High-temperature Aquifer Thermal Energy Storage Research Articles

Recovery efficiency in high-temperature aquifer thermal energy storage systems

Aquifer Thermal Energy Storage (ATES) uses excess thermal energy to heat water which is stored in an aquifer until it is needed, at which time the hot water is recovered and the heat used for some purpose e.g. electricity generation. The recovery efficiency (i.e. the ratio of heat energy recovered to heat energy injected, R) is one of the most important factors dictating the viability of ATES systems.The variation of R with various aquifer properties and operating parameters is explored for high temperature (HT) ATES systems with injection temperatures ≥90∘C, extending the results of previous studies to higher temperatures and a broader range of aquifer properties and operating conditions. R values are calculated using numerical models of a single-well ATES system, which is validated by comparison with previous field and modelling studies.The results show that HT-ATES may be viable with injection temperatures as high as 300 ∘C, depending on the aquifer properties and operating parameters. Daily cycles are very efficient over a broad range of conditions, whereas the efficiency of annual cycles is much more variable. The most important parameters governing R are aquifer thickness, injection temperature, horizontal and vertical permeability, and dispersion length.The R values are used to derive an improved version of the Rayleigh number relationship proposed by Schout et al. (2014), extending the applicability of this relationship to daily cycles and improving its accuracy for annual cycles. An alternative method for estimating R using a convolutional neural network is proposed.The calculated R values may be considered best-case because aspects such as background groundwater flow and geochemical effects are ignored. Practical factors such as energy supply/demand requirements, reservoir and above-ground engineering, financial or regulatory aspects, and public acceptance are not considered. Nevertheless, the results of this study can be used for rapid screening of large areas for potential HT-ATES sites, defining requirements for potential sites, and estimating R values for specific sites, before performing detailed feasibility studies.

Numerical investigation of a high temperature heat injection test

High Temperature-Aquifer Thermal Energy Storage (HT-ATES) is a promising option to compensate for the seasonal mismatch between heating supply and demand in the heating sector based on renewable energies. To test and verify numerical and experimental methods for predicting HT-ATES thermo-hydraulic impacts, a small-scale heat injection test with injection temperatures of >70 °C was conducted in a shallow aquifer and monitored using a dense temperature sensor network. Prior to the heat injection test, the hydraulic and thermal properties of the field site were investigated and a predictive high-resolution numerical simulation model of the coupled thermo-hydraulic processes was derived based only on this a priori information. The comparison of measured and predicted temperature breakthrough curves showed a good correspondence, suggesting that the model is able to predict the overall thermal behavior. The model predictions were most accurate for long-term and far-field temperature evolution, with lower accuracy for temperature peaks closer to the injection well. Density-driven buoyancy flow was identified as an active heat transport process, due to the relatively high vertical hydraulic conductivity. The numerical model, parameterized based only on a priori site investigation data, is shown suitable for predicting heat transport processes due to a high temperature heat injection, as well as the induced thermal impacts of an HT-ATES system.

Minimum transmissivity and optimal well spacing and flow rate for high-temperature aquifer thermal energy storage

Aquifer thermal energy storage (ATES) is a time-shifting thermal energy storage technology where waste heat is stored in an aquifer for weeks or months until it may be used at the surface. It can reduce carbon emissions and HVAC costs. Low-temperature (<25 °C) aquifer thermal energy storage (LT-ATES) is already widely-deployed in central and northern Europe, and there is renewed interest in high-temperature (>50 °C) aquifer thermal energy storage (HT-ATES). However, it is unclear if LT-ATES guidelines for well spacing, reservoir depth, and transmissivity will apply to HT-ATES. We develop a thermo-hydro-mechanical-economic (THM$) analytical framework to balance three reservoir-engineering and economic constraints for an HT-ATES doublet connected to a district heating network. We find the optimal well spacing and flow rate are defined by the “reservoir constraints” at shallow depth and low permeability and are defined by the “economic constraints” at great depth and high permeability. We find the optimal well spacing is 1.8 times the thermal radius. We find that the levelized cost of heat is minimized at an intermediate depth. The minimum economically-viable transmissivity (MEVT) is the transmissivity below which HT-ATES is sure to be economically unattractive. We find the MEVT is relatively insensitive to depth, reservoir thickness, and faulting regime. Therefore, it can be approximated as 5⋅10−13 m3. The MEVT is useful for HT-ATES pre-assessment and can facilitate global estimates of HT-ATES potential.

Temperature management potentially affects carbon mineralization capacity and microbial community composition of a shallow aquifer.

High-temperature aquifer thermal energy storage (HT-ATES) is a promising technique to reduce the CO2 footprint of heat supply in the frame of transitioning to renewable energies. However, HT-ATES causes temperature fluctuations in groundwater ecosystems potentially affecting important microbial-mediated ecosystem services. Hence, assessing the impact of increasing temperatures on the structure and functioning of aquifer microbiomes is crucial to evaluate potential environmental risks associated with HT-ATES. In this study, we investigated the effects of temperature variations (12-80°C) on microbial communities and their capacity to mineralize acetate in aerobically incubated sediment sampled from a pristine aquifer. Compared to natural conditions (12°C), increased acetate mineralization rates were observed at 25°C, 37°C and 45°C, whereas mineralization was decelerated at 60°C and absent at 80°C. Sequencing of 16S rRNA genes revealed that the bacterial diversity in acetate-amended and non-acetate-amended sediments decreased with rising temperatures. Distinct communities dominated by bacterial groups affiliated with meso- and thermophilic bacteria established at 45°C and 60°C, respectively, while the number of archaeal phylotypes decreased. The changes in microbial diversity observed at 45°C and 60°C indicate a potential loss of ecosystem functioning, functional redundancy and resilience, while heat storage at 80°C bears the risk of ecological collapse.

The Potential of Depleted Oil Reservoirs for High-Temperature Storage Systems

HT-ATES (high-temperature aquifer thermal energy storage) systems are a future option to shift large amounts of high-temperature excess heat from summer to winter using the deep underground. Among others, water-bearing reservoirs in former hydrocarbon formations show favorable storage conditions for HT-ATES locations. This study characterizes these reservoirs in the Upper Rhine Graben (URG) and quantifies their heat storage potential numerically. Assuming a doublet system with seasonal injection and production cycles, injection at 140 °C in a typical 70 °C reservoir leads to an annual storage capacity of up to 12 GWh and significant recovery efficiencies increasing up to 82% after ten years of operation. Our numerical modeling-based sensitivity analysis of operational conditions identifies the specific underground conditions as well as drilling configuration (horizontal/vertical) as the most influencing parameters. With about 90% of the investigated reservoirs in the URG transferable into HT-ATES, our analyses reveal a large storage potential of these well-explored oil fields. In summary, it points to a total storage capacity in depleted oil reservoirs of approximately 10 TWh a−1, which is a considerable portion of the thermal energy needs in this area.

The feasibility of high-temperature aquifer thermal energy storage in Denmark: the Gassum Formation in the Stenlille structure

Heat storage in the Danish subsurface is gaining increasing interest for optimizing the use of energy resources, but no deep heat storage facilities have yet been established. As an analogue we study the Gassum Formation in the Stenlille structure that is presently used for gas storage. This allows us to discuss geological and technical characteristics of an aquifer relevant for heat storage in Denmark. We develop a 3D model for a high-temperature aquifer thermal energy storage system using analysis of geological core data, sedimentological description, geophysical data including well logs and seismic lines, as well as a finite difference model to calculate the recovery efficiency, heat storage capacity and thermal breakthrough time. Based on geostatistical methods we made three realisations and found similar results for the three cases. In accordance with results from published simplified models we found a high recovery efficiency of 70% after 4 years and 69% after 20 years, a high heat storage capacity of 1.8×1018 J, and a long thermal breakthrough time of 66–77 years. These results reflect the excellent reservoir properties of the Gassum Formation in Stenlille, characterised by a uniformly layered sand/shale sedimentology, a high average porosity of 25% and a high permeability of 1000 to 10 000 mD of sandstone intervals.

Evaluating thermal losses and storage capacity in high-temperature aquifer thermal energy storage (HT-ATES) systems with well operating limits: insights from a study-case in the Greater Geneva Basin, Switzerland

High-temperature aquifer thermal energy storage (HT-ATES) may play a key role in the development of sustainable energies and thereby in the overall reduction of CO2 emission. To this end, a thorough understanding of the thermal losses associated with HT-ATES is crucial. We provide in this study a numerical investigation of the thermal performance of an HT-ATES system for a heterogeneous aquifer modelled after a well-defined region in the Greater Geneva Basin (Switzerland), where the excess heat produced by a nearby waste-to-energy plant is available for storage. We consider different aquifer properties and flow conditions, with complex injection strategies that respect maximum/minimum well pressures and temperatures, as well as legal regulations. Based on the results, we also draw conclusions on the economical feasibility (e.g., energy recovery factor vs. drilling costs) for the different strategies.Our results indicate that the true behaviour of HT-ATES systems may deviate significantly from theoretical performance derived from idealised cases. This is particularly true when the operational pressure and temperature ranges of the wells are restricted, and for heterogeneous aquifers.

Assessment of short-term aquifer thermal energy storage for demand-side management perspectives: Experimental and numerical developments

In the context of demand-side management and geothermal energy production, our proposal is to store thermal energy in shallow alluvial aquifers at shorter frequencies than classical seasonal aquifer thermal energy storage. We first conducted a one-week experiment in a shallow alluvial aquifer, which is characterized by a slow ambient groundwater flow, to assess its potential for thermal energy storage and recovery. This experiment has shown that up to 90% of the stored thermal energy can be recovered and would therefore suggest that aquifer thermal energy storage could be considered for demand-side management applications. We then conceptualized, developed, and calibrated a deterministic 3D groundwater flow and heat transport numerical model representing our study site, and we simulated 77 different scenarios to further assess this potential. This has allowed us to demonstrate that low-temperature aquifer thermal energy storage (temperature differences of −4 K for precooling and 3, 6, and 11 K for preheating) is efficient with energy recovery rates ranging from 78 to 87%, in a single aquifer thermal energy storage cycle. High-temperature aquifer thermal energy storage (temperature differences between 35 and 65 K) presents lower energy recovery rates, from 53 to 71%, with all other parameters remaining equals. Energy recovery rates decrease with increasing storage duration and this decrease is faster for higher temperatures. Retrieving directly useful heat (without upgrading with a groundwater heat pump) using only a single storage and recovery cycle appears to be complicated. Nevertheless, there is room for aquifer thermal energy storage optimization in space and time with regard to improving both the energy recovery rates and the recovered absolute temperatures.

The Impact of Reservoir Heterogeneities on High-Temperature Aquifer Thermal Energy Storage Systems. A Case Study from Northern Oman.

We conducted a geoscientific feasibility study for the development of a high-temperature thermal aquifer energy storage system (HT-ATES) outside the capital of Muscat, northern Oman. The aquifer storage is part of a solar-geothermal cooling project for the sustainable and continuous cooling of office buildings. The main concept is that excess solar energy will be stored in the subsurface through hot water injection and subsequently utilised as auxiliary energy source during peak demand times. The characterisation of aquifer heterogeneities is thus essential to predict subsurface thermal heat plume development and recovery efficiency of the storage system. We considered two aquifer systems as potential storage horizons, (i) a clastic-dominated alluvial fan system where individual channel systems in combination with diagenetic alterations constitute the main heterogeneities and (ii) a carbonate-dominated system represented by a homogenous layer-cake architecture. The feasibility study included a multidisciplinary approach from initial field work, geocellular reservoir modelling to finite element fluid flow and thermal modelling. Our results show that for the HT-ATES system, with a high frequency of injection and production cycles, heat loss mainly occurs due to heterogeneities in the permeability field of the aquifer in combination with buoyancy driven vertical fluid flow. An impermeable cap-rock is needed to keep the heat plume in place. Conductive heat loss is a minor issue. Highly complex heat plume geometries are apparent in the clastic channel system and ATES well planning is challenging due to the complex and interconnected high-permeable channels. The carbonate sequence shows uniform plume geometries due to the layer cake architecture of the system and is tentatively more suitable for ATES development. Based on our findings we propose the general concept of HT-ATES traps, incorporating and building on expertise and knowledge from petroleum and reservoir geology regarding reservoir rocks and suitable trap&seal geometries. The concept can be used as guideline for future high-temperature aquifer storage exploration and development.

Conceptual market potential framework of high temperature aquifer thermal energy storage - A case study in the Netherlands

High temperature aquifer thermal energy storage (HT-ATES) can contribute to the integration of renewable energy sources in the energy system, the replacement of fossil fuel-based heat supply and the utilization of surplus heat from industrial sources. However, there is limited understanding on the drivers, barriers and conditions of HT-ATES implementation. The objective of this study is to partly fill this knowledge gap by developing a methodological framework for a quick scan on market potential of HT-ATES. Based on the application of this framework to a case study in the Netherlands, it is concluded that the proposed method is suitable for a pre-feasibility analysis on the HT-ATES market potential. The investigated case study has a planned district heating system with geothermal energy as the heat source. HT-ATES is found to be cost-effective compared to a reference technology, i.e. a natural gas boiler, in the scenarios under existing and more sustainable alternative policies. The lifetime of HT-ATES and the size of heat demand have a strong influence on the market potential.

Interdisciplinary Review of Medium-deep Aquifer Thermal Energy Storage in North Germany

High Temperature Aquifer Thermal Energy Storage (HT-ATES) has developed from a demonstration stage to a mature technology over the past decades. The specific storage capacity costs are lower by a factor of 20 compared to above-ground storage systems. Depending on geology, system configuration and temperature level, medium deep aquifers (approx. 400 m – 1,000 m) enable seasonal heat storage from 1 GWh/a up to 100 GWh/a. Typical heat recovery factors are in between 60 – 80 %. However, only three systems have been built and reached normal operation in Europe. Moreover, although substantial parts of the subsurface in Germany, for example, are suitable for ATES systems, over 10 years have passed since the most recent project has been put into operation.Despite substantial advantages and a great potential of bridging the gap between constant production and seasonally varying demand, ATES is quite complex and conditional. Critical hydro-geological conditions (e.g. permeability, porosity, mineralisation) as well as relevant ordinances and regulations from the mining and local water authorities should be complied with. In addition, geothermal projects are not always supported by public acceptance as drilling boreholes today is a sensitive and emotional topic.This contribution deals with an interdisciplinary approach to evaluate all parameters (geology, legal classification, public acceptance, water chemistry, applications/revenue models and drilling technology) affecting a cost-effective operation of ATES systems in North Germany. One main objective is to identify possible locations for ATES in the North German Basin and to derive generalizable success factors. Preliminary results and an overview of the project supported by the Federal Ministry of Economic Affairs and Energy are presented. The project consortium consists of Leuphana University of Lüneburg and GeoDienste GmbH, supported by GeoEnergy Celle e.V.

Climate-neutral and sustainable campus Leuphana University of Lueneburg

The Leuphana University of Lueneburg changed to renewable energy supply with the first climate-neutral energy balance for heat, electricity, cars and business trips in 2014. The heating network is based on two biomethane-powered combined-heat-and-power (CHP) units of 525 kWel. each. A total of 720 kWp photovoltaics with 95% self-consumption covers > 20% of the electrical demand. We present the campus development and transformation to provide a best-practice example for conversion to exergy-efficient renewable energy systems.The new central building provides a large auditorium, seminar rooms, offices, a cafeteria, machine hall and space for exhibitions and events. It uses low-grade heat at 58 °C for optimized integration of short and long term heat storage installations. The architecture and façade design significantly lower cooling demand (≈ 2.5 kWh/m2a), modern lighting systems and user integration allow for superior overall energy efficiency. Exergy efficiency, storage options and emissions of the campus system as well as energy efficiency of the buildings were analysed. A high-temperature aquifer thermal energy storage (HT-ATES) installation perfectly matches the low-exergy heating demands and increases the share of CHP-heat, resulting in an additional surplus of 2.3 GWh/a of renewable electricity and additional savings of 2.424 t CO2-eq./a.

Numerical simulation of a high-temperature aquifer thermal energy storage system coupled with heating and cooling of a thermal plant in a cold region, China

This study investigates the performance of an aquifer thermal energy storage system (ATES) that is coupled with the cooling tower of a seasonally-running thermal plant. The ATES supplies cool water and stores heated water for the cooling tower during the runtimes of the thermal plant. Moreover, it supplies warm water for bathing or irrigation during downtimes of the thermal plant. The performance of ATES is evaluated numerically for a full year, and well placement is optimized. Findings indicate that the ATES system could be optimized by locating the cool water supply well upstream of the storage well. In the optimized ATES, the outflow temperature from the cool water supply well can be maintained below 15 °C, which satisfies the temperature requirement for the cooling tower. The injection of heated water (with temperature of 70 °C) at 8400 m3/d for six months leads to over 140,000 m3 of warm water (with temperature ≥ 40 °C) stored in the aquifer. This warm water can supply at least 12,000 m3/d of warm water for six months. The recovery efficiency is estimated at 60.9%, and the energy loss is attributed to rainfall infiltration, thermal diffusion into underlying low-permeability layer and advection downstream.

The use of salinity contrast for density difference compensation to improve the thermal recovery efficiency in high-temperature aquifer thermal energy storage systems

The efficiency of heat recovery in high-temperature (>60 °C) aquifer thermal energy storage (HT-ATES) systems is limited due to the buoyancy of the injected hot water. This study investigates the potential to improve the efficiency through compensation of the density difference by increased salinity of the injected hot water for a single injection-recovery well scheme. The proposed method was tested through numerical modeling with SEAWATv4, considering seasonal HT-ATES with four consecutive injection-storage-recovery cycles. Recovery efficiencies for the consecutive cycles were investigated for six cases with three simulated scenarios: (a) regular HT-ATES, (b) HT-ATES with density difference compensation using saline water, and (c) theoretical regular HT-ATES without free thermal convection. For the reference case, in which 80 °C water was injected into a high-permeability aquifer, regular HT-ATES had an efficiency of 0.40 after four consecutive recovery cycles. The density difference compensation method resulted in an efficiency of 0.69, approximating the theoretical case (0.76). Sensitivity analysis showed that the net efficiency increase by using the density difference compensation method instead of regular HT-ATES is greater for higher aquifer hydraulic conductivity, larger temperature difference between injection water and ambient groundwater, smaller injection volume, and larger aquifer thickness. This means that density difference compensation allows the application of HT-ATES in thicker, more permeable aquifers and with larger temperatures than would be considered for regular HT-ATES systems.

Sensitivity analysis of recovery efficiency in high-temperature aquifer thermal energy storage with single well

High-temperature aquifer thermal energy storage system usually shows higher performance than other borehole thermal energy storage systems. Although there is a limitation in the widespread use of the HT-ATES system because of several technical problems such as clogging, corrosion, etc., it is getting more attention as these issues are gradually alleviated. In this study, a sensitivity analysis of recovery efficiency in two cases of HT-ATES system with a single well is conducted to select key parameters. For a fractional factorial design used to choose input parameters with uniformity, the optimal Latin hypercube sampling with an enhanced stochastic evolutionary algorithm is considered. Then, the recovery efficiency is obtained using a computer model developed by COMSOL Multiphysics. With input and output variables, the surrogate modeling technique, namely the Gaussian-Kriging method with Smoothly Clopped Absolute Deviation Penalty, is utilized. Finally, the sensitivity analysis is performed based on the variation decomposition. According to the result of sensitivity analysis, the most important input variables are selected and confirmed to consider the interaction effects for each case and it is confirmed that key parameters vary with the experiment domain of hydraulic and thermal properties as well as the number of input variables.

Analysis of recovery efficiency in high-temperature aquifer thermal energy storage: a Rayleigh-based method

High-temperature aquifer thermal energy storage (HT-ATES) is an important technique for energy conservation. A controlling factor for the economic feasibility of HT-ATES is the recovery efficiency. Due to the effects of density-driven flow (free convection), HT-ATES systems applied in permeable aquifers typically have lower recovery efficiencies than conventional (low-temperature) ATES systems. For a reliable estimation of the recovery efficiency it is, therefore, important to take the effect of density-driven flow into account. A numerical evaluation of the prime factors influencing the recovery efficiency of HT-ATES systems is presented. Sensitivity runs evaluating the effects of aquifer properties, as well as operational variables, were performed to deduce the most important factors that control the recovery efficiency. A correlation was found between the dimensionless Rayleigh number (a measure of the relative strength of free convection) and the calculated recovery efficiencies. Based on a modified Rayleigh number, two simple analytical solutions are proposed to calculate the recovery efficiency, each one covering a different range of aquifer thicknesses. The analytical solutions accurately reproduce all numerically modeled scenarios with an average error of less than 3 %. The proposed method can be of practical use when considering or designing an HT-ATES system.