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01773 Toward a theoretical limit of solar cell efficiency with light trapping and sub-structure
07 A&native
energy soumes (wind energy)
Ml764 Solar powor and climate changa policy In dovolop Ing count&a Drknen, T. E. et al., Energy PO&~, Jan. 1996, 24. (l), 9-16. Solar ener is one 0 tion for reducing future ecnhouse gas emissions. Offsetting Y 0% of al P future growth in thcrma r electricity generation by hotovoltaics (PVs) would reduce annual global carbon dioxide emission Rom projected increased levels by 1096 in 20 years and 32% in 50 years. Several projects are under way worldwide to demonstrate the feasibility of PV systems. The paper examines the economic competitiveness of PV systems and concludes that even after including externality costs, without agnificant technological breakthroughs, the economics of PV applications are unlikely to allow for an unsubsidized, widespread adoption of this technology in the near future. Further, if the goal of PV transfer programmed is to is to limit future greenhouse gas emissions, there are larger and cheaper opportunities available in industrialized countries to achieve reductions. 96/017% Solar ataam gonaratlng l yatama ualng parabolic trough concentratora Thomas, A. Eneru Convers. Mgmt., Feb. 1996, 37, (2), 215-245. Solar steam generating systems using parabolic trough concentrators have been in use for the past decade in several countries in the world. During the past years, various-R 8c D efforts have been put into use to improve the performance. The paper reviews various aspects of solar steam generating systems and the operational problems that were encountered by various users of these systems. 96/017% A l olar thermal water pump Sumathy, K. et al., Applied Energy, 1996, 53, (3), 235-243. The pump employs pentane as the working substance - an organic fluid with a low boding point. A flat-plate solar collector generates vapour and its ressure is adequate to pump water from a well. Provision of a separate tanf: for storing the vapour under pressure improves the performance of the pump. Experiments prove its feasibility and yield useful performance characteristics.
t2itT7
Solar-deaallnatlon
prospects
for the Sultanate
of
Al-Ismaily, H. A. and Probert, S. D. Applied Energy, 1995, 52, (4), 341-368. Climatic data (for the three years 1988-1990) have been surveyed for various locations in Oman and hence the prospects there for the solar desalination of water have been assessed.In particular, the behaviour of a solar still on Masirah Island has been predicted. The use of average monthly insolation data, measured for 3 years from 1988 to 1990, enabled the calculation of how much of this radiation is incident on the still’s inclined transparent cover. Assumin (pessimistically) that only 50% of this transmitted radiation stimulates ti e evaporation process, the rate of distillate is predicted to be approximately 2 litres day” rn-’ of the inclined cover. Study of the actlva layer In hydrogenated amoralllcon solar calls ualng @actrlcal and analytlcal tachnlquea Bhattach ya, T. K. et al., Solar Energy Materials & Solar Cells, Nov. 1995, 39,“r l), 99-108. An attemp; was made to understand the distribution of defect states in the active layers of -i-n hydrogenated amorphous silicon solar cells. Capacitance-Voltage (8 V) measurements were used to study the defect distribution in the i-layer, both in the bulk as well as near the p-i interface for cells fabricated on different substrates. The effect of insertink a buffer layer between the p and i-layers were also investigated. A combination of secondarv ion mass soectroscoov. secondarv neutral mass soectroscoov and electroi s~&ctrosco~y for ch&&al analyiis measuremen& were u&i to study the elemental cflstribution in the active layer, specially those of the elemerits for the neighbouring p and transparent conducting oxide layers.
%I01 770 Thormal and optical conaa uoncea of thr lntroduo tlon of baffles Into compound parabo 1 Ic concentrating aolar energy collector cavltlea Earns, P. C. and Norton, B. Solar Energy, Aug. 1995,55, (2), 139-150. A theoretical and experimental investi ation into the modifications in optical and thermal performance resulting b m introduction of a kffle into the cavity of a c£ parabolic co&entrating solar energy collector has been performed. Results are presented in the form of velocity vector diagrams and isothermal plots. A comparison is made of the collector loss coefticient and Hottel-Whiller-Bliss gra hs are produced for cavities with and without a baffle present. The int rot uction of a baffle reduces internal convection thereby riducing heat losses. The associated reduction in optical efticiency is small. %I01 771 Thermal erformance of aolar alr heaters: matlcal modal and ao Putlon procedura Ong, K. S. Solar Energy, Aug. 1995, 55, (2). 93-109.
Mathe-
collector designs were considered. The surface temperatures of the walls surrounding the air streams were assumed uniform whereas the air temperatures were assumed to vary linearly along the collector. In the mathematical model, the solar collector was assumed sufficiently short for which the assumptions were valid. Q6tOl772 Thermohydraullc performance of packed-bed solar alr heaters Ahmad, A. et al., Energy Comers. Mgmt., Feb. 19%,37, (2), 205-214. This work is aimed at experimentally investigating the thermohydraulic performance characteristics of packed-bed solar air heaters. The thermohydraulic performance parameter called ‘effective effkziency’ has been emoloved to exoreS8 the net useful thermal enemv nain. taking into account ihe*quivaleni thermal energy rquired to prod;&‘ihe work eierg necessary to overcome the additional friction or hydraulic losses as a resurt of packin the solar air heater duct with absorber matrices. It is observed that the tfi ermohydraulic efficiency decreases with the increases in the values of bed depth to element size ratio and bed porosity, but it increases with an increase in mass flow rate. The use of a packed-bed will be beneficial if it is o erated in the higher temperature-rise parameter range, i.e. when relative Py higher grade thermal energy output is required. 96101773 Toward a thaoratlcal llmlt of solar cell afflclancy wlth light trappln and sub-structure Pelanchon, F. and 8 lalhe, P. Solar Energy, Jul. 1995. 54, (6), 381-385. The performance of Si - n+ - p solar cells are calculated using the cell width as a parameter and taking into account Ii ht trapping effect and infrared light excitation due to the inclusion of a cfefect layer near the n-p junction. A model is developed to describe light confinement and optrmized cell structures are considered. The low adsorption of long wavelength photons in thin solar cells is shown to be compensated by the light confinement. Higher values of the maximum output power are obtained and the effect is particularly significant for thin base cells (H&O urn) with a 3.5 mW cm.’ maximal increase of the maximum output power.
%I01 7% phous
Thaoratlcal study of GaSb PV call l fflclancy as a %I01 7% function of tamparatura Ferguson, L G. and Fraas, L M. Solar Energy Materials & Solar Cells, Nov. 1995, 39, (l), 11-18. In this article the maximum power., voltage at maximum power point, and short-circuit current of allium antlmonide photovoltaic cells are predicted based on theoretical c it culations and the best available experimental data. The GaSb photovoltaic cell is of prime importance in the construction of higb performance thermophotovoltaic (TPV) generators. Data is presented for blackbody emitters maintained at 1350 K, 1600 K, and 1800 K. The Important result is that the energy conversion efficiency of tbe GaSb cell decreases much more slowly with increasing temperature for the TPV application than for the solar application.
120
Furl and Enargy Abstracts
March 19%
Q6lOl774 Use of burled lpea for energy conaawatlon In cooling of agricultural green R0~aa8 Santamouris, M. et al., Solar Energy, Aug. 1995, 55, (2), 111-124. Earth-to-air heat exchangers can be used for energy conservation in cooling of agricultural greenhouses. A parametric analysis performed for a typical grass greenh&e illustrates th’e effect of pipe ien th. pipe diameter, and air velocltv inside the oioes on the oerformance oB the svstem. Measured data of {ndoor air tehperature collected from a 1000 I? fibreglass covered greenhouse, equipped with four buried pipes, are compared with calculated data and are found to be in very good agreement.
Wind Energy Evaluatlon of wlnd-ganarator potantlality 96IQl775 Pallabazzer, R. Solar Energy, Jul. 1995, 55, (l), 49-59. Presents a method to analyse wind data for wind-turbine siting. Two oarameters are defined bv means of which the sitinn can be ootimised. the bite effectiveness (ratio &&t/available energy) an; the cut-& s eed..It is shown that the site effectiveness achieves a maximum for a vaPue of the cut-in speed which depends on the rated speed and on the site. The cut-in speed of a WECS should be chosen according to the rated speed of the turbine and the cubic mean wind speed of the site. The wind data of two regions (Somalia and Calabria, Italy) with very different climates are examined and compared, showing correlation with the cubic mean wind speed. 1: is also shown that the WeibulI and. Rayleigh wind-frquency dgp models are not reliable for evaluating the output energy of a
energy soumes (wind energy)
Ml764 Solar powor and climate changa policy In dovolop Ing count&a Drknen, T. E. et al., Energy PO&~, Jan. 1996, 24. (l), 9-16. Solar ener is one 0 tion for reducing future ecnhouse gas emissions. Offsetting Y 0% of al P future growth in thcrma r electricity generation by hotovoltaics (PVs) would reduce annual global carbon dioxide emission Rom projected increased levels by 1096 in 20 years and 32% in 50 years. Several projects are under way worldwide to demonstrate the feasibility of PV systems. The paper examines the economic competitiveness of PV systems and concludes that even after including externality costs, without agnificant technological breakthroughs, the economics of PV applications are unlikely to allow for an unsubsidized, widespread adoption of this technology in the near future. Further, if the goal of PV transfer programmed is to is to limit future greenhouse gas emissions, there are larger and cheaper opportunities available in industrialized countries to achieve reductions. 96/017% Solar ataam gonaratlng l yatama ualng parabolic trough concentratora Thomas, A. Eneru Convers. Mgmt., Feb. 1996, 37, (2), 215-245. Solar steam generating systems using parabolic trough concentrators have been in use for the past decade in several countries in the world. During the past years, various-R 8c D efforts have been put into use to improve the performance. The paper reviews various aspects of solar steam generating systems and the operational problems that were encountered by various users of these systems. 96/017% A l olar thermal water pump Sumathy, K. et al., Applied Energy, 1996, 53, (3), 235-243. The pump employs pentane as the working substance - an organic fluid with a low boding point. A flat-plate solar collector generates vapour and its ressure is adequate to pump water from a well. Provision of a separate tanf: for storing the vapour under pressure improves the performance of the pump. Experiments prove its feasibility and yield useful performance characteristics.
t2itT7
Solar-deaallnatlon
prospects
for the Sultanate
of
Al-Ismaily, H. A. and Probert, S. D. Applied Energy, 1995, 52, (4), 341-368. Climatic data (for the three years 1988-1990) have been surveyed for various locations in Oman and hence the prospects there for the solar desalination of water have been assessed.In particular, the behaviour of a solar still on Masirah Island has been predicted. The use of average monthly insolation data, measured for 3 years from 1988 to 1990, enabled the calculation of how much of this radiation is incident on the still’s inclined transparent cover. Assumin (pessimistically) that only 50% of this transmitted radiation stimulates ti e evaporation process, the rate of distillate is predicted to be approximately 2 litres day” rn-’ of the inclined cover. Study of the actlva layer In hydrogenated amoralllcon solar calls ualng @actrlcal and analytlcal tachnlquea Bhattach ya, T. K. et al., Solar Energy Materials & Solar Cells, Nov. 1995, 39,“r l), 99-108. An attemp; was made to understand the distribution of defect states in the active layers of -i-n hydrogenated amorphous silicon solar cells. Capacitance-Voltage (8 V) measurements were used to study the defect distribution in the i-layer, both in the bulk as well as near the p-i interface for cells fabricated on different substrates. The effect of insertink a buffer layer between the p and i-layers were also investigated. A combination of secondarv ion mass soectroscoov. secondarv neutral mass soectroscoov and electroi s~&ctrosco~y for ch&&al analyiis measuremen& were u&i to study the elemental cflstribution in the active layer, specially those of the elemerits for the neighbouring p and transparent conducting oxide layers.
%I01 770 Thormal and optical conaa uoncea of thr lntroduo tlon of baffles Into compound parabo 1 Ic concentrating aolar energy collector cavltlea Earns, P. C. and Norton, B. Solar Energy, Aug. 1995,55, (2), 139-150. A theoretical and experimental investi ation into the modifications in optical and thermal performance resulting b m introduction of a kffle into the cavity of a c£ parabolic co&entrating solar energy collector has been performed. Results are presented in the form of velocity vector diagrams and isothermal plots. A comparison is made of the collector loss coefticient and Hottel-Whiller-Bliss gra hs are produced for cavities with and without a baffle present. The int rot uction of a baffle reduces internal convection thereby riducing heat losses. The associated reduction in optical efticiency is small. %I01 771 Thermal erformance of aolar alr heaters: matlcal modal and ao Putlon procedura Ong, K. S. Solar Energy, Aug. 1995, 55, (2). 93-109.
Mathe-
collector designs were considered. The surface temperatures of the walls surrounding the air streams were assumed uniform whereas the air temperatures were assumed to vary linearly along the collector. In the mathematical model, the solar collector was assumed sufficiently short for which the assumptions were valid. Q6tOl772 Thermohydraullc performance of packed-bed solar alr heaters Ahmad, A. et al., Energy Comers. Mgmt., Feb. 19%,37, (2), 205-214. This work is aimed at experimentally investigating the thermohydraulic performance characteristics of packed-bed solar air heaters. The thermohydraulic performance parameter called ‘effective effkziency’ has been emoloved to exoreS8 the net useful thermal enemv nain. taking into account ihe*quivaleni thermal energy rquired to prod;&‘ihe work eierg necessary to overcome the additional friction or hydraulic losses as a resurt of packin the solar air heater duct with absorber matrices. It is observed that the tfi ermohydraulic efficiency decreases with the increases in the values of bed depth to element size ratio and bed porosity, but it increases with an increase in mass flow rate. The use of a packed-bed will be beneficial if it is o erated in the higher temperature-rise parameter range, i.e. when relative Py higher grade thermal energy output is required. 96101773 Toward a thaoratlcal llmlt of solar cell afflclancy wlth light trappln and sub-structure Pelanchon, F. and 8 lalhe, P. Solar Energy, Jul. 1995. 54, (6), 381-385. The performance of Si - n+ - p solar cells are calculated using the cell width as a parameter and taking into account Ii ht trapping effect and infrared light excitation due to the inclusion of a cfefect layer near the n-p junction. A model is developed to describe light confinement and optrmized cell structures are considered. The low adsorption of long wavelength photons in thin solar cells is shown to be compensated by the light confinement. Higher values of the maximum output power are obtained and the effect is particularly significant for thin base cells (H&O urn) with a 3.5 mW cm.’ maximal increase of the maximum output power.
%I01 7% phous
Thaoratlcal study of GaSb PV call l fflclancy as a %I01 7% function of tamparatura Ferguson, L G. and Fraas, L M. Solar Energy Materials & Solar Cells, Nov. 1995, 39, (l), 11-18. In this article the maximum power., voltage at maximum power point, and short-circuit current of allium antlmonide photovoltaic cells are predicted based on theoretical c it culations and the best available experimental data. The GaSb photovoltaic cell is of prime importance in the construction of higb performance thermophotovoltaic (TPV) generators. Data is presented for blackbody emitters maintained at 1350 K, 1600 K, and 1800 K. The Important result is that the energy conversion efficiency of tbe GaSb cell decreases much more slowly with increasing temperature for the TPV application than for the solar application.
120
Furl and Enargy Abstracts
March 19%
Q6lOl774 Use of burled lpea for energy conaawatlon In cooling of agricultural green R0~aa8 Santamouris, M. et al., Solar Energy, Aug. 1995, 55, (2), 111-124. Earth-to-air heat exchangers can be used for energy conservation in cooling of agricultural greenhouses. A parametric analysis performed for a typical grass greenh&e illustrates th’e effect of pipe ien th. pipe diameter, and air velocltv inside the oioes on the oerformance oB the svstem. Measured data of {ndoor air tehperature collected from a 1000 I? fibreglass covered greenhouse, equipped with four buried pipes, are compared with calculated data and are found to be in very good agreement.
Wind Energy Evaluatlon of wlnd-ganarator potantlality 96IQl775 Pallabazzer, R. Solar Energy, Jul. 1995, 55, (l), 49-59. Presents a method to analyse wind data for wind-turbine siting. Two oarameters are defined bv means of which the sitinn can be ootimised. the bite effectiveness (ratio &&t/available energy) an; the cut-& s eed..It is shown that the site effectiveness achieves a maximum for a vaPue of the cut-in speed which depends on the rated speed and on the site. The cut-in speed of a WECS should be chosen according to the rated speed of the turbine and the cubic mean wind speed of the site. The wind data of two regions (Somalia and Calabria, Italy) with very different climates are examined and compared, showing correlation with the cubic mean wind speed. 1: is also shown that the WeibulI and. Rayleigh wind-frquency dgp models are not reliable for evaluating the output energy of a