- Email: [email protected]
Geothermal energy
07 Alternative energy sources (geothermal energy) significant trend towards decreased height with increasing planting density at the ends of the growing seasons. Both varieties demonstrated phenotypic plasticity, with individual plant weight and stem number decreasing as a function of increasing density. A range of parameters including stem width reduction, stem mortality and plant mortality were seen to vary. The population of primary stems was found to increase up to the time of canopy closure, on a per plant basis and per unit ground area basis. After this time, competition for light resulted in self-thinning of stems through until final harvest for S. dasyclados but not S. viminalis. Stem numbers per plant, recorded after leaf fall, showed different responses between both harvesting frequency and variety. With S. viminalis, stem numbers remained constant after cut back for up to 2 year, but increased rapidly as a result of a harvest after 2 year. With S. x dasyclados, a similar regrowth of stems was observed after a 2-year harvest. Prior to the harvest, stem numbers per plant decreased steadily for 2 of the 3 year depending on harvest cycle. After 3 year stem populations with S. x dasyclados were also decreasing. The degree to which non-destructive measurements could be used to (a) determine annual increment and (b) be used to predict eventual yield was examined. Cylindrical volume was the only growth measurement that enabled a reasonable tit between crop morphology and final yield to be made. The relationship was found to be a good fit and the fit improved with a longer harvest interval. Regression equations were not significantly different between sample sites but were significantly different between both variety (P < 0.001) and harvest interval (P < 0.05). In summary, it was deduced that modern varieties of S. viminalis such as Jorunn, are more suited to higher planting density and intensive harvesting, due to more erect growth reducing intra-specific competition at high planting densities.
Yield improvements through modification of planting density and harvest frequency in short rotation coppice Saiix spp. - 2. Resource capture and use in two morphoiogicaiiy diverse varieties
MI02527
Bullard, M. C. et al. Biomass and Bioenergy, 2002, 22, (l), 27-39. In the second paper in this series factorial combinations of two short rotation coppice (SRC) willow varieties (S. viminalis cv. Jorunn and S. x dasyclados) and five planting densities (10000-111000 plants ha-‘) were compared at a site in Cambridgshire, UK. Frequent measurements of above-ground and below-ground biomass accumulation (AGBA and BGBA), canopy radiation interception (0, green leaf area index (GLAI), radiation use efficiency (RUE), and attenuation coefftcient (k) were made in 1997, 1998 and 1999 in order to explain density, variety and harvest interval related yield effects. At full canopy, the highest GLAIs attained, usually by the highest plant density, were in the range 5-6.5. GLAI declined rapidly once this peak had been attained. GLAI decreased following canopy closure (radiation interception > 90%), due to loss of leaves lower down the canopy profile. Despite a more rapid loss of leaf area by the highest planting density, GLAD values were consistently greater at the highest planting density (P z 0.05) and GLAD for S. dasyclados was significantly greater than S. viminalis in each year (P < 0.05). GLAD was related to final dry matter production. Higher planting densities also had earlier dates of canopy closure, which were correlated with increased final yield, k values were in the range -0.2 to -0.51, indicating differences in morphology between the varieties although no consistent trends could be determined. Patterns of AGBA mirrored canopy development. Peak AGBA in the first season was I9 and 14 t ha-’ for S. viminalis and S. x dasyclados, respectively. End of season yield was significantly lower (11.5 and 12.9 t ha-’ for S. viminalis and S. x dasyclados, respectively) due to leaf fall and carbohydrate movement. End of season yields followed a clear, significant trend of increased yield with increasing plant density in the case of S. viminalis. This trend was not apparent with S. x dasyclados after the first season. RUE values were significantly increased (P < 0.05) by planting density and variety, ranging from 1.55 to 2.55 g MJJ’ for 10000 and 111000 plant ha-‘, respectively, in S. viminalis, which had significantly higher RUE values than S. x dasyclados. Plant mortality, after three seasons, was approximately 15% at the highest density but less than 5% at the three lowest densities. The two varieties behaved similarly. Thus, very high plant populations were sustained at the high planting densities. An inverse relationship between individual plant weight and planting density was evident, but there was no linear relationship. Higher plant densities supported larger plants than would have been expected from a linear relationship. As a consequence, yields at high densities were higher than yields at low densities.
Geothermal
energy
02/02528 A 3-D water/rock chemical interaction model for prediction of HDR/HWR geothermal reservoir performance Jing, Z. e/ a/. Georhermics,
2002, 31, (1). l-28.
A three-dimensional (3-D) water/rock chemical interaction model has been developed to examine the effect of water/rock chemical interaction (WRCI) on the long-term performance of hot dry rock and hot wet rock (HDFUHWR) reservoirs. The model, which integrates many field observations and thus generates a fracture network very similar to the natural fracture distribution in the reservoir, can predict the influence of WRCI on the overall fractured reservoir. Factors affecting WRCI and the effect of WRCI on long-term performance of Hijiori deep reservoir (Japan) have been modelled. Simulated results show that fluid chemistry, initial rock temperature, magnitude of flow rate and well spacing have a major effect on WRCI, and for such a multi-well Hijiori geothermal system, WRCI seems to make the flow distribution tend towards uniformity. The model described deals solely with chemical interactions as a function of flow rate and temperature, and takes no account of aperture variation as a result of thermoelastic effects. It is only a partial model, though it could form an important module of a coupled model.
Appraisal of the Tokaanu-Waihi geothermal field an~,~;eiationshrp with the Tongarrro geothermal freid, New 02/02529
Risk, Cl. F. et al. Geofhermics, 2002, 31, (I), 45-68. Tokaanu-Waihi geothermal field is situated near the southern end of the Taupo Volcanic Zone, New Zealand. Neutral chloride thermal waters discharge at Tokaanu and Waihi in the north of the field on flat land between the andesite volcanoes Tihia and Kakaramea and the shore of Lake Taupo, while steam-heated thermal features occur at Hipaua on the northern flanks of Kakaramea. Electrical resistivity surveys have been made over the field using several different measurement techniques. In the north of the field where roads and tracks allow vehicle access, resistivity profiling using Schlumberger arrays with electrode spacings (AB/2) of 500 m and 1000 m show that Tokaanu, Waihi and Hipaua all lie within a continuous region of low apparent resistivity (S-20 Dm) and are thus part of the same geothermal system. Along the eastern edge of the system there is a sharp transition to apparent resistivities greater than 100 Qm in the cold surrounding region. Surveys on Lake Taupo using an equatorial bipole-bipole electrode array towed behind boats (spacing equivalent to AB/2 = 500 m) found that the low resistivity zone extends offshore by about 1 km. The steep, bush-clad, southern part of the field was surveyed with magnetotelluric (MT) resistivity measurements using both naturally occurring signals and the 50 Hz radiation from the power wires as sources. These measurements found low resistivities over the north-eastern slopes and around the summits of Tihia and Kakaramea, indicating thermal activity. However, the measurements were too widely spaced to allow the field boundary to be clearly delineated. Interpretation of the resistivity and other data suggests that the Tokaanu-Waihi thermal waters rise nearly vertically from a source deep beneath the elevated southwestern part of the field to the water table. These waters then flow north to discharge at the surface near Lake Taupo. Neighbouring geothermal systems, which occur at Tongariro about 18 km south of Tokaanu-Waihi, and at Motuoapa about 10 km to the northeast, are separated from the Tokaanu-Waihi field by high resistivity ground. This suggests that the thermal fluids discharging at the three fields do not have a common source, as has been suggested previously.
Experimental results of silica removal from simulated solutions of geothermal brine of Kiziidere field, Turkey 02/02530
Badruk, M. and Matsunaga, I. Geofhermics, 2001, 30, (S), 561-570. The Denizli-Kizildere geothermal power plant in western Anatolia, Turkey, has a capacity of 20 MW. The waste brine from the plant has a flow rate of 1500 ton/h and contains approximately 400 mg/dm3 of silica, which cause scaling. This paper describes experimental work carried out to investigate the optimum conditions of silica removal from Denizli-Kizildere geothermal wastewater by precipitation.
Flashing point compressibiii of geothermal fluids with low COz content and its use7 n estimating reservoir volume
02/02531
Satman, A. and Ugur, Z. Geothermics, 2002, 31, (I), 29-44. In this study, the bubble point pressure effect or, as it is more commonly known, the flashing point effect of CO2 on geothermal fluids is shown, and the compressibility of the geothermal fluids containing low concentrations of dissolved COz at the flashing point is formulated for isoenthalpic phase change. The compressibility, termed the isoenthalpic flashing point compressibility, can be calculated with well-known parameters. New, easy-to-use graphs are presented to estimate the compressibility for such systems. Correction for ionic strength of the geothermal brine is also considered. The practical use of the compressibility is illustrated to estimate the fluid content of a geothermal reservoir. A material balance method incorporating the isoenthalpic flashing point compressibility in geothermal modeling is investigated. The material balance method presented in the paper is of Fuel and Energy Abstracts
September 2002
335
07 A/femafive energy sources (solar enegy) primary importance in the evaluation of geothermal reservoirs since both the area1 extent and the vertical thickness can not be accurately determined, particularly in the initial development stages of the reservoirs. Applications of the method to geothermal fields are discussed. 02/53532 Fumaroiic gas chemistry at Wairakei, New Zealand, 1925-1998 Glover, R. B. el al. Geofhermics, 2001, 30, (5), 51I-525. The Wairakei geothermal field fumarolic discharges are at their greatest intensity from the Karapiti Thermal Area. This part of the geothermal field contains numerous steamdominated features in an area of approximately 1 km’. Since 1952 there have been many changes to the surface features and thermal activity at Karapiti related to the development-induced pressure drawdown over most of the field. A greatly expanded steam cap fed by a large low-pressure steam zone in the Wairakei reservoir has replaced the hot chloride water originally underlying Karapiti. There have been intermittent chemical surveys of the steam vents at Karapiti since 1951, with major chemical surveys undertaken in 1961 and 1990. In 1990, the concentrations of COz were found to be about 200 mmol/lOO mol HzO, double the 1961 values. Of particular interest is the change between 1936 and 1987 in gas chemistry of the main Karapiti feature, the Karapiti Blowhole (F712), which follows the change in heatflow from the Karapiti Thermal Area. Since 1990, gas concentrations appear to be dropping to low, pre-development levels, most likely due to the decreasing pressures in the lower pressure steam zone. Underground processes leading to a high gas content in a large fumarole formed in 1967 and other fumaroles in different parts of the Wairakei field are discussed. 02/02533 Geochemistry of the surface and deep fiulds of the Miravaiies volcano geothermal system (Costa Rica) Gherardi, F. ef al. Georhermics, 2002, 31, (I), 91-128. 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 COz, with minor amounts of HzS and Nz. Relative Nz, Ar and He contents reveal a typical arc-type signature and significant inflow of meteoric-derived gases. Cl-SiOz-enthalpy and 61s0-6ZH-CI 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 Sod-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 Hz.? oxidation or inflow of “immature” volcanic waters. 03/02534 Mixing of thermal and non-thermal waters in the Steamboat Hills area, Nevada, USA Skalbeck, J. D. er al. Geofhermfcs, 2002, 31, (I), 69-90. Groundwater monitoring began in 1985 at two geothermal facilities in the Steamboat Hills area, Nevada. Wells representing non-thermal, thermal, and mixed waters are evaluated by assessing temporal variations in B and Cl concentrations, water levels, and temperature. The objective is to assess the hydrologic and geochemical connection between the fractured bedrock geothermal reservoir and the alluvial aquifer. Results suggest that fault-controlled groundwater flow between the geothermal system and the alluvial aquifer is the dominant hydrologic process. Temporal trends suggest that the thermal water component in the alluvial aquifer has increased in most areas but decreased in at least one area.
method also gives a representative (order of magnitude) estimate of the total heat discharged by fumarole clouds if measurements from a single, large fumarole can be used in conjunction with a recent airphoto.
Solar energy 02lO2525 A contactless hotoconductance technique to evaluate the quantum eff Pciency of solar ceil emitters Cuevas, A. el al. Solar Energy Materials di Solar Cells, 2002, 71, 295312.
A new technique, the spectral response of the steady-state photoconductance, is roposed for solar cell characterization in research and development. T1 e emphasis of this paper is on the evaluation of the carrier collection efficiency of the emitter region based on a simple, two-wavelength approach. It is shown that in addition to the wellestablished determination of the wafer recombination properties that results from a long-wavelength photoconductance measurement, detailed emitter quantum-efficiency information can be obtained by performing a second measurement with short-wavelength light. The method is experimentally demonstrated with silicon solar cell precursors having emitters with markedly different levels of surface and bulk recombination losses. The main advantages of the spectral photoconductance technique are that it is fast, contactless, and can be used immediately after junction formation before metaiiization; these properties make it very appropriate for routine monitoring of the emitter region, including in-line process control. 03/02537 A high-efficiency triple cycle for solar power generation Kribus, A. Solar Energy, 2002, 72, (l), 1-l 1. The last three decades have witnessed a trend in solar thermal electricity generation of increasing the concentration of sunlight, the operating temperature, and subsequently the efficiency of conversion from sunlight to electricity. The current state of the art concept is a solar-driven combined cycle, with sunlight concentration ratio of a few thousands, temperatures of about lOOO-1300°C and overall annual average conversion efficiency of about 20%. A possible next step in this trend is presented: a solar triple cycle, with a high-temperature MHD generator and two additional cycles in series. This tripe cycle is powered by solar heat at temperatures around 2000°C and solar concentration of about 10,000. The overall peak conversion efficiency of the solar triple cycle is shown to be significantly higher than the solar combined cycle scheme. The sensitivity of this result to several system parameters and the technological feasibility of the solar triple cycle are also discussed. 03/02538 A new heat-pipe type solar domestic hot water system Mathioulakis, E. and Belessiotis, V. Solar Energy, 2002, 72, (I), 13-20. The performance of a new solar hot water system with an integrated heat-pipe is investigated theoretically and experimentally. The new system uses a wickless gravity assisted loop heat-pipe for the heat transfer from the collector-evaporator to the tank through a heat exchanger-condenser. A detailed heat transfer experimental study is performed, focused on the thermal behaviour of the different parts of the system. The results show that the system can reach satisfactory efficiencies which, in combination with manufacturing simplicity, absence of moving parts and good behaviour under freeze conditions, make it an interesting technological solution. Furthermore, a theoretical model for the collector is proposed and comparison with experimental results is performed. This model can be used for the optimization of the system design.
03lO2535 Steam cloud characteristics and heat output of fumaroies Hochstein, M. P. and Bromley, C. J. Georhermics, 2001, 30, (5), 547-
03/02539 A photovoitaiclthermai (PWT) collector with a po;$n$r absorber plate. Experimental study and analytical
559.
Sandnes, B. and Rekstad, J. Solar Energy, 2002, 72, (I), 63-73. A polymer solar heat collector was combined with single-crystal silicon PV cells in a hybrid energy-generating unit that simultaneously produced low temperature heat and electricity. The PV/T unit was tested experimentally to determine its thermal and photovoltaic performance, in addition to the interaction mechanisms between the PV and thermal energy systems. Thermal efficiency measurements for different collector configurations are compared, and PV performance and temperature readings are presented and discussed. An analytical model for the PVfl system simulated the temperature development and the performance of both the thermal and photovoltaic units.
The heat transferred to the atmosphere by fumarole clouds is linearly proportional to the cloud area that is visible in vertical air-photos. Using measured outputs of a few accessible fumaroles, the total heat output of all fumaroles in a fumarole field can be assessed from the total area of the steam clouds. Normalized heat outputs, Q,, and normalized cloud areas, A., were used as variables. Two surveys of the large Karapiti fumarole field (Wairakei, New Zealand) show that the total heat discharged by fumaroles with cloud areas > IO m* was 99 MW and 88 MW in 1999 and 2000, respectively. The output of vents with smaller cloud areas has to be obtained
336
Fuel and Energy Abstracts
from ground
September 2002
surveys.
The
Yield improvements through modification of planting density and harvest frequency in short rotation coppice Saiix spp. - 2. Resource capture and use in two morphoiogicaiiy diverse varieties
MI02527
Bullard, M. C. et al. Biomass and Bioenergy, 2002, 22, (l), 27-39. In the second paper in this series factorial combinations of two short rotation coppice (SRC) willow varieties (S. viminalis cv. Jorunn and S. x dasyclados) and five planting densities (10000-111000 plants ha-‘) were compared at a site in Cambridgshire, UK. Frequent measurements of above-ground and below-ground biomass accumulation (AGBA and BGBA), canopy radiation interception (0, green leaf area index (GLAI), radiation use efficiency (RUE), and attenuation coefftcient (k) were made in 1997, 1998 and 1999 in order to explain density, variety and harvest interval related yield effects. At full canopy, the highest GLAIs attained, usually by the highest plant density, were in the range 5-6.5. GLAI declined rapidly once this peak had been attained. GLAI decreased following canopy closure (radiation interception > 90%), due to loss of leaves lower down the canopy profile. Despite a more rapid loss of leaf area by the highest planting density, GLAD values were consistently greater at the highest planting density (P z 0.05) and GLAD for S. dasyclados was significantly greater than S. viminalis in each year (P < 0.05). GLAD was related to final dry matter production. Higher planting densities also had earlier dates of canopy closure, which were correlated with increased final yield, k values were in the range -0.2 to -0.51, indicating differences in morphology between the varieties although no consistent trends could be determined. Patterns of AGBA mirrored canopy development. Peak AGBA in the first season was I9 and 14 t ha-’ for S. viminalis and S. x dasyclados, respectively. End of season yield was significantly lower (11.5 and 12.9 t ha-’ for S. viminalis and S. x dasyclados, respectively) due to leaf fall and carbohydrate movement. End of season yields followed a clear, significant trend of increased yield with increasing plant density in the case of S. viminalis. This trend was not apparent with S. x dasyclados after the first season. RUE values were significantly increased (P < 0.05) by planting density and variety, ranging from 1.55 to 2.55 g MJJ’ for 10000 and 111000 plant ha-‘, respectively, in S. viminalis, which had significantly higher RUE values than S. x dasyclados. Plant mortality, after three seasons, was approximately 15% at the highest density but less than 5% at the three lowest densities. The two varieties behaved similarly. Thus, very high plant populations were sustained at the high planting densities. An inverse relationship between individual plant weight and planting density was evident, but there was no linear relationship. Higher plant densities supported larger plants than would have been expected from a linear relationship. As a consequence, yields at high densities were higher than yields at low densities.
Geothermal
energy
02/02528 A 3-D water/rock chemical interaction model for prediction of HDR/HWR geothermal reservoir performance Jing, Z. e/ a/. Georhermics,
2002, 31, (1). l-28.
A three-dimensional (3-D) water/rock chemical interaction model has been developed to examine the effect of water/rock chemical interaction (WRCI) on the long-term performance of hot dry rock and hot wet rock (HDFUHWR) reservoirs. The model, which integrates many field observations and thus generates a fracture network very similar to the natural fracture distribution in the reservoir, can predict the influence of WRCI on the overall fractured reservoir. Factors affecting WRCI and the effect of WRCI on long-term performance of Hijiori deep reservoir (Japan) have been modelled. Simulated results show that fluid chemistry, initial rock temperature, magnitude of flow rate and well spacing have a major effect on WRCI, and for such a multi-well Hijiori geothermal system, WRCI seems to make the flow distribution tend towards uniformity. The model described deals solely with chemical interactions as a function of flow rate and temperature, and takes no account of aperture variation as a result of thermoelastic effects. It is only a partial model, though it could form an important module of a coupled model.
Appraisal of the Tokaanu-Waihi geothermal field an~,~;eiationshrp with the Tongarrro geothermal freid, New 02/02529
Risk, Cl. F. et al. Geofhermics, 2002, 31, (I), 45-68. Tokaanu-Waihi geothermal field is situated near the southern end of the Taupo Volcanic Zone, New Zealand. Neutral chloride thermal waters discharge at Tokaanu and Waihi in the north of the field on flat land between the andesite volcanoes Tihia and Kakaramea and the shore of Lake Taupo, while steam-heated thermal features occur at Hipaua on the northern flanks of Kakaramea. Electrical resistivity surveys have been made over the field using several different measurement techniques. In the north of the field where roads and tracks allow vehicle access, resistivity profiling using Schlumberger arrays with electrode spacings (AB/2) of 500 m and 1000 m show that Tokaanu, Waihi and Hipaua all lie within a continuous region of low apparent resistivity (S-20 Dm) and are thus part of the same geothermal system. Along the eastern edge of the system there is a sharp transition to apparent resistivities greater than 100 Qm in the cold surrounding region. Surveys on Lake Taupo using an equatorial bipole-bipole electrode array towed behind boats (spacing equivalent to AB/2 = 500 m) found that the low resistivity zone extends offshore by about 1 km. The steep, bush-clad, southern part of the field was surveyed with magnetotelluric (MT) resistivity measurements using both naturally occurring signals and the 50 Hz radiation from the power wires as sources. These measurements found low resistivities over the north-eastern slopes and around the summits of Tihia and Kakaramea, indicating thermal activity. However, the measurements were too widely spaced to allow the field boundary to be clearly delineated. Interpretation of the resistivity and other data suggests that the Tokaanu-Waihi thermal waters rise nearly vertically from a source deep beneath the elevated southwestern part of the field to the water table. These waters then flow north to discharge at the surface near Lake Taupo. Neighbouring geothermal systems, which occur at Tongariro about 18 km south of Tokaanu-Waihi, and at Motuoapa about 10 km to the northeast, are separated from the Tokaanu-Waihi field by high resistivity ground. This suggests that the thermal fluids discharging at the three fields do not have a common source, as has been suggested previously.
Experimental results of silica removal from simulated solutions of geothermal brine of Kiziidere field, Turkey 02/02530
Badruk, M. and Matsunaga, I. Geofhermics, 2001, 30, (S), 561-570. The Denizli-Kizildere geothermal power plant in western Anatolia, Turkey, has a capacity of 20 MW. The waste brine from the plant has a flow rate of 1500 ton/h and contains approximately 400 mg/dm3 of silica, which cause scaling. This paper describes experimental work carried out to investigate the optimum conditions of silica removal from Denizli-Kizildere geothermal wastewater by precipitation.
Flashing point compressibiii of geothermal fluids with low COz content and its use7 n estimating reservoir volume
02/02531
Satman, A. and Ugur, Z. Geothermics, 2002, 31, (I), 29-44. In this study, the bubble point pressure effect or, as it is more commonly known, the flashing point effect of CO2 on geothermal fluids is shown, and the compressibility of the geothermal fluids containing low concentrations of dissolved COz at the flashing point is formulated for isoenthalpic phase change. The compressibility, termed the isoenthalpic flashing point compressibility, can be calculated with well-known parameters. New, easy-to-use graphs are presented to estimate the compressibility for such systems. Correction for ionic strength of the geothermal brine is also considered. The practical use of the compressibility is illustrated to estimate the fluid content of a geothermal reservoir. A material balance method incorporating the isoenthalpic flashing point compressibility in geothermal modeling is investigated. The material balance method presented in the paper is of Fuel and Energy Abstracts
September 2002
335
07 A/femafive energy sources (solar enegy) primary importance in the evaluation of geothermal reservoirs since both the area1 extent and the vertical thickness can not be accurately determined, particularly in the initial development stages of the reservoirs. Applications of the method to geothermal fields are discussed. 02/53532 Fumaroiic gas chemistry at Wairakei, New Zealand, 1925-1998 Glover, R. B. el al. Geofhermics, 2001, 30, (5), 51I-525. The Wairakei geothermal field fumarolic discharges are at their greatest intensity from the Karapiti Thermal Area. This part of the geothermal field contains numerous steamdominated features in an area of approximately 1 km’. Since 1952 there have been many changes to the surface features and thermal activity at Karapiti related to the development-induced pressure drawdown over most of the field. A greatly expanded steam cap fed by a large low-pressure steam zone in the Wairakei reservoir has replaced the hot chloride water originally underlying Karapiti. There have been intermittent chemical surveys of the steam vents at Karapiti since 1951, with major chemical surveys undertaken in 1961 and 1990. In 1990, the concentrations of COz were found to be about 200 mmol/lOO mol HzO, double the 1961 values. Of particular interest is the change between 1936 and 1987 in gas chemistry of the main Karapiti feature, the Karapiti Blowhole (F712), which follows the change in heatflow from the Karapiti Thermal Area. Since 1990, gas concentrations appear to be dropping to low, pre-development levels, most likely due to the decreasing pressures in the lower pressure steam zone. Underground processes leading to a high gas content in a large fumarole formed in 1967 and other fumaroles in different parts of the Wairakei field are discussed. 02/02533 Geochemistry of the surface and deep fiulds of the Miravaiies volcano geothermal system (Costa Rica) Gherardi, F. ef al. Georhermics, 2002, 31, (I), 91-128. 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 COz, with minor amounts of HzS and Nz. Relative Nz, Ar and He contents reveal a typical arc-type signature and significant inflow of meteoric-derived gases. Cl-SiOz-enthalpy and 61s0-6ZH-CI 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 Sod-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 Hz.? oxidation or inflow of “immature” volcanic waters. 03/02534 Mixing of thermal and non-thermal waters in the Steamboat Hills area, Nevada, USA Skalbeck, J. D. er al. Geofhermfcs, 2002, 31, (I), 69-90. Groundwater monitoring began in 1985 at two geothermal facilities in the Steamboat Hills area, Nevada. Wells representing non-thermal, thermal, and mixed waters are evaluated by assessing temporal variations in B and Cl concentrations, water levels, and temperature. The objective is to assess the hydrologic and geochemical connection between the fractured bedrock geothermal reservoir and the alluvial aquifer. Results suggest that fault-controlled groundwater flow between the geothermal system and the alluvial aquifer is the dominant hydrologic process. Temporal trends suggest that the thermal water component in the alluvial aquifer has increased in most areas but decreased in at least one area.
method also gives a representative (order of magnitude) estimate of the total heat discharged by fumarole clouds if measurements from a single, large fumarole can be used in conjunction with a recent airphoto.
Solar energy 02lO2525 A contactless hotoconductance technique to evaluate the quantum eff Pciency of solar ceil emitters Cuevas, A. el al. Solar Energy Materials di Solar Cells, 2002, 71, 295312.
A new technique, the spectral response of the steady-state photoconductance, is roposed for solar cell characterization in research and development. T1 e emphasis of this paper is on the evaluation of the carrier collection efficiency of the emitter region based on a simple, two-wavelength approach. It is shown that in addition to the wellestablished determination of the wafer recombination properties that results from a long-wavelength photoconductance measurement, detailed emitter quantum-efficiency information can be obtained by performing a second measurement with short-wavelength light. The method is experimentally demonstrated with silicon solar cell precursors having emitters with markedly different levels of surface and bulk recombination losses. The main advantages of the spectral photoconductance technique are that it is fast, contactless, and can be used immediately after junction formation before metaiiization; these properties make it very appropriate for routine monitoring of the emitter region, including in-line process control. 03/02537 A high-efficiency triple cycle for solar power generation Kribus, A. Solar Energy, 2002, 72, (l), 1-l 1. The last three decades have witnessed a trend in solar thermal electricity generation of increasing the concentration of sunlight, the operating temperature, and subsequently the efficiency of conversion from sunlight to electricity. The current state of the art concept is a solar-driven combined cycle, with sunlight concentration ratio of a few thousands, temperatures of about lOOO-1300°C and overall annual average conversion efficiency of about 20%. A possible next step in this trend is presented: a solar triple cycle, with a high-temperature MHD generator and two additional cycles in series. This tripe cycle is powered by solar heat at temperatures around 2000°C and solar concentration of about 10,000. The overall peak conversion efficiency of the solar triple cycle is shown to be significantly higher than the solar combined cycle scheme. The sensitivity of this result to several system parameters and the technological feasibility of the solar triple cycle are also discussed. 03/02538 A new heat-pipe type solar domestic hot water system Mathioulakis, E. and Belessiotis, V. Solar Energy, 2002, 72, (I), 13-20. The performance of a new solar hot water system with an integrated heat-pipe is investigated theoretically and experimentally. The new system uses a wickless gravity assisted loop heat-pipe for the heat transfer from the collector-evaporator to the tank through a heat exchanger-condenser. A detailed heat transfer experimental study is performed, focused on the thermal behaviour of the different parts of the system. The results show that the system can reach satisfactory efficiencies which, in combination with manufacturing simplicity, absence of moving parts and good behaviour under freeze conditions, make it an interesting technological solution. Furthermore, a theoretical model for the collector is proposed and comparison with experimental results is performed. This model can be used for the optimization of the system design.
03lO2535 Steam cloud characteristics and heat output of fumaroies Hochstein, M. P. and Bromley, C. J. Georhermics, 2001, 30, (5), 547-
03/02539 A photovoitaiclthermai (PWT) collector with a po;$n$r absorber plate. Experimental study and analytical
559.
Sandnes, B. and Rekstad, J. Solar Energy, 2002, 72, (I), 63-73. A polymer solar heat collector was combined with single-crystal silicon PV cells in a hybrid energy-generating unit that simultaneously produced low temperature heat and electricity. The PV/T unit was tested experimentally to determine its thermal and photovoltaic performance, in addition to the interaction mechanisms between the PV and thermal energy systems. Thermal efficiency measurements for different collector configurations are compared, and PV performance and temperature readings are presented and discussed. An analytical model for the PVfl system simulated the temperature development and the performance of both the thermal and photovoltaic units.
The heat transferred to the atmosphere by fumarole clouds is linearly proportional to the cloud area that is visible in vertical air-photos. Using measured outputs of a few accessible fumaroles, the total heat output of all fumaroles in a fumarole field can be assessed from the total area of the steam clouds. Normalized heat outputs, Q,, and normalized cloud areas, A., were used as variables. Two surveys of the large Karapiti fumarole field (Wairakei, New Zealand) show that the total heat discharged by fumaroles with cloud areas > IO m* was 99 MW and 88 MW in 1999 and 2000, respectively. The output of vents with smaller cloud areas has to be obtained
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Fuel and Energy Abstracts
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September 2002
surveys.
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