Enthalpy Resources Research Articles

Geothermal resources in southern Thailand – part of a renewable energy mix

Electrical energy demand for Southern Thailand is continuously increasing partly due to an increase in tourism. Around 3,000 MW of coal fired power plants are planned by the government, but the proposal was put on hold due to the resistance of local communities and civil society groups. Besides this, coal fired power plants are not only large CO2 emitters, thus intensifying the on-going climate change processes, but also require lengthy environmental impact assessments, and their technology costs remain stagnant at comparable high levels. Solar and wind energy can be produced at far lower costs than coal, however, their shares on the renewable energy mix are comparable small in Thailand, but with a steady increase. A disadvantage of solar and wind energy production is that the production is not constant due to day/night and weather, respectively. These disadvantages can be compensated by adding geothermal energy, as this energy from deeper geological sources is continuously reaching the Earth’s surface. This allows the continuous feed to geothermal power plants which by this can act as a backbone of a renewable energy mix. In Southern Thailand hot springs from the north to the south are the surface expressions of active geothermal systems at depth. Surface exit temperatures can reach up to 80 degree Celsius, thus considered as low enthalpy resources, which can be utilized applying state-of-the-art binary power plant technology. In the current renewable power plan of the government geothermal energy is not considered due to the low availability of this resource. However, recent research has shown that Southern Thailand holds promising quantities of geothermal resources; with further scientific investigations needed. Finally, the only current geothermal power plant in Thailand located in Fang, Northern Thailand, is situated close to a national park in a beautiful landscape and environment, thus acting as a positive example for Southern Thailand.

Evaluation of groundwater hydrogeochemical characteristics and delineation of geothermal potentialities using multi criteria decision analysis: Case of Tozeur region, Tunisia

The use of geothermal energy in Tunisia is limited to its instant use because of the low enthalpy resources, especially in the southern part of the country. The Djerid Basin has remarkable geothermal resources with low to moderate temperatures that have been used only for irrigation of oases and heating greenhouses. In order to evaluate the geothermal potential of groundwater resources of Tozeur region located in the Djerid Basin, a synthetic approach including geological, geophysical, physicochemical, hydrogeological and geothermometric characteristics of groundwater is indispensable. It aims to determine: (1) the evolution of the water chemistry, (2) the origin of thermal waters and their reservoir temperature, (3) the mixing mechanism of geothermal fluid and (4) the mapping of geothermal potentialities with Multi-Criteria-Decision-Analysis (MCDA) using GIS platform.The hydrogeochemical approach revealed that the studied geothermal system is characterized by temperature values ranging between 25 and 75°C and total dissolved solids (TDS) values between 0.7 and 5.8 g/l.Furthermore, the use of silica geothermometers and saturation indices for different solid phases gave estimated geothermal reservoir temperature ranging between 92 and 104 °C and between 100 and 125 °C, respectively.In addition, the equilibrium processes elucidated that the thermal waters are mostly in the oversaturated condition with respect to calcite, aragonite and dolomite, but they are saturated with evaporate minerals.According to the obtained results of the MCDA, the spatial assessment of the potential geothermal areas using Weighted overlay and Boolean logic Models are 37 % and 5 % respectively.The findings in this study contribute to a better understanding of groundwater sustainability for supporting geothermal project on renewable energy and can be used as a synthetic document for realistic management of groundwater resources.

Geological field investigation for the assessment of the low-grade geothermal resources from volcanic terrains of the Island of Salina (Aeolian Islands, Italy)

The subsoil as a “thermal reservoir” is a modern concept that is leading to continuous developments of innovative methods of energy production. If volcanic areas have been so far considered suitable for exploitation of medium-to-high enthalpy resources, it is also true that an incredible potential confined to low grade resources is available. The geological background of Sicily makes the island as one of the most suitable contexts of southern Italy where geothermal resources could have great potential to increase their whole usage. Several active volcanic zones or areas at high hydrothermalism offer advantageous exploitation from low to high enthalpy geothermal resources. Here we present a case study from Santa Marina Salina (Aeolian Island Arc) with a detailed field survey providing information on lithostratigraphic features and on hydrogeological conditions of the area. The study is aimed at testing the thermal conductivity distribution at various depths by means of a theoretical model. Such an approach allowed the definition of the most suitable areas and their low-grade geothermal potential through different thematic maps for thermal conductivity in the shallow subsurface (0-150 m). Collected data become crucial for correct sizing of low-enthalpy geothermal installations, leading to optimization of the final planned technical solutions efficiency.

Assessment of Geothermal Resources of South America - A New Look

The present work provides a new look into the nature and distribution of geothermal resources of South America, on the basis of recent advances in data analysis and regional assessments. Notable in this context is the progress achieved in the use of a procedure termed as magmatic heat budget (MHB) that allow estimation of heat flux in areas of recent volcanic activity. In addition, an updated compilation of temperature gradients and heat flux have been completed. Such advances have allowed new resource assessments for 6526 sites. These span over more than 100 crustal blocks, distributed in thirteen countries of the continent. Following this, a 2ox2ogrid system with homogenized data sets were employed for calculating the in-situ heat content. Determinations of resource base based on observational data are now available for 253 out of a total of 418 cells in this grid system. Values of resource base based on estimated heat flow were calculated for the remaining 165 grid elements. The data and model results on temperatures of subsurface strata at depths less than three kilometers have been employed in classifying the resources, into three general categories: hot dry rock (HDR), hot wet rock (HWR) and low enthalpy (LE). HDR type resources, classified as those with temperatures higher than 150oC, occur in 318 localities mainly in the Andean regions. Similarly, HWR type resources, classified as those with temperatures in the range of 90 to 150oC, occur in 352 localities. Low enthalpy (LE) resources, with temperatures < 90oC, are numerous mainly in the eastern parts of the continent. The total resource base (RB) of HDR systems is estimated to be 1329x1021J and the corresponding resource base per unit area (RBUA) is 513GJ/m2. The HWR systems have a total resource base of 586x1021J, while the corresponding value for RBUA is 409GJ/m2. The low enthalpy systems, with temperatures in the range of 60 to 90oC, have a total resource base of 240GJ/m2, while those with temperatures less than 60oCis estimated to be 210GJ/m2. There are indications that HDR resources, with temperatures higher than 150oC at depths less than three kilometers, occur in 318 localities of the Andean regions. The total resource base (RB) of HDR systems is estimated to be 1329x1021J, while the corresponding weighted mean resource base per unit area (RBUA) is estimated to be 513GJ/m2. The new results have also been useful in regional scale identification of resources with notable pore fluid circulation, classified as HWR systems. Such systems with temperatures in the range of 90 to 150oC, are inferred to occur at depths less than three kilometers, in 352 localities of the Andean region. The total resource base of HWR systems is estimated to be 586x1021J, while the corresponding value for RBUA is estimated to be 409GJ/m2. Low enthalpy (LE) resources, with temperatures in the range of < 90oC, are numerous in the remaining parts of Andean regions and also in the eastern parts of the continent. The resource base per unit area of low enthalpy systems with temperatures in the range of 60 to 90oC is estimated to be 240GJ/m2, while that for systems with temperatures less than 60oCis estimated to be 210GJ/m2.

Geothermal Power Generation Worldwide: Global Perspective, Technology, Field Experience, and Research and Development

This article discusses the state of art in harnessing geothermal power for medium- and large-scale generation of electricity (and for space heating) worldwide. It reviews technology, field experience, research, and development, together with current, probable, possible and potential developments in the USA, developed, and developing countries in near future and long term.First, world consumption of geothermal energy is discussed. Here, worldwide installed capacities for geothermal electricity, the countries with the highest share of electricity generated from geothermal power, capacity factors, and direct use of geothermal energy is reviewed. Then, cost of renewable energy, i.e., current installation cost for electricity generation and heat generation, for biomass, solar photovoltaic, solar thermal, hydro, geothermal, wind, and tidal power is reviewed. Geothermal power in the United States is examined. Highlighted is heat flow, tectonic controls, types of geothermal systems, United States geothermal potential, geothermal energy in the United States, operating conditions for electricity generation, and environmental constraints.The central part of the article discusses field experience with innovative geothermal plants considering geothermal power plant analysis and design (optimization in design of geothermal power plants, optimization of prime movers, heat cycle considerations, resource considerations, and environmental considerations). A review of experimental plants (proposed systems and tested systems), and innovative power plants in commercial operation (low, moderate, and high enthalpy resources) is then discussed.The article goes on to examine R&D programs that are underway to significantly enhance the use of geothermal power. Highlighted is typical research and development projects such as enhanced heat transfer in air-cooled condensers, materials research, instruments for real time monitoring of geothermal processes, plant optimization, removal of non-condensable gases from binary power plants, silica and metals extraction, and small-scale power plant field verification projects. Geothermal drilling R&D is also reviewed.

Electrical characterization of Cu(In,Ga)Se 2 thin-film solar cells and the role of defects for the device performance

Geothermal resources have been classified as low, medium and high enthalpy resources according to their reservoir fluid temperatures. There is no general agreement on the arbitrary temperature ranges used. Classification of a geothermal resource by its reservoir fluid temperature can be ambiguous because two independent properties are required to define the thermodynamic state of a fluid. Geothermal resources should be classified to reflect their ability to do thermodynamic work. In this paper, it is proposed that geothermal resources be classified as low, medium and high quality resources with reference to their specific exergy indices (SExI), SExI<0.05, 0.05⩽SExI<0.5 and SExI⩾0.5, respectively. The demarcation limits for these indices are exergies of saturated water and dry saturated steam at 1 bar absolute. These demarcation lines can be plotted on a Mollier diagram to form a classification map of geothermal resources.

Classification of geothermal resources by exergy

Geothermal resources have been classified as low, medium and high enthalpy resources according to their reservoir fluid temperatures. There is no general agreement on the arbitrary temperature ranges used. Classification of a geothermal resource by its reservoir fluid temperature can be ambiguous because two independent properties are required to define the thermodynamic state of a fluid. Geothermal resources should be classified to reflect their ability to do thermodynamic work. In this paper, it is proposed that geothermal resources be classified as low, medium and high quality resources with reference to their specific exergy indices (SExI), SExI<0.05, 0.05⩽SExI<0.5 and SExI⩾0.5, respectively. The demarcation limits for these indices are exergies of saturated water and dry saturated steam at 1 bar absolute. These demarcation lines can be plotted on a Mollier diagram to form a classification map of geothermal resources.

Geophysical exploration for geothermal low enthalpy resources in Lipari Island, Italy

Integrated geophysical surveys were performed in two sites, Fossa di Fuardo and Terme di San Calogero in Lipari Island, Southern Italy with the intent of the exploration of low-enthalpy geothermal fluids. Both sites show strong geochemical and geologic evidences of hydrothermal activity. The geophysical methods consist of two microgravimetric surveys, two 2D geoelectric profiles, a seismic reflection profile and a five seismic refraction profiles. The seismic methods allowed us to locate the main subsurface seismic discontinuities and to evaluate their geometrical relationships. The gravity field was used to constraint the seismic discontinuities, while the electric prospecting let discriminate more conductive areas, which could correspond to an increase in thermal fluid circulation in the investigated sites.The results obtained by the different geophysical methods are in good agreement and permit the definition of a reliable geo-structural model of the subsurface setting of the two investigated areas. A low-enthalpy geothermal reservoir constituted by a permeable pyroclastic and lava sequence underlying two shallow impermeable formations was found at Fossa del Fuardo. The reservoir is intersected by some sub-vertical faults/fractures that probably play an important role in convoying the thermal water up to the surface. At the other site, Terme di S. Calogero, the geophysical surveys showed that an intense circulation of fluids affects the subsurface of the area. This circulation concentrates along a ENE-trending fault located at a little distance from the thermal resort. The hot fluids may upraise along the fault if the width of the ascent area is smaller than 20m.

Small Geothermal Resources: A Review

Abstract Geothermal resources are present, in different forms and quantities, all over the world. The high-enthalpy resources (temperatures above 225°C) and part of the medium enthalpy resources (between 225° and 125°C) are concentrated mainly along belts that coincide with the margins of the lithospheric plates. The low-enthalpy resources (less than 125°C) are present in all countries. Small geothermal resources belong for the most pan to the category of medium-low enthalpy resources and are capable of feeding electric power plants of a maximum capacity of 10 MWe, and any type of nonelectric plant. Electricity generation is the best known and most important utilization of geothermal energy. In 1993 the total installed geothermoelectric capacity in the world had reached 5915 MWe. This figure includes the approximately 80 MWe coming from small geothermal resources. For the year 2000 the total installed geothermoelectric capacity is expected to reach 10,197 MWe. Electricity generation can be achieved utilizing fluids at temperatures above 150°C in conventional condensing or back-pressure power plants, and fluids with a temperature as low as 85°C, in binary-cycle plants. Direct applications of geothermal heat (nonelectric uses) are a viable option with resources of any temperature. At the moment there are nonelectric plants in the world to a total of more than 11,000 MWe The most common nonelectric uses of geothermal energy are district heating, agriculture (greenhouse heating and animal husbandry), aquaculture, and industrial processes. There are, however, numerous other forms of utilization that have been in operation for many years (such as oil recovery) or are now being experimented (such as fog dispersal systems on airport runways). The environmental impact of geothermal energy is related mainly to the atmosphere (chemical pollution) and the surface and underground waters (chemical and thermal pollution). It is a relatively minor impact, especially with regard to the nonelectric uses, and is certainly lower than the pollution deriving from fossil fuel plants.

Geothermal situation in Greece

Exploration for geothermal resources in Greece started in 1970.The Institute of Geology and Mineral Exploration (IGME) was responsible for implementing the exploration programme. Initially the programme covered areas considered to contain high enthalpy resources, and was financed by the State and Public Power Corporation (PPC). During the last eight years, following on the energy crisis, the programme has been extended to the medium and mainly low enthalpy fields.At the same time as PPC launched an exploitation and power-station programme, the Banks for Industrial and Agriculture Development, as well as national and local authorities and private enterprise started a programme for exploitation of low enthalpy resources.

Present status of geothermal reconnaissance studies in the Republic of Panama

The geothermal reconnaissance studies of the Republic of Panama were conceived with the object of carrying out a systematic evaluation of its geothermal potential. So far these studies have been directed at areas with high enthalpy resources capable of producing electric energy. Exploratory work is in progress in El Valle de Anton, which appears to be the most promising area, in Chitra-Calabre, Baru-Colorado, Isla de Coiba and Tonosi areas.

Geothermal resources of the United Kingdom

Geothermal prospects in the UK are represented by low enthalpy resources in deep sedimentary basins and 'Hot Dry Rock' (HDR) resources in radiothermal granites, and possibly in deep basement rocks where they are overlain by thick low conductivity sediments. The low enthalpy resources are in Permo-Triassic sandstones at temperatures of more than 40°C. Four deep exploration wells have been drilled to investigate the potential of these sedimentary aquifers. The main HDR resource potential is associated with major granite batholiths in southwest and northern England where temperatures are predicted to be 200°C at about 5.4 and 6 km respectively. The HDR potential is being investigated by the Camborne School of Mines at their test site in Cornwall where three boreholes have been drilled to depths of between 2 and 2.5 km. The Hot Dry Rock Accessible Resource Base at temperatures of more than 100°C and depths of less than 7 km is 36 X 10 21 joules (equivalent to 130 × 10 4 million tons of coal). The low enthalpy Geothermal Resource of the Permo-Triassic sandstones at temperatures of more than 40°C is 200 × 10 l8 joules (equivalent to about 8000 million tons of coal). If only a small fraction of these resources could be developed, it would be significant in terms of the UK’s energy balance.