Nina Rman

Cooling-dominated cold-storage systems are an underexplored application for shallow geothermal energy, yet they offer near-continuous surplus heat that can be recovered, stored, or rejected depending on operating conditions. This study develops and empirically parameterises a reduced-order, temperature-driven framework that quantifies the role of shallow geothermal coupling in such hybrid systems. It integrates 15-minute field monitoring, an enhanced thermal response test on a dedicated 100 m borehole, reduced-order energy-system modelling, and discounted techno-economic analysis, applied to a rural cold-storage facility in Slovenia. Operation follows a temperature-driven criterion in which the selection between ground-coupled and air-based heat rejection emerges from condensation-temperature conditions rather than predefined control rules. The model is calibrated and validated against the monitored period (reproducing the daily-electricity distribution within 14 %), then used to reconstruct annual energy flows and to perform a multi-parameter sensitivity and uncertainty analysis of installed geothermal capacity. Of the 134 MWh of heat rejected annually, about 14 MWh is recovered for heating, 25 MWh is injected into the ground, and the remainder (~95 MWh) is rejected to ambient air, confirming that the subsurface acts as a constrained thermal buffer rather than a fully regenerative seasonal store. Performance improves with installed capacity but with strongly diminishing returns, yielding a least-cost optimum at approximately 8–16 kW. Although net present value stays negative over the 20-year lifetime, this optimum is robust across the tested electricity-price, investment-cost, and discount-rate ranges. At farm scale the coupling is best deployed as an efficiency-and-stability measure in large, continuously operated systems.

Cooling-dominated cold storage systems represent an underexplored application for shallow geothermal energy, particularly in hybrid configurations where surplus heat from refrigeration can be recovered, stored, or rejected depending on operating conditions.This study develops an integrated framework combining field monitoring, reduced-order energy modelling, and techno-economic analysis to evaluate the role of shallow geothermal energy in such systems. The framework is applied to a monitoring-based case study of a rural cold storage system, using site-specific operational and subsurface data.A temperature-driven modelling approach is used to represent system operation, in which the selection between ground-coupled and air-based heat exchange emerges from thermodynamic conditions rather than predefined control rules. Parametric analysis of geothermal capacity is performed to assess system performance under varying operating conditions.Results indicate that approximately 24.9 MWh of thermal energy is injected into the ground annually, confirming that the subsurface primarily functions as a constrained thermal buffer rather than a fully regenerative seasonal storage. Increasing geothermal capacity improves performance, but with diminishing returns due to temperature equalisation and limited subsurface heat transfer. Optimal techno-economic performance is achieved at moderate installed capacities.The findings demonstrate that shallow geothermal energy can enhance efficiency and thermal stability in cooling-dominated agricultural systems when applied as part of a hybrid configuration, while highlighting the importance of site-specific conditions, realistic load profiles, and temperature-driven operation for system design.

In times of climate change, when drinking water resources and the water needed for the survival of groundwater-dependent ecosystems, such as lowland forests depend on the availability of water, the sustainable use of groundwater requires strategic planning based on an assessment of the amount of groundwater available. To properly assess and plan the amount of available and accessible water resources, it is first necessary to understand the processes of the water cycle.About 25 years ago (in 2000), a high mortality rate was observed in the groundwater-dependent ecosystem (GDE) of several lowland oak forests in Slovenia and Europe. Understanding the processes of the hydrological cycle is becoming increasingly important, mainly because of the high mortality of these forests, whose main problem is probably the lowering of the groundwater table and the reduced accessibility of water to these trees as a result of changes in weather patterns or the regime and amount of precipitation recharging the aquifers in the area of these forests.By short-term monitoring of the composition of stable water isotopes (δ18O and δ2H) in precipitation in the area of lowland oak forests Murska šuma (northeast Slovenia) and Krakovski gozd (southeast Slovenia), we have obtained important results on the variability of the precipitation signal, which will be compared with the results of the neighbouring long-term stations (e.g. Murska Sobota, Ljubljana, Vienna, Graz and Zagreb). In the future, we will expand our research and also monitor the isotope signal of stable water isotopes in soil, groundwater and xylem water of adult trees. This will allow us to assess the origin of water sources used by trees and to identify physiological responses to changing climatic conditions such as drought stress or altered precipitation regimes. By integrating water isotope data into ecological and hydrological models, we can better predict how trees will respond to current and future climate change, providing information for conservation strategies and sustainable management practices.Activities for this presentation were funded in last decade by the Slovenian Research Agency (Grants P1-0143, N1-0054, N1-0309 and P1-0020), IAEA (CRP F31006, TC RER7013, TC RER7017, SLO7001) and projects Mladi forum and FREYA which are co-funded by the Slovenian Research and Innovation Agency within the framework of Developmental funding pillar.

Since the heating and cooling sectors consume most of the energy in Europe through fossil fuels, the transition to a low-carbon and sustainable energy system is crucial. Underground Thermal Energy Storage (UTES) systems, such as aquifer thermal energy storage (ATES) and borehole thermal energy storage (BTES), offer promising solutions by enabling seasonal storage of renewable thermal energy, balancing the mismatch between supply and demand. ATES and BTES systems store excess heat or cold for later use, making them suitable for large-scale applications like residual heat storage from industrial or power generation processes by offering flexibility in heating and cooling. This review explores the geological and hydrogeological requirements for ATES and BTES systems, pointing out the importance of basic geological knowledge, laboratory and field investigations, and operational monitoring to optimize their performance. The study highlights the need for Slovenia to use the experiences of other European nations to overcome initial challenges, develop effective site evaluation methods, and integrate these systems into existing energy infrastructure.

Two Neogene sub-basins of the Miocene Extensional Pannonian Superbasin are located in Slovenia: the Mura-Zala Basin in the NE and the Krško Basin in the east of the country. Their predominantly clastic sedimentary fill hosts diverse geoenergy resources in different geological formations. The basin evolution (e.g. very high Miocene heat flow) was not favourable for the accumulation of large amounts of hydrocarbons. Consequently, oil and gas deposits are limited to the Petišovci–Dolina Field, which was discovered in 1942. The field is located along the Ormož–Selnica–Lovászi Anticline, an inverted Miocene graben structure. Currently, minor amounts of natural gas are produced from Miocene (Badenian and Pannonian) horizons, while oil production stopped in 2021. Coal deposits formed in deltaic environments during the late Pannonian and were exploited until the 1970s, in both the Mura-Zala Basin and the Krško Basin. Depleted oil and gas reservoirs at depths greater than 800 m, saline aquifers and deeply buried coals in the Mura-Zala Basin provide potential sites for CO ₂ storage, albeit with limited volumes.

The Groundwater quantitative status assessment is part of River Basin Management Plan 2022–2027 (RBMP III) and is used to evaluate, according to certain criteria, the 21 groundwater bodies (GWBs) in Slovenia. GWB can achieve good or poor quantitative status. The assessment is carried out with four tests, where the impact of groundwater abstraction (pumped quantities) on: groundwater quantity and water balance, the ecological status of associated surface water bodies, groundwater dependent terrestrial ecosystems and the intrusion of saline or poor water quality into the aquifer is analyzed. The final overall assessment of each groundwater body, based on the completed tests, is determined by the criterion of the worst test assessment. Based on the results of the tests, within the assessment period, 20 GWBs in Slovenia achieved good quantitative status. GWB Dravska kotlina achieved poor quantitative status, because the pumping of groundwater causes poor quality water intrusions into the deeper aquifer of that groundwater body. Within the last assessment period 1991–2020, approx. 4 billion m3 of groundwater was available annually in shallow aquifers within groundwater bodies. Groundwater abstraction (pumper quantities) in the period 2014–2019 reached an average of 135 million m3. In the area of deep geothermal aquifers of the Mura basin, abstractions were estimated to sum up to 2.5 million m3 per year. Latest numerical simulations point out induced aquifer recharge of approx. 2.3 million m3 of thermal water.