Chilean geothermal resources and their possible utilization

Most of the hot spring areas in Chile are located along the Andean Cordillera, associated with Quaternary volcanism. The volcanic—geothermal activity is mainly controlled by the subduction processes of the Nazca and Antarctic oceanic plates under the South America continental plate, and occurs at three well-defined zones of the Chilean Andes: the northern zone (17°30′–28°S), the central—south zone (33φ–46°S) and the southern-most or Austral zone (48°–56°S).Some tested high temperature geothermal fields, and geological and geochemical surveys of many other hot spring areas, evidence a great potential of geothermal resources in this country. Both electrical and non-electrical applications of this potential are considered in this paper.Taking into account the potentially available geothermal resources, the development of natural resources, the geographic and social—economic conditions existing in the different regions of Chile, it is concluded that power generation, desalination of geothermal waters, recovery of chemicals from evaporite deposits and brines and sulfur-refining are the main possible applications of geothermal energy in northern Chile; in central—south Chile geothermal energy is suitable for agribusiness such as greenhouses, aquaculture and animal husbandry.     

First solar radiation atlas for the Arab world

In the year 1998, the Arab League Educational, Cultural and Scientific Organization (ALESCO), Directorate of Science and Scientific Research, Tunis, had launched the “Solar Radiation Atlas for the Arab World”. This atlas contains three sets of maps (using Mercator projection) for monthly means, where each stands for one month. These are sunshine duration, global solar radiation and diffuse solar radiation. The atlas contains data for nearly 280 stations from 19 Arab states which cover latitudes from 0° (tropic) to 37°N and longitudes 19°E to nearly 60°E with different elevations from the sea level. It also contains useful tables of the monthly recorded means of the direct, diffuse and global solar radiation as well as the sunshine duration for 16 Arab states including 207 cities.The maximum recorded annual mean (10 years) of the global solar radiation in the Arab world was 6.7 kW h/m²/day in Nouakchott (latitude 20°56′N, longitude 17°02′E), Mauritania, and 6.6 kW h/m²/day in Tamenraset (latitude 36°11′N and longitude 5°31′E), Algeria, while the lowest recorded annual mean global solar radiation was 4.1 kW h/m²/day in Mosul (latitude 43°N and longitude 36°E), Iraq. Furthermore, the maximum recorded annual mean sunshine duration in the Arab world was 10.7 h in Aswan (latitude 23°58′N, longitude 32°47′E), Egypt, and the lowest was 7.5 h in Tunis (latitude 36°50′N, longitude 10°14′E), Tunisia.     

Equations for estimating global solar radiation in data sparse regions

The knowledge of the amount of solar radiation in an area/region is very essential in the field of Solar Energy Physics. In this work two equations are put forward for estimating global solar radiation from common climate variables in data sparse regions. The first is the Hargreaves equation, R_s=0.16R_aT_d^0.5 where R_a is the extraterrestrial solar radiation and T_d is the temperature difference (maximum minus minimum), while the second is the Angstrom equation, R_s=R_a(0.28+0.39n/N) where n and N are the measured sunshine hours and the maximum daylight duration respectively. The global solar radiation estimated by the two equations for three sites, Owerri (5°28′N, 7°2′E), Umudike (5°29′N, 7°33′E) and Ilorin (8°32′N, 4°46′E), located in different climate zones of in Nigeria, West Africa, are in agreement with those of earlier workers and that from Photovoltaic Geographic Information System (PVGIS) project. The implication of this in solar photovoltaic applications has been stressed.     

Measurement and interpretation of terrestrial heat flow in Israel

Sixty-eight new determinations of terrestrial heat flow in Israel have a range of 0.17-11.07 μcal/cm²s. The average value of deep conductive heat flow in the undisturbed complex of the Arabo-Nubian Massif is 0·94 μcal/cm²s; it is least affected by circulation of groundwater. This value is only slightly higher than the heat flow of 0·88 μcal/cm²s in the Levantine Basin of the Mediterranean Sea. Several values that exceed 2·0 μcal/cm²s are due either to (probable) deep hydrothermal activity or to small domal structures of the basement.Within the sedimentary sequence which blankets the crystalline massif, terrestrial heat flow is often redistributed by circulating groundwater. Recharge regions, particularly Judean-Samarian Galilee, where cool meteoric waters percolate into the subsurface have anomalously low heat flow, ranging from 0·17 to about 1·0 μcal/cm²s. Part of the original deep thermal flux in those regions is intercepted at moderate depths by the recharge flow, and is carried into deeper aquifers of the Foothills, Coastal Plain, or the Jordan-Dead Sea Rift. Movement of groundwater occurs mainly along faults.Deep faults associated with the Jordan-Dead Sea Rift system act as conduits for hot waters ascending from deep confined aquifers. The most tangible surface expression of the convective hydrothermal system are the numerous warm to hot springs, emerging along the margins of the Rift. However, the waters emerging on the surface as the warm and hot springs are a minor fraction of the convective system. Most of the ascending thermal waters are absorbed by shallow aquifers with lower hydraulic potential. Such regions are characterized by anomalously high heat flow; several values exceed 2 and one value is 11 μcal/cm²s.     

Geochemistry of the surface and deep fluids of the Miravalles volcano geothermal system (Costa Rica)

The Miravalles high-temperature geothermal reservoir, located in the northwestern part of Costa Rica, is liquid-dominated. Reservoir temperatures generally range between 230 and 240 °C. The highest measured value is 255 °C. Bottom-hole measurements and solute geothermometry indicate that thermal conditions within the reservoir are very stable over time. The waters discharged from the wells have a neutral or slightly alkaline pH and are of the sodium-chloride type. Based on isotope data, the main recharge zone appears to be located on the northeastern side of the Guanacaste Cordillera. Several mixing trends have been identified between reservoir fluids and regional groundwaters. Gas discharges are dominated by CO₂, with minor amounts of H₂S and N₂. Relative N₂, Ar and He contents reveal a typical arc-type signature and significant inflow of meteoric-derived gases. Cl–SiO₂-enthalpy and δ¹⁸O–δ²H–Cl relationships suggest the existence of a maturation trend that is the result of both natural (i.e. direct drainage of deeper fluids) and anthropogenic causes (reinjection of Cl-rich waste waters). Acid fluids with SO₄-acidity (pH ranging between 2.4 and 3.7) have been encountered in three wells at the eastern border of the well field. Preliminary data assessment indicates two possible sources, either superficial H₂S oxidation or inflow of “immature” volcanic waters.     

An application of the multilayer perceptron: Solar radiation maps in Spain

In this work an application of a methodology to obtain solar radiation maps is presented. This methodology is based on a neural network system [Lippmann, R.P., 1987. An introduction to computing with neural nets. IEEE ASSP Magazine, 4–22] called Multi-Layer Perceptron (MLP) [Haykin, S., 1994. Neural Networks. A Comprehensive Foundation. Macmillan Publishing Company; Hornik, K., Stinchcombe, M., White, H., 1989. Multilayer feedforward networks are universal approximators. Neural Networks, 2(5), 359–366]. To obtain a solar radiation map it is necessary to know the solar radiation of many points spread wide across the zone of the map where it is going to be drawn. For most of the locations all over the world the records of these data (solar radiation in whatever scale, daily or hourly values) are non-existent. Only very few locations have the privilege of having good meteorological stations where records of solar radiation have being registered. But even in those locations with historical records of solar data, the quality of these solar series is not as good as it should be for most purposes. In addition, to draw solar radiation maps the number of points on the maps (real sites) that it is necessary to work with makes this problem difficult to solve. Nevertheless, with the application of the methodology proposed in this paper, this problem has been solved and solar radiation maps have been obtained for a small region of Spain: Jaén province, a southern province of Spain between parallels 38°25′ N and 37°25′ N, and meridians 4°10′ W and 2°10′ W, and for a larger region: Andalucía, the most southern region of Spain situated between parallels 38°40′ N and 36°00′ N, and meridians 7°30′ W and 1°40′ W.     

Correlation of global solar radiation values estimated and measured on an inclined surface for clear days in Bogotá

An empirical expression developed to estimate global solar radiation in clear days, on inclined surfaces located at any geographical position, is presented. This expression allows determining the global solar radiation in a specific day of the year, considering the attenuation of radiation in the atmosphere, the air mass factor, astronomic geometric and geographic parameters, and in particular, the altitude.Data calculated with this expression were correlated with those obtained experimentally in Bogotá, Colombia (74°4′W, 4°35′N and 2580 m altitude). The correlation of the calculated with the experimental data yielded a coefficient of 0.9980, which indicates the reliability of the former and that the developed expression facilitates the construction of data bases with information on solar radiation potential in ample regions characterized by their locations at different altitudes above sea level. These data bases will supply preliminary information on sites adequate for the installation of photovoltaic systems.     

Chemical variations in hydrothermal minerals of the Los Humeros geothermal system, Mexico

The Los Humeros geothermal system is composed of more than 2200 m of Quaternary altered volcanic rocks and an underlying Cretaceous sedimentary sequence. The low salinity of the fluids discharged at present (Na⁺ and Cl⁻ concentrations <500 ppm), and the excess steam, indicate that the reservoir contains a mixture of steam and dilute groundwater. Water-rock equilibrium is not attained. Hydrothermal minerals are present in veinlets, vugs, and replacing primary minerals. Three mineral zones are recognized: 1) a shallow argillic zone (<400 m depth), 2) a propylitic zone (ranging between 500 and 1800 m) and 3) a skarn zone (>1800 m). Petrographic examination of cuttings from five wells and temperature data indicate at least two stages of hydrothermal activity. Temperature is the main factor that affects the chemical composition of chlorite, epidote and biotite. Fe²⁺ and Al^IV increase in chlorite with temperature [from 1.4 formula position unit (fpu) to 2.8, and from 0.7 to 2.4 fpu, respectively]. The pistacite content of epidote varies from 18 to 33 mol% in high-temperature regions (>270 °C) and from 13 to 26 mol% in low-temperature regions (<250 °C). Biotite displays a slight increase in Al^IV contents (1.55–2.8) and octahedral occupancy (5.93–6.0 fpu) with temperature. Whole rock composition and variations in oxygen fugacity conditions are factors that also affect the concentrations of Fe, Al and Mg in the octahedral sites of chlorite, epidote, biotite and amphiboles. Chemical variations observed in alteration minerals at different depths in the Colapso Central-Xalapazco region could be used as indicators of relict physico-chemical conditions in the reservoir, before the present economic exploitation.     

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.     

Direct methanol fuel cell performance of sulfonated polyimide membranes

Sulfonated polyimides (SPIs) derived from 1,4,5,8-naphthalene tetracarboxylic dianhydride, 4,4′-bis(4-aminophenoxy) biphenyl-3,3′-disulfonic acid and hydrophobic aromatic diamines showed the much lower methanol permeability and the lower proton conductivity than Nafion 112. The performance and the water and methanol crossover for direct methanol fuel cells (DMFCs) with the SPI membranes were investigated in comparison with Nafion membranes. The methanol and water fluxes increased significantly with increasing load current density for Nafion membranes but not for the SPI membranes, indicating that they were controlled by both the electro-osmotic drag and the molecular diffusion for the former but by only the molecular diffusion for the latter. These resulted in the much better DMFC performance for the SPIs than Nafion membranes especially at high methanol feed concentrations. The Faraday's efficiency and overall DMFC efficiency at 60 °C and 200 mA cm⁻² for SPI membrane with IEC of 1.51 meq g⁻¹ were 75% and 21%, respectively, at 5 wt.% methanol feed concentration, and 36% and 9.5%, respectively, at 20 wt.% methanol concentration. They were about two times and three times higher at 5 wt.% and 20 wt.% methanol concentrations, respectively, than those for Nafion 112. The short-term durability test for 300 h at 60 °C revealed no deterioration in the DMFC performance. The SPI membranes have high potential for DMFC applications at mediate temperatures (40–80 °C).     

Solar radiation data for Beer Sheva, Israel

A number of years of data on the global irradiation incident on a horizontal surface in Beer Sheva, Israel (lat. = 31°15′N, long. = 34°48′E, elevation 240 m) have been correlated. It is apparent from these data that this locale possesses a relatively high abundance of sunshine. The average cumulative annual irradiation is 6722MJ/m² and the average daily irradiation is 18.43 MJ/m². The percentage frequency of days possessing irradiation rates greater than 20 MJ/m² is 46 per cent, whereas that possessing less than 10 MJ/m²d is 11.9 per cent. The percentage frequency of cloudy days (K_T < 0.34) is low, 7.5 per cent, whereas that for clear days (K_T > 0.65) is 29.2 per cent.     

Fluid flow processes in the BEPPU geothermal system, Japan

The Beppu geothermal system is centred beneath the late Quaternary volcanoes of Tsurumi and Garandake at the northern end of the Ryukyu volcanic arc. The deep fluid has a temperature of at least 250–300°C, and an inferred chloride concentration of 1400–1600 mg/kg. Apart from fumarolic areas near the summits of the two volcanoes, most thermal activity occurs at low elevation along the two main outflow paths towards the coast. The hot spring waters of downtown Beppu have originated from outflow along the Asamigawa Fault, with their chemistry indicating predominantly dilution of the deep fluid by groundwater. The second outflow zone towards the hot spring area of downtown Kamegawa coincides with a ridge of lavas. Here boiling, steam loss, and subsequent mixing with steam-heated groundwaters have significantly modified both the deep fluid and host rocks. The area of the geothermal system above 200°C is at least 15 km² at sea level, and the total natural heat output is inferred to be at least 250 MW. Most of this heat output occurs as subsurface hot water outflows towards the coast due to the 1300 m of topographic relief across the system.     

Aluto-langano geothermal field, ethiopian rift valley: physical characteristics and the effects of gas on well performance

This study, which focuses on the Aluto-Langano geothermal field, is part of the ongoing investigations of the geothermal systems in the Ethiopian Rift Valley. Aluto-Langano is a water-dominated gas-rich geothermal field, with a maximum temperature close to 360°C, in the Lakes District region of the Ethiopian Rift Valley. The upflow zone for the system lies along a deep, young NNE trending fault and is characterized by boiling. As a result, the deep upflow zone loses some water as steam and produces a cooler saline shallow aquifer. The high partial pressure of carbon dioxide (about 30 bar in the reservoir) depresses the water table and restricts boiling to deeper levels. The main aquifer for the system is in the Tertiary ignimbrite, which lies below 1400 m. The capacity of the existing wells is close to 7 MW_c; the energy potential of the area is estimated to be between 3000 and 6000 MW_t yr km⁻³, or 10–20 MW_c km⁻³ for over 30 years.     

The design and experimental characterisation of an asymmetric compound parabolic photovoltaic concentrator for building façade integration in the UK

A novel non-imaging asymmetric compound parabolic photovoltaic concentrator (ACPPVC) has been designed, constructed and experimentally characterised at the University of Ulster, Northern Ireland (54°36^′N, 5°37^′W). Different numbers of PV strings connected in series were experimentally characterised under outdoor conditions both with and without concentrators. Transient I–V curves for each set of parameter data points were determined and the maximum power generation, fill factor and efficiency of the system calculated for each individual I–V curve. Experiments showed that the use of an ACPPVC increased the maximum power point by 62% (i.e. the power by a factor of 1.62) when compared to a similar non-concentrating PV panel.     

Determination of glazing area in direct gain systems for three different climatic zones

This study determines the glazing area in direct gain passive systems needed to ensure thermal comfort inside a building (room air temperature 20 ± 2°C). A 4 m × 4 m × 3 m single zone isolated house is analyzed in three different types of climates namely composite (8°C to 20°C, New Delhi), cold-cloudy (−2°C to 5°C, Srinagar), and cold-sunny (−14°C to −3°C, Leh). The analysis is based on the periodic solution of the heat conduction equations describing heat transmission in the building components, floor, walls, and roof, and the Fourier representation of the ambient temperature vnd the total solar radiation intercepted by the building envelope. Two types of construction are analyzed: the first type is a traditional construction with 22-cm-thick brick wall, plastered 15 mm on both the sides (U = 2.0 W m⁻² K⁻¹); and the second one is of the same type but with 10 cm of expanded polystyrene insulation on all the four walls and the roof (U = 0.31 W m⁻² K⁻¹). It is found that for traditional construction with U = 2.0 W m⁻² K⁻¹, the glazing U value has almost no effect on the room temperature even for large variation of the glazing area (10% to 40%, expressed in terms of percentage of floor area). For a well-insulated house (U = 0.31 W m⁻² K⁻¹), the glazing U value has no effect upon the room air temperature if the glazing area is small (less than 10%). The position of the insulation on the external surfaces is more effective in reducing large inroom air temperature. Finally, for an insulated house, we recommended glazing is 30%, 20%, and 10% for cold-sunny, cold-cloudy, and composite climates, respectively.     

Diurnal pattern of global solar radiation in the tropics: a case study in Malaysia

Global solar radiation patterns in Bangi (2°56′7.3″N, 105°47′0.2″E), Malaysia are discussed. The frequency of occurrence of the various solar radiation patterns observed over a 5-year period is derived. These observations will provide useful information for the design of solar energy systems and equipment for installation in tropical countries having a similar global solar radiation pattern.     

Stochastic modelling of daily global solar radiation measured in Marrakesh, Morocco

Two stochastic models are presented of the daily global solar radiation obtained from three years of data measured on a horizontal surface in Marrakesh, Morocco (latitude 31°37′N, longitude 08°02′W, elevation 463 m). The development of these models is based on the removal of the annual periodicity and seasonal variation of solar radiation using two types of normalisation. The first model is developed using a classical decomposition of the daily radiation as the sum of two components: a trend component and a stochastic component. This model is most useful for long simulated sequences. The second model is developed using a non-dimensional variable, the clearness index, which is modelled as a stochastic process after a preliminary transformation leading to a stationary time series. Both models have satisfactorily passed validation tests for forecasting and simulation of daily global solar radiation data.     

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.     

A statistical analysis of wind power density based on the Weibull and Rayleigh models at the southern region of Turkey

The electric generating capacity of Turkey must be tripled by 2010 to meet Turkey’s electric power consumption, if the annual 8% growth in electric power consumption continues. Turkey has to make use of its renewable energy resources, such as wind and solar, not only to meet the increasing energy demand, but also for environmental reasons. Studies show that Iskenderun (36°35′N; 36°10′E) located on the Mediterranean coast of Turkey is amongst the possible wind energy generation regions. In the present study, the wind energy potential of the region is statistically analyzed based on 1-year measured hourly time-series wind speed data. The probability density distributions are derived from time-series data and distributional parameters are identified. Two probability density functions are fitted to the measured probability distributions on a monthly basis. The wind energy potential of the location is studied based on the Weibull and the Rayleigh models.     

Aquifer thermal storage (ATES) for air-conditioning of a supermarket in Turkey

A heating, ventilation and air-conditioning (HVAC) system with integrated aquifer thermal energy storage (ATES) was designed for a supermarket building in Mersin, a city near the Mediterranean coast in Turkey (36° 49′ N and 34° 36′ E). This is the first ATES application carried out in Turkey. The peak cooling and heating loads of the building are 195 and 74 kW, respectively. The general objective of the system is to use the groundwater from the aquifer to cool down the condenser of the HVAC system and at the same time storing this waste heat in the aquifer. Cooling with groundwater at around 18 °C instead of utilizing outside summer air at 30–35 °C decreases consumption of electrical energy significantly. In addition, stored heat can be recovered when it is needed in winter. The HVAC system with ATES started operation in August 2001 in cooling mode with an average coefficient of performance (COP) of 4.18, which is almost 60% higher than a conventional system.