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01830 A comparison of methods of extreme wind speed estimation
13 Alternative energy supplies (wind energy) of greenhouse air temperature, which were verified in terms of root mean square of percent deviation and correlation coefficient, exhibited fair agreement.
06•01825 Performance analysis of a solar energy driven heating system Martinez, P. J. et al. Energy and Buildings, 2005, 37, (10), 1028 1034. Operation temperature of solar heating systems makes the use of a radiant floor to transfer heat into the conditioned spaces suitable. Performance data related to solar heating systems are scarce. Knowledge of these data is important to establish control strategies that lead to an optimal operation of these systems. The objectives of this study were to acquire and analyse the performance data of a residential solar heating system in Murcia (Spain), and to compare the recorded data with the performance estimate provided by the f-chart method used for sizing the system. The solar fractions registered in the system during the months of January and February 2004 were 20% lower than those predicted by the/:chart method. This lack of coincidence was assumed as inherent to the f-chart method.
06/01826 Performance evaluation of various hourly slope irradiation models using Mediterranean experimental data of Ajaccio Notton, G. et al. Energy Conversion and Management, 2006, 47, (2), 147-173. Hourly global irradiations on tilted planes are required in various engineering calculations for solar systems. In many sites, at best, only global irradiations on horizontal planes are available. This work calculated the global irradiation on inclined surfaces from horizontal global irradiation. In a first step, several correlations were estimated between the horizontal diffuse component and the global irradiation. The second step was to test various models to compute hourly global irradiations on tilted planes from horizontal diffuse and global irradiations using solar data collected on the French Mediterranean site of Ajaccio.
06/01827 Potential for improvement in estimation of solar diffuse irradiance Muneer, T. and Munawwar, S. Energy Conversion and Management, 2006, 47, (1), 68 86. Most of the meteorological stations around the world measure global irradiation and provide information on weather elements. Diffuse radiation measurement, however, is unavailable for many of those sites. This accentuates the need to estimate it whereupon it can be used for the simulation of solar applications. This paper explores the role of synoptic information, e.g. sunshine fraction, cloud cover and air mass on the basic k k, relationship for nine sites across the globe. The influence on the k-kt regressions is studied qualitatively, and the inclusion of these parameters is suggested based on that. Thus, it is recommended to use the complementary data usually provided with the database apart from the global irradiation in order to estimate the diffuse irradiation more accurately. It was found by analysing each synoptic parameter individually that while the sunshine fraction showed a strong bearing, it was followed closely by cloud cover. Air mass, on the other hand, was found to be a weak parameter for general estimation of diffuse radiation. It was concluded that air mass if coupled with other synoptic parameters might improve the estimation accuracy, but it does not show much promise on its own when used with the global irradiation.
06/01828 Potential of quarterwave interference stacks for colored thermal solar collectors Schiller, A. et al. Solar Energy, 2005, 79, (2), 122 130. The architectural integration of thermal solar collectors into buildings is often limited by their black colour and the visibility of tubes and corrugations of the absorber sheets. A certain freedom in colour choice would be desirable, but the coloured appearance should not cause excessive energy losses. Multi-layered interference filters on the collector glazing can produce a coloured reflection, hiding the corrugated metal sheet, while transmitting the non-reflected radiation entirely to the absorber. The authors investigate the potential of quarterwave stacks by simulation of their optical behaviour, yielding the visible reflectance Rvls, the solar transmittance T~o~, a figure of merit M = Rvls/Rsol, and the CIE colour coordinates. The necessary number of individual layers in the multi-layer stack as well as the choice of refractive indices and thus of thin film materials are discussed. Finally, examples for realistic multi-layer designs are proposed.
06/01829 The impact of photovoltaic systems on distribution transformer: a case study Jimenez, H. et al. Energy Conversion and Management, 2006, 47, (4), 311-321.
278
Fuel and Energy Abstracts July 2006
In this paper, the results obtained after monitoring a distribution transformer during an 18-month period are described and discussed. The transformer fed several households, each with a grid connected photovoltaic system, and it was found that the power factor at the transformer attained unusually low levels. This was due to the fact that under some conditions, the systems provided a large portion of the active power demanded by the households, while the grid supplied all the reactive and distortion powers. The operating temperature was used as an indicator of the stress on the transformer. The temperature was at its lowest when the systems were providing the maximum energy available from the solar cells.
Wind energy 06/01830 A comparison of methods of extreme wind speed estimation An, Y. and Pandey, M. D. Journal of Wind Engineering and Industrial Aerodynamics, 2005, 93, (7), 535 545. The paper presents a comparative assessment of methods for extreme value analysis of the US wind speed data using four different methods, namely standard gumbel, modified gumbel, peaks-over-threshold (POT) and method of independent storms (MIS). The analysis highlights the influence of methodological assumptions on the estimates of design wind speed corresponding to 50-year and 500-year return period. The results demonstrate that the MIS method leads to more stable quantile estimates than the POT method.
06/01831 A new direct version of the Cook-Mayne method for wind pressure probabilities in temperate storms Harris, R. I. Journal of Wind Engineering attd Industrial Aerodynamics, 2005, 93, (7), 581-600. The original Cook-Mayne (CM) method for obtaining a wind pressure or load of a prescribed probability is reviewed. A new direct calculation method is introduced. This does not require either Monte Carlo simulations or the assumption that extreme pressures conform to the ultimate Fisher-Tippett Type I asymptote. The required value is calculated directly with no intermediate stages. The new method still relies on the original assumptions that both the pressure coefficient and the wind dynamic head have extremes which conform to the ultimate FT1 asymptote. Violation of these two assumptions is studied in some cases where calculations based on these assumptions are compared with exact results. The direct CM method is found to retain accuracy in spite of departures from the assumptions and therefore can provide a robust design tool.
06/01832 A parametric, experimental analysis of conical vortices on curved roofs of low-rise buildings Franchini, S. et al. Journal of Wind Engineering and Industrial Aerodynamics, 2005, 93, (8), 639 650. Different methods to reduce the high suction caused by conical vortices have been reported in the literature: vertical parapets, either solid or porous, placed at the roof edges being the most analysed configuration. Another method for alleviating the high suction peaks due to conical vortices is the use of some non-standard parapet configuration like cantilever parapets. In this paper the influence of roof curvature on the conical vortex pattern appearing on a curved roof (Fig. 1) when subject to oblique winds is experimentally analysed by testing the mean pressure distribution on the curved roofs of low-rise building models in a wind tunnel. Also, the efficiency of cantilever parapets to reduce mean suction loads on curved roofs is experimentally checked. Very high suction loads have been measured on curved roofs, the magnitude of these high suction loads being significantly decreased when cantilever parapets are used. Thus, the suitability of these parapets to reduce wind pressure loads on curved roofs is demonstrated.
06/01833 An assessment of governmental wind power p rogrammes in Sweden - using a systems approach Astrand, K. and Neij, L. Energy Policy, 2006, 34, (3), 277 296. The purpose of this paper is to assess the effects, the cost efficiency, and the goal achievement of policy instruments aimed for the development and deployment of wind power in Sweden during the period 1975 to 2000. The paper presents an empirical example of a socio-technical system-based approach for impact assessment, in which changes in the wind power system are described and analysed with respect to technology development, cost development and actors' involvement. The results show that the policy instruments were not designed to have a broad, system-oriented perspective but targeted and included restricted technology concepts - i.e. large, two-bladed turbines - and limited involvement of actors. The assessment shows that early inflexible steering of technology and market development, together with a lack of comprehensive, long-term strategy, lack of
06•01825 Performance analysis of a solar energy driven heating system Martinez, P. J. et al. Energy and Buildings, 2005, 37, (10), 1028 1034. Operation temperature of solar heating systems makes the use of a radiant floor to transfer heat into the conditioned spaces suitable. Performance data related to solar heating systems are scarce. Knowledge of these data is important to establish control strategies that lead to an optimal operation of these systems. The objectives of this study were to acquire and analyse the performance data of a residential solar heating system in Murcia (Spain), and to compare the recorded data with the performance estimate provided by the f-chart method used for sizing the system. The solar fractions registered in the system during the months of January and February 2004 were 20% lower than those predicted by the/:chart method. This lack of coincidence was assumed as inherent to the f-chart method.
06/01826 Performance evaluation of various hourly slope irradiation models using Mediterranean experimental data of Ajaccio Notton, G. et al. Energy Conversion and Management, 2006, 47, (2), 147-173. Hourly global irradiations on tilted planes are required in various engineering calculations for solar systems. In many sites, at best, only global irradiations on horizontal planes are available. This work calculated the global irradiation on inclined surfaces from horizontal global irradiation. In a first step, several correlations were estimated between the horizontal diffuse component and the global irradiation. The second step was to test various models to compute hourly global irradiations on tilted planes from horizontal diffuse and global irradiations using solar data collected on the French Mediterranean site of Ajaccio.
06/01827 Potential for improvement in estimation of solar diffuse irradiance Muneer, T. and Munawwar, S. Energy Conversion and Management, 2006, 47, (1), 68 86. Most of the meteorological stations around the world measure global irradiation and provide information on weather elements. Diffuse radiation measurement, however, is unavailable for many of those sites. This accentuates the need to estimate it whereupon it can be used for the simulation of solar applications. This paper explores the role of synoptic information, e.g. sunshine fraction, cloud cover and air mass on the basic k k, relationship for nine sites across the globe. The influence on the k-kt regressions is studied qualitatively, and the inclusion of these parameters is suggested based on that. Thus, it is recommended to use the complementary data usually provided with the database apart from the global irradiation in order to estimate the diffuse irradiation more accurately. It was found by analysing each synoptic parameter individually that while the sunshine fraction showed a strong bearing, it was followed closely by cloud cover. Air mass, on the other hand, was found to be a weak parameter for general estimation of diffuse radiation. It was concluded that air mass if coupled with other synoptic parameters might improve the estimation accuracy, but it does not show much promise on its own when used with the global irradiation.
06/01828 Potential of quarterwave interference stacks for colored thermal solar collectors Schiller, A. et al. Solar Energy, 2005, 79, (2), 122 130. The architectural integration of thermal solar collectors into buildings is often limited by their black colour and the visibility of tubes and corrugations of the absorber sheets. A certain freedom in colour choice would be desirable, but the coloured appearance should not cause excessive energy losses. Multi-layered interference filters on the collector glazing can produce a coloured reflection, hiding the corrugated metal sheet, while transmitting the non-reflected radiation entirely to the absorber. The authors investigate the potential of quarterwave stacks by simulation of their optical behaviour, yielding the visible reflectance Rvls, the solar transmittance T~o~, a figure of merit M = Rvls/Rsol, and the CIE colour coordinates. The necessary number of individual layers in the multi-layer stack as well as the choice of refractive indices and thus of thin film materials are discussed. Finally, examples for realistic multi-layer designs are proposed.
06/01829 The impact of photovoltaic systems on distribution transformer: a case study Jimenez, H. et al. Energy Conversion and Management, 2006, 47, (4), 311-321.
278
Fuel and Energy Abstracts July 2006
In this paper, the results obtained after monitoring a distribution transformer during an 18-month period are described and discussed. The transformer fed several households, each with a grid connected photovoltaic system, and it was found that the power factor at the transformer attained unusually low levels. This was due to the fact that under some conditions, the systems provided a large portion of the active power demanded by the households, while the grid supplied all the reactive and distortion powers. The operating temperature was used as an indicator of the stress on the transformer. The temperature was at its lowest when the systems were providing the maximum energy available from the solar cells.
Wind energy 06/01830 A comparison of methods of extreme wind speed estimation An, Y. and Pandey, M. D. Journal of Wind Engineering and Industrial Aerodynamics, 2005, 93, (7), 535 545. The paper presents a comparative assessment of methods for extreme value analysis of the US wind speed data using four different methods, namely standard gumbel, modified gumbel, peaks-over-threshold (POT) and method of independent storms (MIS). The analysis highlights the influence of methodological assumptions on the estimates of design wind speed corresponding to 50-year and 500-year return period. The results demonstrate that the MIS method leads to more stable quantile estimates than the POT method.
06/01831 A new direct version of the Cook-Mayne method for wind pressure probabilities in temperate storms Harris, R. I. Journal of Wind Engineering attd Industrial Aerodynamics, 2005, 93, (7), 581-600. The original Cook-Mayne (CM) method for obtaining a wind pressure or load of a prescribed probability is reviewed. A new direct calculation method is introduced. This does not require either Monte Carlo simulations or the assumption that extreme pressures conform to the ultimate Fisher-Tippett Type I asymptote. The required value is calculated directly with no intermediate stages. The new method still relies on the original assumptions that both the pressure coefficient and the wind dynamic head have extremes which conform to the ultimate FT1 asymptote. Violation of these two assumptions is studied in some cases where calculations based on these assumptions are compared with exact results. The direct CM method is found to retain accuracy in spite of departures from the assumptions and therefore can provide a robust design tool.
06/01832 A parametric, experimental analysis of conical vortices on curved roofs of low-rise buildings Franchini, S. et al. Journal of Wind Engineering and Industrial Aerodynamics, 2005, 93, (8), 639 650. Different methods to reduce the high suction caused by conical vortices have been reported in the literature: vertical parapets, either solid or porous, placed at the roof edges being the most analysed configuration. Another method for alleviating the high suction peaks due to conical vortices is the use of some non-standard parapet configuration like cantilever parapets. In this paper the influence of roof curvature on the conical vortex pattern appearing on a curved roof (Fig. 1) when subject to oblique winds is experimentally analysed by testing the mean pressure distribution on the curved roofs of low-rise building models in a wind tunnel. Also, the efficiency of cantilever parapets to reduce mean suction loads on curved roofs is experimentally checked. Very high suction loads have been measured on curved roofs, the magnitude of these high suction loads being significantly decreased when cantilever parapets are used. Thus, the suitability of these parapets to reduce wind pressure loads on curved roofs is demonstrated.
06/01833 An assessment of governmental wind power p rogrammes in Sweden - using a systems approach Astrand, K. and Neij, L. Energy Policy, 2006, 34, (3), 277 296. The purpose of this paper is to assess the effects, the cost efficiency, and the goal achievement of policy instruments aimed for the development and deployment of wind power in Sweden during the period 1975 to 2000. The paper presents an empirical example of a socio-technical system-based approach for impact assessment, in which changes in the wind power system are described and analysed with respect to technology development, cost development and actors' involvement. The results show that the policy instruments were not designed to have a broad, system-oriented perspective but targeted and included restricted technology concepts - i.e. large, two-bladed turbines - and limited involvement of actors. The assessment shows that early inflexible steering of technology and market development, together with a lack of comprehensive, long-term strategy, lack of