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H2 pressure effect on microcrystalline silicon thin films growth and structure
13 Altemative energy supplies (solar energy) satisfy parasitic electrical d e m a n d and the burning of biogas to satisfy t h e r m a l d e m a n d was found to be more advantageous than using biogas in a combined heat and power (CHP) p l a n t to cover parasitic electrical and t h e r m a l demand. The D R A N C O process p r o d u c e d more fuel than the C A D process due to the lower t h e r m a l d e m a n d of the digester. The economics of the D R A N C O process were superior to the C A D process due to the greater gate fee (it is assumed that no gate fee is obtained from agricultural slurry) and the greater quantity of biogas available for sale. The D R A N C O process leads to greater greenhouse-gas savings than the C A D process due to the d i s p l a c e m e n t of more O F M S W from landfill and more petrol from transport. The options w h e n applied to Ireland could lead to a substitution of 1% of p e t r o l and diesel and to a 12% reduction in greenhouse-gas emissions from the t r a n s p o r t sector.
06•01346 Total SiH4/H2 pressure effect on microcrystalline silicon thin films growth and structure Katsia, E. et al. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 157 167. The effect of the total SiH4/H2 gas pressure (1 10 Torr) on the growth rate, the film crystallinity and the nature of hydrogen bonding of microcrystalline silicon thin films deposited by 13.56 M H z plasmae n h a n c e d chemical v a p o u r deposition ( P E C V D ) was investigated u n d e r well-controlled discharge conditions. The deposition rate presents an o p t i m u m for 2.5 Tort, which does not follow the trend of silane c o n s u m p t i o n that increases with pressure and is attributed to an increase in p l a s m a density. The film crystallinity increases with pressure from 1 2.5 Torr and then remains a l m o s t the same, whereas the films deposited at 1 Torr are highly stressed. On the other hand, hydrogen bonding is also drastically affected.
Solar energy 06•01349 Adaptation of monocrystalline solar cell process to multicrystalline materials Ponce-Alc(mtara , S. et al. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 411 421. Due to its low cost and high possibilities, multicrystalline silicon (mcSi) is an attractive substrate to produce solar cells. Trying to reach high efficiencies with a simple and repetitive method, a standard monocrystalline process was a d a p t e d to multicrystalline material. Different gettering methods (Phosphorous, A l u m i n i u m and P and A1 cogettering) have been studied. In the laboratory, 15.2% efficiency have been achieved to date. PC1D simulations shows that, with a reduction of bulk r e c o m b i n a t i o n and a b e t t e r front and rear passivation schemes, efficiencies higher than 18% could be obtained.
06•01350
Advances in Bragg stack quantum well solar cells
Johnson, D. C. et al. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 169 179. Strain-balanced q u a n t u m well solar cells (SB-QWSC) extend the p h o t o n absorption edge beyond that of bulk G a A s by incorporation of q u a n t u m wells in the i-region of a p i n device. The addition of a distributed Bragg reflector ( D B R ) can substantially increase the p h o t o c u r r e n t with little or no d e t r i m e n t to the dark-current. E x p e r i m e n t a l results are p r e s e n t e d that show i m p r o v e m e n t s of D B R cell efficiencies over SB-QWSC's without DBR's. In addition, at high dark-current levels appropriate to high concentration, it was observed that the dark-currents of the SB-QWSC's exhibit ideal diode behaviour. The authors present evidence that the ideality n = 1 darkcurrent is reduced in the D B R cells and discuss the possible efficiency improvements if the dark-current is radiatively dominant.
06•01351 Augmentation of heat transfer coefficient by using 90 ° broken transverse ribs on absorber plate of solar air heater
Geothermal energy
06•01347 Light hydrocarbons as redox and temperature indicators in the geothermal field of El Tatio (northern Chile) Tassi, F. et al. Applied Geochemistry, 2005, 20, (11), 2049 2062. E1 Tatio (northern Chile), one of the largest g e o t h e r m a l fields of South America, is presently u n d e r g o i n g a new p r o g r a m of g e o t h e r m a l exploration, after the failure of the first exploration phase in the early 1970s. The geochemical features of the fluid discharges characterizing this system mainly consist of boiling pools and fumaroles, and r e p r e s e n t the result of a complex mixing process involving three main components: (i) hydrothermal; (ii) atmospheric; (iii) magmatic. Chemical reactions involving light hydrocarbons equilibrate at higher t e m p e r a t u r e than those directly m e a s u r e d in the g e o t h e r m a l wells and calculated on the basis of the composition of the inorganic gas species. This suggests that in the d e e p e r parts of the h y d r o t h e r m a l system t e m p e r a t u r e s higher than 300°C may be achieved. Such results can have a strong impact for the evaluation of the p o t e n t i a l resources of this g e o t h e r m a l system. Moreover, the chemical characteristics of the organic gas fraction allow the a s s e s s m e n t of the c h e m i c a l ~ h y s i c a l conditions governing the geochemical processes acting on g e o t h e r m a l fluids at depth.
06•01348 Secondary mineral-fluid equilibria in the Krafla and N~mafjall geothermal systems, Iceland G u d m u n d s s o n , B. T. and Arn6rsson, S. Applied Geochemistry, 2005, 20, (9), 1607 1625. Aquifer fluid compositions and aqueous species distribution have been calculated for 22 samples collected from p r o d u c i n g wells in the Krafla and N~tmafjall g e o t h e r m a l areas, Iceland. Overall m i n e r a l solution equilibrium is rather closely a p p r o a c h e d in the aquifer beyond the depressurisation zone a r o u n d wells for all major c o m p o n e n t s entering h y d r o t h e r m a l minerals. The minerals involved are in alphabetical order: albite, calcite, chlorite, epidote, K-feldspar (adularia), prehnite, pyrite, pyrrhotite, quartz and wairakite. Calculated saturation indices for O H - b e a r i n g A1 silicates show more scatter than for minerals of simpler composition. A large scatter is also observed for pyrite and pyrrhotite. The main uncertainty involved in calculating m i n e r a l saturation indices, particularly in the case of 'excess' enthalpy well discharges, lies in the model adopted to calculate the aquifer water composition and its aqueous species distribution and not in the quality of the t h e r m o d y n a m i c data on the aqueous species and the minerals with the possible exception of epidote and Fe z + .
Sahu, M. M. and Bhagoria, J. L. Renewable Energy, 2005, 30, (13), 2057 2073. A n e x p e r i m e n t a l investigation has b e e n carried out to study the heat transfer coefficient by using 90 ° b r o k e n transverse ribs on absorber plate of a solar air heater; the r o u g h e n e d wall being h e a t e d while the r e m a i n i n g three walls are insulated. The r o u g h e n e d wall has roughness with pitch (P), ranging from 10 30 mm, height of the rib of 1.5 m m and duct aspect ratio of 8. The air flow rate corresponds to Reynolds n u m b e r between 3000 12,000. The heat transfer results have been c o m p a r e d with those for smooth ducts u n d e r similar flow and t h e r m a l b o u n d a r y condition to d e t e r m i n e the t h e r m a l efficiency of solar air heater.
06•01352 Design of chemical composition and optimum working conditions for trivalent black chromium electroplating bath used for solar thermal collectors Bayati, M. R. et al. Renewable Energy, 2005, 30, (14), 2163 2178. Black c h r o m i u m is one of the selective surfaces which are commonly used in solar t h e r m a l systems. The aim of this research was to design an electroplating bath, using c h r o m i u m trivalent ions instead of its hexavalent ions because of its toxicity, for black c h r o m i u m coating to produce a good metallurgical and light p r o p e r t i e s at low cost and reproducibility. The effect of the additives was investigated and a coating with an absorption coefficient of 0.96 was prepared. The bath contained inexpensive constituents such as c h r o m i u m sulfate, cobalt chloride, sodium fluoride, sodium hypophosphite and sodium dihydrogen p h o s p h a t e and did not need any p H control. T h e r m a l resistance, corrosion resistance and adhesion of the coatings as well as throwing power of the bath were investigated. The effect of bright Ni as an u n d e r c o a t before black c h r o m i u m electroplating was also investigated. SEM and X R D techniques were employed to characterize the surface microstructure and chemical composition. Spectroscopy was also used to measure absorptance of the coatings.
06/01353 Didactic software for solar cells and materials parameters analysis Patryn, A. and Pietruszko, S. M. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 271 285. The authors p r e s e n t a package of c o m p u t e r applications g a t h e r e d in a form of virtual laboratory as a package of the virtual exercises to solar cells p a r a m e t e r s analysis at a student university laboratory. The applications may also be used to analyse some aspects of silicon materials or solar cell structures as a research tool. The package consists of three blocks of exercises. Each of the blocks solves different tasks and is based on different software platforms (LabWindows, Visual Basic, Java and Flash). The range of the tasks is relatively wide: from analysis of the role of p a r a m e t e r s of the material (silicon) on the
Fuel and Energy Abstracts
May 2006
201
06•01346 Total SiH4/H2 pressure effect on microcrystalline silicon thin films growth and structure Katsia, E. et al. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 157 167. The effect of the total SiH4/H2 gas pressure (1 10 Torr) on the growth rate, the film crystallinity and the nature of hydrogen bonding of microcrystalline silicon thin films deposited by 13.56 M H z plasmae n h a n c e d chemical v a p o u r deposition ( P E C V D ) was investigated u n d e r well-controlled discharge conditions. The deposition rate presents an o p t i m u m for 2.5 Tort, which does not follow the trend of silane c o n s u m p t i o n that increases with pressure and is attributed to an increase in p l a s m a density. The film crystallinity increases with pressure from 1 2.5 Torr and then remains a l m o s t the same, whereas the films deposited at 1 Torr are highly stressed. On the other hand, hydrogen bonding is also drastically affected.
Solar energy 06•01349 Adaptation of monocrystalline solar cell process to multicrystalline materials Ponce-Alc(mtara , S. et al. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 411 421. Due to its low cost and high possibilities, multicrystalline silicon (mcSi) is an attractive substrate to produce solar cells. Trying to reach high efficiencies with a simple and repetitive method, a standard monocrystalline process was a d a p t e d to multicrystalline material. Different gettering methods (Phosphorous, A l u m i n i u m and P and A1 cogettering) have been studied. In the laboratory, 15.2% efficiency have been achieved to date. PC1D simulations shows that, with a reduction of bulk r e c o m b i n a t i o n and a b e t t e r front and rear passivation schemes, efficiencies higher than 18% could be obtained.
06•01350
Advances in Bragg stack quantum well solar cells
Johnson, D. C. et al. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 169 179. Strain-balanced q u a n t u m well solar cells (SB-QWSC) extend the p h o t o n absorption edge beyond that of bulk G a A s by incorporation of q u a n t u m wells in the i-region of a p i n device. The addition of a distributed Bragg reflector ( D B R ) can substantially increase the p h o t o c u r r e n t with little or no d e t r i m e n t to the dark-current. E x p e r i m e n t a l results are p r e s e n t e d that show i m p r o v e m e n t s of D B R cell efficiencies over SB-QWSC's without DBR's. In addition, at high dark-current levels appropriate to high concentration, it was observed that the dark-currents of the SB-QWSC's exhibit ideal diode behaviour. The authors present evidence that the ideality n = 1 darkcurrent is reduced in the D B R cells and discuss the possible efficiency improvements if the dark-current is radiatively dominant.
06•01351 Augmentation of heat transfer coefficient by using 90 ° broken transverse ribs on absorber plate of solar air heater
Geothermal energy
06•01347 Light hydrocarbons as redox and temperature indicators in the geothermal field of El Tatio (northern Chile) Tassi, F. et al. Applied Geochemistry, 2005, 20, (11), 2049 2062. E1 Tatio (northern Chile), one of the largest g e o t h e r m a l fields of South America, is presently u n d e r g o i n g a new p r o g r a m of g e o t h e r m a l exploration, after the failure of the first exploration phase in the early 1970s. The geochemical features of the fluid discharges characterizing this system mainly consist of boiling pools and fumaroles, and r e p r e s e n t the result of a complex mixing process involving three main components: (i) hydrothermal; (ii) atmospheric; (iii) magmatic. Chemical reactions involving light hydrocarbons equilibrate at higher t e m p e r a t u r e than those directly m e a s u r e d in the g e o t h e r m a l wells and calculated on the basis of the composition of the inorganic gas species. This suggests that in the d e e p e r parts of the h y d r o t h e r m a l system t e m p e r a t u r e s higher than 300°C may be achieved. Such results can have a strong impact for the evaluation of the p o t e n t i a l resources of this g e o t h e r m a l system. Moreover, the chemical characteristics of the organic gas fraction allow the a s s e s s m e n t of the c h e m i c a l ~ h y s i c a l conditions governing the geochemical processes acting on g e o t h e r m a l fluids at depth.
06•01348 Secondary mineral-fluid equilibria in the Krafla and N~mafjall geothermal systems, Iceland G u d m u n d s s o n , B. T. and Arn6rsson, S. Applied Geochemistry, 2005, 20, (9), 1607 1625. Aquifer fluid compositions and aqueous species distribution have been calculated for 22 samples collected from p r o d u c i n g wells in the Krafla and N~tmafjall g e o t h e r m a l areas, Iceland. Overall m i n e r a l solution equilibrium is rather closely a p p r o a c h e d in the aquifer beyond the depressurisation zone a r o u n d wells for all major c o m p o n e n t s entering h y d r o t h e r m a l minerals. The minerals involved are in alphabetical order: albite, calcite, chlorite, epidote, K-feldspar (adularia), prehnite, pyrite, pyrrhotite, quartz and wairakite. Calculated saturation indices for O H - b e a r i n g A1 silicates show more scatter than for minerals of simpler composition. A large scatter is also observed for pyrite and pyrrhotite. The main uncertainty involved in calculating m i n e r a l saturation indices, particularly in the case of 'excess' enthalpy well discharges, lies in the model adopted to calculate the aquifer water composition and its aqueous species distribution and not in the quality of the t h e r m o d y n a m i c data on the aqueous species and the minerals with the possible exception of epidote and Fe z + .
Sahu, M. M. and Bhagoria, J. L. Renewable Energy, 2005, 30, (13), 2057 2073. A n e x p e r i m e n t a l investigation has b e e n carried out to study the heat transfer coefficient by using 90 ° b r o k e n transverse ribs on absorber plate of a solar air heater; the r o u g h e n e d wall being h e a t e d while the r e m a i n i n g three walls are insulated. The r o u g h e n e d wall has roughness with pitch (P), ranging from 10 30 mm, height of the rib of 1.5 m m and duct aspect ratio of 8. The air flow rate corresponds to Reynolds n u m b e r between 3000 12,000. The heat transfer results have been c o m p a r e d with those for smooth ducts u n d e r similar flow and t h e r m a l b o u n d a r y condition to d e t e r m i n e the t h e r m a l efficiency of solar air heater.
06•01352 Design of chemical composition and optimum working conditions for trivalent black chromium electroplating bath used for solar thermal collectors Bayati, M. R. et al. Renewable Energy, 2005, 30, (14), 2163 2178. Black c h r o m i u m is one of the selective surfaces which are commonly used in solar t h e r m a l systems. The aim of this research was to design an electroplating bath, using c h r o m i u m trivalent ions instead of its hexavalent ions because of its toxicity, for black c h r o m i u m coating to produce a good metallurgical and light p r o p e r t i e s at low cost and reproducibility. The effect of the additives was investigated and a coating with an absorption coefficient of 0.96 was prepared. The bath contained inexpensive constituents such as c h r o m i u m sulfate, cobalt chloride, sodium fluoride, sodium hypophosphite and sodium dihydrogen p h o s p h a t e and did not need any p H control. T h e r m a l resistance, corrosion resistance and adhesion of the coatings as well as throwing power of the bath were investigated. The effect of bright Ni as an u n d e r c o a t before black c h r o m i u m electroplating was also investigated. SEM and X R D techniques were employed to characterize the surface microstructure and chemical composition. Spectroscopy was also used to measure absorptance of the coatings.
06/01353 Didactic software for solar cells and materials parameters analysis Patryn, A. and Pietruszko, S. M. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 271 285. The authors p r e s e n t a package of c o m p u t e r applications g a t h e r e d in a form of virtual laboratory as a package of the virtual exercises to solar cells p a r a m e t e r s analysis at a student university laboratory. The applications may also be used to analyse some aspects of silicon materials or solar cell structures as a research tool. The package consists of three blocks of exercises. Each of the blocks solves different tasks and is based on different software platforms (LabWindows, Visual Basic, Java and Flash). The range of the tasks is relatively wide: from analysis of the role of p a r a m e t e r s of the material (silicon) on the
Fuel and Energy Abstracts
May 2006
201