Werner Platzer - Academia.edu (original) (raw)

Papers by Werner Platzer

Proceedings of SPIE, Sep 9, 1994

A number of different thermotropic materials are now known, which operate on the principle of a r... more A number of different thermotropic materials are now known, which operate on the principle of a reversible change between a homogeneous, transparent state at lower temperatures and a heterogeneous, scattering state at higher temperatures. Depending on the switching temperature, which is between 20 and 100 degree(s)C for the samples investigated, these materials can be used to prevent overheating in different solar energy applications, e.g. overhead glazing, transparently insulated walls and flat-plate collectors. In this paper, such materials are characterized experimentally by the temperature dependence of the direct-direct and direct-hemispherical transmittance and reflectance spectra over the solar spectral range. The results from multiple scattering theory for Mie scatterers and models for scattering in random media are compared to determine their correctness in describing the material structure in its scattering state. On the basis of the results obtained (diameter of scattering center or typical correlation length for a refractive index domain and difference between the component dielectric constants), suggestions are made on the changes required for a further optimization of the solar radiation switching performance.

Proceedings of SPIE, Sep 24, 1986

Transparent insulation materials for solar energy applications are classified and described in th... more Transparent insulation materials for solar energy applications are classified and described in this paper. An experimental setup with an integrating sphere for the whole global spectrum range having a large entrance port is capable of measuring angle-dependent directional-hemispherical transmittances for planar samples and nonplanar structures with acceptable accuracy up to 70 °. The theoretical description of such structures allows to calculate directional transmittances even for combinations of different kinds of layers, for instance to determine seasonal variations of monthly-averaged transmittances for the whole cover system.

IEEE Journal of Photovoltaics, Nov 1, 2017

The effect of soiling on PV systems impacts negatively the energy production. This phenomenon is ... more The effect of soiling on PV systems impacts negatively the energy production. This phenomenon is highly dependant on the environmental context and conditions of operation. Indeed dirt, dust, and other air contaminants are site-specific and their accumulation on PV modules depends on the installation configuration. This study, conducted in Santiago de Chile over a period of two and half years, focuses on analyzing power production and soiling losses of three photovoltaic technologies, monocrystalline, polycrystalline, and thin-film Si. We present the method used for analyzing time series of production data, and demonstrate the seasonality of soiling rates in Santiago city. Indeed, soiling rate values for winter season, where contamination is high, are three times higher than values for summer season, where contamination is low. A yearly trend of soiling is determined and used to study the link between economical parameters and cleaning pattern applied. The results allow us to define an optimal cleaning period depending on the period of the year.

Proceedings of SPIE, Sep 9, 1994

ABSTRACT A new type of transparent insulation with glass capillaries allows the construction of h... more ABSTRACT A new type of transparent insulation with glass capillaries allows the construction of high temperature flat-plate solar collectors reaching stagnation temperatures of 260 degree(s)C and more. In the temperature range above 100 degree(s)C, the radiant heat is the dominant heat loss mechanism. For the plastic honeycomb materials used up to now, the heat losses were described adequately with a non-spectral `grey' model. To describe the radiant heat losses for the new glass capillary collector covers, a spectral analysis is necessary, due to the strong spectral dependence of the absorptance in glass. A new experimental set-up allows the measurements of the spectral radiant heat emitted by large samples, not only integrated over a hemisphere but also with angular resolution. A theoretical model for the calculation of the spectral, angle-dependent total emission of a Tl/absorber construction has been developed. The presented results of the calculations for glass capillaries show good agreement with the measurements.

Proceedings of SPIE, Sep 9, 1994

ABSTRACT Integral as well as spectral methods to characterize the thermal properties of Silica Ae... more ABSTRACT Integral as well as spectral methods to characterize the thermal properties of Silica Aerogel and Xerogel samples are presented. A new method to determine the effective thermal conductivity with the help of an infrared camera was developed, which allows for measuring small samples. Keeping the lower surface of the samples at a constant temperature, the IR camera monitors the upper surface temperature. With the help of a reference sample of known thermal conductivity, the total heat flux through the samples can be calculated. This is done under different pressure conditions in order to observe the Knudsen effect. As there is a complex coupling between the different modes of heat transport, the spectrum of the emitted radiation is of interest. Emission spectroscopy on Silica Aerogel has not been previously investigated in detail. An emission chamber was constructed, which permits measuring of the emitted spectra due to an applied temperature gradient using a Perkin Elmer Infrared Grating spectrometer. Different boundary emissivities and varying pressure conditions can be applied. For a correct interpretation of the measured spectra, a numerical treatment of the underlying heat transport mechanism is necessary. Measurements as well as computer simulations are presented. Computer simulations show that a variation of the total thermal conductivity in the range between 1 mW/mK and 30 mW/mK leads to a characteristic damping of the emitted radiation between 500 cm-1 and 2000 cm-1. This characteristic damping of the emitted radiation can be observed by measuring the emitted spectra of Silica Aerogel/Xerogel at varying pressure conditions. Therefore, in principle, it should be possible to extract the thermal conductivity through the gas pores and through the silica skeleton. Boundary effects, however, prevent this data from being extracted. Hopefully these problems will be solved in the near future.

Proceedings of SPIE, Sep 9, 1994

ABSTRACT After more than ten years of research and development on a new generation of transparent... more ABSTRACT After more than ten years of research and development on a new generation of transparent insulation materials in the more restricted sense, namely honeycomb type and other geometric structures, granular and monolithic aerogel, a critical overview of existing materials is presented. During the last years considerable progress has been made, and still more is to be expected as well on the theoretical understanding of the physical properties as on the actual material development. On the other hand there still are problems when one looks at the application aspect, e.g. temperature stability, inflammability, optical appearance, irregularities of the structures, and production costs. The development objectives in the past have been either to physically optimize a material for an application, or to produce a lower-quality cheap material. An example of the first strategy is the recent development of glass capillary structures. The question here, of course, is, whether production, handling and transport can be made easy enough to meet the target of reasonable costs. It should be emphasized, that material costs are not the key issue, but system costs. A continuous and intensive collaboration between production engineer, system or design engineer, scientist and salesman is probably the only chance to meet the requirements of high quality products, adapted to the application, with reasonable costs. An engineer designing an application with transparent insulation materials without understanding the physics of the material type used may run the risk of deteriorating the performance severely.

Elsevier eBooks, 1988

ABSTRACT Transparently insulated massive walls reduce heating loads to an impressive degree. The ... more ABSTRACT Transparently insulated massive walls reduce heating loads to an impressive degree. The heating season of a building can be shortened by several months. Good transparent insulation materials (TIM's) have transmittances of up to 70 percent for diffuse irradiation and U-values in the range from 0.5 to 1.5 Wm−2K−1.The combined effect of thermal insulation and collecting solar radiation allows the use of these materials not only for southern, but also for other orientations. Steady-state theory gives upper limits for the potential of this passive component to reverse the heat flow towards the interior. Experimental data indicate that it may be applied for periods greater than the time constant of the wall. Apart from overheating in summer, which makes some shading device necessary in most cases, there is always some mismatch between solar heat gains and heating demand. This leads to a non-utilizable fraction of the solar gains. Simulations allow the inclusion of dynamical, non-linear effects and non-utilizability depending on the storage capacity of the system, but easy and rapid design methods are desirable. The Solar-Savings-Fraction method of Heidt (1985) and the method of Monsen (1982) shall be compared with simulation results. Results show that the most relevant parameters can be incorporated in the steady-state theory. Corrections are due to the storage capacity of the house, which influences utilizability especially in spring and autumn. The wall heat capacity has little influence on heat gains, but determines the maximum absorber temperatures.

Proceedings of SPIE, Nov 25, 1992

ABSTRACT

Proceedings of SPIE, Sep 9, 1994

ABSTRACT Errors in performing optical measurements of scattering samples are analyzed. Measuremen... more ABSTRACT Errors in performing optical measurements of scattering samples are analyzed. Measurements are described from a Perkin-Elmer Lambda-9 spectrophotometer with an integrating sphere of 15 cm diameter for spectral data between 300 and 2500 nm and from a 65 cm integrating sphere for broadband data on larger samples. The influence of the size of the illuminated sample area, the size of the sphere ports and sample thickness are investigated. Results are compared with Monte Carlo simulations.

Elsevier eBooks, 1991

ABSTRACT

Minerals Engineering, 2017

Bioleaching of chalcopyrite is only possible in the presence of thermophilic microorganisms. Whil... more Bioleaching of chalcopyrite is only possible in the presence of thermophilic microorganisms. While suitable conditions can be generated within a heap naturally through the exothermic reaction, the effectiveness of the process can be improved with an additional heat source. Chilean copper mines are primarily located in the Atacama Desert, which has the highest solar irradiation levels on the planet. Solar thermal energy can be incorporated into the heap bioleaching process to raise the temperature in the heap and increase the copper extraction rates. A heap bioleaching system, including ponds and a solar thermal collector field, has been simulated over one year using HeapSim and TRNSYS. The maximum copper extraction achievable for the system without a solar thermal field is 67% with a 7 kg/h m 2 solution flow rate. A maximum extraction of 85% over one year could be achieved with a collector field to heap area ratio of 1:1 and a 10 kg/h m 2 solution flow rate. An economic analysis compares the capital cost of the solar thermal system to the revenue from additional copper extraction. The net present value and internal rate of return were positive for collector areas in the range of 10,000-150,000 m 2 for a heap area of 200,000 m 2. The peak NPV occurs at 50,000 m 2 at which point an extractionof 76% is achieved over one year of leaching.

SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems, 2018

This publication presents a newly developed procedure for performance evaluation of direct steam ... more This publication presents a newly developed procedure for performance evaluation of direct steam generating collectors. Performance testing and evaluation of solar collectors operating with direct steam are not yet standardized, since accredited testing standard procedures do not foresee testing with compressible heat transfer media. Due to the existence of two-phase flow, the measurement concept as well as the collector simulation model needs to be adjusted. Two approaches of steady-state and dynamic performance evaluation are introduced. The corresponding methodology is applicable to small-and large-scale parabolic trough as well as linear Fresnel collectors. The application of the newly developed simulation model and evaluation procedure to measurement data proves the practicability and reliability of the introduced approach. On the basis of exemplary results, the benefits and remaining drawbacks of the procedure are thoroughly discussed. They particularly demonstrate the adapted testing method to be a valuable tool for fast and simple performance checks of steam generating systems. Meaningful performance testing is considered highly beneficial for a further dissemination and global acceptance of steam collectors and solar process heat in general.

Physical review, Apr 15, 1983

ColSim is a simulation software initially designed and further developed at Fraunhofer ISE to per... more ColSim is a simulation software initially designed and further developed at Fraunhofer ISE to perform calculations for solar thermal systems. ColSim can perform quasi-dynamic hydraulic simulations and allows for the integration of complex control strategies.

Elsevier eBooks, 2012

Abstract: In this chapter, different approaches and properties of absorber coatings for receivers... more Abstract: In this chapter, different approaches and properties of absorber coatings for receivers in parabolic trough and linear Fresnel collectors are discussed. The receiver is a central and crucial element determining the optical efficiency of the conversion of solar radiation on the one hand, and the heat losses on the other. High solar absorptance and low thermal emittance in the temperature range of operation are important. The exact definitions of these Key characterizing parameters are given. As the receivers should retain their performance over many years of operation, degradation processes and service lifetime are important as well.

Solar Energy, Nov 1, 1992

ABSTRACT The directional-hemispherical (also sometimes called direct-diffuse) solar transmittance... more ABSTRACT The directional-hemispherical (also sometimes called direct-diffuse) solar transmittance for several different honeycomb-type structures has been measured with an indoor solar simulator and a 40 cm diameter integrating sphere for incidence angles up to 70°. The samples have been fabricated by commeriial companies from different plastics, with cell wall thicknesses between 15 and 70 μm and have approximately square or circular cell cross sections. After a discussion of the measurement errors and problems associated with a limited number of nonideal samples, a fit procedure based on a physically based transmittance model is presented and applied to the data. The resulting coefficients describe the angular and thickness dependence of the solar transmittance for each type of material. They may be used in order to feed data easily and flexibly into simulation models for solar collectors, windows or building.

Proceedings of SPIE, Sep 9, 1994

A number of different thermotropic materials are now known, which operate on the principle of a r... more A number of different thermotropic materials are now known, which operate on the principle of a reversible change between a homogeneous, transparent state at lower temperatures and a heterogeneous, scattering state at higher temperatures. Depending on the switching temperature, which is between 20 and 100 degree(s)C for the samples investigated, these materials can be used to prevent overheating in different solar energy applications, e.g. overhead glazing, transparently insulated walls and flat-plate collectors. In this paper, such materials are characterized experimentally by the temperature dependence of the direct-direct and direct-hemispherical transmittance and reflectance spectra over the solar spectral range. The results from multiple scattering theory for Mie scatterers and models for scattering in random media are compared to determine their correctness in describing the material structure in its scattering state. On the basis of the results obtained (diameter of scattering center or typical correlation length for a refractive index domain and difference between the component dielectric constants), suggestions are made on the changes required for a further optimization of the solar radiation switching performance.

Proceedings of SPIE, Sep 24, 1986

Transparent insulation materials for solar energy applications are classified and described in th... more Transparent insulation materials for solar energy applications are classified and described in this paper. An experimental setup with an integrating sphere for the whole global spectrum range having a large entrance port is capable of measuring angle-dependent directional-hemispherical transmittances for planar samples and nonplanar structures with acceptable accuracy up to 70 °. The theoretical description of such structures allows to calculate directional transmittances even for combinations of different kinds of layers, for instance to determine seasonal variations of monthly-averaged transmittances for the whole cover system.

IEEE Journal of Photovoltaics, Nov 1, 2017

The effect of soiling on PV systems impacts negatively the energy production. This phenomenon is ... more The effect of soiling on PV systems impacts negatively the energy production. This phenomenon is highly dependant on the environmental context and conditions of operation. Indeed dirt, dust, and other air contaminants are site-specific and their accumulation on PV modules depends on the installation configuration. This study, conducted in Santiago de Chile over a period of two and half years, focuses on analyzing power production and soiling losses of three photovoltaic technologies, monocrystalline, polycrystalline, and thin-film Si. We present the method used for analyzing time series of production data, and demonstrate the seasonality of soiling rates in Santiago city. Indeed, soiling rate values for winter season, where contamination is high, are three times higher than values for summer season, where contamination is low. A yearly trend of soiling is determined and used to study the link between economical parameters and cleaning pattern applied. The results allow us to define an optimal cleaning period depending on the period of the year.

Proceedings of SPIE, Sep 9, 1994

ABSTRACT A new type of transparent insulation with glass capillaries allows the construction of h... more ABSTRACT A new type of transparent insulation with glass capillaries allows the construction of high temperature flat-plate solar collectors reaching stagnation temperatures of 260 degree(s)C and more. In the temperature range above 100 degree(s)C, the radiant heat is the dominant heat loss mechanism. For the plastic honeycomb materials used up to now, the heat losses were described adequately with a non-spectral `grey' model. To describe the radiant heat losses for the new glass capillary collector covers, a spectral analysis is necessary, due to the strong spectral dependence of the absorptance in glass. A new experimental set-up allows the measurements of the spectral radiant heat emitted by large samples, not only integrated over a hemisphere but also with angular resolution. A theoretical model for the calculation of the spectral, angle-dependent total emission of a Tl/absorber construction has been developed. The presented results of the calculations for glass capillaries show good agreement with the measurements.

Proceedings of SPIE, Sep 9, 1994

ABSTRACT Integral as well as spectral methods to characterize the thermal properties of Silica Ae... more ABSTRACT Integral as well as spectral methods to characterize the thermal properties of Silica Aerogel and Xerogel samples are presented. A new method to determine the effective thermal conductivity with the help of an infrared camera was developed, which allows for measuring small samples. Keeping the lower surface of the samples at a constant temperature, the IR camera monitors the upper surface temperature. With the help of a reference sample of known thermal conductivity, the total heat flux through the samples can be calculated. This is done under different pressure conditions in order to observe the Knudsen effect. As there is a complex coupling between the different modes of heat transport, the spectrum of the emitted radiation is of interest. Emission spectroscopy on Silica Aerogel has not been previously investigated in detail. An emission chamber was constructed, which permits measuring of the emitted spectra due to an applied temperature gradient using a Perkin Elmer Infrared Grating spectrometer. Different boundary emissivities and varying pressure conditions can be applied. For a correct interpretation of the measured spectra, a numerical treatment of the underlying heat transport mechanism is necessary. Measurements as well as computer simulations are presented. Computer simulations show that a variation of the total thermal conductivity in the range between 1 mW/mK and 30 mW/mK leads to a characteristic damping of the emitted radiation between 500 cm-1 and 2000 cm-1. This characteristic damping of the emitted radiation can be observed by measuring the emitted spectra of Silica Aerogel/Xerogel at varying pressure conditions. Therefore, in principle, it should be possible to extract the thermal conductivity through the gas pores and through the silica skeleton. Boundary effects, however, prevent this data from being extracted. Hopefully these problems will be solved in the near future.

Proceedings of SPIE, Sep 9, 1994

ABSTRACT After more than ten years of research and development on a new generation of transparent... more ABSTRACT After more than ten years of research and development on a new generation of transparent insulation materials in the more restricted sense, namely honeycomb type and other geometric structures, granular and monolithic aerogel, a critical overview of existing materials is presented. During the last years considerable progress has been made, and still more is to be expected as well on the theoretical understanding of the physical properties as on the actual material development. On the other hand there still are problems when one looks at the application aspect, e.g. temperature stability, inflammability, optical appearance, irregularities of the structures, and production costs. The development objectives in the past have been either to physically optimize a material for an application, or to produce a lower-quality cheap material. An example of the first strategy is the recent development of glass capillary structures. The question here, of course, is, whether production, handling and transport can be made easy enough to meet the target of reasonable costs. It should be emphasized, that material costs are not the key issue, but system costs. A continuous and intensive collaboration between production engineer, system or design engineer, scientist and salesman is probably the only chance to meet the requirements of high quality products, adapted to the application, with reasonable costs. An engineer designing an application with transparent insulation materials without understanding the physics of the material type used may run the risk of deteriorating the performance severely.

Elsevier eBooks, 1988

ABSTRACT Transparently insulated massive walls reduce heating loads to an impressive degree. The ... more ABSTRACT Transparently insulated massive walls reduce heating loads to an impressive degree. The heating season of a building can be shortened by several months. Good transparent insulation materials (TIM's) have transmittances of up to 70 percent for diffuse irradiation and U-values in the range from 0.5 to 1.5 Wm−2K−1.The combined effect of thermal insulation and collecting solar radiation allows the use of these materials not only for southern, but also for other orientations. Steady-state theory gives upper limits for the potential of this passive component to reverse the heat flow towards the interior. Experimental data indicate that it may be applied for periods greater than the time constant of the wall. Apart from overheating in summer, which makes some shading device necessary in most cases, there is always some mismatch between solar heat gains and heating demand. This leads to a non-utilizable fraction of the solar gains. Simulations allow the inclusion of dynamical, non-linear effects and non-utilizability depending on the storage capacity of the system, but easy and rapid design methods are desirable. The Solar-Savings-Fraction method of Heidt (1985) and the method of Monsen (1982) shall be compared with simulation results. Results show that the most relevant parameters can be incorporated in the steady-state theory. Corrections are due to the storage capacity of the house, which influences utilizability especially in spring and autumn. The wall heat capacity has little influence on heat gains, but determines the maximum absorber temperatures.

Proceedings of SPIE, Nov 25, 1992

ABSTRACT

Proceedings of SPIE, Sep 9, 1994

ABSTRACT Errors in performing optical measurements of scattering samples are analyzed. Measuremen... more ABSTRACT Errors in performing optical measurements of scattering samples are analyzed. Measurements are described from a Perkin-Elmer Lambda-9 spectrophotometer with an integrating sphere of 15 cm diameter for spectral data between 300 and 2500 nm and from a 65 cm integrating sphere for broadband data on larger samples. The influence of the size of the illuminated sample area, the size of the sphere ports and sample thickness are investigated. Results are compared with Monte Carlo simulations.

Elsevier eBooks, 1991

ABSTRACT

Minerals Engineering, 2017

Bioleaching of chalcopyrite is only possible in the presence of thermophilic microorganisms. Whil... more Bioleaching of chalcopyrite is only possible in the presence of thermophilic microorganisms. While suitable conditions can be generated within a heap naturally through the exothermic reaction, the effectiveness of the process can be improved with an additional heat source. Chilean copper mines are primarily located in the Atacama Desert, which has the highest solar irradiation levels on the planet. Solar thermal energy can be incorporated into the heap bioleaching process to raise the temperature in the heap and increase the copper extraction rates. A heap bioleaching system, including ponds and a solar thermal collector field, has been simulated over one year using HeapSim and TRNSYS. The maximum copper extraction achievable for the system without a solar thermal field is 67% with a 7 kg/h m 2 solution flow rate. A maximum extraction of 85% over one year could be achieved with a collector field to heap area ratio of 1:1 and a 10 kg/h m 2 solution flow rate. An economic analysis compares the capital cost of the solar thermal system to the revenue from additional copper extraction. The net present value and internal rate of return were positive for collector areas in the range of 10,000-150,000 m 2 for a heap area of 200,000 m 2. The peak NPV occurs at 50,000 m 2 at which point an extractionof 76% is achieved over one year of leaching.

SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems, 2018

This publication presents a newly developed procedure for performance evaluation of direct steam ... more This publication presents a newly developed procedure for performance evaluation of direct steam generating collectors. Performance testing and evaluation of solar collectors operating with direct steam are not yet standardized, since accredited testing standard procedures do not foresee testing with compressible heat transfer media. Due to the existence of two-phase flow, the measurement concept as well as the collector simulation model needs to be adjusted. Two approaches of steady-state and dynamic performance evaluation are introduced. The corresponding methodology is applicable to small-and large-scale parabolic trough as well as linear Fresnel collectors. The application of the newly developed simulation model and evaluation procedure to measurement data proves the practicability and reliability of the introduced approach. On the basis of exemplary results, the benefits and remaining drawbacks of the procedure are thoroughly discussed. They particularly demonstrate the adapted testing method to be a valuable tool for fast and simple performance checks of steam generating systems. Meaningful performance testing is considered highly beneficial for a further dissemination and global acceptance of steam collectors and solar process heat in general.

Physical review, Apr 15, 1983

ColSim is a simulation software initially designed and further developed at Fraunhofer ISE to per... more ColSim is a simulation software initially designed and further developed at Fraunhofer ISE to perform calculations for solar thermal systems. ColSim can perform quasi-dynamic hydraulic simulations and allows for the integration of complex control strategies.

Elsevier eBooks, 2012

Abstract: In this chapter, different approaches and properties of absorber coatings for receivers... more Abstract: In this chapter, different approaches and properties of absorber coatings for receivers in parabolic trough and linear Fresnel collectors are discussed. The receiver is a central and crucial element determining the optical efficiency of the conversion of solar radiation on the one hand, and the heat losses on the other. High solar absorptance and low thermal emittance in the temperature range of operation are important. The exact definitions of these Key characterizing parameters are given. As the receivers should retain their performance over many years of operation, degradation processes and service lifetime are important as well.

Solar Energy, Nov 1, 1992

ABSTRACT The directional-hemispherical (also sometimes called direct-diffuse) solar transmittance... more ABSTRACT The directional-hemispherical (also sometimes called direct-diffuse) solar transmittance for several different honeycomb-type structures has been measured with an indoor solar simulator and a 40 cm diameter integrating sphere for incidence angles up to 70°. The samples have been fabricated by commeriial companies from different plastics, with cell wall thicknesses between 15 and 70 μm and have approximately square or circular cell cross sections. After a discussion of the measurement errors and problems associated with a limited number of nonideal samples, a fit procedure based on a physically based transmittance model is presented and applied to the data. The resulting coefficients describe the angular and thickness dependence of the solar transmittance for each type of material. They may be used in order to feed data easily and flexibly into simulation models for solar collectors, windows or building.