The feasibility of using geothermal energy in hydrogen production

A feasibility study exploring the use of geothermal energy in hydrogen production is presented. It is possible to use a thermal energy to supply heat for high temperature electrolysis and thereby substitute a part of the relatively expensive electricity needed. A newly developed HOT ELLY high temperature steam electrolysis process operates at 800 – 1000°C. Geothermal fluid is used to heat fresh water up to 200°C steam. The steam is further heated to 900°C by utilising heat produced within the electrolyser. The electrical power of this process is reduced from 4.6 kWh per normalised cubic meter of hydrogen (kWh/Nm³ H₂) for conventional process to 3.2 kWh/Nm³ H₂ for the HOT ELLY process implying electrical energy reduction of 29.5%. The geothermal energy needed in the process is 0.5 kWh/Nm³ H₂. Price of geothermal energy is approximately 8–10% of electrical energy and therefore a substantial reduction of production cost of hydrogen can be achieved this way. It will be shown that using HOT ELLY process with geothermal steam at 200°C reduces the production cost by approximately 19%.     

Research and development of geothermal energy production in Hungary

The basement of the Pannonian (Carpathian) basin is represented by Paleozoic metamorphic and Mesozoic dolomite and limestone formations. The Tertiary basin gradually subsided during the Alpine orogeny down to 6000 m and was filled by elastic sediments with several water horizons.A heat flow of 2.0 to 3.4 μcal/cm²s gives temperature gradients between 45 and 70 °C/km in the basin. At 2000 m depth the virgin rock temperature is between 110 and 150°C. 80 geothermal wells about 2000 m deep have shown the great geothermal potential of the basin.The main hot water reservoir is the Upper Pliocene (Pannonian) sandstone formation. Hot water is produced by wells from the blanket or sheet sand and sandstone, intercalated frequently by siltstone. Between a 100–300 m interval, 3 to 8 permeable layers are exploited resulting in 1–3 m³/min hot water at 80–99°C temperature.Wells at present are overflowing with shut-in pressures of 3–5 atm.The Pannonian basin is a conduction-dominated reservoir. Convection systems are negligible, hot igneous systems do not exist. The assessment of geothermal resources revealed that the content of the water-bearing rocks down to 3000 m amounts to 12,600 × 10¹⁸cal. In the Tertiary sediments 10,560 × 10¹⁸cal and in the Upper Pannonian, 1938 × 10¹⁸cal are stored. In the Upper Pannonian geothermal reservoir, below 1000 m, where the virgin rock temperature is between 70 and 140°C, the stored heat is 768 × 10⁸cal. A 10¹⁸ cal is equivalent to the combustion heat of 100 million tons of oil. The amount of recoverable geothermal energy from 768 × 10⁸cal is 7.42 × 10¹⁸cal, i.e. about 10,000 MW century, not considering reinjection.At present the Pannonian geothermal reservoir stores the greatest amount of identified heat which can be mobilized and used. Hungary has 496 geothermal wells with a nominal capacity of 428 m³/min, producing 1342 MW heat. 147 wells have an outflow temperature of more than 60°C producing 190 m³/min, that is, 845 MW. In 1974 290 MWyear of geothermal energy was utilized in agriculture, district heating and industry.     

Chemical and isotope characteristics of the Chachimbiro geothermal fluids (Ecuador)

The parent geothermal water proposed for the Chachimbiro geothermal area has calculated values of 2250 mg/L Cl and approximately 5 bar P_CO2. It comes from a reservoir having an estimated temperature of 225–235 °C, although temperatures somewhat higher than 260 °C may be present at the roots of the system. The geothermal reservoir at Chachimbiro is recharged mainly by meteoric water (about 92%) and secondarily by arc-type magmatic water. Carbon and sulfur isotope data support a magmatic origin for the C and S species entering the geothermal system from below, consistent with indications provided by He isotopes.The thermal springs of Na–Cl to Na–Cl–HCO₃ type located in the Chachimbiro area originate through dilution of the parent geothermal water and have reached different degrees of re-equilibration with country rocks at lower temperatures.     

Hot spring activity in the Dakongbeng geothermal area, China

The Dakongbeng geothermal area, whose hot springs reach a temperature of up to 96°C, has been considered one of the potential high-temperature hydrothermal systems in south-west China. The concentration of dominant cations and anions indicates an NaHCO₃ type of thermal water, whose major constituents in decreasing order are: Na>K>Ca>Mg, HCO₃>SiO₂>Cl>SO₄. On the basis of the silica geothermometer, cation geothermometers, gas geothermometer and activity diagram, the reservoir temperature is estimated at about 200°C. All the thermal waters have originated from meteoric water of a higher altitude that circulated as ground water at considerable depth along faults. The stability of their contents of Cl, SiO₂, δD, δ¹⁸O and of the Cl/B, Na/Li ratios suggests that the main heat loss process is through steam loss. The geochemistry of the initial liquid has been estimated by single and continuous steam loss. On the basis of its geologic and geographic setting, the Dakongbeng geothermal area appears to belong to the Himalayan geothermal belt and is thus regarded as an area of interest for further study.     

Sodium/lithium ratio in water applied to geothermometry of geothermal reservoirs

We propose here a new geothermometer for natural waters. Analyses from many explored geothermal fields allow us to define two empirical thermometric relationships.One is for waters of low to moderate salinity (Cl⁻< 0·3 M) log Na/Li = 1000/T −0·38 and one for marine waters and brines (Cl⁻ > 0·3 M) log Na/Li = 1195/T + 0·38 These relationships, which at present are not well understood, result mainly from the increase of Li concentrations in waters with temperature.Equation (a) proved to be adequate for spring waters from mostly known geologic origin; this is an important feature in geochemical surveys for geothermal prospecting.Furthermore, when comparison between springs and drillhole chemistry of a given geothermal field is possible, the Na/Li geothermometer gives more reliable temperature estimates from the spring compositions than do classical geothermometers.     

Geoelectric study of some indian geothermal areas

The electrical resistivity technique has been used extensively in the Indian sub-continent for the exploration of geothermal areas. The first systematic application of the resistivity method for locating the geothermal reservoir was made in the Puga area, which is situated very close to the collision junction of the Indian and the Asian plates and has numerous hot springs with temperatures varying from 30 to 84°C (boiling point at that altitude). The resistivity depth probes indicated the presence of a conductive zone, with a value of 10–25 ohm·m and a thickness varying from 50 to 300 m over an area of 3 km², which was inferred to correspond to a shallow thermal reservoir. Thermal surveys also revealed a significant anomaly corresponding to this zone, which, when drilled, encountered a reservoir of wet steam with a temperature of up to 135°C, thus confirming the results of the resistivity surveys. Somewhat similar results have been obtained in the adjoining area, where much thicker zones with moderate electrical conductivity have been mapped.Another significant application of the electrical resistivity method has been made in the NNW-SSE extending West Coast geothermal belt of India, which is covered by Traps (Basalts) of the Cretaceous-Eocene. The area is characterized by the existence of a number of hot springs, with temperature up to 70°C, along a 400 km long alignment, associated with steep gravity gradients and an isolated occurrence of native mercury in the zone of a gravity “high”. The enigmatic geology of this area has been mapped, giving quantitative estimates of the thickness of the Traps and inferring the structural features. In addition, the electrical resistivity depth probes have also been used to identify the pre-Trappean geology, thereby locating the probable areas which could act as geothermal reservoirs.This paper presents the results of the electrical resistivity surveys in the form of geoelectric sections for some of the geothemal fields in the Indian sub-continent.     

Geothermal development in Hungary—country update report 2000–2002

This paper describes the status of geothermal energy utilization—direct use—in Hungary, with emphasis on developments between 2000 and 2002. The level of utilization of geothermal energy in the world increased in this period and geothermal energy was the leading producer, with 70% of the total electricity production, of all the renewable energy sources (wind, solar, geothermal and tidal), followed by wind energy at 28%. The current cost of direct heat use from biomass is 1–5 US¢/kWh, geothermal 0.5–5 US¢/kWh and solar heating 3–20 US¢/kWh. The data relative to direct use in Hungary decreased in this period and the contribution of geothermal energy to the energy balance of Hungary, despite significant proven reserves (with reinjection) of 380 million m³/year, with a heat content of 63.5 PJ/a at ΔT=40 °C, remained very low (0.25%). Despite the fact that geothermal fluids with temperatures at the surface higher than 100 °C are available, no electricity has been generated. As of 31 December 2002, the geothermal capacity utilised in direct applications in Hungary is estimated to be 324.5 MW_t and to produce 2804 TJ/year. Geothermal heat pumps represent about 4.0 MW_t of this installed capacity. The quantity of thermal water produced for direct uses in 2002 was approximately 22 million m³, with an average utilization temperature of 31 °C. The main consumer of geothermal energy is agriculture (68% of the total geothermal heat dedicated to direct uses). The geothermal water is used only in five spas for space heating and sanitary hot water (SHW), although there are 260 spas in the country, and the thermal water produced has an average surface temperature of 68 °C. The total heat capacity installed in the spas is approximately 1250 MW_t; this is not provided by geothermal but could be, i.e., geothermal could provide more than three times the geothermal capacity utilized in direct uses by 31 December 2002 (324.5 MW_t).     

Processes controlling the isotopic composition of steam and water discharges from steam vents and steam-heated pools in geothermal areas

On the basis of isotopic analyses of steam and water discharges from the Wairakei, El Tatio and The Geysers geothermal areas, underground steam separation from the rising geothermal fluid appears to be adequately described in terms of a single-step process at temperatures of around 230°C. Absorption of this steam into nearly stagnant pools gives rise to the formation of isotopically enriched waters with compositions following a line with slope σ = ε′_D / (Δ_rw + ε′_¹⁸O − ε_{¹⁸O .230°C}), where ε′_D and ε′_¹⁸O are the effective kinetic isotope fractionation factors (50‰ and 16‰) for steam heated pools, ε_{¹⁸O .230°C} is the equilibrium fractionation factor for oxygen-18 at 230°C (2‰) and δ_rw is the difference in ¹⁸O-content of deep chloride and local groundwater (oxygen shift) respectively. The sulfate content of these pools is a function of the proportion of steam absorbed and its H₂S-content.     

Temperature evaluation of the Bugok geothermal system, South Korea

Using a variety of chemical geothermometers and statistical analysis, we estimate the temperature of a possible deeper geothermal reservoir at Bugok, Southern Korea. Shallow thermal aquifers (down to about 400 m depth) are under exploitation in this area; the temperatures (up to 78 °C) of the produced fluids are the highest found in South Korea. Based on hydrochemical data and occurrence, the groundwaters at Bugok can be classified under three groups: Na-SO₄ thermal groundwaters (CTGW) occurring in the central (about 0.24 km²) part of the area; Ca-HCO₃ cold groundwater (SCGW) found in shallow peripheral parts of the CTGW; the intermediate-type groundwater (STGW). The CTGW type is typical of the Bugok thermal waters; they have the highest discharge temperatures and contain very high concentrations of Na (75.1–101.0 mg/L), K (2.9–6.9 mg/L) and SiO₂ (62.0–84.5 mg/L) and are rich in sulfates.The major ion composition of the CTGW suggests that these waters are in partial equilibrium with rocks at depth. The application of various alkali-ion geothermometers yields temperature estimates in the 88–198 °C range for the thermal reservoir. Multiple-mineral equilibrium calculations indicate a similar but narrower temperature range (from about 100 to 155 °C). These estimates for CTGW are significantly higher than the measured discharge temperatures. Considering the heat losses occurring during the ascent of the waters, one can infer the presence of a deeper (around 1.8 km) thermal reservoir in the Bugok area that could be developed for district heating or other direct applications of geothermal heat.     

CO2 emissions from geothermal power plants and natural geothermal activity in Iceland

The ratio of CO₂ emissions from power plants to natural emissions is a measure of the environmental impact associated with geothermal power production. Emissions from Icelandic geothermal power plants amounted to 1.6 × 10⁸ kg year⁻¹ in 2002. Two independent estimates of natural CO₂ emissions range between 1 × 10⁸ and 2 × 10⁹ kg year⁻¹. Thus, power plant emissions are significant compared to estimated total emissions (i.e., not less than 8–16%). However, direct CO₂ flux measurements from four of the approximately 40 geothermal/volcanic systems in the country amounted to 3 × 10⁸ kg year⁻¹, indicating that these estimates of the total natural flux may be too low.     

Oxygen and hydrogen isotopes in deep thermal waters from the south meager creek geothermal area, british columbia, canada

Deuterium and oxygen-18 (¹⁸O) have been measured in deep thermal, shallow thermal and non-thermal water samples collected at various times between 1982 and 1989 from the Meager Creek area, with the aim of assessing the origin of the thermal waters. The isotopic composition of the reservoir waters (δ¹⁸O = −13‰ and δD = −114.8‰) was calculated from data on post-flash deep thermal waters, using a two-stage steam loss model. The reservoir composition shows an oxygen shift of 2.4‰ relative to the local meteoric water line. The composition of the recharge, obtained by removing the oxygen shift, is isotopically heavier than the average local meteoric waters, suggesting that the recharge may be from an area to the west of Mt Meager where isotopically heavier ground-waters are likely to be found. The small δ¹⁸O shift of the deep high-temperature waters is indicative of dominance of fracture-related permeability in the reservoir. Analysis of the chemistry and the temperature of the waters from hot springs and shallow thermal wells suggests that these waters have evolved from the deep geothermal waters through dilution by meteoric waters and about 40°C adiabatic cooling (steam loss).     

Evidence for thermal mining in low temperature geothermal areas in Iceland

This study deals with thermal mining in several geothermal systems in Iceland. A number of 2500- to 3000-m deep drillholes have been drilled into low temperature geothermal areas in the country. The conductive gradient outside active geothermal areas has also been mapped, and shows a systematic variation from lower than 50°C/km in the outer parts of the Tertiary basalts to over 100°C/km on the borders of the volcanic zones (rift zones). The difference between formation temperatures inside geothermal systems and the surrounding conductive gradient can be computed as a function of depth. This difference is termed ΔT in this paper. The ΔT-curves show that the upper parts of the geothermal systems are heated and the lower parts are cooled compared to the undisturbed conductive gradient. In many cases the cooling of the lower part is greater than the heating in the upper part, so that a net thermal mining has occurred. This thermal mining is calculated for several geothermal systems, and the systems are compared. The net thermal mining in the top 3000 m appears to be much greater in formations of Pleistocene and Pliocene age. It gradually decreases to zero for formations older than 6 million years. However, the net thermal mining is critically dependent on the maximum depth of water convection in these systems, which is unknown.     

Contact resistivities of sputtered TiN and Ti---TiN metallizations on solar-cell-type-silicon

Contact resistivities of TiN and Ti---TiN contacts on a shallow junction solar-cell-type silicon substrate have been investigated. The contact materials were sputter-deposited. The method of the transmission line model was applied for contact resistivity measurements. The contact resistivity of the n⁺Si---TiN contact system was 2 × 10⁻³ Ωcm² ± 50 per cent and remained constant after annealing up to 700°C for 30 min. For the n⁺Si---Ti---TiN system, the contact resistivity of 9 × 10⁻⁴ Ωcm² ± 50 per cent was measured. A heat treatment of 700°C. 30 min decreases this value by one order of magnitude and the interposed Ti fully reacts with Si and forms a TiSi₂ layer. The voltage drop caused by the n⁺Si---TiN contact system in a standard non-concentrator solar cell is negligible. The n⁺Si---TiSi₂---TiN contact system should be acceptable for Si solar cells used at up to 100 times solar concentration.     

Hydrogeochemical exploration of geothermal prospects in the Tecuamburro Volcano region, Guatemala

Chemical and isotopic analyses of thermal and nonthermal waters and of gases from springs and fumaroles are used to evaluate the geothermal potential of the Tecuamburro Volcano region, Guatemala. Chemically distinct geothermal surface manifestations generally occur in separate hydrogeologic areas within this 400 km² region: low-pressure fumaroles with temperatures near local boiling occur at 1470 m elevation in a sulfur mine near the summit of Tecuamburro Volcano; non-boiling acid-sulfate hot springs and mud pots are restricted to the Laguna Ixpaco area, about 5 km NNW of the sulfur mine and 350–400 m lower in elevation; steam-heated and thermal-meteoric waters are found on the flanks of Tecuamburro Volcano and several kilometers to the north in the andesitic highland, where the Infernitos fumarole (97°C at 1180 m) is the primary feature; neutral-chloride hot springs discharge along Rio Los Esclavos, principally near Colmenares at 490 m elevation, about 8–10 km SE of Infernitos. Maximum geothermometer temperatures calculated from Colmenares neutral-chloride spring compositions are 180°C, whereas maximum subsurface temperatures based on Laguna Ixpaco gas compositions are 310°C. An exploration core hole drilled to a depth of 808 m about 0.3 km south of Laguna Ixpaco had a bottom-hole temperature of 238°C but did not produce sufficient fluids to confirm or chemically characterize a geothermal reservoir. Hydrogeochemical data combined with regional geologic interpretations indicate that there are probably two hydrothermal-convection systems, which are separated by a major NW-trending structural boundary, the Ixpaco fault. One system with reservoir temperatures near 300°C lies beneath Tecuamburro Volcano and consists of a large vapor zone that feeds steam to the Laguna Ixpaco area, with underlying hot water that flows laterally to feed a small group of warm, chloriderich springs SE of Tecuamburro Volcano. The other system is located beneath the Infernitos area in the andesitic highland and consists of a lower-temperature (150–190°C) reservoir with a large natural discharge that feeds the Colmenares hot springs.     

Hydrology of the Greater Tongonan geothermal system, Philippines, as deduced from geochemical and isotopic data

Fluids in the Greater Tongonan geothermal system exhibit a large positive ¹⁸ O shift from the Leyte meteoric water line. However, there is also a significant shift in ²H. The δ²H−δ¹⁸O plot shows that the geothermal fluids may be derived by the mixing of meteoric water (δ¹⁸O = −7‰ and δ²H = −41‰) with local magmatic water (δ¹⁸O = 10 ± 2‰ and δ²H = −20 ± 10‰). The most enriched water in the Greater Tongonan system, in terms of δ¹⁸O, δ²H and Cl, is comprised of approximately 40% magmatic water. Baseline isotope results support a hydrogeochemical model in which there is increasing meteoric water dilution to the southeast, from Mahiao to Sambaloran and towards Malitbog. The Cl−δ¹⁸O plot confirms that the geothermal fluid in Mahanagdong, further southeast, is distinct from that of the Mahiao-Sambaloran-Malitbog system.     

Geothermal district heating for reno, Nevada, U.S.A.

The City of Reno is one of the most obvious candidates for geothermal district heating in the United States. Lying within a helt of major thermal anomalies, it has within its boundaries the Moana Hot Springs geothermal reservoir and probably other reservoirs, and only 14 km to the south is the major reservoir at Steamboat Hot Springs.This paper discusses the alternative heat sources that can be used, and selects Steamboat as the most conservative choice for a “worst-case” analysis of the details and economics of a model district heating system. A closed 16 km transmission loop between Steamboat and downtown Reno is envisaged, carrying 121°C water in the supply line and 65°C in the return line. This loop is isolated by heat exchangers from both the 176°C geothermal fluids at the Steamboat end of the line, and from the Reno user systems at the other. Detailed analysis of thermal demand densities in different parts of the City led to a model distribution network 48 km long, that serves the optimum grouping of zones of concentrated heat users. A large proportion of existing heating systems are hydronic and retrofitting of the selected buildings to the district heating system is relatively straightforward. Total peak load for the proposed system is 138 MJ s⁻¹ (139 MW_t) and annual consumption is 1.1 × 10¹⁵ J. Capital costs total about $55.4 million, in 1981 dollars. The economic analysis shows this system could provide considerable savings relative to the cost of natural gas, if revenue bond financing at 13% is employed for the construction and startup of the system. Even more favorable economic results could be achieved if a geothermal resource could be developed closer to downtown Reno, eliminating the high cost of the 16 km transmission pipeline. Reducing the service area to the most concentrated area of heat use in downtown Reno produces an even more viable system, about half the size of the full system.     

Structural and electrical properties of CuGaS2 thin films by electron beam evaporation

Single phase CuGaS₂ thin film with a highest diffraction peak of (1 1 2) at a diffraction angle (2θ) of 28.8° was made at a substrate temperature of 70°C, an annealing temperature of 350°C and an annealing time of 60 min. Second highest (2 0 4) peak was shown at diffraction angle of (2θ) 49.1°. Lattice constant of a and c of that CuGaS₂ thin film was 5.37 and 10.54 Å, respectively. The greatest grain size of the thin film was about 1 μm. The (1 1 2) peak of single phase of CuGaS₂ thin film at an annealing temperature of 350°C with excess S supply appeared at a little higher about 10% than that of no excess S supply. The resistivity, mobility and hole density at room temperature of p-type CuGaS₂ thin film was 1.4 Ω cm, 15 cm²/V s and 2.9×10¹⁷ cm⁻³, respectively. It was known that carrier concentration had considerable effect than mobility on a variety of resistivity of the fabricated CuGaS₂ thin film, and the polycrystalline CuGaS₂ thin films were made at these conditions were all p-type.     

The geothermal industry in Iceland

Direct (non-electrical) uses of geothermal energy in Iceland in 1984 amounted to 5517 GWh and the installed power was 889 MW_t, assuming 35°C discharge temperature. The bulk of this thermal power was for district heating, called hitaveita in Icelandic. In recent years this utilization has increased moderately. The installed geothermal electric power is currently 41 MW_e and is unlikely to change in the near future. Icelandic personnel have participated in many geothermal projects of the United Nations during the last 35 years. Contract work has been carried out by Icelandic consulting firms in several developing countries.     

The Iceland Deep Drilling Project: a search for deep unconventional geothermal resources

The Iceland Deep Drilling Project (IDDP) is a long-term program to improve the economics of geothermal energy by producing supercritical hydrous fluids from drillable depths. Producing supercritical fluids will require the drilling of wells and the sampling of fluids and rocks to depths of 3.5–5 km, and at temperatures of 450–600 °C. The IDDP plans to drill and test a series of such deep boreholes in the Krafla, Nesjavellir and Reykjanes geothermal fields in Iceland. Beneath these three developed high-temperature systems frequent seismic activity continues below 5 km, indicating that, even at supercritical temperatures, the rocks are brittle and therefore likely to be permeable, even where the temperature is assumed to exceed 550–650 °C. Temperature gradients are greater and fluid salinities smaller at Nesjavellir and Krafla than at Reykjanes. However, an active drilling program is underway at Reykjanes to expand the existing generating capacity and the field operator has offered to make available one of a number of 2.5 km deep wells to be the first to be deepened to 5 km by the IDDP. In addition to its potential economic significance, drilling deep at this location, on the landward extension of the Mid-Atlantic Ridge, is of great interest to the international science community. This paper examines the prospect of producing geothermal fluids from deep wells drilled into a reservoir at supercritical temperatures and pressures. Since fluids drawn from a depth of 4000–5000 m may prove to be chemically hostile, the wellbore and casing must be protected while the fluid properties are being evaluated. This will be achieved by extracting the fluids through a narrow retrievable liner called the “pipe”. Modelling indicates that if the wellhead enthalpy is to exceed that of conventionally produced geothermal steam, the reservoir temperature must be higher than 450 °C. A deep well producing 0.67 m³/s steam (2400 m³/h) from a reservoir with a temperature significantly above 450 °C could, under favourable conditions, yield enough high-enthalpy steam to generate 40–50 MW of electric power. This exceeds by an order of magnitude the power typically obtained from a conventional geothermal well in Iceland. The aim of the IDDP is to determine whether utilization of heat from such an unconventional geothermal resource at supercritical conditions will lead to increased productivity of wells at a competitive cost. If the IDDP is an economic success, this same approach could be applied in other high-temperature volcanic geothermal systems elsewhere, an important step in enhancing the geothermal industry worldwide.