Isotope work applied to geothermal systems at the institute of nuclear sciences, New Zealand

A number of isotope techniques are being applied to the study of the New Zealand geothermal areas. Stable isotope equilibria have been used to estimate temperature profiles underground. Present results indicate that the hydrogen-water and sulphate-water (¹⁸O) equilibria represent temperatures close to the surface, while the ¹³CO₂---¹²CH₄ and H³⁴SO₄⁻---H₂³²S equilibria are much slower to re-establish and probably represent temperatures at greater depth. Dating by natural radioactive carbon-14 and tritium techniques have so far only been able to show that the water circulation times are greater than 20 yr. Hydrogen and oxygen-18 measurements indicate that the geothermal waters originate mainly from local groundwaters but may have undergone varying oxygen shifts by reaction with rocks in the system. Ore bodies in the Tertiary volcanics of New Zealand are being studied as indicators of past geothermal conditions.     

Accurate outdoor glass thermographic thermometry applied to solar energy devices

The measurement of the temperature of the glass that covers solar collectors or photovoltaic modules is very important for the characterization of the performance of these converters. Thermography is a non-contact thermometry technique that is capable to quickly scan and record surface temperature fields, but its accuracy depends on knowing the limitations and possible errors involved with the use of this technique. This paper identifies glass infrared reflection errors and their consequences when performing outdoor thermographs. The work also proposes and experimentally validates a correction method for correcting these errors. Finally is also presented a method for estimating a thermographic equivalent sky temperature that can be used in correction procedures for the own outdoor thermographic measurements.     

A comparison of economic evaluation models as applied to geothermal energy technology

Several cost estimation and financial cash flow models have been applied to a series of geothermal case studies. In order to draw conclusions about relative performance and applicability of these models to geothermal projects, the consistency of results was assessed. The model outputs of principal interest in this study were net present value, internal rate of return, or levelized breakeven price. The models used were VENVAL, a DuPont, Inc. venture analysis model; the Geothermal Probabilistic Cost Model (GPC Model) and the Alternative Power Systems Economic Analysis Model (APSEAM), which were developed at the Jet Propulsion Laboratory (JPL); the MITRE Corporation's Geothermal Loan Guarantee Cash Flow Model (GCFM); and the GEOCOST and GEOCITY geothermal models developed by Battelle Pacific Northwest Laboratories. The case studies to which the models were applied include a geothermal reservoir at Heber, CA; a geothermal electric power plant to be located at the Heber site; an alcohol fuels production facility to be built at Raft River, ID; and a direct-use, district heating system in Susanville, CA.     

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.     

Geochemical research in relation to hot dry rock geothermal systems

This paper summarises the discussion of the potential value of geochemistry in HDR technology. The applications of geochemistry are discussed in terms of the nature and origins of fluids in granitic systems and the mineralogy of the granite. The use of chemical species as reservoir diagnostic tools is also discussed.     

关于增强型地热系统的技术研究

随着世界能源格局的变化,人类不断开发出更优质、对环境影响更小的新能源,其中干热岩的开发备受关注。干热岩开发的具体工程技术称为增强型地热系统(Enhanced Geothermal Systems,简称EGS)。从资源品质来讲,干热岩资源主要用于发电,可以解决国家能源根本需求;从环境保护来讲,增强型地热系统可用二氧化碳作为携热介质,可以将二氧化碳进行地质埋存,更好地解决环境问题。文中介绍了世界EGS关键技术的新进展,剖析了发展过程中存在的问题以及未来的发展方向。     

Chromatic dispersion concentrator applied to photovoltaic systems

The aim of this paper is to show how it is possible to realise a chromatic dispersion concentrator which collects the different monochromatic components of the solar spectrum separately in subsequently concentric rings in the focal zone. This comes about without an increase in the energetic losses compared to any other type of concentrator. If different photovoltaic elements with energy gaps equal to the photon energy falling on the focal zone are put in the latter, energy losses due to incomplete utilization of the solar spectrum and to incomplete utilization of the energy of a single photon can be drastically reduced. How the losses due to the voltage factor and the fill-factor of the photovoltaic elements of the system can be reduced compared to the normal silicon cells is also demonstrated. The other contributions to losses in the conversion process have only been mentioned, foreseeing their possible variation.     

Stable isotopic studies of japanese geothermal systems

Stable isotopic studies on Arima type brines, Green Tuff type thermal waters and three volcanic systems, Hakone, Ibusuki and Satsuma-Iwojima, were reviewed with emphasis on the origins of the water and sulfur species in these systems. Of the three volcanic systems. Hakone is a subaerial volcano consisting of calderas, central cones and a caldera lake, whereas Ibusuki belongs to a caldera half-drowned in the ocean. Satsuma-Iwojima is a volcanic island erupted within a drowned caldera ca. 40 km off the southern coast of Kyushu. Comparisons of the isotopic data of the waters and sulfur species from the three different volcanoes indicated that the waters of meteoric, oceanic and magmatic origins are involved in various ways and proportions in the volcanic activities. A considerable fraction of the volcanic sulfur species is shown to be recyclic in origin. It was demonstrated that a combined use of chemical and isotopic data on thermal waters and dissolved sulfates would yield useful information on the hydrological aspects of many geothermal systems.     

Availability modeling methodology applied to solar power systems

Availability is discussed as a measure for estimating the expected performance for solar- and wind-powered generation systems and for identifying causes of performance loss. Applicable analysis techniques, ranging from simple system models to probablistic fault tree analysis, are reviewed. A methodology incorporating typical availability models is developed for estimating reliable plant capacity. Examples illustrating the impact of design and configurational differences on the expected capacity of a solar-thermal power plant with a fossil-fired backup unit are given.     

Utilization of geothermal systems in South-East Hungary

Thermal wells have been used in Hungary for over 140 years. As thermal water production has increased during the past decades, the pressure drawdown has increased in the geothermal systems of the Pannonian basin, showing that their sustainable management is lacking. The Hódmez?vásárhely, Szeged, and Szentes case histories are presented, including the very first indications of stabilization and recharge of the Pannonian thermal aquifers, as a result of reduction of thermal water production. Sustainable production and overall resource management of geothermal systems in SE-Hungary can only be achieved by injection.     

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.     

Environmental isotope investigations of New Zealand geothermal systems—A review

Environmental isotope investigations of geothermal systems at the New Zealand Institute of Nuclear Sciences have concentrated in recent years on combining several isotopes with chemical analyses. Geothermal hydrology has been studied by the use of hydrogen and oxygen isotopes with chloride and other water analyses. Rocks and minerals in well cores have added information to the geology and chemistry through the use of oxygen isotope techniques. Oxygen, hydrogen, carbon and sulphur isotope geothermometry have been combined in an attempt to derive temperature profiles with depth. ²²²Rn measurements in soil indicate leakage through faults, while ²²²Rn measurement of well discharges show evidence of underground processes. Future work will include noble gas isotope measurements. Measurements of ¹H and ¹⁴C are reported in an associated paper on tracing of underground water movements.     

北京大学地热能应用的实例分析

介绍了北京大学的地热资源应用实例。经济性分析结果显示,地热井的经济效益是相当可观的。文章还介绍了在地热开发和利用中,为防止盲目投资地热井项目应注意的事项,提出了投资风险、保护井距和梯级开发的概念。     

Factors influencing greenhouse heating and geothermal heating systems

Low profits, stagnation and other negative consequences of the energy crisis of the early '70s gave renewed impetus to research and development programs in the European countries in an attempt at reducing the energy demand of the rural sectors and discovering new sources of energy. The results of these efforts can be summarized as follows: (1) The specific energy demand in agriculture has been reduced in a number of European countries. New, so-called “energy-saving” technologies have been developed and introduced in plant cultivation and animal husbandry. (2) Renewable resources have been re-discovered and are under exploration or commercial utilization: solar and wind, biomass, industrial waste, geothermal. But the significance of these resources in energy terms is not determined only by the amount consumed and the amount of other resources saved, but also by their role within the economy of the country and the effects on the trade balance. The alternative energies were therefore very much a question of policy, of assessing the influence on more productive sectors and on energy consumption on the whole. These were the factors that determined the different approaches taken in the European nations, and the different results achieved, rather than the availability of the resources. Geothermal energy could make a contribution to the energy requirements of most European countries, for the following reasons: (1) high enthalpy resources can be found in some countries (e.g. Turkey); (2) large quantities of low enthalpy resources at temperatures of 30–80°C can be found in aquifers in most European countries; (3) the rational utilization of low grade heat in district heating, agriculture and process heating could lead to considerable savings of imported fuels, since these sectors account for 40–60% of the total heat demand in Europe; (4) great progress has been made in the last few years in know-how and technology for utilizing different temperature ranges of geothermal fluids in agriculture, animal husbandry, food processing and other applications. It is difficult to assess the future of geothermal energy in agriculture in Europe, in the current world energy market. The factors influencing our assessment vary from country to country, depending on the development stage, short- and long-term policy for resource development and utilization, economic climate, investments available, etc. It is therefore equally difficult to compare the validity of the investment of the various countries in geothermal development and utilization. Much depends on the quality and quantity of the technical, technological and economical information required to reach an accurate estimate. For this reason the first target of the collaboration of scientists from different European countries is to collect all the information available in Europe, then select and reorganize this data in such a way that it can be used by different countries with different local circumstances for different types of assessment. At the present level of technology, there are many possible applications of geothermal energy. The limits change continually with advances in technology. In greenhouse heating, for example, nearly all the temperature ranges required for hot beds and hot water irrigation are actually available, which explains why the most widely developed application of geothermal resources is in agriculture, food processing and greenhouse heating. Many projects in European countries are successful, showing profits. However, the main drawback is the relatively high investment costs compared to conventional heating systems. Some technical problems have also to be solved in order to achieve the specific light, ventilation and other conditions required in greenhouse systems. An important factor in low-temperature installations is location of the installation, which affects climatization and heat transfer. This paper will discuss the different aspects of this problem.     

Thermal analysis of indirect geothermal district heating systems

Low- and moderate-temperature geothermal resources have been discovered in many areas of the world, and are being used increasingly for district heating. Due to the corrosive action of some geothermal waters, heat exchangers are used to avoid circulating the geothermal fluid directly through the district heating systems, in what are called Indirect Geothermal District Heating Systems (IGDHS). In this case, the geothermal water acts as a heat source directly heating the network fluid through a heat exchanger. However, it is different from that of conventional systems in which hot water from a fossil fuel boiler is used directly. In the former (IGDHS), the geothermal water is regarded as a heat source with constant temperature, and in the latter the boiler is considered a heat source with variable heat flux. This paper presents a thermal analysis of a simple IGDHS, and discusses the selection of heat exchangers and optimum operating conditions.     

Rapid estimation of geothermal coverage by district-heating systems

An algorithm is developed for the quick estimation of the fraction of annual heat-load that is covered by geothermal energy in district-heating systems. The cases of direct use, heat exchange and heat-pump application are distinguished. The algorithm proved accurate enough for pre-feasibility study purposes and for preliminary considerations with regard to the management of geothermal energy. It is demonstrated that for coverage estimation, detailed heat-supply calculations can be substituted by the use of degree-days, which are quite often available for various base temperatures. Furthermore, the analytic expressions of the algorithm allow the quantitative evaluation of several parameters. Specifically, for low temperature geothermal fluids the coverage is an increasing second-degree function of the temperature of the fluids. Increasing network return temperatures has also a decreasing effect on the coverage. The required geothermal-flow is inversely proportional to the heat exchanger effectiveness, for the same coverage. Application of a heat pump results in a higher coverage that should otherwise require a higher temperature fluid. It is consequently defined as an equivalent geothermal-temperature increase – due to the heat pump – that is proved to be proportional to the compressor capacity. Last, the network supply-temperatures have a rather secondary effect upon the coverage, affecting the flow through the network and so the effectiveness of the heat exchanger.     

Design of geothermal steam supply systems in Iceland

The role of the geothermal steam supply system is to receive the geothermal fluid from the geothermal wells, separate the steam from the water and to deliver steam and/or water to a user of the thermal energy. It may be for direct use in any kind of an industrial process, such as drying, heating, cooling, etc., or it may be intended for electric power generation. The steam supply system delivers the fluid at a specified temperature, pressure and quality to the user.The steam supply system consists of wellheads, steam collection pipelines, nowadays in Iceland normally designed for two-phase flow of water and steam, steam-water separators, main steam/water lines, moisture separators, control valves, exhaust system, and effluent disposal equipment as needed and may include compressors and/or pumps for long distance transportation.Design criteria for the system depend on one hand upon the characteristics of the geothermal field, and on the other upon the intended use and required steam quality and economy. High enthalpy fields, for example, are capable of producing high pressure steam which is relatively economical when electric power generation alone is being considered. For such systems, high quality of the steam is of utmost importance.The paper gives a general overview of the steam supply systems in Iceland and describes the main features of the Nesjavellir steam supply system where the main emphasis was laid on high steam quality in order to prevent scaling in turbines, control valves and heat exchangers. New systems or systems needing restoration should be based on the same features.     

Numerical modeling of Basin and Range geothermal systems

Basic qualitative relationships for extensional geothermal systems that include structure, heat input, and permeability distribution have been established using numerical models. Extensional geothermal systems, as described in this paper, rely on deep circulation of groundwater rather than on cooling igneous bodies for heat, and rely on extensional fracture systems to provide permeable upflow paths. A series of steady-state, two-dimensional simulation models is used to evaluate the effect of permeability and structural variations on an idealized, generic Basin and Range geothermal system of the western U.S.Extensional geothermal systems can only exist in a relatively narrow range of basement (bulk) permeability (10⁻¹⁵ m² to 10⁻¹⁶ m²). Outside of this window, shallow subsurface fault zone temperatures decrease rapidly. Mineral self-sealing does not significantly affect the flow system until the flow path is almost completely sealed off. While topography gives an extra “kick” to convective circulation, it is not a requirement for geothermal system development. Flow from the ranges to the fault dominates the circulation, while secondary flow systems exist on the range front slopes. A permeable fault in one valley can also induce cross-range flow if there are no equally good upflow paths in the adjacent valleys. When bulk permeability is high enough, additional deep circulation cells develop in adjacent valleys, diverting heat and fluid from the fault and consequently reducing temperatures in the fault itself. Qualitative comparison between temperature–depth logs from actual geothermal systems and from the generic models is a significant aid to understanding real-world geothermal fluid flow, and suggests new or better interpretations of existing systems.     

A review of methods to evaluate borehole thermal resistances in geothermal heat-pump systems

In the design of a ground-source heat pump (GSHP) system, the heat transfer from the fluid to the ground is influenced by the thermal borehole resistance between the fluid and the borehole surface and also by the interference resistance between the two (or four) pipes inside the borehole. Several authors have proposed empirical and theoretical relations to evaluate these resistances as well as methods to evaluate them experimentally. The paper compares the different approaches and proposes good practice to evaluate the resistances. The impact of the different approaches on the design of heat exchanger is also examined. Two-dimensional and fully three-dimensional numerical simulations are used to evaluate the different methods. A new method is also proposed to evaluate the borehole resistances from in situ tests.