Average Heat Production Research Articles

Investigation on a novel hybrid system based on radiative sky cooling and split thermoelectric cooler driven by photovoltaic cell

This paper develops a novel cooling and heating system by integrating a novel split thermoelectric cooler (STEC) with photovoltaic power generation and radiative sky cooling. The system uses photovoltaic driven STEC modules to generate cooling and heating combined with radiative sky cooling to improve cooling capacity. By harnessing the distinctive characteristics of photovoltaic technology and radiative sky cooling, the new system is capable of operating continuously for 24 h without requiring any additional energy input. The system mathematical model is established, and the effects of STEC module number, solar illumination intensity, area ratio and ambient temperature on the performance are studied. Results demonstrate that the cooling efficiency of the system is 3.02 and the heating efficiency is 1.86 when the number of STEC modules is 3. In a year, the monthly average heat production of the system fluctuates due to changes in the solar illumination intensity, while the fluctuation of cooling capacity is small. The system cold production is larger than heat production, which is more suitable for application in the area with high demand for year-round refrigeration. The new system has good energy and economic performance with payback time being shorter than that of the photovoltaic-air conditioning system.

Risk assessment due to natural radioactivity of stone dust and crushed stone Commercialized in construction stores in the state of Rio de Janeiro

A systematic study of the distribution of the Naturally Occurring Radioactivity in stone dust and crushed stone, has been carried out with an objective of establishing reliable baseline data on the radiation level and hence to evaluate hazard indices approach and the production of radioactive heat (RHP) due to radiation exposure to the workers and to the inhabitants of the studied area. Twenty-six samples have been collected from different locations in the State of Rio de Janeiro (Brazil). To calculate the specific activity, gamma ray spectrometry and a detector of High Purity Germanium (HPGe; Canberra, 30% relative efficiency) was used. The activity concentration of 238U, 226Ra 232Th and 40K ranged from 29.3 ± 18.6 to 206.8 ± 21.5 Bq kg−1, 30.3 ± 1.0 to 134.3 ± 1.8, 27.9 ± 0.7 to 86.2 ± 0.9 Bq kg−1, and 734.9 ± 35.1 to 1204.8 ± 53.5 Bq kg−1, respectively. The mean values of the Iex, Iin, Iγ, Iα, AUI, IRP112Rn, IPA, IPI and IYu indices were 0.68 ± 0.09, 0.92 ± 0.12, 0.93 ± 0.12, 0.43 ± 0.07, 0.88 ± 0.20, 1.25 ± 0.21, 0.34 ± 0.05, 0.75 ± 0.10, 0.63 ± 0.08 and 34. ± 6.31, respectively. The average radioactive heat production (RHP) of 2.01 ± 0.28 μ Wm−3 was above the values found in the literature, which may contribute to the heat flow in the study area because the raw materials that make up the samples showed a high value of environmental radioactivity. The Brazilian Hazard Index to assess the radiological risk of crushed stone and stone dust was created and the average value was 0.74 ± 0.10, a value below 1, which means only moderate control over the use of these materials, with no indication of restriction to the its use.

Biogas Production Potential of Mixed Banana and Pineapple Waste as Assessed by Long-Term Laboratory-Scale Anaerobic Digestion

Biogas is a renewable energy source generated through the anaerobic digestion (AD) of organic feedstocks. This study aims to quantify the biogas production potential (BPP) of fruit wastes via semi-continuous lab-scale mesophilic AD over a total of 100 days. The feed was composed of 80% banana peelings and 20% pineapple residues, mimicking the waste composition of a Costa Rican fruit processing facility used as a test case. The average loading rate of volatile suspended solids (VSS) corresponded to 3.6 kg VSS·m−3·d−1. Biogas yield and composition were monitored, along with the concentration of ammonium, volatile fatty acids, and pH. Discounting the start-up phase, the BPP averaged to 526 LN (kg VSS)−1 with a methane concentration of around 54%, suggesting suitability of the substrate for AD. We calculated that if upscaled to the Costa Rican test case facility, these values translate into a gross average heat and electricity production via AD of around 5100 MWhel·a−1 and 5100 MWhth·a−1, respectively. Deducting self-consumption of the AD treatment, this is equivalent to 73% of the facility’s electricity demand, and could save about 450,000 L of heavy oil per year for heat generation. To circumvent nitrogen shortage, the addition of a co-substrate such as dry manure seems advisable.

Radiogenic geothermal systems of Bangka Island, Indonesia: Implications of high heat production and tectonic framework

The presence of geothermal manifestation in Bangka Island (Southeast Sumatra, Indonesia) with the absence of Quaternary volcanic activity and also relatively low seismicity events has raised intriguing questions on the control of the geothermal system in this area. As the regional tectonic setting of Indonesia volcanic geothermal systems has been known, that of non-volcanic geothermal systems such as radiogenic system become an issue to be investigated. This study reports the geochemistry and petrography analysis of Triassic granite related to radiogenic production at the vicinity of hot springs in Bangka Island. Surface temperatures of the Bangka hot springs range from 37 to 70.7 °C and pH values vary between 5.6 and 7.5. These hot springs are discharging either in close to massive granite bodies or occur in between two major NE-SW striking faults zones, i.e., Pemali fault and Payung fault. Our results indicate the average radiogenic heat production of Late Triassic Klabat granite in the northern area ranges from 28.5 to 38.34 μWm−3 and the southern area ranges from 28.3 to 49.5 μWm−3. In comparison to similar granite belt located in Malaysia, heat production of granitoid in Bangka hot springs is four times higher, possibly due to their different granite origins.

Petrogenesis of high heat producing granites and their contribution to geothermal resource in the Huangshadong geothermal field, South China

The Huangshadong geothermal field (HGF), situated in the contact zone between Mesozoic granites and NE-striking dominant faults in South China, has great geothermal potential. Petrogenesis of reservoir rock plays an important role in understandings its genetic mechanism and assessing geothermal potential. However, due to the lack of rock sample at depth collected from the geothermal reservoir, the petrogenesis of granites in the geothermal reservoirs of the HGF, remains an enigma. This study elucidated the petrogenetic characteristics of these granites sampled directly from geothermal reservoir at the depth of ∼3,000 km and their geothermal implications through zircon U-Pb dating, geochemical analysis, and Hf isotopic analysis. The zircon U-Pb ages indicate that the magmatism evolution of HGF contains three eras, namely, Cretaceous (135 ± 4 to 143.6 ± 2.8 Ma), Jurassic (152.7 ± 2.7 to 176.7 ± 1.8 Ma), and Permian granites (251 ± 9.1 to 251 ± 5 Ma) from the youngest to oldest. The reservoir granites were emplaced during the latest stage of Cretaceous intrusion, as indicated by the zircon U-Pb ages (135 ± 4 Ma and 135.3 ± 2.4 Ma) of rock samples from the deep part of well HR-1. These Cretaceous rocks are highly fractionated I-type granites, featuring high SiO2, K2O, and Na2O contents, high Rb/Sr ratios, low Zr/Hf, Nb/Ta, and Th/U ratios, and A/CNK values of 1.05–1.13. Compared to other Cretaceous granites outcropping on the margin of the HGF, these granites have undergone the strongest fractional differentiation. The Cretaceous granites in the HGF are high-heat-producing rocks (>5 μW/m3), with an average heat production rate of 6.63 μW/m3. Notably, the Cretaceous reservoir granites (as reservoir rocks) serve as an important heat source for the formation of geothermal resources in the HGF. In addition, the zircon Hf isotopic composition indicates that the reservoir Cretaceous granites originated from Meso-to Paleo-Proterozoic lower crustal materials (TDM2: 1,385 to 1907 Ma).

Contributions of 238U, 232Th, and 40K to the radiogenic heat production in selected river sediment samples of South Africa

In this study, 16 sediment samples were collected from Bree, Klein-Brak, Bakens and uMngeni rivers of South Africa and were prepared, analysed and evaluated for the activity concentration of 238U, 232Th and 40K concerning its radiogenic heat production using a high-purity germanium detector. The results show that 238U is the prevalent radionuclide in radiogenic heat production, with 232Th and 40K emerging as trace elements. The mean activity concentrations are 28.97%, 63.69% and 7.34% for uranium, thorium and potassium, respectively, from all sampling locations. This shows that a high radioactive concentration of a specific radionuclide does not necessarily imply its increased contribution to radiogenic heat production. The radionuclide contributions to radiogenic heat production at all sampled locations are 59.39%, 35.11% and 5.50% for uranium, thorium and potassium, respectively. The mean radiogenic heat production rate in the study area ranged from 0.0180 μW m − 3 in sediment samples from the Bree River in Western Cape to 0.0072 μW m − 3 in sediment samples of uMgeni River in KwaZulu-Natal. All values obtained for this study are five times lower than the average continental radiogenic heat production of 1 μW m − 3 . This study provides insight into the radiogenic heat production rate due to the presence of radionuclides in all river samples.

Radioelement abundances and heat production in the paleoarchaean and early neoarchaean granitoids of the Singhbhum Craton, eastern India: thermal and geodynamic implications

Summary Distributions of long-lived radioelements (Th, U, K) in the upper crust play a vital role in lithospheric thermal modeling and understanding of underlying geodynamic processes. In the present study, we report Th, U, K and radiogenic heat production (A) in Paleoarchaean and early Neoarchaean granitoids from the Singhbhum Craton, located in the eastern part of the Indian shield, for the first time in a systematic way, using laboratory gamma-ray spectrometric set-up. We have studied 204 samples consisting of Paleoarchaean gneiss, three phases of Paleoarchaean Singhbhum Granite and early Neoarchaean granitoid. Th, U, K and A in the Paleoarchaean Singhbhum Granite (10.8 ppm, 1.4 ppm, 2.4 per cent, and 1.3 μWm−3, N = 115) are found to be marginally higher than the Paleoarchaean gneiss (9.6 ppm, 1.7 ppm, 1.8 per cent, and 1.3 μWm−3, N = 74). In comparison, such values are much higher in the early Neoarchaean granitoid (31.1 ppm, 4.2 ppm, 3.9 per cent, and 3.6 μWm−3, N = 15). The surface heat production (1.36 μWm−3) of this craton is comparatively low compared to most cratons worldwide. In addition, it has the lowest average crustal heat production (0.42 µWm−3), due to which it will contribute little to the observed surface heat flow. Moreover, Th is a dominant component in heat production, followed by U and K in these granitoids. Spatially, radioelement ratios Th/U and K/U show similar trends as the radioelements, indicating systematic depletion of Th and U, compared to K. The study also indicates that the spatially separated coeval granitoids are formed from different magma sources in the heterogeneous crust that prevailed during the Archaeans. The lower radioelement abundances in the Paleoarchaean granitoids mostly resulted from the partial melting of mafic sources, whereas higher radioelement abundances in the early Neoarchaean granitoids resulted from the partial melting of the felsic source.

Development of a novel induction-heated reactor to enhance the performance of waste tires pyrolysis

Waste tire pyrolysis (WTP) is well-known as a promising technique for waste tires (WTs) management. However, the requirements of high cost and intense energy, as well as steel wire stripping remain the major drawbacks for the widespread applications of WTP technologies. In this research, a novel induction-heated pyrolysis (IHP) reactor has been developed to enhance the performance of WTP and the results were compared with a conventional fixed bed pyrolysis (FBP) reactor. The performance of the IHP reactor has been evaluated using three different feedstocks of sidewall (no steel wire), tread section (20% steel wire), and real mode (14% steel wire) at two different sizes of A and B. The results revealed that the presence of steel wire in the IHP reactor not only reduced the effect of WTs particles size, but also improved the average heat and oil production rate up to 36 % and 60 %, respectively through better heat distribution. The minimum REC (13.03 KJ/g) was achieved for the tread section after 12 min of the IHP process. The comparison of the results of the IHP reactor and the FBP reactor proved that using IHP reactor could significantly improve the performance WTP in terms of optimum heating time, heat rate, REC and power consuming cost up to 68 %, 44 %, 56 % and 61 % respectively. The findings of this study suggest IHP reactor which eliminates the need of stripping steel wires as novel and promising approach for sustainable WTs management.

Development of a Mobile Open-Circuit Respiration Head Hood System for Measuring Gas Exchange in Camelids in the Andean Plateau.

Peru has the largest inventory of alpacas worldwide. Despite their importance as a source of net income for rural communities living at the Andean Plateau, data on energy requirements and methane (CH4) emissions for alpacas are particularly lacking. In 2019, the International Panel on Climate Change (IPCC; 2006, and Refinement 2019) outlined methods for estimating CH4 emissions from enteric fermentation and no methane (CH4) conversion factors were reported for camelids. IPCC has since updated its guidelines for estimating CH4 emissions from the enteric fermentation of livestock at a national scale. For greenhouse gas (GHG) inventory purposes, conversion factors were developed for ruminants but not for domestic South American camelids (SAC), with this category including alpacas. A mobile open-circuit respirometry system (head hood) for the rapid determination of CH4 and CO2 production, O2 consumption, and thereafter, heat production (HP) for camelids was built and validated. In addition, an experimental test with eight alpacas was conducted for validation purposes. The average HP measured by indirect calorimetry (respiratory quotient (RQ) method) was close to the average HP determined from the carbon-nitrogen balance (CN method); 402 kJ/kg BW0.75 and 398 kJ/kg BW0.75, respectively. Fasting HP was determined by the RQ method and 250 kJ/kg BW0.75 was obtained. The metabolizable energy requirement for maintenance (MEm) was calculated to be 323 kJ/kg BW0.75 with an efficiency of energy utilization of 77%. When intake was adjusted to zero energy retention by linear regression, the MEm requirement increased to 369 kJ/kg BW0.75 and the efficiency decreased up to 68%. The CH4 conversion factor (Ym) was 5.5% on average. Further research is required to gain a better understanding of the energy requirements and CH4 emissions of alpacas in conditions of the Andean Plateau and to quantify them with greater accuracy.

Enhanced heat extraction performance from deep buried U-shaped well using the high-pressure jet grouting technology

Heat extraction from the single-well geothermal heating system (SWGHS) is significantly restricted by the high thermal resistance of the surrounding host rocks. To improve heat production efficiency of this geothermal system, the high-pressure jet grouting (HPJG) technology is proposed to enhance thermal output in deep buried U-shaped well (DBUSW) system. By means of this technology, an artificial jet grouting column (JGC) with high thermal conductivity is built near the horizontal well segment. The emphasize of this work is to evaluate the feasibility and efficiency of the proposed heat production method. Numerical simulations were conducted via a field validated model from in-situ experiments in Xian. Results demonstrated that average annual heat production rate is improved by about 22% in the 30-year heating period, with building an artificial JGC with 1.0 m radius near the wellbore. These results indicate that the proposed method is a promising strategy for enhancing thermal output in the DBUSW. Sensitivity analyses suggest heat production rate and outlet temperature are mainly controlled by the radius of the JGC, while very high JGC thermal conductivity has less effect. Given the field conditions, the suggested thermal conductivity and radius of artificial JGC is 30 W/m °C and 2.0 m, respectively.

Geothermal regime and implications for basin resource exploration in the Qaidam Basin, northern Tibetan Plateau

• Geothermal field characteristics of the Qaidam Basin, northeastern Tibetan Plateau, were analysed. • The crustal contribution to the surface heat flow was approximately 55%. • The existence of abnormally high-temperature zones significantly dominated the hydrocarbon distribution. • The Qaidam Basin is favourable for low- and medium-temperature geothermal resources development. • Certain deep high-temperature geothermal resource is prospective if using abandoned oil wells. The Qaidam Basin was formed under the background of the continuous uplift of the Tibetan Plateau, and its tectonic location imparts unique geothermal regime. The geothermal regime of the Qaidam Basin was studied based on oil-test static temperatures from 60 wells, 195 thermal conductivities measured by the optical scanning method, and 142 radiogenic heat production values. The geothermal gradient in the Qaidam Basin is 17.1–47.6 °C/km, with an average of 31.3 °C/km, and the thermal conductivity is 0.523–4.379 W/m‧K. The heat flow is 28.3–83.1 mW/m 2 , with an average of 59.6 mW/m 2 , and it is “high in the west and low in the east.” The heat flow can exceed 70 mW/m 2 in the northern marginal fold-and-thrust belt of western Kunlun and Nanyishan and generally exceeds 65 mW/m 2 in the Mangya Depression. The average radiogenic heat production rate (HPR) is 2.53 μW/m 3 , which is close to the HPR of granite in northern Tibetan Plateau. The crustal and mantle heat flows in the Qaidam Basin are 32.9 mW/m 2 and 26.7 mW/m 2 , respectively. The crustal contribution to the surface heat flow was approximately 55 %. The geothermal regime may be dominated by lithospheric thickness, HPR of sedimentary cover, and extra heat production related to late Cenozoic tectonic movement. The proven hydrocarbon reserves are primarily distributed around hydrocarbon-generating kitchens, and the existence of abnormally high-temperature zones significantly influences hydrocarbon distribution. The Qaidam Basin satisfies the fundamental temperature conditions for the development of low- and medium-temperature geothermal resources using abandoned oil and gas drilling wells.

Characterizing the Effects of High Fat and High Carbohydrate Diets on Feeding Behavior and Energy Expenditure in Mice

ObjectiveWe sought to characterize how different compositions of the diet can alter feeding behavior and energy expenditure in mice, ultimately driven by changes in sympathetic activation and thermogenesis.HypothesisMice on a high fat diet (HFD) will consume more calories/day compared to high carbohydrate diet (HCD) and standard chow fed mice. Mice on HFD will have decreased expression of UCP1 in both brown and white adipose tissue. There will be decreased expression for several lipolytic enzymes in the white adipose of HFD mice.MethodsA total of 21 mice were divided into three ad libitum fed diet groups: HFD, HCD, and standard chow. Each group was fed their respective diet for 7 weeks. Changes in weight and percent body fat were recorded by NMR. At week 5, glucose tolerance tests were performed on all mice. Both a 24‐hour heat production and respiratory exchange ratio were collected on each group using a metabolic cage system. Mice were sacrificed at the conclusion of week 7 and organs were collected for molecular analysis.ResultsWe show that mice on both ad libitum HFD and HCD consume significantly more calories/day when compared to standard chow. Both HFD and HCD fed mice have a significantly increased body weight and percent body fat when compared to standard chow; however, the HFD mice had a far greater increase in weight compared to HCD fed mice despite no difference in calorie consumption. Mice on a HFD had a lower 24‐hour average heat production per body mass when compared to standard chow and HCD mice and a significantly impaired glucose tolerance test. Furthermore, UCP1 mRNA expression is significantly elevated in brown adipose tissue (BAT) of HCD mice compared to that of HFD and standard chow mice. There were no differences in UCP1 expression in subcutaneous or visceral white adipose tissue (WAT) among all groups. There were also no differences in tyrosine hydroxylase (TH) expression in BAT between all mice. Three markers of lipolysis were decreased in visceral WAT of HFD mice compared to HCD and standard chow counterparts.DiscussionMice consumed significantly more calories when fed a HFD or HCD. These mice gain significantly more weight compared to chow with HFD mice gaining weight far more than the HCD group. This major difference in weight gain despite no significant difference in calorie consumption between HFD and HCD suggests differences may be determined by energy expenditure. This evidence is further supported by the fact that HFD fed mice had a significantly lower daily heat production compared to HCD and standard chow mice. We also show that HCD increases thermogenesis in mouse BAT which may be protective against weight gain. Finally, lipolysis signaling seems to be impaired in HFD mice, but no data supports that this is due to differences in sympathetic activation. Further work will include analyzing the same tissues in isocaloric, restricted diet fed mice.

Study on the influence of randomly distributed fracture aperture in a fracture network on heat production from an enhanced geothermal system (EGS)

In the attempt to reduce the CO2 emissions to the atmosphere and therefore the dependence on fossil fuels, geothermal energy has started to receive increased scientific interest. With the development of the Enhanced Geothermal System (EGS) technology, extensive geothermal energy applications have become feasible. However, enhanced geothermal reservoirs are usually situated several kilometers below the ground, which makes their experimental investigation challenging. Therefore, numerical models capable of simulating thermohydraulic (TH) effects are an essential additional tool for analyzing geothermal reservoir efficiency. To simulate fluid migration and heat propagation within a fractured geothermal reservoir in EGS, discrete fracture models (DFMs) of the TH processes are widely used. However, the variability of aperture size from one fracture to another is typically ignored in these models. In this work, a discrete fracture model considering variable aperture fractures is presented and used to investigate the performance of a geothermal reservoir in EGS. The outlet temperature and energy production rate are used as the evaluation criteria. Statistically generated fracture networks with different apertures were applied. The fractures are represented as lower-dimensional elements. The fracture apertures are randomly distributed within the networks, but constant for one single fracture. The simulation results show that the coefficient of variation of the DFN apertures strongly affects the performance of the geothermal reservoir. The heat production rate and outlet temperature can be divided into three stages based on the value of coefficient of variation of fracture apertures. The higher variability results in the low heat production rate but high outlet temperature. The investigation on fracture density in turn indicates that the average heat production rate is proportional to the fracture density. However, the effect of fracture density is reduced with an increase of coefficient of variation. Furthermore, the comparison between fracture aperture and fracture density shows that, the increase in mean fracture aperture leads to a higher increase in average heat production rate than an increase in fracture density.

Performance evaluation of novel photovoltaic and Stirling assisted hybrid micro combined heat and power system

Since both heat and electricity are produced in the cogeneration system, residential heating can be done independently from the grid. Stirling engine is proposed to use for rural areas where electricity cannot reach. It can be used also for independence from power cuts and increasing energy security and distributed energy production. In this study a novel micro-combined heat and power production system (μ-CHP) which consisted of photovoltaic modules (PV), Beta type Stirling engine and coal-fired boiler was designed and manufactured to heating of multi-family house in Muğla, Turkey. Performance and economic analyses of μ-CHP system were performed. The daily average electricity production of Stirling engine and PV was 3.126 kWh. The daily average heat production of Stirling engine and coal boiler was 985.97 kWh. Average thermal efficiencies of the μ-CHP system with and without Stirling engine were 31.78% and 30.78%, respectively. Average Carnot efficiency of the Stirling engine was 30.2%. Electricity was charged in battery. Electricity need of auxiliary equipment of the heating system was met from battery. Thus, μ-CHP system can be used for residential heating independently from the grid, especially in rural areas. This study will provide insight using μ-CHP systems in residential heating and real conditions.

Decarbonization strategies of Helsinki metropolitan area district heat companies

District heating is of great significance for the Nordic countries due to the high heat demand. The Finnish government has set a national target of carbon neutrality in 2035. This implies a huge challenge and rapid system change. The Helsinki metropolitan area consists of Helsinki, Espoo and Vantaa, and in each city a different district heating company operates, and the technologies planned for decarbonization are different. This research aims to analyze these strategies with respect to carbon dioxide emissions and production costs, assuming different future European Union emissions carbon trading prices. The software EnergyPRO is used to provide least-cost optimal district heating operation solutions. From 2010 to 2030, carbon dioxide emissions from the Helsinki metropolitan area district heating will decrease by about 4.2 million tonnes. However, the average heat production costs are expected to increase considerably by almost threefold; while heat trade between the cities will reinforce the feasibility and decreases the system operation costs and total emissions. Helsinki will import heat, especially from Vantaa waste incineration plants. Higher carbon dioxide prices would reduce the total emissions, increase the total district heating operation costs, and lower the heat imported to Helsinki. As all the cities plan biomass as an alternative to fossil fuels, a higher biomass price would limit its consumption but increase natural gas usage the carbon dioxide emissions. In the future, combined heat and power plants will be used significantly less, leading to lost income on electricity sales and profoundly changing the business of the district heating companies.

Radiogenic heat production from natural radionuclides in sediments of the Tigris river in Mosul City, Iraq

In this paper, the concentration of the activity of natural radionuclides is represented by 238U, 232Th and 40K. This concentration was measured by gamma spectroscopy, which was used to determine and calculate radioactive heat production for all radionuclides and their distribution pattern in the sediment samples from the Tigris River in Iraq. The results showed that the activity concentration of these radionuclides was within the allowed limits by the UNSCEAR. Field observations show that the sediments occurred due to the weathering of pre-existing sedimentary rocks that make up the area's geology. The estimated average radiogenic heat production rate was 0.3634 µW/m³. It ranged from 0.2430 to 0.6453 µW/m³, and within the internationally permissible limits, the radiogenic heat production rate in Tigris River sediments was low. It is recommended to conduct a comprehensive radiometric survey to cover all the areas through which the Tigris River passes in Iraq. It will help characterise the radiogenic heat produced for each geological area.

Techno-Economic Performance of Closed-Loop Geothermal Systems for Heat Production and Electricity Generation

• Closed-loop geothermal systems evaluated for heat and electricity production • Slow heat transfer in rock and limited heat transfer area pose challenges • Targeting high temperatures, existing wells, and multi-laterals beneficial • Relatively high levelized costs for greenfields, unless drilling at low cost Closed-loop geothermal systems, recently referred to as advanced geothermal systems (AGS), have received renewed interest for geothermal heat and power production. These systems consist of a co-axial, U-loop, or other configuration in which the heat transfer or working fluid does not permeate the reservoir but remains within a closed-loop subsurface heat exchanger. Advocates indicate its potential for developing geothermal energy anywhere, independent of site-specific geologic uncertainties, and with limited risk of induced seismicity. Here, we present a technical and economic analysis of closed-loop geothermal systems using a Slender-Body Theory (SBT) model, COMSOL Multiphysics simulator, and the GEOPHIRES analysis tool. We consider a number of different scenarios and evaluate the influence of variations in reservoir temperature (100 to 500℃), well termination depth (2 to 4 km), mass flow rate (10 to 40 kg/s), injection temperature (10 to 40℃), fluid type (liquid water vs. supercritical carbon dioxide), design configuration (co-axial vs. U-loop), and degree of reservoir convection (natural, forced or conduction-only). The resulting average heat production rates range from about 2 to 15 GWh per year for cases considering a co-axial design and from 9 to 67 GWh per year for cases with a U-loop design. Assuming generous economic and operating conditions, estimates of levelized cost of heat range from ∼$20 – $110 per MWh (∼$6 – 32/MMBtu) and ∼$10 – $70 per MWh (∼$3 – $20/MMBtu) for greenfield co-axial and U-loop cases, respectively. In the scenarios in which electricity generation is considered, annual electricity production ranged between 0.12 and 7.5 GWh per year at a levelized cost of electricity from roughly $83 to $2,200 per MWh. In all scenarios, the results exhibit a large rapid drop in production temperature after initiation of operations that levels off to a steady value significantly below the initial reservoir temperature. Operating at lower flow rate increases the production temperature but also lowers the total heat production. The consistently low production temperatures hinder efficient electricity generation in most cases considered. Natural or forced convection can increase thermal output but requires sufficiently high reservoir permeability or formation fluid flow. As expected, overall system costs are heavily dependent on drilling costs; hence, repurposing existing wells could significantly lower capital and levelized costs. In comparison with other types of geothermal systems, our results for closed-loop geothermal systems predict long-term production temperatures considerably below the initial reservoir temperature, and relatively high levelized costs for greenfield closed-loop geothermal systems, particularly for electricity production, unless significant reductions in drilling costs are obtained.

Evaluation of deep geothermal exploration drillings in the crystalline basement of the Fennoscandian Shield Border Zone in south Sweden

The 3.1- and 3.7-km-deep FFC-1 and DGE-1 geothermal explorations wells drilled into the Precambrian crystalline basement on the southern margin of the Fennoscandian Shield are evaluated regarding experiences from drilling, geological conditions, and thermal properties. Both wells penetrate an approximately 2-km-thick succession of sedimentary strata before entering the crystalline basement, dominated by orthogneiss, metabasite and amphibolite of the (1.1–0.9 Ga) Eastern Interior Sveconorwegian Province. The upper c. 400 m of the basement is in FFC-1 severely fractured and water-bearing which disqualified the use of percussion air drilling and conventional rotary drilling was, therefore, performed for the rest of the borehole. The evaluation of the rotary drillings in FFC-1 and DGE-1 showed that the average bit life was very similar, 62 m and 68 m, respectively. Similarly, the average ROP varied between 2 and 4 m/h without any preferences regarding bit-type (PDC or TCI) or geology. A bottomhole temperature of 84.1 °C was measured in FFC-1 borehole with gradients varying between 17.4 and 23.5 °C/km for the main part of the borehole. The calculated heat flow varies between 51 and 66 mW/m2 and the average heat production is 3.0 µW/m3. The basement in FFC-1 is, overall, depleted in uranium and thorium in comparison to DGE-1 where the heat productivity is overall higher with an average of 5.8 µW/m3. The spatial distribution of fractures was successfully mapped using borehole imaging logs in FFC-1 and shows a dominance of N–S oriented open fractures, a fracture frequency varying between 0.85 and 2.49 frac/m and a fracture volumetric density between 1.68 and 3.39 m2/m3. The evaluation of the two boreholes provides insight and new empirical data on the thermal properties and fracturing of the concealed crystalline basement in the Fennoscandian Shield Border Zone that, previously, had only been assessed by assumptions and modelling. The outcome of the drilling operation has also provided insight regarding the drilling performance in the basement and statistical data on various drill bits used. The knowledge gained is important in feasibility studies of deep geothermal projects in the crystalline basement in south Sweden.

Heat flow constraints on the mafic character of Archean continental crust

The bulk composition of the continental crust can be constrained from its surface heat flow. Published values of heat flow and heat production from 17 areas ranging in age from 3.3 to 0.4 Ga are compared. In the Superior province, the ca. 2.7 Ga accreted belts have a heat flow of 41mWm−2, significantly higher than that in the older, ca. 3.0 Ga, craton core (32mWm−2) (Jaupart et al., 2014). The mean surface heat flow values are 40±1.2mWm−2 for the Archaean areas, and 53±1.9mWm−2 for the post-Archaean. Heat flow values into the base of the crust are constrained from P-T estimates in lithospheric mantle xenoliths, and subtracted from the surface heat flow to calculate the bulk crustal heat production, whereupon there is a strong correlation between the surface heat flow data and the calculated average bulk crustal heat production values. Average crustal heat production values are described in terms of two component mixtures of felsic crust with >57% SiO2, and mafic crust with <57% SiO2, which is suggested to be more robust than relying on an average seismic model, given the complexity of the crustal structure and how it varies between provinces, and sometimes within a single province. The proportions of the mafic crustal component required to account for the regional bulk heat production values in 5 areas older than 2.8 Ga range from 60–78% consistent with a fixed mafic proportion of ∼70%. This is higher than the proportion of lower, mafic crust in the present bulk crust of Rudnick and Gao (2014), which is 43%, and the estimated bulk crust MgO values change from 10–6.6% in areas older than 2.8 Ga, to ∼5% MgO for the younger areas. The bulk crust in the late Archaean was on average more mafic than the bulk crust at the present day, and it had a bulk crust Rb/Sr value of 0.12±0.04.

Applying Harmonised Geothermal Life Cycle Assessment Guidelines to the Rittershoffen Geothermal Heat Plant

Heat production from a geothermal energy source is gaining increasing attention due to its potential contribution to the decarbonization of the European energy sector. Obtaining representative results of the environmental performances of geothermal systems and comparing them with other renewables is of utmost importance in order to ensure an effective energy transition as targeted by Europe. This work presents the outputs of a Life Cycle Assessment (LCA) performed on the Rittershoffen geothermal heat plant applying guidelines that were developed within the H2020 GEOENVI project. The production of 1 kWhth from the Rittershoffen heat plant was compared to the heat produced from natural gas in Europe. Geothermal heat production performed better than the average heat production in climate change and resource use, fossil categories. The LCA identified the electricity consumption during the operation and maintenance phase as a hot spot for several impact categories. A prospective scenario analysis was therefore performed to assess the evolution of the environmental performances of the Rittershoffen heat plant associated with the future French electricity mixes. The increase of renewable energy shares in the future French electricity mix caused the impact on specific categories (e.g., land use and mineral and metals resource depletion) to grow over the years. However, an overall reduction of the environmental impacts of the Rittershoffen heat plant was observed.