energy Storage System with Reinjection

The accurate temperature and thermal front prediction in aquifer thermal energy storage systems during reinjection are crucial for optimal management and sustainable utilization. In this paper, a novel two-way fully coupled thermo–hydro model was developed to investigate the dynamic thermal performance and fronts for multiple aquifer thermal energy storage systems. The model was validated using a typical model, and the evolution characteristics of wellbore temperature before and after the breakthrough of the hydraulic front and thermal front were deeply studied. Sensitivity analysis was conducted to delineate the influence of various reservoir and reinjection factors on the thermal extraction temperature (TET). The results revealed that thermal conductivity significantly impacts the thermal extraction rate among the various reservoir factors. In contrast, volumetric heat capacity has the weakest influence and negatively correlates with the TET. Concerning the reinjection factors, the effect of the reinjection volume rate on the TET was significantly more significant than the reinjection temperature. Furthermore, the correlation between the TET and different properties was observed to be seriously affected by the exploitation period. The coupled model presented in this study offers insight into designing the exploitation scheme in deep reservoirs and geothermal resources.

Dimensionless Thermal Efficiency Analysis for Aquifer Thermal Energy Storage

AbstractSeasonal warm and cold water storage in groundwater aquifers is a cost‐effective renewable energy technology for indoor heating and cooling. Simple dimensionless analytical solutions for the thermal recovery efficiency of Aquifer Thermal Energy Storage (ATES) systems are derived, subject to heat losses caused by thermal diffusion and mechanical dispersion. The analytical solutions pertain to transient pumping rates and storage durations, and multiple cycles of operation, and are applicable to various well configurations and thermal plume geometries. Heat losses to confining layers, its implications for optimizing plume geometries and aspect ratios, and heat spreading due to free convection are also discussed. This provides a general tool for broad and rapid assessment of aquifers and ATES systems. We show that if heat exchange with the confining layers is negligible, the thermal recovery efficiency of thermal plumes with cylindrical geometry is independent of the aquifer porosity and heat capacity C0. Therefore, if mechanical dispersion is negligible as is often the case, the only aquifer property that affects the recovery efficiency is the aquifer thermal conductivity. The field‐scale aquifer thermal conductivity λ can therefore be inferred from the recovery efficiency of a push‐pull heat recovery test. Remarkably, an increase in C0 could either increase, decrease, or not affect the recovery efficiency, depending on the thermal plume geometry. Hence, the analytical solutions reveal that the recovery efficiency is affected by complex interactions between the thermal plume geometry and aquifer properties. Approximate analytical solutions for subsurface temperature profiles over an entire ATES cycle are also derived.

Numerical Investigation and Optimization of a District-Scale Groundwater Heat Pump System

Groundwater heat pump (GWHP) systems are acknowledged as renewable and sustainable energy sources that can effectively fulfill the heating and cooling requirements of buildings on a district level. These systems harness geothermal sources available at shallow depths. To ensure the long-term sustainability of the system, the thermally used water is generally reinjected into the aquifer, creating a thermal plume starting from the injection well. Over time, this thermal plume may reach the abstraction well in the long term, potentially leading to a reduction in system efficiency. The operation types have a significant impact on this matter, and their effects have not been extensively studied in the existing literature. Therefore, this study aims to determine the optimal operating configurations for the Northern Gateway Heat Network, a GWHP system established in Colchester, UK. In this study, four distinct operation types are considered: (1) continuous heating (actual system), (2) heating and recovery, (3) heating and cooling, and (4) aquifer thermal energy storage (ATES). The results indicate that ATES operation yields the highest thermal energy output due to its ability to benefit from stored energy from the previous operation. However, implementing the ATES system may encounter challenges due to factors such as well development, hydraulic conductivity, and hydraulic gradient. On the other hand, implementing heating and cooling operations does not require additional considerations and offers not only free cooling to buildings but also a delay in thermal feedback time.

Drivers to allow widespread adoption of ATES systems: a reflection on 40 years experience in The Netherlands

Drivers to allow widespread adoption of ATES systems: a reflection on 40 years experience in The Netherlands

Creation of expanded diameter gravel wells in unconsolidated for-mations for High-Temperature Aquifer Thermal Energy Storage Sys-tems: Theoretical and numerical evaluation of borehole stability

High-Temperature Aquifer Thermal Energy Storage (HT-ATES) systems have the potential to cost-effectively store large volumes of thermal energy, bridging the supply-demand gap for variable renewable heat sources, such as solar thermal or power-2-heat conversion [3, 4]. These systems involve the injection and extraction of heated and cooled groundwater in aquifers via tube wells [11]. A HT-ATES system will be showcased at TU Delft, which involves the use of an Expanded Diameter Gravel Well (EDGW) to increase well capacity and reduce mechanical clogging compared to conventional wells [9]. This has the potential to reduce the number of wells needed and lower the costs of the HT-ATES system.&#x0D; An EDGW has previously been constructed at depth in unconsolidated formations using a jetting technique for borehole expansion [8]. This well (expanded 2.6 fold from 600 mm to 1570 mm diameter) was taken into routine operation for drinking water production. A second expanded borehole (expanded 4.1 fold from 600 to 2460 mm diameter) collapsed upon testing the enhanced removal of the filter cake before it could be completed as EDGW. The missing explanation for the collapse of the second well highlights a knowledge gap regarding the stability of an expanded diameter borehole in unconsolidated formations. To prevent collapse of future expanded boreholes and to better manage the drilling process, this study aims to investigate the effects of an enlarged diameter on well stability through a theoretical analysis.&#x0D; The stability of the EDGW borehole is evaluated in two ways, see Figure 1 for a schematic of the workflow. Firstly, the effects of an enlarged diameter on the stability of the well are evaluated analytically using a poroelastic framework [1, 2, 7]. Different conditions are taken into account regarding the stress state, mud pressure, and hydraulic conductivity of the aquifer. Secondly, field test conditions for the anticipated EDGW in the HT-ATES system are simulated numerically using the two and three-dimensional finite element software. The EDGW to be built in Delft, will be constructed within the Maassluis formation. The target aquifer is located at a depth of 120 – 182 m and is mainly composed of sandy units [5]. The simulation is divided into an initial, drilling, and open borehole (seepage) stage [6, 10]:&#x0D; &#x0D; During the initial stage, in-situ stresses and pore pressures are applied.&#x0D; The well bore volume will be removed during the drilling stage, resulting in a stress state that is no longer in equilibrium, and a mud pressure is applied to the borehole wall.&#x0D; For the open borehole prior to backfilling stage, the effect of time-dependent fluid flow due to mud losses is evaluated on well stability.&#x0D; &#x0D; During the open borehole stage, both situations with and without the presence of a filter cake (varying in thickness and hydraulic permeability) will be evaluated. Furthermore, the effect of the presence of thin clay/silt layers on the stability problem will also be taken into account, where special attention is paid to the roof of the well.&#x0D; The final results of this study are presented in the form of critical conditions regarding stress state, required mud pressure, and hydraulic conductivity for enlarged diameter boreholes in unconsolidated formations. Additionally, a design for the EDGW field test as part of the HT-ATES system in Delft is proposed, taking into account uncertainties such as the in-situ stress state and strength parameters of the formation.

Thermo-hydro-mechanical (THM) coupled simulation of the land subsidence due to aquifer thermal energy storage (ATES) system in soft soils

Aquifer thermal energy storage (ATES) system has received attention for heating or cooling buildings. However, it is well known that land subsidence becomes a major environmental concern for ATES projects. Yet, the effect of temperature on land subsidence has received practically no attention in the past. This paper presents a thermo-hydro-mechanical (THM) coupled numerical study on an ATES system in Shanghai, China. Four water wells were installed for seasonal heating and cooling of an agriculture greenhouse. The target aquifer at a depth of 74–104.5 m consisted of alternating layers of sand and silty sand and was covered with clay. Groundwater level, temperature, and land subsidence data from 2015 to 2017 were collected using field monitoring instruments. Constrained by data, we constructed a field scale three-dimensional (3D) model using TOUGH (Transport of Unsaturated Groundwater and Heat) and FLAC3D (Fast Lagrangian Analysis of Continua) equipped with a thermo-elastoplastic constitutive model. The effectiveness of the numerical model was validated by field data. The model was used to reproduce groundwater flow, heat transfer, and mechanical responses in porous media over three years and capture the thermo- and pressure-induced land subsidence. The results show that the maximum thermo-induced land subsidence accounts for about 60% of the total subsidence. The thermo-induced subsidence is slightly greater in winter than that in summer, and more pronounced near the cold well area than the hot well area. This study provides some valuable guidelines for controlling land subsidence caused by ATES systems installed in soft soils.

Optimizing the thermal energy storage performance of shallow aquifers based on gray correlation analysis and multi-objective optimization

The operation parameters and well layout parameters of aquifer thermal energy storage (ATES) system directly influence the thermal energy storage performance. How to optimize the parameters to obtain the optimal process scheme is of great significance to promote the field application of ATES. Taking the thermal storage performance of shallow aquifer as the optimization objective, this paper compares the influence degrees of key factors on thermal storage performance by means of gray correlation analysis (GCA), and prepares the optimal thermal storage scheme by using the multi-objective optimization method. The following results are obtained. First, the great difference between inlet temperature and aquifer weakens the thermal storage capacity of the system, while the thermal interference between thermal storage wells of the same type is favorable for thermal storage capacity instead. Second, aquifer thickness and well number have a greater impact on the thermal loss rate, while injection rate and well spacing have a significant influence on the thermal recovery rate. The inlet temperature has the least effect on both of them. Third, the optimal thermal storage scheme is the single well system with inlet temperature of 25 °C, aquifer thickness of 106.597 m and injection rate of 30 kg/s. In conclusion, the influence degrees of the key parameters on thermal loss rate and thermal recovery rate are different, so in order to improve the thermal storage performance, equilibrium optimization is necessary between both of them. In addition, the optimization scheme effectively expands the thermal storage volume, and reduces the heat loss while improving the thermal recovery, with thermal loss rate and thermal recovery rate of the whole system optimized by 12.69% and 3.19% respectively on the basic case, which can provide a reference for the rational design of ATES system.

Assessing the potential of low-transmissivity aquifers for aquifer thermal energy storage systems: a case study in Flanders (Belgium)

The Member States of the European Union pledged to reduce greenhouse gas emissions by 80–95% by 2050. Shallow geothermal systems might substantially contribute by providing heating and cooling in a sustainable way through seasonally storing heat and cold in the shallow ground (<200 m). When the minimum yield associated with the installation of a cost-effective aquifer thermal energy storage (ATES) system cannot be met, borehole thermal energy storage, relying mostly on the thermal conductivity of the ground, is proposed. However, for large-scale applications, this requires the installation of hundreds of boreholes, which entails a large cost and high disturbance of the underground. In such cases, ATES systems can nevertheless become interesting. This paper presents a case study performed on a Ghent University campus (Belgium), where the feasibility of ATES in an area with a low transmissivity was determined. The maximum yield of the aquifer was estimated at 5 m3/h through pumping tests. Although this low yield was attributed to the fine grain size of the aquifer, membrane filtering index tests and long-term injection tests revealed that the clogging risk was limited. A groundwater model was used to optimize the well placement. It was shown that a well arrangement in a checkerboard pattern was most effective to optimize the hydraulic efficiency while maintaining the thermal recovery efficiency of the ATES system. Hence, for large-scale projects, efficient thermal energy storage can also be achieved using a (more cost-effective) ATES system even in low-permeability sediments.

Analysis of heat transfer in an aquifer thermal energy storage system: On the role of two-dimensional thermal conduction

Aquifer thermal energy storage (ATES) system plays an important role in application of renewable energy, efficient energy utilization, and reduction of CO2 emission. To realize the successful operation of ATES systems, it is essential to understand the thermal behaviors thoroughly during heat injection. Serving as a powerful tool, analytical model is widely adopted while the existing analytical models usually simplify ATES systems by ignoring aquifer transverse thermal conduction and rock longitudinal thermal conduction. This study develops a novel analytical model for an ATES system, which accounts for thermal convection, dispersion, longitudinal and transverse thermal conduction in the aquifer, and longitudinal and transverse thermal conduction in the surrounding rocks. The Green's function method is applied to derive the semi-analytical solutions of temperature. A global sensitivity analysis is conducted to analyze the relative importance of each parameter. The results indicate that ignoring the aquifer transverse thermal conductivity will overestimate the temperature in the aquifer and ignoring the caprock longitudinal thermal conductivity may underestimate the heat loss in ATES systems. Similar conclusion can be made about the bedrock longitudinal thermal conductivity. The global sensitivity analysis indicates that temperature is sensitive to the changes in the flow velocity, thermal dispersivity and aquifer thickness.

Semi-analytical model of heat transport around a well with wellbore mixing effect under multi-step flow rate

Modeling heat transport around a well is critical for evaluations of aquifer thermal energy storage (ATES). In this study, an innovative heat transport model considering the wellbore mixing effect under multi-step flow rate in an aquifer system is proposed, where thermal conduction, thermal dispersion, and convection occur in the aquifer. Wellbore mixing effect refers to the influence of mixing processes between the injected water and original water in the well on heat transport in aquifer, which was ignored in existing models. A semi-analytical solution derived from Laplace transform method and Green’s function method has been validated by the numerical modeling and field experimental studies. Results show that the wellbore mixing effect should not be ignored in analyzing heat transport around a well in the ATES system, and the new solution satisfactorily interprets the field data. The influence of the thermal dispersion on thermal transfer near the injection/extraction well is sensitive and should not be negligible. Morris global sensitivity analysis demonstrates that the output temperature is most sensitive to the variations of the parameters of wellbore water volume and extraction rate than the others. The influence of water volume decreases with time, and the most sensitive parameter becomes extraction rate in the late stage of the extraction phase. The newly developed model can shed some light on the thermal transfer processes in the ATES system and better interpret the experimental data of the single-well push–pull tests.

Indicator of suitability for evaluating the aquifer thermal energy storage using the GIS-based MCDA technique in the Halabja-Khurmal sub-basin

Thermal energy is one of the eco-friendly sources of energy used worldwide for storing heat and cold between seasons. The aquifer thermal energy storage system effectively reduces carbon dioxide emission gas in the Halabja governorate. It is an economical way to be used in cooling and heating applications. This study evaluates the suitability of aquifer thermal energy storage in the Halabja-Khurmal sub-basin. Six critical criteria were selected: the type of aquifers, groundwater recharge, fresh/saline groundwater, groundwater quality, seepage velocity, and mean annual temperature by applying decision-maker judgment. The hydrogeological and climate criteria analysis combination has a consistency ratio of 0.008 in AHP. As a result, the Aquifer thermal energy storage suitability map in the Halabja-Khurmal sub-basin displays a surface area of 62.1% as strongly suitable, 7.7% as suitable in northern and southern parts, 29.2% as weakly suitable in southwestern, east, southeast, and northeast, and 1% as not suitable for aquifer thermal energy storage system.

Predicting the risk of saltwater contamination of freshwater aquifers during aquifer thermal energy storage

Aquifer thermal energy storage (ATES) is an underground thermal energy storage technology with a large potential to decarbonise the heating and cooling of buildings. ATES installations typically store thermal energy in aquifers that are also exploited for potable water, so a major consideration during development is ensuring that system operation will not lead to groundwater pollution. In this study, the risk of contamination due to upconing of a shallow freshwater/saltwater interface during ATES operation is investigated. Fluid flow, and heat and salt (chloride ion) transport are simulated in a homogeneous aquifer during ATES operation via a well doublet. The impact of geological, hydrological and operational parameters is investigated in a sensitivity analysis. Two new dimensionless numbers are proposed to characterise salt upconing and redistribution during ATES operation and provide a close match to simulated concentrations: CR,w characterises the contamination risk at the ATES installation, and CR,d characterises the risk at locations downstream of the ATES installation with respect to background groundwater flow. ATES systems with CR,w and CR,d < 10 introduce low risk of contamination in a homogenous aquifer, with chloride concentration at, and downstream of, the ATES system, remaining below the World Health Organisation’s advised limit. ATES installations with CR,w and CR,d > 10 cause a rapid increase in aquifer chloride concentration. The results are used to estimate an exclusion distance beyond which ATES system operation will not cause contamination in a homogenous aquifer. The dimensionless parameters proposed allow rapid assessment of the potential for saltwater contamination during ATES operation.

Thermal performance of the aquifer thermal energy storage system considering vertical heat losses through aquitards

The aquifer thermal energy storage (ATES) system is an efficient method to overcome the gap between energy supply and demand over time and space. Heat storage and preservation abilities are key issues of a successful ATES project. However, most of previous studies only focus on heat storage and recovery abilities of the ATES, while the heat preservation ability of aquitards is neglected. Besides, effects of key factors on heat losses into aquitards still remain unclear, which makes appropriately selecting reservoirs for the heat storage challenging. Thus, the heat loss efficiency is defined to represent the heat preservation ability of aquitards, through which ATES thermal performances are comprehensively evaluated. Effects of key factors on thermal performances are analyzed and optimal reservoirs for the heat storage are recommended. Results indicated that key factors had different impacts on heat losses and thermal recovery. The conduction was the major loss mode and was sensitively affected by aquitard parameters. An aquifer with a lower thermal conductivity, a higher porosity and a superior heat capacity was more suitable for the heat storage. The aquitard with lower porosity, thermal conductivity and heat capacity was better. On the premise of sealing, increasing the aquitard permeability was conducive.