Abstract
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$) analytical framework to balance three reservoir-engineering and economic constraints for an HT-ATES doublet connected to a district heating network. We find the optimal well spacing and flow rate are defined by the “reservoir constraints” at shallow depth and low permeability and are defined by the “economic constraints” at great depth and high permeability. We find the optimal well spacing is 1.8 times the thermal radius. We find that the levelized cost of heat is minimized at an intermediate depth. The minimum economically-viable transmissivity (MEVT) is the transmissivity below which HT-ATES is sure to be economically unattractive. We find the MEVT is relatively insensitive to depth, reservoir thickness, and faulting regime. Therefore, it can be approximated as 5⋅10−13 m3. The MEVT is useful for HT-ATES pre-assessment and can facilitate global estimates of HT-ATES potential.
Highlights
The heating and cooling of buildings comprise roughly half of the world’s final total energy consumption and are driven primarily by fossil fuels, resulting in substantial emissions of greenhouse gases [1], NOx, and SOx [2]
We develop a thermo-hydro-mechanical-economic (THM$) analytical framework to balance three reservoir-engineering and economic constraints for an HT-Aquifer thermal energy storage (ATES) doublet connected to a district heating network
We developed a THM$ analytical approach to balance three constraints on HT-ATES operations
Summary
The heating and cooling of buildings comprise roughly half of the world’s final total energy consumption and are driven primarily by fossil fuels, resulting in substantial emissions of greenhouse gases [1], NOx, and SOx [2]. Thermal energy storage may reduce greenhouse gas emissions in two ways. In a system where heating and electricity networks are integrated, thermal energy storage can facilitate demand side management, which may lead to augmented use of variable renewable electricity sources like wind and solar [3]. Seasonal thermal energy storage can shift the thermal energy supply to times of thermal energy demand [1], thereby potentially reducing the amount of energy required and carbon emitted. Seasonal thermal storage can be located in underground pits, tanks, mines, caverns, and aquifers, where large amounts of sensible heat can be stored with high efficiency. Aquifer thermal energy storage (ATES) has the largest storage capacity among these options [1]
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