The Experts below are selected from a list of 2859 Experts worldwide ranked by ideXlab platform

Bernhard Mayer - One of the best experts on this subject based on the ideXlab platform.

  • atmospheric extinction in Solar Tower Plants absorption and broadband correction for mor measurements
    Atmospheric Measurement Techniques, 2015
    Co-Authors: Natalie Hanrieder, Stefan Wilbert, Robert Pitzpaal, Claudia Emde, Josef Gasteiger, Bernhard Mayer
    Abstract:

    Abstract. Losses of reflected Direct Normal Irradiance due to atmospheric extinction in concentrated Solar Tower Plants can vary significantly with site and time. The losses of the direct normal irradiance between the heliostat field and receiver in a Solar Tower Plant are mainly caused by atmospheric scattering and absorption by aerosol and water vapor concentration in the atmospheric boundary layer. Due to a high aerosol particle number, radiation losses can be significantly larger in desert environments compared to the standard atmospheric conditions which are usually considered in ray-tracing or Plant optimization tools. Information about on-site atmospheric extinction is only rarely available. To measure these radiation losses, two different commercially available instruments were tested, and more than 19 months of measurements were collected and compared at the Plataforma Solar de Almeria. Both instruments are primarily used to determine the meteorological optical range (MOR). The Vaisala FS11 scatterometer is based on a monochromatic near-infrared light source emission and measures the strength of scattering processes in a small air volume mainly caused by aerosol particles. The Optec LPV4 long-path visibility transmissometer determines the monochromatic attenuation between a light-emitting diode (LED) light source at 532 nm and a receiver and therefore also accounts for absorption processes. As the broadband Solar attenuation is of interest for Solar resource assessment for concentrated Solar power (CSP), a correction procedure for these two instruments is developed and tested. This procedure includes a spectral correction of both instruments from monochromatic to broadband attenuation. That means the attenuation is corrected for the time-dependent Solar spectrum which is reflected by the collector. Further, an absorption correction for the Vaisala FS11 scatterometer is implemented. To optimize the absorption and broadband correction (ABC) procedure, additional measurement input of a nearby sun photometer is used to enhance on-site atmospheric assumptions for description of the atmosphere in the algorithm. Comparing both uncorrected and spectral- and absorption-corrected extinction data from 1-year measurements at the Plataforma Solar de Almeria, the mean difference between the scatterometer and the transmissometer is reduced from 4.4 to 0.57 %. Applying the ABC procedure without the usage of additional input data from a sun photometer still reduces the difference between both sensors to about 0.8 %. Applying an expert guess assuming a standard aerosol profile for continental regions instead of additional sun photometer input results in a mean difference of 0.8 %. Additionally, a simulation approach which just uses sun photometer and common meteorological data to determine the on-site atmospheric extinction at surface is presented and corrected FS11 and LPV4 measurements are validated with the simulation results. For T1 km equal to 0.9 and a 10 min time resolution, an uncertainty analysis showed that an absolute uncertainty of about 0.038 is expected for the FS11 and about 0.057 for the LPV4. Combining both uncertainties results in an overall absolute uncertainty of 0.068 which justifies quite well the mean RMSE between both corrected data sets. For yearly averages several error influences average out and absolute uncertainties of 0.020 and 0.054 can be expected for the FS11 and the LPV4, respectively. Therefore, applying this new correction method, both instruments can now be utilized to sufficiently accurately determine the Solar broadband extinction in Tower Plants.

  • atmospheric extinction in Solar Tower Plants absorption and broadband correction for mor measurements
    Atmospheric Measurement Techniques, 2015
    Co-Authors: Natalie Hanrieder, Stefan Wilbert, Robert Pitzpaal, Claudia Emde, Josef Gasteiger, Bernhard Mayer
    Abstract:

    Abstract. Losses of reflected Direct Normal Irradiance due to atmospheric extinction in concentrated Solar Tower Plants can vary significantly with site and time. The losses of the direct normal irradiance between the heliostat field and receiver in a Solar Tower Plant are mainly caused by atmospheric scattering and absorption by aerosol and water vapor concentration in the atmospheric boundary layer. Due to a high aerosol particle number, radiation losses can be significantly larger in desert environments compared to the standard atmospheric conditions which are usually considered in ray-tracing or Plant optimization tools. Information about on-site atmospheric extinction is only rarely available. To measure these radiation losses, two different commercially available instruments were tested, and more than 19 months of measurements were collected and compared at the Plataforma Solar de Almeria. Both instruments are primarily used to determine the meteorological optical range (MOR). The Vaisala FS11 scatterometer is based on a monochromatic near-infrared light source emission and measures the strength of scattering processes in a small air volume mainly caused by aerosol particles. The Optec LPV4 long-path visibility transmissometer determines the monochromatic attenuation between a light-emitting diode (LED) light source at 532 nm and a receiver and therefore also accounts for absorption processes. As the broadband Solar attenuation is of interest for Solar resource assessment for concentrated Solar power (CSP), a correction procedure for these two instruments is developed and tested. This procedure includes a spectral correction of both instruments from monochromatic to broadband attenuation. That means the attenuation is corrected for the time-dependent Solar spectrum which is reflected by the collector. Further, an absorption correction for the Vaisala FS11 scatterometer is implemented. To optimize the absorption and broadband correction (ABC) procedure, additional measurement input of a nearby sun photometer is used to enhance on-site atmospheric assumptions for description of the atmosphere in the algorithm. Comparing both uncorrected and spectral- and absorption-corrected extinction data from 1-year measurements at the Plataforma Solar de Almeria, the mean difference between the scatterometer and the transmissometer is reduced from 4.4 to 0.57 %. Applying the ABC procedure without the usage of additional input data from a sun photometer still reduces the difference between both sensors to about 0.8 %. Applying an expert guess assuming a standard aerosol profile for continental regions instead of additional sun photometer input results in a mean difference of 0.8 %. Additionally, a simulation approach which just uses sun photometer and common meteorological data to determine the on-site atmospheric extinction at surface is presented and corrected FS11 and LPV4 measurements are validated with the simulation results. For T1 km equal to 0.9 and a 10 min time resolution, an uncertainty analysis showed that an absolute uncertainty of about 0.038 is expected for the FS11 and about 0.057 for the LPV4. Combining both uncertainties results in an overall absolute uncertainty of 0.068 which justifies quite well the mean RMSE between both corrected data sets. For yearly averages several error influences average out and absolute uncertainties of 0.020 and 0.054 can be expected for the FS11 and the LPV4, respectively. Therefore, applying this new correction method, both instruments can now be utilized to sufficiently accurately determine the Solar broadband extinction in Tower Plants.

Natalie Hanrieder - One of the best experts on this subject based on the ideXlab platform.

  • modeling beam attenuation in Solar Tower Plants using common dni measurements
    Solar Energy, 2016
    Co-Authors: Natalie Hanrieder, Stefan Wilbert, Manajit Sengupta, Yu Xie, Robert Pitzpaal
    Abstract:

    Abstract Solar radiation reflected by concentrating mirrors is attenuated due to atmospheric extinction as it travels to the receiver of a Solar Tower Plant. The lack of information on the magnitude of extinction increases the uncertainties in yield analysis and Tower Plant design. In-situ measurements of atmospheric extinction as well as measurement correction methods have been recently performed and developed (Hanrieder et al., 2012, 2015), but specific information is unavailable for individual Plant projects. It is well known though that the extinction varies significantly with site and time. To overcome this absence of information a model to derive the attenuation loss between heliostat and receiver from common direct normal irradiance (DNI) measurements was developed by Sengupta and Wagner (2011) (SW2011 model). We present an updated version of that model and a comparison between the performance of the models using extinction measurements. In the new approach presented here, different precipitable water vapor (PWV) amounts are considered and the model is adjusted to the elevation of the investigated site. The strongest assumption in this approach is the assumption about the aerosol extinction height profile. Three different height profiles are tested for the Plataforma Solar de Almeria (PSA) resulting in three different new transmittance models. The SW2011 as well as the three new models are evaluated with one year of corrected extinction data derived with the ABC (absorption and broadband correction) method of Hanrieder et al. (2015) and a Vaisala FS11 scatterometer at PSA. The new models show a mean difference to the reference data set of 0.01, 0.05 and 0.03 and a root mean square error (RMSE) of 0.052, 0.056 and 0.049 (compared to a mean bias of −0.08 and RMSE of 0.095 for the SW2011 model for transmittances through a 1 km slant range). These results indicate the importance of adequate assumptions for the aerosol height profile. Testing the developed TM with the LIVAS height profile (Amiridis et al., 2015) for PSA shows satisfying results and this motivates testing the approach for other sites. By applying an additional correction for the Linke turbidity (TL) derived as in Ineichen and Perez (2002) the mean bias can be further lowered. An uncertainty analysis shows that the absolute uncertainty coincide with the RMSE levels of the evaluation. Performing the additional TL correction promises an improvement of the overall performance of the model. The new models outperform the SW2011 model due to the PWV and elevation adjustments. The approach can be applied for different sites and incorporated in already existing ray-tracing or Plant optimization tools. It is expected to be valuable for reducing uncertainty in power Tower design and operations.

  • atmospheric extinction in Solar Tower Plants absorption and broadband correction for mor measurements
    Atmospheric Measurement Techniques, 2015
    Co-Authors: Natalie Hanrieder, Stefan Wilbert, Robert Pitzpaal, Claudia Emde, Josef Gasteiger, Bernhard Mayer
    Abstract:

    Abstract. Losses of reflected Direct Normal Irradiance due to atmospheric extinction in concentrated Solar Tower Plants can vary significantly with site and time. The losses of the direct normal irradiance between the heliostat field and receiver in a Solar Tower Plant are mainly caused by atmospheric scattering and absorption by aerosol and water vapor concentration in the atmospheric boundary layer. Due to a high aerosol particle number, radiation losses can be significantly larger in desert environments compared to the standard atmospheric conditions which are usually considered in ray-tracing or Plant optimization tools. Information about on-site atmospheric extinction is only rarely available. To measure these radiation losses, two different commercially available instruments were tested, and more than 19 months of measurements were collected and compared at the Plataforma Solar de Almeria. Both instruments are primarily used to determine the meteorological optical range (MOR). The Vaisala FS11 scatterometer is based on a monochromatic near-infrared light source emission and measures the strength of scattering processes in a small air volume mainly caused by aerosol particles. The Optec LPV4 long-path visibility transmissometer determines the monochromatic attenuation between a light-emitting diode (LED) light source at 532 nm and a receiver and therefore also accounts for absorption processes. As the broadband Solar attenuation is of interest for Solar resource assessment for concentrated Solar power (CSP), a correction procedure for these two instruments is developed and tested. This procedure includes a spectral correction of both instruments from monochromatic to broadband attenuation. That means the attenuation is corrected for the time-dependent Solar spectrum which is reflected by the collector. Further, an absorption correction for the Vaisala FS11 scatterometer is implemented. To optimize the absorption and broadband correction (ABC) procedure, additional measurement input of a nearby sun photometer is used to enhance on-site atmospheric assumptions for description of the atmosphere in the algorithm. Comparing both uncorrected and spectral- and absorption-corrected extinction data from 1-year measurements at the Plataforma Solar de Almeria, the mean difference between the scatterometer and the transmissometer is reduced from 4.4 to 0.57 %. Applying the ABC procedure without the usage of additional input data from a sun photometer still reduces the difference between both sensors to about 0.8 %. Applying an expert guess assuming a standard aerosol profile for continental regions instead of additional sun photometer input results in a mean difference of 0.8 %. Additionally, a simulation approach which just uses sun photometer and common meteorological data to determine the on-site atmospheric extinction at surface is presented and corrected FS11 and LPV4 measurements are validated with the simulation results. For T1 km equal to 0.9 and a 10 min time resolution, an uncertainty analysis showed that an absolute uncertainty of about 0.038 is expected for the FS11 and about 0.057 for the LPV4. Combining both uncertainties results in an overall absolute uncertainty of 0.068 which justifies quite well the mean RMSE between both corrected data sets. For yearly averages several error influences average out and absolute uncertainties of 0.020 and 0.054 can be expected for the FS11 and the LPV4, respectively. Therefore, applying this new correction method, both instruments can now be utilized to sufficiently accurately determine the Solar broadband extinction in Tower Plants.

  • atmospheric extinction in Solar Tower Plants absorption and broadband correction for mor measurements
    Atmospheric Measurement Techniques, 2015
    Co-Authors: Natalie Hanrieder, Stefan Wilbert, Robert Pitzpaal, Claudia Emde, Josef Gasteiger, Bernhard Mayer
    Abstract:

    Abstract. Losses of reflected Direct Normal Irradiance due to atmospheric extinction in concentrated Solar Tower Plants can vary significantly with site and time. The losses of the direct normal irradiance between the heliostat field and receiver in a Solar Tower Plant are mainly caused by atmospheric scattering and absorption by aerosol and water vapor concentration in the atmospheric boundary layer. Due to a high aerosol particle number, radiation losses can be significantly larger in desert environments compared to the standard atmospheric conditions which are usually considered in ray-tracing or Plant optimization tools. Information about on-site atmospheric extinction is only rarely available. To measure these radiation losses, two different commercially available instruments were tested, and more than 19 months of measurements were collected and compared at the Plataforma Solar de Almeria. Both instruments are primarily used to determine the meteorological optical range (MOR). The Vaisala FS11 scatterometer is based on a monochromatic near-infrared light source emission and measures the strength of scattering processes in a small air volume mainly caused by aerosol particles. The Optec LPV4 long-path visibility transmissometer determines the monochromatic attenuation between a light-emitting diode (LED) light source at 532 nm and a receiver and therefore also accounts for absorption processes. As the broadband Solar attenuation is of interest for Solar resource assessment for concentrated Solar power (CSP), a correction procedure for these two instruments is developed and tested. This procedure includes a spectral correction of both instruments from monochromatic to broadband attenuation. That means the attenuation is corrected for the time-dependent Solar spectrum which is reflected by the collector. Further, an absorption correction for the Vaisala FS11 scatterometer is implemented. To optimize the absorption and broadband correction (ABC) procedure, additional measurement input of a nearby sun photometer is used to enhance on-site atmospheric assumptions for description of the atmosphere in the algorithm. Comparing both uncorrected and spectral- and absorption-corrected extinction data from 1-year measurements at the Plataforma Solar de Almeria, the mean difference between the scatterometer and the transmissometer is reduced from 4.4 to 0.57 %. Applying the ABC procedure without the usage of additional input data from a sun photometer still reduces the difference between both sensors to about 0.8 %. Applying an expert guess assuming a standard aerosol profile for continental regions instead of additional sun photometer input results in a mean difference of 0.8 %. Additionally, a simulation approach which just uses sun photometer and common meteorological data to determine the on-site atmospheric extinction at surface is presented and corrected FS11 and LPV4 measurements are validated with the simulation results. For T1 km equal to 0.9 and a 10 min time resolution, an uncertainty analysis showed that an absolute uncertainty of about 0.038 is expected for the FS11 and about 0.057 for the LPV4. Combining both uncertainties results in an overall absolute uncertainty of 0.068 which justifies quite well the mean RMSE between both corrected data sets. For yearly averages several error influences average out and absolute uncertainties of 0.020 and 0.054 can be expected for the FS11 and the LPV4, respectively. Therefore, applying this new correction method, both instruments can now be utilized to sufficiently accurately determine the Solar broadband extinction in Tower Plants.

Robert Pitzpaal - One of the best experts on this subject based on the ideXlab platform.

  • modeling beam attenuation in Solar Tower Plants using common dni measurements
    Solar Energy, 2016
    Co-Authors: Natalie Hanrieder, Stefan Wilbert, Manajit Sengupta, Yu Xie, Robert Pitzpaal
    Abstract:

    Abstract Solar radiation reflected by concentrating mirrors is attenuated due to atmospheric extinction as it travels to the receiver of a Solar Tower Plant. The lack of information on the magnitude of extinction increases the uncertainties in yield analysis and Tower Plant design. In-situ measurements of atmospheric extinction as well as measurement correction methods have been recently performed and developed (Hanrieder et al., 2012, 2015), but specific information is unavailable for individual Plant projects. It is well known though that the extinction varies significantly with site and time. To overcome this absence of information a model to derive the attenuation loss between heliostat and receiver from common direct normal irradiance (DNI) measurements was developed by Sengupta and Wagner (2011) (SW2011 model). We present an updated version of that model and a comparison between the performance of the models using extinction measurements. In the new approach presented here, different precipitable water vapor (PWV) amounts are considered and the model is adjusted to the elevation of the investigated site. The strongest assumption in this approach is the assumption about the aerosol extinction height profile. Three different height profiles are tested for the Plataforma Solar de Almeria (PSA) resulting in three different new transmittance models. The SW2011 as well as the three new models are evaluated with one year of corrected extinction data derived with the ABC (absorption and broadband correction) method of Hanrieder et al. (2015) and a Vaisala FS11 scatterometer at PSA. The new models show a mean difference to the reference data set of 0.01, 0.05 and 0.03 and a root mean square error (RMSE) of 0.052, 0.056 and 0.049 (compared to a mean bias of −0.08 and RMSE of 0.095 for the SW2011 model for transmittances through a 1 km slant range). These results indicate the importance of adequate assumptions for the aerosol height profile. Testing the developed TM with the LIVAS height profile (Amiridis et al., 2015) for PSA shows satisfying results and this motivates testing the approach for other sites. By applying an additional correction for the Linke turbidity (TL) derived as in Ineichen and Perez (2002) the mean bias can be further lowered. An uncertainty analysis shows that the absolute uncertainty coincide with the RMSE levels of the evaluation. Performing the additional TL correction promises an improvement of the overall performance of the model. The new models outperform the SW2011 model due to the PWV and elevation adjustments. The approach can be applied for different sites and incorporated in already existing ray-tracing or Plant optimization tools. It is expected to be valuable for reducing uncertainty in power Tower design and operations.

  • atmospheric extinction in Solar Tower Plants absorption and broadband correction for mor measurements
    Atmospheric Measurement Techniques, 2015
    Co-Authors: Natalie Hanrieder, Stefan Wilbert, Robert Pitzpaal, Claudia Emde, Josef Gasteiger, Bernhard Mayer
    Abstract:

    Abstract. Losses of reflected Direct Normal Irradiance due to atmospheric extinction in concentrated Solar Tower Plants can vary significantly with site and time. The losses of the direct normal irradiance between the heliostat field and receiver in a Solar Tower Plant are mainly caused by atmospheric scattering and absorption by aerosol and water vapor concentration in the atmospheric boundary layer. Due to a high aerosol particle number, radiation losses can be significantly larger in desert environments compared to the standard atmospheric conditions which are usually considered in ray-tracing or Plant optimization tools. Information about on-site atmospheric extinction is only rarely available. To measure these radiation losses, two different commercially available instruments were tested, and more than 19 months of measurements were collected and compared at the Plataforma Solar de Almeria. Both instruments are primarily used to determine the meteorological optical range (MOR). The Vaisala FS11 scatterometer is based on a monochromatic near-infrared light source emission and measures the strength of scattering processes in a small air volume mainly caused by aerosol particles. The Optec LPV4 long-path visibility transmissometer determines the monochromatic attenuation between a light-emitting diode (LED) light source at 532 nm and a receiver and therefore also accounts for absorption processes. As the broadband Solar attenuation is of interest for Solar resource assessment for concentrated Solar power (CSP), a correction procedure for these two instruments is developed and tested. This procedure includes a spectral correction of both instruments from monochromatic to broadband attenuation. That means the attenuation is corrected for the time-dependent Solar spectrum which is reflected by the collector. Further, an absorption correction for the Vaisala FS11 scatterometer is implemented. To optimize the absorption and broadband correction (ABC) procedure, additional measurement input of a nearby sun photometer is used to enhance on-site atmospheric assumptions for description of the atmosphere in the algorithm. Comparing both uncorrected and spectral- and absorption-corrected extinction data from 1-year measurements at the Plataforma Solar de Almeria, the mean difference between the scatterometer and the transmissometer is reduced from 4.4 to 0.57 %. Applying the ABC procedure without the usage of additional input data from a sun photometer still reduces the difference between both sensors to about 0.8 %. Applying an expert guess assuming a standard aerosol profile for continental regions instead of additional sun photometer input results in a mean difference of 0.8 %. Additionally, a simulation approach which just uses sun photometer and common meteorological data to determine the on-site atmospheric extinction at surface is presented and corrected FS11 and LPV4 measurements are validated with the simulation results. For T1 km equal to 0.9 and a 10 min time resolution, an uncertainty analysis showed that an absolute uncertainty of about 0.038 is expected for the FS11 and about 0.057 for the LPV4. Combining both uncertainties results in an overall absolute uncertainty of 0.068 which justifies quite well the mean RMSE between both corrected data sets. For yearly averages several error influences average out and absolute uncertainties of 0.020 and 0.054 can be expected for the FS11 and the LPV4, respectively. Therefore, applying this new correction method, both instruments can now be utilized to sufficiently accurately determine the Solar broadband extinction in Tower Plants.

  • atmospheric extinction in Solar Tower Plants absorption and broadband correction for mor measurements
    Atmospheric Measurement Techniques, 2015
    Co-Authors: Natalie Hanrieder, Stefan Wilbert, Robert Pitzpaal, Claudia Emde, Josef Gasteiger, Bernhard Mayer
    Abstract:

    Abstract. Losses of reflected Direct Normal Irradiance due to atmospheric extinction in concentrated Solar Tower Plants can vary significantly with site and time. The losses of the direct normal irradiance between the heliostat field and receiver in a Solar Tower Plant are mainly caused by atmospheric scattering and absorption by aerosol and water vapor concentration in the atmospheric boundary layer. Due to a high aerosol particle number, radiation losses can be significantly larger in desert environments compared to the standard atmospheric conditions which are usually considered in ray-tracing or Plant optimization tools. Information about on-site atmospheric extinction is only rarely available. To measure these radiation losses, two different commercially available instruments were tested, and more than 19 months of measurements were collected and compared at the Plataforma Solar de Almeria. Both instruments are primarily used to determine the meteorological optical range (MOR). The Vaisala FS11 scatterometer is based on a monochromatic near-infrared light source emission and measures the strength of scattering processes in a small air volume mainly caused by aerosol particles. The Optec LPV4 long-path visibility transmissometer determines the monochromatic attenuation between a light-emitting diode (LED) light source at 532 nm and a receiver and therefore also accounts for absorption processes. As the broadband Solar attenuation is of interest for Solar resource assessment for concentrated Solar power (CSP), a correction procedure for these two instruments is developed and tested. This procedure includes a spectral correction of both instruments from monochromatic to broadband attenuation. That means the attenuation is corrected for the time-dependent Solar spectrum which is reflected by the collector. Further, an absorption correction for the Vaisala FS11 scatterometer is implemented. To optimize the absorption and broadband correction (ABC) procedure, additional measurement input of a nearby sun photometer is used to enhance on-site atmospheric assumptions for description of the atmosphere in the algorithm. Comparing both uncorrected and spectral- and absorption-corrected extinction data from 1-year measurements at the Plataforma Solar de Almeria, the mean difference between the scatterometer and the transmissometer is reduced from 4.4 to 0.57 %. Applying the ABC procedure without the usage of additional input data from a sun photometer still reduces the difference between both sensors to about 0.8 %. Applying an expert guess assuming a standard aerosol profile for continental regions instead of additional sun photometer input results in a mean difference of 0.8 %. Additionally, a simulation approach which just uses sun photometer and common meteorological data to determine the on-site atmospheric extinction at surface is presented and corrected FS11 and LPV4 measurements are validated with the simulation results. For T1 km equal to 0.9 and a 10 min time resolution, an uncertainty analysis showed that an absolute uncertainty of about 0.038 is expected for the FS11 and about 0.057 for the LPV4. Combining both uncertainties results in an overall absolute uncertainty of 0.068 which justifies quite well the mean RMSE between both corrected data sets. For yearly averages several error influences average out and absolute uncertainties of 0.020 and 0.054 can be expected for the FS11 and the LPV4, respectively. Therefore, applying this new correction method, both instruments can now be utilized to sufficiently accurately determine the Solar broadband extinction in Tower Plants.

Elena Carra - One of the best experts on this subject based on the ideXlab platform.

  • analysis of Solar Tower Plant performance influenced by atmospheric attenuation at different temporal resolutions related to aerosol optical depth
    Solar Energy, 2017
    Co-Authors: Jesús Ballestrín, Elena Carra, Joaquin Alonsomontesinos, Gabriel Lopezrodriguez, J L Bosch, Javier Barbero, Jesus Fernandezreche, F J Batlles
    Abstract:

    Abstract The optical losses associated with the attenuation of the reflected direct irradiance by the heliostats along the optical path to the receiver may be significant in large Solar Tower Plants. This phenomenon, known as atmospheric attenuation loss, may have a stronger impact at those Tower Plants where high aerosol loads are expected. Performance models like the System Advisor Model (SAM) and the ray-tracing models (DELSOL, MIRVAL) usually estimate the atmospheric attenuation loss by a polynomial expression which is function of the slant range (the optical path between the heliostat and the receiver). Most of the polynomial models proposed to determine this optical loss use two established extreme attenuating conditions corresponding to a clear or hazy atmosphere. This paper presents a sensitivity study of the impact of time-dependent variability of the atmospheric attenuation in the yield performance of two reference large Solar Tower Plants (one similar to Ivanpah 1 and the other one to Crescent Dunes as examples of direct steam and molten salt Tower Plants, respectively). Five sites have been selected from the AERONET ground station network to obtain the aerosol loading at different time-scales: annual, monthly and daily. Multiple SAM runs have been performed to simulate the annual yield of each Plant and site creating different inputs to the code corresponding to each time-scale condition. The results show a significant impact of the time-scale for modeling the atmospheric attenuation on the annual yield and daily energy output of the Plant. Although the annual and monthly means produce some compensation of the impact, the differences in several particular days can be significant. Up to 20% difference in the daily energy output is found when the extinction is modeled as a steady-state polynomial representing the annual mean compared to the case of daily time-dependent variability of the attenuation. The sensitivity results presented here show that for more realistic yield performance calculations in Solar Tower Plants, particularly at desert and arid climates, the modeling of the atmospheric attenuation should be performed in a time-dependent way according to the climatological variability conditions characteristic of the site.

  • Sensitivity study for modelling atmospheric attenuation of Solar radiation with radiative transfer models and the impact in Solar Tower Plant production
    Solar Energy, 2016
    Co-Authors: Jesús Ballestrín, Elena Carra
    Abstract:

    Abstract The Solar radiation reflected by the heliostats towards the receiver in Solar Tower Plants may be attenuated by scattering and absorption processes along the optical path. This phenomenon has been traditionally computed by the Solar Tower Plant codes using simple models based on polynomial functions of the slant range and taking very extreme conditions for the turbidity based on the standard visual range. Radiative transfer codes (libRadtran) allow modelling the atmospheric attenuation as a function of the slant range considering different aerosol conditions taken from several AERONET stations in regions of interest for CSP. The methodology presented in this work for modelling atmospheric attenuation with libRadtran can be used with any other radiative transfer model. The results showing the sensitivity of the attenuation loss to the aerosol optical depth, assuming homogeneous vertical distribution, have been fit to a simple model that can be used in Solar Advisor Model (SAM). The attenuation loss in the model proposed reaches around 20% at 1 km of slant range for highly aerosol load typical of some desert sites. Sensitivity estimations with SAM have been performed also for two reference Solar Tower Plants (Ivanpah 1 and GemaSolar) to study the impact of atmospheric attenuation in the output power of the Plant. The different attenuation loss between low and very high turbidity conditions can result in a reduction of the power output of a large Plant like Ivanpah 1 of around 12% of average daily production, 20% in the field optical efficiency and 11% in the power absorbed by the receiver. In smaller Plants with large thermal storage system (GemaSolar) the impact of the attenuation loss is significantly smaller (around 4%). Modelling the atmospheric attenuation in the Solar Tower codes should include aerosol optical depth as input in a daily basis for allowing the inclusion of the expected aerosol variability of desert and arid sites.

Stefan Wilbert - One of the best experts on this subject based on the ideXlab platform.

  • modeling beam attenuation in Solar Tower Plants using common dni measurements
    Solar Energy, 2016
    Co-Authors: Natalie Hanrieder, Stefan Wilbert, Manajit Sengupta, Yu Xie, Robert Pitzpaal
    Abstract:

    Abstract Solar radiation reflected by concentrating mirrors is attenuated due to atmospheric extinction as it travels to the receiver of a Solar Tower Plant. The lack of information on the magnitude of extinction increases the uncertainties in yield analysis and Tower Plant design. In-situ measurements of atmospheric extinction as well as measurement correction methods have been recently performed and developed (Hanrieder et al., 2012, 2015), but specific information is unavailable for individual Plant projects. It is well known though that the extinction varies significantly with site and time. To overcome this absence of information a model to derive the attenuation loss between heliostat and receiver from common direct normal irradiance (DNI) measurements was developed by Sengupta and Wagner (2011) (SW2011 model). We present an updated version of that model and a comparison between the performance of the models using extinction measurements. In the new approach presented here, different precipitable water vapor (PWV) amounts are considered and the model is adjusted to the elevation of the investigated site. The strongest assumption in this approach is the assumption about the aerosol extinction height profile. Three different height profiles are tested for the Plataforma Solar de Almeria (PSA) resulting in three different new transmittance models. The SW2011 as well as the three new models are evaluated with one year of corrected extinction data derived with the ABC (absorption and broadband correction) method of Hanrieder et al. (2015) and a Vaisala FS11 scatterometer at PSA. The new models show a mean difference to the reference data set of 0.01, 0.05 and 0.03 and a root mean square error (RMSE) of 0.052, 0.056 and 0.049 (compared to a mean bias of −0.08 and RMSE of 0.095 for the SW2011 model for transmittances through a 1 km slant range). These results indicate the importance of adequate assumptions for the aerosol height profile. Testing the developed TM with the LIVAS height profile (Amiridis et al., 2015) for PSA shows satisfying results and this motivates testing the approach for other sites. By applying an additional correction for the Linke turbidity (TL) derived as in Ineichen and Perez (2002) the mean bias can be further lowered. An uncertainty analysis shows that the absolute uncertainty coincide with the RMSE levels of the evaluation. Performing the additional TL correction promises an improvement of the overall performance of the model. The new models outperform the SW2011 model due to the PWV and elevation adjustments. The approach can be applied for different sites and incorporated in already existing ray-tracing or Plant optimization tools. It is expected to be valuable for reducing uncertainty in power Tower design and operations.

  • atmospheric extinction in Solar Tower Plants absorption and broadband correction for mor measurements
    Atmospheric Measurement Techniques, 2015
    Co-Authors: Natalie Hanrieder, Stefan Wilbert, Robert Pitzpaal, Claudia Emde, Josef Gasteiger, Bernhard Mayer
    Abstract:

    Abstract. Losses of reflected Direct Normal Irradiance due to atmospheric extinction in concentrated Solar Tower Plants can vary significantly with site and time. The losses of the direct normal irradiance between the heliostat field and receiver in a Solar Tower Plant are mainly caused by atmospheric scattering and absorption by aerosol and water vapor concentration in the atmospheric boundary layer. Due to a high aerosol particle number, radiation losses can be significantly larger in desert environments compared to the standard atmospheric conditions which are usually considered in ray-tracing or Plant optimization tools. Information about on-site atmospheric extinction is only rarely available. To measure these radiation losses, two different commercially available instruments were tested, and more than 19 months of measurements were collected and compared at the Plataforma Solar de Almeria. Both instruments are primarily used to determine the meteorological optical range (MOR). The Vaisala FS11 scatterometer is based on a monochromatic near-infrared light source emission and measures the strength of scattering processes in a small air volume mainly caused by aerosol particles. The Optec LPV4 long-path visibility transmissometer determines the monochromatic attenuation between a light-emitting diode (LED) light source at 532 nm and a receiver and therefore also accounts for absorption processes. As the broadband Solar attenuation is of interest for Solar resource assessment for concentrated Solar power (CSP), a correction procedure for these two instruments is developed and tested. This procedure includes a spectral correction of both instruments from monochromatic to broadband attenuation. That means the attenuation is corrected for the time-dependent Solar spectrum which is reflected by the collector. Further, an absorption correction for the Vaisala FS11 scatterometer is implemented. To optimize the absorption and broadband correction (ABC) procedure, additional measurement input of a nearby sun photometer is used to enhance on-site atmospheric assumptions for description of the atmosphere in the algorithm. Comparing both uncorrected and spectral- and absorption-corrected extinction data from 1-year measurements at the Plataforma Solar de Almeria, the mean difference between the scatterometer and the transmissometer is reduced from 4.4 to 0.57 %. Applying the ABC procedure without the usage of additional input data from a sun photometer still reduces the difference between both sensors to about 0.8 %. Applying an expert guess assuming a standard aerosol profile for continental regions instead of additional sun photometer input results in a mean difference of 0.8 %. Additionally, a simulation approach which just uses sun photometer and common meteorological data to determine the on-site atmospheric extinction at surface is presented and corrected FS11 and LPV4 measurements are validated with the simulation results. For T1 km equal to 0.9 and a 10 min time resolution, an uncertainty analysis showed that an absolute uncertainty of about 0.038 is expected for the FS11 and about 0.057 for the LPV4. Combining both uncertainties results in an overall absolute uncertainty of 0.068 which justifies quite well the mean RMSE between both corrected data sets. For yearly averages several error influences average out and absolute uncertainties of 0.020 and 0.054 can be expected for the FS11 and the LPV4, respectively. Therefore, applying this new correction method, both instruments can now be utilized to sufficiently accurately determine the Solar broadband extinction in Tower Plants.

  • atmospheric extinction in Solar Tower Plants absorption and broadband correction for mor measurements
    Atmospheric Measurement Techniques, 2015
    Co-Authors: Natalie Hanrieder, Stefan Wilbert, Robert Pitzpaal, Claudia Emde, Josef Gasteiger, Bernhard Mayer
    Abstract:

    Abstract. Losses of reflected Direct Normal Irradiance due to atmospheric extinction in concentrated Solar Tower Plants can vary significantly with site and time. The losses of the direct normal irradiance between the heliostat field and receiver in a Solar Tower Plant are mainly caused by atmospheric scattering and absorption by aerosol and water vapor concentration in the atmospheric boundary layer. Due to a high aerosol particle number, radiation losses can be significantly larger in desert environments compared to the standard atmospheric conditions which are usually considered in ray-tracing or Plant optimization tools. Information about on-site atmospheric extinction is only rarely available. To measure these radiation losses, two different commercially available instruments were tested, and more than 19 months of measurements were collected and compared at the Plataforma Solar de Almeria. Both instruments are primarily used to determine the meteorological optical range (MOR). The Vaisala FS11 scatterometer is based on a monochromatic near-infrared light source emission and measures the strength of scattering processes in a small air volume mainly caused by aerosol particles. The Optec LPV4 long-path visibility transmissometer determines the monochromatic attenuation between a light-emitting diode (LED) light source at 532 nm and a receiver and therefore also accounts for absorption processes. As the broadband Solar attenuation is of interest for Solar resource assessment for concentrated Solar power (CSP), a correction procedure for these two instruments is developed and tested. This procedure includes a spectral correction of both instruments from monochromatic to broadband attenuation. That means the attenuation is corrected for the time-dependent Solar spectrum which is reflected by the collector. Further, an absorption correction for the Vaisala FS11 scatterometer is implemented. To optimize the absorption and broadband correction (ABC) procedure, additional measurement input of a nearby sun photometer is used to enhance on-site atmospheric assumptions for description of the atmosphere in the algorithm. Comparing both uncorrected and spectral- and absorption-corrected extinction data from 1-year measurements at the Plataforma Solar de Almeria, the mean difference between the scatterometer and the transmissometer is reduced from 4.4 to 0.57 %. Applying the ABC procedure without the usage of additional input data from a sun photometer still reduces the difference between both sensors to about 0.8 %. Applying an expert guess assuming a standard aerosol profile for continental regions instead of additional sun photometer input results in a mean difference of 0.8 %. Additionally, a simulation approach which just uses sun photometer and common meteorological data to determine the on-site atmospheric extinction at surface is presented and corrected FS11 and LPV4 measurements are validated with the simulation results. For T1 km equal to 0.9 and a 10 min time resolution, an uncertainty analysis showed that an absolute uncertainty of about 0.038 is expected for the FS11 and about 0.057 for the LPV4. Combining both uncertainties results in an overall absolute uncertainty of 0.068 which justifies quite well the mean RMSE between both corrected data sets. For yearly averages several error influences average out and absolute uncertainties of 0.020 and 0.054 can be expected for the FS11 and the LPV4, respectively. Therefore, applying this new correction method, both instruments can now be utilized to sufficiently accurately determine the Solar broadband extinction in Tower Plants.