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01357 Exergy analysis of domestic-scale solar water heaters
13 Altemative energy supplies (solar energy) F V a n d spectral curves of a solar cell up to simulation of the m e t h o d of solar quality silicon p a r a m e t e r testing evaluation of a value of the m i n o r i t y carriers diffusion length from surface p h o t o v o l t a g e spectra.
06•01354 Effects of deposition variables on spraydeposited MnO2 thin films prepared from Mn(C2H302)2.4H20 Farid UI Islam, A. K. M. et al. Renewable Energy, 2005, 30, (15), 2289 2302. U n d o p e d MnO2 thin films have been p r e p a r e d by a modified spray pyrolysis technique u n d e r various deposition conditions and the effects of different variables on electrical and optical p r o p e r t i e s have been studied in detail. It is found that substrate temperature, spray rate, solution concentration, carrier air pressure and post-deposition heattreatment, spray outlet to substrate distance play i m p o r t a n t role in obtaining o p t i m u m films. Electrical conductivity study shows an anomaly in conductivity at a t e m p e r a t u r e 323 K and its thickness d e p e n d e n t resistivity follows Fuchs S o n d h e i m e r theory. The Hall effect and thermoelectric studies indicate that the deposited sample is an n-type semiconductor. Optical study in the entire wavelength 0.3 2.5 g m m range exhibits a high transmittance in the visible as well as in the near infrared. Calculation from optical data, the sample exhibits a band gap at 0.28 eV, which also supports the value obtained from the Hall effect study. These studies may be of i m p o r t a n c e for the applications of this material in energy efficient surface coating devices.
06•01355 Enhancing solar cell efficiency by using spectral converters van Sark, W. G. J. H. M. et al. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 395 409. Planar converters containing q u a n t u m dots as wavelength-shifting moieties on top of a multi-crystalline silicon and an a m o r p h o u s silicon solar cell were studied. The highly efficient q u a n t u m dots are to shift the wavelengths where the spectral response of the solar cell is low to wavelengths where the spectral response is high, in order to improve the conversion efficiency of the solar cell. It was calculated that q u a n t u m dots with an emission at 603 nm increase the multi-crystalline solar cell short-circuit current by nearly 10%. Simulation results for p l a n a r converters on hydrogenated a m o r p h o u s silicon solar cells show no beneficial effects, due to the high spectral response at low wavelength.
06•01356 Estimation of global radiation using clearness index model for sizing photovoltaic system Kumar, R. and U m a n a n d , L. Renewable Energy, 2005, 30, (15), 2221 2233. A methodology for developing a simple theoretical model for calculating global insolation on a horizontal surface is described in this paper. The input p a r a m e t e r s to the m o d e l are the latitude of the desired location and the a m o u n t of total precipitable water content in the vertical column at that location. Both the p a r a m e t e r s are easily m e a s u r a b l e with inexpensive i n s t r u m e n t such as global positioning system (GPS). The principal idea b e h i n d the p a p e r is to have a m o d e l that could be used for designing a photovoltaic system quickly and within reasonable accuracy. The model in this p a p e r has been developed using m e a s u r e d data from 12 locations in I n d i a covering length and b r e a d t h of the country over a period of 9 22 years. The m o d e l is validated by calculating theoretical global insolation for five locations, one in north (New Delhi), one in south (Thiruvanandapuram), one in east (Kolkata), one in west (Mumbai) and one in central (Nagpur) part of India and comparing t h e m with the m e a s u r e d insolation values for these five locations. The m e a s u r e d values of all these locations had been considered for developing the model. The m o d e l is further validated for a location (Goa) whose m e a s u r e d data is not considered for developing the model, by comparing the calculated and m e a s u r e d values of the insolation. Over the range of latitudes covering most parts of India, the error is within 20% of the m e a s u r e d value. This gives the credibility of the model and the methodology used for developing the model for any region in the world.
06•01357 heaters
Exergy analysis of domestic-scale solar water
Wang, X. and Hua, B. Renewable and Sustainable Energy Reviews, 2005, 9, (6), 638 645. Solar water heater is the most p o p u l a r means of solar energy utilization because of technological feasibility and economic attraction c o m p a r e d with other kinds of solar energy utilization. Earlier assessments of domestic-scale solar water heaters were based on the first thermodynamic law. However, this kind of assessment cannot perfectly describe the performance of solar water heaters, since the essence of energy utilization is to extract available energy as much as possible. So, it is necessary to evaluate domestic-scale solar water heaters based on the second t h e r m o d y n a m i c law. No matter the technology process, from the property of energy utilization perspective, the technology process can be s e p a r a t e d into three intimately related sub-procedures, namely conversion procedure, utilization procedure, and recycling procedure.
202
Fuel and Energy Abstracts
May 2006
A n energy analysis entitled 'Three Procedure Theory' can be conveniently conducted. C o m p a r e d with other theories of energy analysis, three p r o c e d u r e theory exhibits great advantages. The utilization p r o c e d u r e puts forth r e q u i r e m e n t for the design of p a r a m e t e r s in conversion p r o c e d u r e and sets up limits in the consideration of recycling procedure. Of course, u n d e r specific conditions, the utilization p r o c e d u r e also receives feedback from other procedures. T h r e e p r o c e d u r e theory furnishes us a good platform to perform energy analysis. The study in this p a p e r is based on three p r o c e d u r e theory. Exergy analysis is conducted with the aim of providing some methods to save cost and k e e p the efficiency of domestic-scale solar water heater to desired extent and at the same time figuring out related exergy losses. F r o m this survey, it is shown that for an ordinary thermally insulated domestic-scale solar water heater, Dju (exergy losses due to imperfectly thermal insulation in collector) a n d / ) j R (exergy losses due to imperfectly thermal insulation in storage barrel) c a n n o t be avoided. Dku (exergy losses due to irreversibility in collector) is m a i n l y caused by irreversibility of heat transfer and DkR (exergy losses due to irreversibility in storage barrel) is d o m i n a t e d by the mixing of water at different temperature. Dku acts as the driving force for the system while DkR is of little contribution. A good design of storage barrel w i t h little DkR will go a long way in i m p r o v i n g exergy efficiency. A n equation for c o m p u t i n g DkR is presented. For the collector, which is the core of the domestic-scale solar water heater, a judicious choice of w i d t h of plate W and layer n u m b e r of cover is necessary. Collector exergy efficiency r/xc is defined to be r/xc = Exo/Exu. The relation between collector exergy efficiency and w i d t h of plate together with layer n u m b e r of cover is also analysed.
06/01358 Extraction and analysis of solar cell parameters from the illuminated current-voltage curve H a o u a r i - M e r b a h , M. et al. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 225 233. This work describes, applies and analyses a p r o c e d u r e to extract the physical p a r a m e t e r s of a solar cell from its F V curve under illumination. It is compared with other procedures and the statistical significance of the p a r a m e t e r s assessed. The method, called APTIV, uses separate fitting in two different zones in the F V curve. In the first one, near short circuit, current fitting is used because the error in current dominates. In the second one, near open circuit, voltage fitting is used because this is the d o m i n a n t error. The m e t h o d overcomes some d r a w b a c k s of c o m m o n procedures: voltage errors are properly m a n a g e d and no accurate initial guesses for the p a r a m e t e r s are needed. In addition, the numerical i m p l e m e n t a t i o n is very simple.
06/01359 Forecast of solar irradiance using recurrent neural networks combined with wavelet analysis Cao, S. and Cao, J. Applied Thermal Engineering, 2005, 25, (2 3), 161 172. In this paper, artificial neural network is combined with wavelet analysis for the forecast of solar irradiance. This m e t h o d is characteristic of the preprocessing of sample data using wavelet transformation for the forecast, i.e. the data sequence of solar irradiance as the sample is first m a p p e d into several time-frequency domains, and then a r e c u r r e n t BP network is established for each domain. The forecasted solar irradiance is exactly the algebraic sum of all the forecasted c o m p o n e n t s obtained by the respective networks, which correspond respectively the time-frequency domains. Discount coefficients are applied to take account of different effect of different time-step on the accuracy of the u l t i m a t e forecast when u p d a t i n g the weights and biases of the networks in network training. On the basis of combination of r e c u r r e n t BP networks and wavelet analysis, a model is developed for more accurate forecasts of solar irradiance. A n example of the forecast of day-by-day solar irradiance is p r e s e n t e d in the paper, the historical day-by-day records of solar irradiance in Shanghai constituting the data sample. The results of the example show that the accuracy of the m e t h o d is more satisfactory than that of the methods reported before.
06/01360 Gallium-doped ZnO thin films deposited by chemical spray Gomez, H. et al. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 107 116. G a l l i u m - d o p e d zinc oxide ( Z n O : G a ) thin films were deposited on glass substrates by the spray pyrolysis technique. The effect of the variation of the [Ga]/[Zn] rate in the starting solution, the substrate t e m p e r a t u r e as well as the post-annealing t r e a t m e n t s on the physical p r o p e r t i e s was examined. The electrical p r o p e r t i e s of the films show an i m p r o v e m e n t with the G a incorporation and the annealing treatment. All the films were found to be polycrystalline and show a (0 0 2) preferential growth, irrespective of the deposition conditions. The films were of n-type conductivity with an electrical resistivity in the order of 8 x 1 0 f~ cm and optical t r a n s m i t t a n c e higher than 80% in the visible region. These results makes chemically sprayed Z n O : G a potentially applicable as t r a n s p a r e n t electrode in photovoltaic devices.
06•01354 Effects of deposition variables on spraydeposited MnO2 thin films prepared from Mn(C2H302)2.4H20 Farid UI Islam, A. K. M. et al. Renewable Energy, 2005, 30, (15), 2289 2302. U n d o p e d MnO2 thin films have been p r e p a r e d by a modified spray pyrolysis technique u n d e r various deposition conditions and the effects of different variables on electrical and optical p r o p e r t i e s have been studied in detail. It is found that substrate temperature, spray rate, solution concentration, carrier air pressure and post-deposition heattreatment, spray outlet to substrate distance play i m p o r t a n t role in obtaining o p t i m u m films. Electrical conductivity study shows an anomaly in conductivity at a t e m p e r a t u r e 323 K and its thickness d e p e n d e n t resistivity follows Fuchs S o n d h e i m e r theory. The Hall effect and thermoelectric studies indicate that the deposited sample is an n-type semiconductor. Optical study in the entire wavelength 0.3 2.5 g m m range exhibits a high transmittance in the visible as well as in the near infrared. Calculation from optical data, the sample exhibits a band gap at 0.28 eV, which also supports the value obtained from the Hall effect study. These studies may be of i m p o r t a n c e for the applications of this material in energy efficient surface coating devices.
06•01355 Enhancing solar cell efficiency by using spectral converters van Sark, W. G. J. H. M. et al. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 395 409. Planar converters containing q u a n t u m dots as wavelength-shifting moieties on top of a multi-crystalline silicon and an a m o r p h o u s silicon solar cell were studied. The highly efficient q u a n t u m dots are to shift the wavelengths where the spectral response of the solar cell is low to wavelengths where the spectral response is high, in order to improve the conversion efficiency of the solar cell. It was calculated that q u a n t u m dots with an emission at 603 nm increase the multi-crystalline solar cell short-circuit current by nearly 10%. Simulation results for p l a n a r converters on hydrogenated a m o r p h o u s silicon solar cells show no beneficial effects, due to the high spectral response at low wavelength.
06•01356 Estimation of global radiation using clearness index model for sizing photovoltaic system Kumar, R. and U m a n a n d , L. Renewable Energy, 2005, 30, (15), 2221 2233. A methodology for developing a simple theoretical model for calculating global insolation on a horizontal surface is described in this paper. The input p a r a m e t e r s to the m o d e l are the latitude of the desired location and the a m o u n t of total precipitable water content in the vertical column at that location. Both the p a r a m e t e r s are easily m e a s u r a b l e with inexpensive i n s t r u m e n t such as global positioning system (GPS). The principal idea b e h i n d the p a p e r is to have a m o d e l that could be used for designing a photovoltaic system quickly and within reasonable accuracy. The model in this p a p e r has been developed using m e a s u r e d data from 12 locations in I n d i a covering length and b r e a d t h of the country over a period of 9 22 years. The m o d e l is validated by calculating theoretical global insolation for five locations, one in north (New Delhi), one in south (Thiruvanandapuram), one in east (Kolkata), one in west (Mumbai) and one in central (Nagpur) part of India and comparing t h e m with the m e a s u r e d insolation values for these five locations. The m e a s u r e d values of all these locations had been considered for developing the model. The m o d e l is further validated for a location (Goa) whose m e a s u r e d data is not considered for developing the model, by comparing the calculated and m e a s u r e d values of the insolation. Over the range of latitudes covering most parts of India, the error is within 20% of the m e a s u r e d value. This gives the credibility of the model and the methodology used for developing the model for any region in the world.
06•01357 heaters
Exergy analysis of domestic-scale solar water
Wang, X. and Hua, B. Renewable and Sustainable Energy Reviews, 2005, 9, (6), 638 645. Solar water heater is the most p o p u l a r means of solar energy utilization because of technological feasibility and economic attraction c o m p a r e d with other kinds of solar energy utilization. Earlier assessments of domestic-scale solar water heaters were based on the first thermodynamic law. However, this kind of assessment cannot perfectly describe the performance of solar water heaters, since the essence of energy utilization is to extract available energy as much as possible. So, it is necessary to evaluate domestic-scale solar water heaters based on the second t h e r m o d y n a m i c law. No matter the technology process, from the property of energy utilization perspective, the technology process can be s e p a r a t e d into three intimately related sub-procedures, namely conversion procedure, utilization procedure, and recycling procedure.
202
Fuel and Energy Abstracts
May 2006
A n energy analysis entitled 'Three Procedure Theory' can be conveniently conducted. C o m p a r e d with other theories of energy analysis, three p r o c e d u r e theory exhibits great advantages. The utilization p r o c e d u r e puts forth r e q u i r e m e n t for the design of p a r a m e t e r s in conversion p r o c e d u r e and sets up limits in the consideration of recycling procedure. Of course, u n d e r specific conditions, the utilization p r o c e d u r e also receives feedback from other procedures. T h r e e p r o c e d u r e theory furnishes us a good platform to perform energy analysis. The study in this p a p e r is based on three p r o c e d u r e theory. Exergy analysis is conducted with the aim of providing some methods to save cost and k e e p the efficiency of domestic-scale solar water heater to desired extent and at the same time figuring out related exergy losses. F r o m this survey, it is shown that for an ordinary thermally insulated domestic-scale solar water heater, Dju (exergy losses due to imperfectly thermal insulation in collector) a n d / ) j R (exergy losses due to imperfectly thermal insulation in storage barrel) c a n n o t be avoided. Dku (exergy losses due to irreversibility in collector) is m a i n l y caused by irreversibility of heat transfer and DkR (exergy losses due to irreversibility in storage barrel) is d o m i n a t e d by the mixing of water at different temperature. Dku acts as the driving force for the system while DkR is of little contribution. A good design of storage barrel w i t h little DkR will go a long way in i m p r o v i n g exergy efficiency. A n equation for c o m p u t i n g DkR is presented. For the collector, which is the core of the domestic-scale solar water heater, a judicious choice of w i d t h of plate W and layer n u m b e r of cover is necessary. Collector exergy efficiency r/xc is defined to be r/xc = Exo/Exu. The relation between collector exergy efficiency and w i d t h of plate together with layer n u m b e r of cover is also analysed.
06/01358 Extraction and analysis of solar cell parameters from the illuminated current-voltage curve H a o u a r i - M e r b a h , M. et al. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 225 233. This work describes, applies and analyses a p r o c e d u r e to extract the physical p a r a m e t e r s of a solar cell from its F V curve under illumination. It is compared with other procedures and the statistical significance of the p a r a m e t e r s assessed. The method, called APTIV, uses separate fitting in two different zones in the F V curve. In the first one, near short circuit, current fitting is used because the error in current dominates. In the second one, near open circuit, voltage fitting is used because this is the d o m i n a n t error. The m e t h o d overcomes some d r a w b a c k s of c o m m o n procedures: voltage errors are properly m a n a g e d and no accurate initial guesses for the p a r a m e t e r s are needed. In addition, the numerical i m p l e m e n t a t i o n is very simple.
06/01359 Forecast of solar irradiance using recurrent neural networks combined with wavelet analysis Cao, S. and Cao, J. Applied Thermal Engineering, 2005, 25, (2 3), 161 172. In this paper, artificial neural network is combined with wavelet analysis for the forecast of solar irradiance. This m e t h o d is characteristic of the preprocessing of sample data using wavelet transformation for the forecast, i.e. the data sequence of solar irradiance as the sample is first m a p p e d into several time-frequency domains, and then a r e c u r r e n t BP network is established for each domain. The forecasted solar irradiance is exactly the algebraic sum of all the forecasted c o m p o n e n t s obtained by the respective networks, which correspond respectively the time-frequency domains. Discount coefficients are applied to take account of different effect of different time-step on the accuracy of the u l t i m a t e forecast when u p d a t i n g the weights and biases of the networks in network training. On the basis of combination of r e c u r r e n t BP networks and wavelet analysis, a model is developed for more accurate forecasts of solar irradiance. A n example of the forecast of day-by-day solar irradiance is p r e s e n t e d in the paper, the historical day-by-day records of solar irradiance in Shanghai constituting the data sample. The results of the example show that the accuracy of the m e t h o d is more satisfactory than that of the methods reported before.
06/01360 Gallium-doped ZnO thin films deposited by chemical spray Gomez, H. et al. Solar Energy Materials and Solar Cells, 2005, 87, (1 4), 107 116. G a l l i u m - d o p e d zinc oxide ( Z n O : G a ) thin films were deposited on glass substrates by the spray pyrolysis technique. The effect of the variation of the [Ga]/[Zn] rate in the starting solution, the substrate t e m p e r a t u r e as well as the post-annealing t r e a t m e n t s on the physical p r o p e r t i e s was examined. The electrical p r o p e r t i e s of the films show an i m p r o v e m e n t with the G a incorporation and the annealing treatment. All the films were found to be polycrystalline and show a (0 0 2) preferential growth, irrespective of the deposition conditions. The films were of n-type conductivity with an electrical resistivity in the order of 8 x 1 0 f~ cm and optical t r a n s m i t t a n c e higher than 80% in the visible region. These results makes chemically sprayed Z n O : G a potentially applicable as t r a n s p a r e n t electrode in photovoltaic devices.