Deep Geothermal Heat Research Articles

Analysis of Different Climate-Neutral Heat Supply Concepts for a District Heating System near Munich with Deep Geothermal Heat as the Primary Heat Source

District heating systems are one key element of the transition towards a climate-neutral heat supply since they allow for the use of various renewable energy sources and the increase of renewable heat generation, in particular when combined with seasonal thermal energy storage. Deep geothermal heat is a renewable heat source that can be used to cover the thermal base load of such a district heating system. Also in combination with other renewable heat sources, such as solar thermal or heat pumps, a climate-neutral heat supply for districts or even complete cities can be realised. This paper deals with the analysis of different climate-neutral heat supply concepts that were elaborated for a district heating system currently in the planning phase using deep geothermal heat as the primary heat source, located in the town of Graefelfing near Munich, Germany. The authors present, discuss and assess various options regarding renewable heat sources and including (seasonal) thermal energy storage, to fully cover the thermal loads of a new district heating system in a technically, economically and environmentally favourable way. As a result of this study, a heat supply concept was selected, in which a heat pump using the return flow of the deep geothermal circuit as a heat source maximises the utilisation of the available deep geothermal heat source to cover more than 95 % of the annual heat demand by deep geothermal heat combined with a heat pump.

Modeling and economic evaluation of deep geothermal heat supply systems using the example of the Wealden near Hannover, Germany

Germany desires to become climate-neutral in its heat supply by 2045. From 2024 onward communities are legally required to develop a plan documenting how the objective will be achieved. Geothermal resources can be a major building block to reach the aspirational target if they can be developed at competitive costs. To evaluate the economic potential of geothermal resources is time and money consuming. Questions which need to be addressed in the context of such evaluations are: how can an economic recovery of geothermal heat be achieved, how can subsurface risks associated with an exploration be managed, and how competitive is a deep geothermal energy recovery compared to other options of heat supply? These questions are key to a development of deep geothermal heat, especially if the geothermal conditions are not as prominent as in already realized projects, but less favorable as in the deep clastic sediments of the North German Basin. With this contribution a procedure is presented and used to determine net present values and the associated levelized costs for deep hydrothermal heat recovery systems. It consists of modelling the geothermal cycle, sizing all necessary components, costing them, and calculating net present value and levelized cost. The thermal model is verified by comparing the modelled state variables pressure and temperature at relevant state points of the thermal cycle with actual data of a geothermal project. The cost model is validated with biding results and cost information from actual projects and modified as appropriate. In applying the model to a setting in the Hannover–Celle area with temperatures of around 70 °C, conditions are determined, which lead to positive net present values. The degree of their influence is determined in sensitivity analyses allowing a systemic optimization. The results show that for a coupled heat plant with geothermal heat supplied at baseload conditions, levelized costs of approx. 8 cents/kWh are achievable. The presented thermodynamic and cost models are considered helpful instruments for developing preliminary conceptual estimates, strategies for optimization, and portfolio management.

Assessing the Environmental Sustainability of Deep Geothermal Heat Plants

The energy sector is responsible for a large share of climate-damaging emissions. Regarding the decarbonization of the energy sector, deep geothermal energy is considered to have high potential, particularly in the area of heat supply. In order to gauge the extent to which heat use from deep geothermal energy can make a positive contribution to climate protection, deep geothermal systems should be appraised using an environmental sustainability assessment. Although electricity generation from deep geothermal power plants has been evaluated in many ways in the literature with respect to its sustainability, no such sustainability evaluations of pure geothermal heat plants have been conducted so far. In order to close this research gap, this study presents a systematic approach that makes it possible to apply suitable sustainability criteria across the individual life stages of deep geothermal heat plants based on life-cycle assessment (LCA) guidelines. To demonstrate the effectiveness of the systematic approach presented here, a planned geothermal heat plant in the Upper Rhine Valley, Germany, serves as an example. Based on the estimated plant parameters and the predicted total heat yield, it was possible to determine, for example, the “energy returned on energy invested” (EROI) of the plant, which was approximately 34, and the specific CO2 emissions, which were approximately 5.6 g/kWhth.

Structural Architecture and Permeability Patterns of Crystalline Reservoir Rocks in the Northern Upper Rhine Graben: Insights from Surface Analogues of the Odenwald

Fracture network is a crucial element to address in any model of the thermo-hydro-mechanical behaviour of a reservoir rock. This study aims to provide quantified datasets and a further understanding of the critical parameters of the fracture network pattern in crystalline rocks. In the Northern Upper Rhine Graben, such rock units are targeted for multiple energy applications, from deep geothermal heat extraction to heat storage. Eleven outcrops were investigated with a combined LiDAR and 2D profiles analysis to extract faults and fracture network geometrical parameters, including length distribution, orientation, connectivity, and topology. These properties are used to decipher the structural architecture and estimate the flow properties of crystalline units. Fracture networks show a multi-scale power-law behaviour for length distribution. Fracture topology and orientation are mainly driven by both fault networks and lithology. Fracture apertures and permeability tensors were then calculated for two application case studies, including the stress field effect on aperture. Obtained permeabilities are in the range of those observed in the sub-surface in currently exploited reservoirs. The dataset provided in this study is thus suitable to be implemented in the modelling during the exploration stage of industrial applications involving fractured crystalline reservoirs.

Study on Thermo-Hydro-Mechanical Coupling and the Stability of a Geothermal Wellbore Structure

For processes such as water injection in deep geothermal production, heat transfer and fluid flow are coupled and affect one another, which leads to numerous challenges in wellbore structure safety. Due to complicated wellbore structures, consisting of casing, cement sheaths, and formations under high temperature, pressure, and in situ stress, the effects of thermo-hydro-mechanical (THM) coupling are crucial for the instability control of geothermal wellbores. A THM-coupled model was developed to describe the thermal, fluid, and mechanical behavior of the casing, cement sheath, and geological environment around the geothermal wellbore. The results show that a significant disturbance of effective stress occurred mainly due to the excess pore pressure and temperature changes during cold water injection. The effective stress gradually propagated to the far-field and disrupted the integrity of the wellbore structure. A serious thermal stress concentration occurred at the junction of the cased-hole and open-hole section. When the temperature difference between the injected water and the formation was up to 160 °C, the maximum hoop tensile stress in the granite formation reached up to 43.7 MPa, as high as twice the tensile strength, which may increase the risk of collapse or rupture of the wellbore structure. The tensile radial stress, with a maximum of 31.9 MPa concentrated at the interface between the casing and cement sheath, can cause the debonding of the cementing sheath. This study provides a reference for both the prediction of THM responses and the design of drilling fluid density in geothermal development.

Conjugated Numerical Approach for Modelling DBHE in High Geothermal Gradient Environments

Geothermal is a renewable energy source that can be untapped through various subsurface technologies. Closed geothermal well solutions, such as deep geothermal heat exchangers (DBHEs), consist of circulating a working fluid to recover the available heat, with less dependency on the local geological settings than conventional geothermal systems. This paper emphasizes a double numerical method to strengthen the assessment of DBHE performances. A computational fluid dynamics (CFD) commercial software and the 1D coupled wellbore-reservoir geothermal simulator T2Well have been used to investigate the heat transfer and fluid flow in a vertical DBHE in high geothermal gradient environments. The use of constant water properties to investigate the energy produced from DBHEs can lead to underestimating the overall heat transfer at high temperature and low mass flow rate. 2D axisymmetric CFD modelling improves the understanding of the return flow at the bottom of the DBHE, readjusting and better estimating the pressures losses commonly obtained with 1D modelling. This paper highlights the existence of convective cells located at the bottom of the DBHE internal tubing, with no significant effects due to the increase of injected water flow. Both codes are shown to constrain the numerical limitations to access the true potential of geothermal heat extraction from DBHEs in high geothermal gradient environments and demonstrate that they can be used for geothermal energy engineering applications.

Investigation of temperature- and pressure-dependent flow characteristics of supercritical carbon dioxide- induced fractures in Harcourt granite: Application to CO2-based enhanced geothermal systems

The use of supercritical carbon dioxide (ScCO2) as the working fluid in enhanced geothermal systems (EGSs) replacing water has attracted attention recently, due to the favourable properties of ScCO2 in terms of deep geothermal reservoir stimulation, heat transmission and transport properties, and long-term reservoir integrity. However, deep geothermal reservoir stimulation using ScCO2, and the flow behaviour of ScCO2-stimulated reservoirs under the extreme reservoir conditions prevailing in deep underground are poorly understood to date. Therefore, the aim of this study is to investigate thermo-hydro-mechanical and chemical (THMC) flow characteristics of ScCO2-induced fractures under extreme reservoir conditions. A series of flow-through experiments was conducted on ScCO2-fractured Harcourt granite specimens under a range of confining pressures and temperatures from 10–60 MPa, and 25–250ºC, respectively. Importantly, the permeability of ScCO2-fractured rock specimens with multiple fractures with secondary branches, is more than three orders greater than that of water-fractured rock specimens with single plane fractures. Approximately 90% of fracture permeability is reduced with the increase of confining pressure from 10MPa to 50MPa due to the stress-induced fracture closure. However, the temperature influences fracture flow characteristics significantly. The increase of temperature up to 100°C results in 80% reduced fracture permeability due to thermally-induced fracture closure as a result of rock volume expansion. A 5–20% increase in fracture permeability results with the further increase of temperature from 100°C. The gradual increase in fracture permeability occurs due to the coupled hydro-thermo-mechanical and chemical behaviour of the fractured rock specimen. In addition, the enhanced mobility of water at high-temperature conditions in terms of viscosity reduces flow resistance and therefore increases flowability along fractures at high temperatures. The chemical analysis shows that the enhanced dissolution of rock minerals with temperature increase, especially quartz influences in increasing the fracture aperture and permeability. Also, minerals dissolution dominates the precipitation of secondary minerals during fluid flow through fractured rock media in the temperature range of 50–250°C.

Specifying boundary conditions for economical closed loop deep geothermal heat production

Geothermal energy utilization does not depend on weather conditions. Among the various types of heat supplies, ground source heat pumps are the most widely used in the geothermal sector; however, their utilization rate is considerably less than the growth rate of other renewable energy sources. This paper reports an overview of a deep borehole heat exchanger (DBHE) with high-grade vacuum insulated tubing (VIT). Using a computational software, wells with various depths and geothermal gradients are evaluated in the same lithology. The calculation method’s outputs are compared with analytical, semi-analytical and experimental steady state results to show reliability of the developed software. DBHEs are evaluated based on calculated theoretical natural convective mass flow rates (NCMFRs). Considering extended typical well structures with 7″ production casings to surface, the heat performance is evaluated, and revenue requirement (RR) is calculated by employing the theoretical NCMFR. In the calculation depth range of 1200 m–3000 m, geothermal gradient ranges from 40 °C/km to 60 °C/km, and inlet temperatures are 12 °C and 40 °C are considered. Based on the results, reliably profitable depths and geothermal gradient ranges are declared and district heating networks with promising wells are identified. It is concluded that DBHE can be financially viable if integrated into the existing local heat market and infrastructure.

How Can Temperature Logs Help Identify Permeable Fractures and Define a Conceptual Model of Fluid Circulation? An Example from Deep Geothermal Wells in the Upper Rhine Graben

Identifying fluid circulation in fracture zones (FZs) is a key challenge in the extraction of deep geothermal heat from natural reservoirs in the Upper Rhine Graben. This study focuses on permeable FZs present within the granitic basement penetrated by deep geothermal well GPK-1 at Soultz and GRT-1 and GRT-2 at Rittershoffen (France). The various temperature (T) log datasets acquired from these wells during production and at equilibrium, with the associated flow logs, allow for the unique opportunity to interpret fluid circulation at the borehole scale. All permeable FZs identified by permeability indicators measured during drilling operations and from image logs spatially coincide with positive or negative T anomalies observed in the T logs during production and/or at equilibrium. However, within the FZs, partially open fractures act as narrower paths for circulation at different temperatures. These temperatures can even be estimated with confidence if the associated flow log is available. The polarity of the T anomalies correlates with the state of equilibrium of the well and thus can change over the well history. During production, the temperature of the water inflow through the fractures can be estimated relative to the mixture of water circulating below the fractures. At thermal equilibrium, the water temperature is estimated with respect to the temperature of the surrounding rock formation. Because temperature fluxes and geothermal fluids are intimately linked, T logs are a useful, reliable, and very sensitive tool to localize the inflow of geothermal water through FZs.

Life cycle assessment of the carbon intensity of deep geothermal heat systems: A case study from Scotland

Deep geothermal energy is widely recognised as a source of low carbon heat. However, to date there have been no specific assessment of the carbon intensity of low-enthalpy deep geothermal; previous studies focussed on geothermal power or higher enthalpy heat. As such, there is no established method for assessing the CO2 emissions from implementing a deep geothermal heating scheme. Here we address these gaps. We perform a life cycle assessment of greenhouse gas emissions relating to a deep geothermal heat system to (i) calculate the carbon intensity of geothermal heat; (ii) identify key factors affecting these values; (iii) consider the carbon abated if geothermal heat substitutes conventional heating; and (iv) present information that future projects can apply to assess the carbon emissions reduction offered by geothermal heat development. Our work is informed by parameters from a feasibility study for a proposed geothermal heat system in Banchory, Scotland. The project planned a 2.5 MWth geothermal plant extracting heat from the Hill of Fare granite via two boreholes, one injection and one production. We find that the majority of the emissions are associated with site construction, and sensitive to site and materials specific factors, for example the depth of the drilled boreholes and type and quantities of steel and cement used to seal them, or soils disturbed for laying pipelines and constructing access roads. During operation the carbon intensity of the electricity grid used to power hydraulic pumps largely determines the carbon intensity of the produced heat. We calculate that the carbon intensity of the heat produced is 9.7–14.0 kg(CO2e) MWhth which is 4.9–7.3% of the emissions from heat from natural gas. These values are compatible with Scotland's plans for long term decarbonisation of heat in line with national emission reduction obligations and would likely be compatible with any country's decarbonisation goals.

Deep Geothermal Single Well heat production: critical appraisal under UK conditions

The idea of Deep Geothermal Single Well (DGSW) heat production has existed for many years, but with no consensus regarding its potential applicability: proponents have made claims regarding thermal outputs that appear exaggerated, whereas detractors have stated that the concept can never be economic unless the capital cost of drilling has already been discounted. However, because this technology offers the potential of delivering geothermal heat projects ‘off the shelf’ with a minimum of site-dependent research, the possibility exists of achieving cost-effective solutions. The present study sets out to investigate this topic subject to environmental and subsidy regimes applicable in the UK; the results might also be useful for other jurisdictions. Under these conditions, the variant of the technology with greatest potential for cost-effectiveness is the hcDGSW, or conductive DGSW with heat production via heat pump. Analytical modelling enables the physics of the heat-exchange processes within a hcDGSW to be approximated. It is thus established that this option can indeed be cost-effective under the current UK subsidy regime for deep geothermal heat, provided boreholes are deep enough and in localities where the geothermal gradient is high enough. The environmentally optimum operational mode (optimizing savings in CO 2 e emissions) involves heat production at a lower rate than the economically optimum mode (maximizing profit). If such projects are subsidized from public funds, a particular operational mode might be specified, maybe as a compromise between these optima. After the 20-year duration of the subsidy, the technology might well no longer be economic, but the infrastructure might be easily repurposed for seasonal heat storage, thus offering the potential of making a significant long-term contribution to sustainable future heat supply. These preliminary results indicate that more detailed appraisal of this technology variant is warranted.

Impact of technical and economic uncertainties on the economic performance of a deep geothermal heat system

This paper presents a techno-economic analysis of a deep, direct use geothermal heat system in a conductive geological setting (Groningen, NE Netherlands). The model integrates the previously discussed uncertainties of the initial reservoir state, geological and operational conditions with the economic uncertainties. These uncertainties are incorporated in the form of probability distributions and 20,000 iterations of the model are performed over a project lifetime of 40 years. A combination of Ex-Ante and Ex-Post criteria are used to evaluate the economic performance of the system based on the Net Present Value (NPV), Levelised Cost of Heat (LCOH) and Expected Monetary Value (EMV). The sensitivity analysis highlights the load factor (effective flowrate) as the most important parameter for the economic performance and energy costs. However, the differences between the NPV and LCOH sensitivities highlight the importance of using both metrics for the economic performance of such systems. The presented project remains economically challenging, exhibiting a 50% probability of marginal revenues over its lifetime. Systematic insights are drawn with regard to potential improvements of technical and economic aspects of such geothermal heat systems.

Permeable fracture zones in the hard rocks of the geothermal reservoir at Rittershoffen, France

AbstractFluid circulation in zones of fractures are a key challenge to exploit deep geothermal heat from natural reservoir. At Rittershoffen (Upper Rhine Graben, France), two geothermal boreholes, GRT‐1 and GRT‐2, were drilled in 2012 and 2014, respectively. They targeted the local Rittershoffen normal fault, which strikes N‐S and dips westward. In this study, major natural fractures were observed in the open holes of both wells from acoustic image logs correlated with other standard geophysical logs (gamma ray, neutron porosity, and caliper). Their permeability was evaluated at the borehole scale from temperature logs, mud losses, and gas surveys. One originally permeable (OP) fracture zone was observed in the granite of GRT‐1. In GRT‐2, four OP fracture zones were observed in the granite and two in sandstones. In GRT‐2, fracture zones are composed by several fluid pathways that could explain the higher natural permeability than in GRT‐1. All OP fractures are associated with positive temperature anomaly, interpreted as circulation of hot geothermal water through the permeable fracture, or negative one, interpreted as the cooling of a porous, altered and fractured zone around the permeable fracture after drilling operations. Permeability of natural fracture oriented N170° seems to be intimately linked to the secondary mineral deposits resulting from paleocirculations. The geometrical fracture model along the wellbore suggests that the inclined trajectory of GRT‐2 increases the connection between the borehole and the nearly vertical fracture network associated to the local fault. A good characterization of zones of fractures in a targeted natural reservoir allows an optimal exploitation of geothermal resource.

Analysis and 3D inversion of magnetotelluric crooked profile data from central Svalbard for geothermal application

Broadband (0.001–1000s) magnetotelluric (MT) data along a crooked profile collected to investigate the geothermal potential on Spitsbergen could not be fully explained by two-dimensional (2D) models; hence we interpret the data with three-dimensional (3D) inversion herein. To better accommodate 3D features and nearby off profile resistivity structures, the full MT impedance tensor data together with the tipper were inverted. As a model control, a detailed bathymetry is systematically incorporated in the inversion. Our results from testing different inversion settings emphasised that appropriately choosing and tuning the starting model, data error floor and the model regularization together are crucial to obtain optimum benefit from MT field data. Through the 3D inversion, we reproduced out of quadrant impedance components and obtained an overall satisfactory data fit (RMS=1.05). The final 3D resistivity model displays a complex geology of the near surface region (<1.5km), which suggests fractures, localized and regional fault systems and igneous intrusions in the Mesozoic platform cover deposits. The Billefjorden fault zone is revealed as a consistent and deep rooted (>2km) conductive anomaly, confirming the regional nature of the fault. The fault zone is positioned between two uplifted basement blocks (>1000Ωm) of presumably pre-Devonian (Caledonian) metamorphic rocks, and the fault may have been responsible for deformation in the overlying Paleozoic-Mesozoic unit. Upper crustal conductive anomalies (<10Ωm) below the Paleozoic-Mesozoic succession in the western part of the 3D model are interpreted as part of a Devonian basin fill. These conductors are laterally and vertically bounded by resistive rocks, suggesting a conducive environment for deep geothermal heat storage. Having this scenario in an area of a known high heat-flow, deep faults and a thinned lithosphere makes the hypothesis on finding a technologically exploitable geothermal resource close to human settlement in the area stronger.

Performance and Feasibility Study of a Standing Column Well (SCW) System Using a Deep Geothermal Well

Deep geothermal heat pump systems have considerable energy saving potential for heating and cooling systems that use stable ground temperature and groundwater as their heat sources. However, deep geothermal systems have several limitations for real applications such as a very high installation cost and a lack of recognition as heating and cooling systems. In this study, we performed a feasibility assessment of a Standing Column Well (SCW) system using a deep geothermal well, based on a real-scale experiment in Korea. The results showed that the temperature of the heat source increased up to 42.04 °C in the borehole after the heating experiment, which is about 30 °C higher than that of normal shallow geothermal wells. Furthermore, the coefficient of performance (COP) of the heat pump during 3 months of operation was 5.8, but the system COP was only 3.6 due to the relatively high electric consumption of the pump. Moreover, the payback period of the system using a deep well for controlled horticulture in a glass greenhouse was calculated as 6 years compared with using a diesel boiler system.

Effects of plant downtime on the microbial community composition in the highly saline brine of a geothermal plant in the North German Basin.

The microbial biocenosis in highly saline fluids produced from the cold well of a deep geothermal heat store located in the North German Basin was characterized during regular plant operation and immediately after plant downtime phases. Genetic fingerprinting revealed the dominance of sulfate-reducing bacteria (SRB) and fermentative Halanaerobiaceae during regular plant operation, whereas after shutdown phases, sequences of sulfur-oxidizing bacteria (SOB) were also detected. The detection of SOB indicated oxygen ingress into the well during the downtime phase. High 16S ribosomal RNA (rRNA) and dsrA gene copy numbers at the beginning of the restart process showed an enrichment of bacteria, SRB, and SOB during stagnant conditions consistent with higher concentrations of dissolved organic carbon (DOC), sulfate, and hydrogen sulfide in the produced fluids. The interaction of SRB and SOB during plant downtimes might have enhanced the corrosion processes occurring in the well. It was shown that scale content of fluids was significantly increased after stagnant phases. Moreover, the sulfur isotopic signature of the mineral scales indicated microbial influence on scale formation.

Energy performance assessment in urban planning competitions

Abstract Many cities today are committed to increase the energy efficiency of buildings and the fraction of renewables especially in new urban developments. However, quantitative data on building energy performance as a function of urban density, building compactness and orientation, building use and supply options are rarely available during the design of new cities or early scenario analysis for existing city quarters, making it difficult for cities to effectively evaluate which concepts work today and in the future. The paper proposes a methodology to assess the energy demand and supply options as a function of the availability of geometry, building standard and use data. An automated procedure was implemented to identify each building’s geometry and volume and transfer the information to a simulation tool, which then calculates heating demand and solar energy generation on roofs and facades. The simulation includes shading calculations for each segment of the facades and roofs and thus allows a very detailed quantification of the building energy demand. By applying the methodology to a case study city quarter designed in an urban competition in Munich, it could be shown how the urban design influences the energy demand of the quarter and which fractions of renewable energy can be integrated into the roofs. While the building insulation standard and use are the is most important criteria for building energy efficiency (with an impact of more than a factor 2), the exact geometrical form, compactness and urban shading effects influences the energy demand by 10–20%. On the other hand, the detailed roof geometry and orientation influences the possible solar coverage of electricity or thermal needs. Zero energy city quarters with solar resources alone are only possible when all available building surface areas are fully optimized and do not need to fulfill other requirements such as providing roof gardens, terraces or others. Combinations with other more centralized renewable resources such as deep geothermal, solar or biomass heat or cogeneration plants are often necessary to achieve zero energy balances.

Electro-pulse-boring (EPB): Novel super-deep drilling technology for low cost electricity

The inexhaustible heat deposit in great depths (5-10 km) is a scientific fact. Such deposit occurs around the globe. Thereby, everybody is enabled to generate autonomously clean and renew- able energy, ample electricity and heat. The economical exploration and exploitation of this super- deep geothermal heat deposit requires a novel drilling technique, because the currently only deep drilling method (Rotary) is limited to about 5 km, due to the rising costs, depending exponentially on depth. Electro-pulse-boring (EPB) is a valuable option to Rotary drilling. EPB, originally investigated in Russia, is ready to be developed for industrialization. The feasibility of EPB is proven by many boreholes drilled up to 200 m in granite (crystalline). Estimates show outstanding low costs for drilling by EPB: 100 €/m for a borehole with a large diameter (O) such as 20" (50 cm), independent on depth and applicable likewise for sediments and crystalline rocks, such as granite. The current rate of pene- tration (ROP) of 3 m per hour is planned to be augmented up to 35 m per hour, and again, irrespec- tive whether in sedimentary or crystalline formations. Consequently, a 10 km deep borehole with O 50 cm will ultimately be drilled within 12 days. EPB will create new markets, such as: (i) EPB shallow drilling for geotechnics, energy piles, measures in order to mitigate natural hazards, etc., (ii) EPB deep drilling (3-5 km) for hydro-geothermics, exploration campaigns etc. and (iii) EPB super-deep drilling (5-10 km) for petro-geothermics, enabling the economic generation of electricity. The autonomous and unlimited supply with cost efficient electricity, besides ample heat, ensures reliably clean and renew- able energy, thus, high supply security. Such development will provide a substantial relief to cope with the global challenge to limit the climate change below 2 oC. The diminution of fossil fuels, due to the energy transition in order to mitigate the climate change, implies likewise the decrease of air pollution.