• 2050 goals
• absorption refrigeration cycle
• advanced geothermal system
• AGS
• ammonia
• ammoniaca
• ciclo frigorifero ad assorbimento
• ciclo Rankine organico
• consumo energetico
• cooling production
• data center
• data centre
• emissioni
• emissions
• energy production
• geotermico
• geothermal
• geothermal plant
• impianto geotermico
• multi-energy systems
• obiettivi 2050
• organic Rankine cycle
• power consumption
• produzione di energia
• produzione di raffreddamento
• Singapore
• sistema geotermico avanzato
• sistemi multi-energetici

In the context of the ongoing expansion of global energy demand, the urgent need to identify and implement clean, renewable, and locally available energy resources has become a matter of strategic importance. Geothermal energy stands out in this regard, offering both environmental advantages and the potential for continuous, base-load energy supply. Unlike solar and wind resources, which are intermittent and dependent on meteorological variability, geothermal systems provide stable outputs that can directly support both electricity production and thermal applications. However, the deployment of conventional hydrothermal resources remains geographically constrained, as many regions lack naturally permeable reservoirs or surface manifestations of geothermal activity. This has motivated the growing interest in Advanced Geothermal Systems (AGS), which rely on engineered reservoirs to exploit deep crustal heat independent of natural permeability.
Singapore presents a particularly interesting case for the application of AGS technologies. The city-state sits on granite bedrock characterized by high concentrations of radiogenic elements, which contribute to elevated heat generation. While traditional hydrothermal resources are absent, the geological setting provides a latent potential that can be unlocked through deep drilling and reservoir engineering. Given the tropical climate and the significant demand for cooling - particularly in energy intensive infrastructures such as data centres - an integrated geothermal system capable of providing both electricity and cooling services could address pressing local energy and environmental challenges. In this context, AGS emerges as a promising solution to support Singapore’s goals of energy diversification, resilience, and decarbonization.
The present study develops a comprehensive parametric and techno-economic analysis of AGS configurations tailored to Singapore’s specific conditions. The objective is to explore the technical feasibility, performance potential and economic viability of integrating geothermal energy into multi-energy systems designed for electricity and cooling production. The research methodology follows a three-phase structure. First, reservoir modelling was conducted to determine optimal well depths, flow rates, and injection conditions. This step was performed using GEOPHIRES-X, a simulation tool capable of capturing subsurface thermal dynamics. Second, surface plant performance was analysed through Python-based simulations, with particular emphasis on the integration of an Organic Rankine Cycle (ORC) for power generation and an Absorption Refrigeration Cycle (ARC) based on a LiBr–water working pair for cooling. Finally, a detailed economic assessment was carried out using the Levelized Cost of Electricity (LCOE) and other financial indicators to evaluate the trade-offs between depth, output, and investment costs.
The starting point of the analysis lies in the estimation of the available geothermal resource at different drilling depths. Three primary depths were selected for comparison: 3.5 km, 6 km, and 8 km. Each depth corresponds to distinct ranges of rock temperature, drilling costs, and technical feasibility.
At 3.5 km, reservoir temperatures are expected to reach approximately 140 °C, sufficient to drive low-temperature ORCs and ARC systems. Although the thermal potential at this depth is more modest, the reduced drilling costs make it economically attractive for small to medium-scale applications. Simulations indicate that such a configuration could provide up to 2 MWel of power or approximately 8 MWth of cooling, sufficient for the operation of a medium-sized data center. Moreover, the condenser duty of the ORC could be exploited to vaporize 30-40 kg/s of ammonia, which, if expanded in a turbine, could yield an additional few megawatts of power. This integration highlights the potential for innovative pathways that couple geothermal energy with ammonia-based energy storage and conversion.
At 6 km, the rock temperature increases to around 210-220 °C, expanding the thermodynamic potential of the reservoir. The available heat was estimated at 16 MWth, corresponding to an output of 3.4 MWel in a power-oriented cycle or a hybrid configuration delivering 2 MWel together with 6 MWth of cooling. This scenario represents a viable compromise between performance and investment, as 6 km is often regarded as the practical upper limit for conventional geothermal drilling. The outputs, while more modest than those of deeper systems, are suitable for medium to large scale infrastructures such as university campuses or commercial hubs.
At 8 km, with temperatures exceeding 250 °C, the potential of the reservoir increases significantly. Using advanced multilateral wells or closed-loop Eavor-type systems, the reservoir can deliver up to 50 MWth of thermal energy. This enables the implementation of a cascade ORC producing 11 MWel at a thermal efficiency of 24%, or a combined ORC-ARC system delivering 8 MWel and 12 MWth of cooling. Such capacities make the 8 km scenario suitable for large-scale urban infrastructures and data centres. However, the high drilling costs and technological challenges associated with ultra-deep wells represent substantial barriers.
The sensitivity analysis conducted on injection temperature, flow rate, and reservoir configuration further underscores the dependence of system performance on subsurface parameters. A 20% increase in flow rate typically resulted in a 15-18% increase in power output, while a 10 °C decrease in injection temperature reduced total output by nearly 10%. These results emphasize the importance of tailoring system design to site specific conditions while confirming the robustness of the overall comparative trends across depths.
The Organic Rankine Cycle (ORC) was selected for electricity generation due to its proven efficiency in converting low and medium grade heat. Aromatic hydrocarbons such as toluene were identified as suitable working fluids for high-temperature sources, while refrigerants such as R245fa are appropriate for lower-temperature cascades. The Absorption Refrigeration Cycle (ARC), based on a LiBr–water solution, was chosen for cooling production, offering a renewable alternative to conventional electricity-driven chillers.
The integration of ORC and ARC in different configurations highlights the multi-energy potential of AGS. At shallow depths (3.5 km), the focus shifts naturally toward cooling, reflecting Singapore’s climatic and industrial priorities. At intermediate depths (6 km), the hybrid ORC-ARC system emerges as the most balanced option, capable of supplying both power and cooling at moderate capacities. At greater depths (8 km), the system tilts toward power-oriented applications, though the availability of large cooling capacity remains a significant advantage.
A notable innovation explored in this study is the integration of ammonia as an auxiliary working fluid. Ammonia can be vaporized using condenser heat from the ORC, then expanded in a turbine to generate additional electricity. At 8 km, up to 250-280 kg/s of ammonia could be vaporized, corresponding to approximately 10 MWel of additional capacity. Even at shallow depths, smaller flowrates (30-40 kg/s) could provide supplementary output. This dual use of geothermal heat enhances system flexibility, supports ammonia-based energy storage, and aligns with Singapore’s strategic exploration of ammonia as both an energy vector and a potential fuel for decarbonization.
The study also evaluated the potential of supercritical CO2 (sCO2) as a geothermal working fluid. Due to its unique thermophysical properties - low viscosity, high compressibility near the critical point, and reduced risk of scaling – sCO2 offers advantages in both reservoir circulation and surface conversion efficiency.
At 10 km depth, using a multilateral configuration with eight laterals of 4 km each, the system achieved 8.3-10.5 MWel, depending on flow rate and injection conditions. When coupled with an ARC, cogeneration reached 7.4-10 MWel of electricity and 4-7 MWth of cooling. At 6 km depth, with a flow rate of 25 kg/s and injection temperature of 70 °C, direct expansion produced 2.8 MWel at an outlet temperature of 65 °C. While outputs are lower at shallower depths, the reduced drilling costs render these scenarios attractive.
Comparisons between water and sCO2 based cycles reveal nuanced trade-offs. At 8 km, water-based ORCs reached 11 MWel, slightly higher than the 10 MWel produced by sCO2 systems. However, when cooling is included, sCO2 based cycles outperform water-based ones in terms of overall exergy utilization. The utilization factor, defined as the ratio between useful energy (electricity plus equivalent cooling) and geothermal input, was observed to increase by 20-30% in sCO2 based cogeneration. This makes sCO2 particularly attractive in Singapore, where cooling demand often surpasses electricity demand.
The environmental and operational benefits of sCO2 further strengthen its case. Reduced pumping power requirements improve net efficiency, while the absence of scaling minimizes maintenance. Nevertheless, uncertainties remain regarding long-term reservoir interactions, including CO2 solubility in rocks and risks of leakage, which require further research and field validation.
The third phase of the study consisted of a techno-economic analysis integrating capital and operating costs, drilling expenses, and system efficiency into the calculation of LCOE and related financial indicators.
From an economic perspective, drilling depth emerges as the dominant factor influencing feasibility. The 3.5 km case, with drilling costs less than half those of 6 km and one order of magnitude lower than 8 km, is attractive for cost-sensitive applications, despite lower outputs. The 6 km configuration represents the best balance between cost and performance, delivering both electricity and cooling with manageable investment. The 8 km case, while technologically impressive, entails prohibitively high costs for all but large-scale strategic applications.
From an environmental standpoint, geothermal energy offers significant reductions in greenhouse gas emissions. For instance, a system delivering 11 MWel could offset 35-40 ktCO2 annually in Singapore, where the grid emission factor is approximately 0.38-0.45 kgCO2/kWh. The integration of geothermal energy into data centres - major electricity and cooling consumers - thus provides substantial sustainability benefits.
A broader reflection underscores the importance of aligning system configuration with end-use priorities. In Singapore, where the electricity supply is already heavily decarbonized but cooling demand continues to grow, hybrid configurations offering cooling alongside electricity are particularly relevant.
At 3.5 km, the system is best suited for medium-sized data centres or district-scale cooling networks. At 6 km, outputs are sufficient to supply large university campuses or commercial hubs. At 8 km, the system could serve urban-scale infrastructures or large data centre campuses, potentially coupled with ammonia-based storage. The flexibility of these configurations confirms the adaptability of AGS to different scales and applications.
This study confirms that Advanced Geothermal Systems can play a pivotal role in Singapore’s energy transition, providing both electricity and cooling in a sustainable and locally sourced manner.
Future work should focus on refining reservoir characterization through field data, implementing Computational Fluid Dynamics (CFD) studies to capture flow and heat transfer dynamics, and exploring pilot-scale demonstrations to validate model predictions. The integration of innovative cycles and hybrid solutions, such as Eavor-like closed loops or ammonia-based energy storage, could further enhance the role of geothermal systems in Singapore’s sustainable energy future.
Ultimately, the results presented in this study provide a robust foundation for policy planning and strategic investment, demonstrating that AGS can contribute meaningfully to the decarbonization of both power generation and cooling in tropical urban contexts.