The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Sichee Tsay - One of the best experts on this subject based on the ideXlab platform.
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a novel nonintrusive method to resolve the thermal dome effect of Pyranometers radiometric calibration and implications
Journal of Geophysical Research, 2011Co-Authors: Sichee Tsay, K M Lau, Richard A Hansell, James J Utle, J W CoopeAbstract:[1] Traditionally the calibration equation for Pyranometers assumes that the measured solar irradiance is solely proportional to the thermopile's output voltage; therefore, only a single calibration factor is derived. This causes additional measurement uncertainties because it does not capture sufficient information to correctly account for a pyranometer's thermal effect. In our updated calibration equation, temperatures from the pyranometer's dome and case are incorporated to describe the instrument's thermal behavior, and a new set of calibration constants are determined, thereby reducing measurement uncertainties. In this paper, we demonstrate why a pyranometer's uncertainty using the traditional calibration equation is always larger than a few percent, but with the new approach can become much less than 1% after the thermal issue is resolved. The highlighted calibration results are based on NIST traceable light sources under controlled laboratory conditions. The significance of the new approach lends itself to not only avoiding the uncertainty caused by a pyranometer's thermal effect but also the opportunity to better isolate and characterize other instrumental artifacts, such as angular response and nonlinearity of the thermopile, to further reduce additional uncertainties. We also discuss some of the implications, including an example of how the thermal issue can potentially impact climate studies by evaluating aerosol's direct radiative effect using field measurements with and without considering the pyranometer's thermal effect. The results of radiative transfer model simulation show that a pyranometer's thermal effect on solar irradiance measurements at the surface can be translated into a significant alteration of the calculated distribution of solar energy inside the column atmosphere.
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a novel nonintrusive method to resolve the thermal dome effect of Pyranometers instrumentation and observational basis
Journal of Geophysical Research, 2010Co-Authors: Sichee TsayAbstract:[1] A new method for improving the ground-based pyranometer measurements of solar irradiance has been employed during the East Asian Study of Tropospheric Aerosols and Impact on Regional Climate field experiment, Asian Monsoon Year in China in 2008. Depending on the temperature difference between its detector and domes, a pyranometer's thermal dome effect (TDE) can vary from a few W m−2 at night to over tens of W m−2 during daytime. Yet in traditional calibration procedures only a single calibration constant is determined, and consequently TDE is misrepresented. None of the methods that have been documented in the literature can capture TDE nonintrusively using the same instrument. For example, although adding a temperature sensor to the detector assembly is straightforward, attaching any sensor on a dome is intrusive and will affect its overall optical and physical properties. Furthermore, in response to the solar elevation and atmospheric variables, the dome temperature distribution is both dynamic and uneven, which makes it exceedingly difficult for locating a representative point on the dome for measuring TDE. However, the effective-dome-temperature is proportional to the pressure of the air trapped between the outer and the inner domes; therefore with a minor modification to a pyranometer, we can utilize the ideal gas law to gauge TDE without affecting the domes. Pyranometers can become climate-quality instruments once their TDE are nonintrusively determined.
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on the dome effect of eppley pyrgeometers and Pyranometers
Geophysical Research Letters, 2000Co-Authors: Sichee TsayAbstract:Pyrgeometers and Pyranometers are fundamental instruments widely used for quantifying atmosphere-surface energetics in climate studies. The dome effect of these instruments can cause a measurement uncertainty larger than 10 W m−2. Based on careful analysis, the dome factors of our two new pyrgeometers are found to lie in the range between 1.1 and 2.0. These values are far smaller than the value of 4.0 suggested by the World Meteorological Organization. The laboratory-determined dome factors fall within this range, if pyrgeometers approach equilibrium with the blackbody target during calibration cycles. From recent field campaigns, consistent results for the dome factors are also obtained by analyzing nighttime pyrgeometer measurements, which were regarded as approaching equilibrium state. Furthermore, we utilized an energy balance equation to describe the thermal dome effect of Pyranometers that is commonly referred to as the nighttime negative outputs or the dark-offset. Lacking direct measurements of the dome and case temperatures of pyranometer, we used measurements from a pyrgeometer to derive and to account for the thermal dome effect of collocated Pyranometers. This approximation revealed a reasonable agreement between calculations and measurements.
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thermal characteristics of Pyranometers and pyrgeometers in atmosphere surface energetic measurements
2000Co-Authors: Sichee Tsay, Franco EinaudiAbstract:Since the introduction of thermopile, Pyranometers (solar, e.g., 0.3 - 3.0 microns) and pyrgeometers (terrestrial, e.g., 4 - 50 microns) have become instruments commonly used for measuring the broadband hemispherical irradiances at the surface in a long-term, monitoring mode for decades. These commercially available radiometers have been manufactured in several countries such as from the United States, Asia, and Europe, and are generally reliable and economical. These worldwide distributions of surface measurements become even more important in the era of Earth remote sensing in studying climate change. However, recent studies from field campaigns have pointed out that erroneous factors (e.g., temperature gradients between the filter dome and detector, emissivity of the thermopile) are responsible for the unacceptable level of uncertainty (e.g., 20 W/sq m). It is best to utilize an energy balance equation to describe the thermal dome effect of Pyranometers and pyrgeometers. Therefore, quality of pyranometer and pyrgeometer measurements can be improved largely by applying proper knowledge of the thermal parameters affecting the operation of the thermopile systems. Data correction procedure and algorithm will be presented and discussed.
Frank Vignola - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of Photodiode-based Pyranometers and Reference Solar Cells on a Two-Axis Tracking System
2018 IEEE 7th World Conference on Photovoltaic Energy Conversion (WCPEC) (A Joint Conference of 45th IEEE PVSC 28th PVSEC & 34th EU PVSEC), 2018Co-Authors: Frank Vignola, Josh Peterson, Rich Kessler, Mike Dooraghi, Manajit Sengupta, Fotis MavromatakisAbstract:The performance of photodiode-based Pyranometers and reference solar cells are examined on a two-axis tracker surface. This is the third in a series of papers examining the performance of photodiode-based Pyranometers and reference solar cells on fixed and tracking surfaces. Because the instruments are oriented normally to the incident radiation, angle-of-incidence effects are minimized. By removing the angle-of-incidence effects inherent in earlier studies, the change in the sensor's clear sky responsivity can be more clearly identified. It was found that the photodiode-based Pyranometers demonstrate a larger change in responsivity than the reference solar cells. Spectral measurements are recommended to verify the cause of this difference.
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use of Pyranometers to estimate pv module degradation rates in the field
Photovoltaic Specialists Conference, 2016Co-Authors: Frank Vignola, Mike Dooraghi, Fotis Mavromatakis, Josh Peterso, Rich Kessle, Manaji SenguptaAbstract:Methodology is described that uses relative measurements to estimate the degradation rates of PV modules in the field. The importance of calibration and cleaning is discussed. The number of years of field measurements needed to measure degradation rates with data from the field is cut in half using relative comparisons.
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uncertainty of rotating shadowband irradiometers and si Pyranometers including the spectral irradiance error
SOLARPACES 2015: International Conference on Concentrating Solar Power and Chemical Energy Systems, 2016Co-Authors: Stefa Wilbe, Stefa Kleindiek, Ija Nouri, Norbe Geude, Aro Habte, Marko Schwand, Frank VignolaAbstract:Concentrating solar power projects require accurate direct normal irradiance (DNI) data including uncertainty specifications for plant layout and cost calculations. Ground measured data are necessary to obtain the required level of accuracy and are often obtained with Rotating Shadowband Irradiometers (RSI) that use photodiode Pyranometers and correction functions to account for systematic effects. The uncertainty of Si-Pyranometers has been investigated, but so far basically empirical studies were published or decisive uncertainty influences had to be estimated based on experience in analytical studies. One of the most crucial estimated influences is the spectral irradiance error because Si-photodiode-Pyranometers only detect visible and color infrared radiation and have a spectral response that varies strongly within this wavelength interval. Furthermore, analytic studies did not discuss the role of correction functions and the uncertainty introduced by imperfect shading. In order to further improve the...
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effects of changing spectral radiation distribution on the performance of photodiode Pyranometers
Solar Energy, 2016Co-Authors: Frank Vignola, Zachary Deroche, Josh Peterso, Laure Vuilleumie, Christia Feli, Julia Grobne, Natalia KouremetiAbstract:Abstract The effect of changes in the spectral distribution of the incident solar radiation on the direct normal responsivity of the LI-COR photodiode pyranometer is examined using DNI spectral data from a PMOD spectroradiometer and the generic spectral response of a LI-COR pyranometer. The direct normal responsivity is found to vary over the day under all weather conditions at Payerne, Switzerland in a systematic manner that can be modeled as a function of air mass or solar zenith angle. This suggests that scattering of other atmospheric constituents plays as a subsidiary role to Rayleigh scattering that preferentially scatters more blue light as the path through the atmosphere increases. The SMARTS2 model is used to examine the effect on the full spectral response range of the photodiode based pyranometer and to refine the estimated response changes. The use of this information is discussed relative to improving adjustments made to Rotating Shadowband Irradiometers measurements. Similar methodology can be used to estimate the spectral effect on the performance of solar modules.
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solar and infrared radiation measurements
2012Co-Authors: Frank Vignola, Joseph J. Michalsky, Thomas StoffelAbstract:Measuring Solar and Infrared Radiation Solar Resource Definitions and Terminology Introduction The Sun Extraterrestrial Radiation Solar Coordinates Zenith, Azimuth, and Hour Angles Solar, Universal, and Local Standard Time Solar Position Calculation Sunrise and Sunset Times Global, Direct Normal, and Diffuse Irradiance Solar Radiation on Tilted Surfaces Spectral Nature of Solar Radiation Fundamentals of Thermodynamics and Heat Transfer Photodiodes and Solar Cell Prerequisites Models Historic Milestones in Solar and Infrared Radiation Measurement Introduction Earliest Observations of the Sun and the Nature of Light Nineteenth-Century Radiometers Operational Radiometers of the Twentieth Century Recent Advances in Solar Measurements Direct Normal Irradiance Overview of Direct Normal Irradiance Pyrheliometer Geometry Operational Thermopile Pyrheliometers Absolute Cavity Radiometers Uncertainty Analysis for Pyrheliometer Calibration Uncertainty Analysis for Operational Thermopile Pyrheliometers Uncertainty Analysis for Rotating Shadowband Radiometer Measurements of Direct Normal Irradiance Direct Normal Irradiance Models Historical and Current Surface-Measured Direct Normal Irradiance Data Measuring Global Irradiance Introduction to Global Horizontal Irradiance Measurements Black-Disk Thermopile Pyranometers Black-and-White Pyranometers Photodiode-Based Pyranometers Calibration of Pyranometers Pyranometer Calibration Uncertainties Diffuse Irradiance Introduction The Measurement of Diffuse Irradiance Calibration of Diffuse Pyranometers Value of Accurate Diffuse Measurements Rotating Shadowband Radiometers Introduction The Rotating Shadowband Radiometer The Multifilter Rotating Shadowband Radiometer Measuring Solar Radiation on a Tilted Surface Introduction Effect of Tilt on Single Black Detector Pyranometers Effect of Tilt on Black-and-White Pyranometers Effect of Tilt on Photodiode Pyranometers Recommendations for Tilted Irradiance Measurements Notes on Modeling PV System Performance with Photodiode Pyranometers Albedo Introduction Broadband Albedo Spectral Albedo Bidirectional Reflectance Distribution Function Albedo Measurements Infrared Measurements Introduction Pyrgeometers Calibration Improved Calibrations Other Pyrgeometer Manufacturers Operational Considerations Net Radiation Measurements Introduction Single-Sensor (All-Wave) Net Radiometers Two-Sensor Net Radiometers Four-Sensor Net Radiometers Accuracy of Net Radiometers A Better Net Radiation Standard Net Radiometer Sources Solar Spectral Measurements Introduction The Extraterrestrial Solar Spectrum Atmospheric Interactions Broadband Filter Radiometry Narrow-Band Filter Radiometry Spectrometry Meteorological Measurements Introduction Ambient Temperature Wind Speed and Wind Direction Relative Humidity Pressure Recommended Minimum Accuracies for Operational Instruments Setting Up a Solar Monitoring Station Introduction Choosing a Site Grounding and Shielding Data Logger and Communications Measurement Interval Cleaning and Maintenance Record Keeping Importance of Reviewing Data Quality Control of Data Field Calibrations Physical Layout of a Solar-Monitoring Station Appendix A: Modeling Solar Radiation Appendix B: Solar Radiation Estimates Derived from Satellite Measurements Appendix C: Sun Path Charts Appendix D: Solar Position Algorithms Appendix E: Useful Conversion Factors Appendix F: Sources for Equipment Appendix G: BORCAL Report Appendix H: Sunshine Duration Appendix I: Failure Modes
J W Coope - One of the best experts on this subject based on the ideXlab platform.
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a novel nonintrusive method to resolve the thermal dome effect of Pyranometers radiometric calibration and implications
Journal of Geophysical Research, 2011Co-Authors: Sichee Tsay, K M Lau, Richard A Hansell, James J Utle, J W CoopeAbstract:[1] Traditionally the calibration equation for Pyranometers assumes that the measured solar irradiance is solely proportional to the thermopile's output voltage; therefore, only a single calibration factor is derived. This causes additional measurement uncertainties because it does not capture sufficient information to correctly account for a pyranometer's thermal effect. In our updated calibration equation, temperatures from the pyranometer's dome and case are incorporated to describe the instrument's thermal behavior, and a new set of calibration constants are determined, thereby reducing measurement uncertainties. In this paper, we demonstrate why a pyranometer's uncertainty using the traditional calibration equation is always larger than a few percent, but with the new approach can become much less than 1% after the thermal issue is resolved. The highlighted calibration results are based on NIST traceable light sources under controlled laboratory conditions. The significance of the new approach lends itself to not only avoiding the uncertainty caused by a pyranometer's thermal effect but also the opportunity to better isolate and characterize other instrumental artifacts, such as angular response and nonlinearity of the thermopile, to further reduce additional uncertainties. We also discuss some of the implications, including an example of how the thermal issue can potentially impact climate studies by evaluating aerosol's direct radiative effect using field measurements with and without considering the pyranometer's thermal effect. The results of radiative transfer model simulation show that a pyranometer's thermal effect on solar irradiance measurements at the surface can be translated into a significant alteration of the calculated distribution of solar energy inside the column atmosphere.
Alberto Garcia De Jalo - One of the best experts on this subject based on the ideXlab platform.
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the influence of sky conditions on the standardized calibration of Pyranometers and on the measurement of global solar irradiation
Solar Energy, 2015Co-Authors: Xabie Olano, Fabienne Sallaberry, Alberto Garcia De Jalo, Marti GastoAbstract:Abstract Global solar irradiance measurement is used for applications such as verifying satellite measurements, studying the distribution and variation of the radiation received or estimating the energy yield of solar plants. This measurement is directly influenced by the reference calibration coefficient and uncertainty of the field pyranometer used. The radiometer calibration laboratory of CENER is accredited by ENAC (Spanish National Accreditation Body) since 2010 according to ISO 9847:1992 for the calibration of field Pyranometers via comparison to a reference pyranometer. The accreditation’s scope covers calibrations “type Ia” (outdoor horizontal calibrations for meteorological and resource measurements, part 5.2.2, annex B.2). For the outdoor calibration, the methodology takes three different sky conditions into account: stable cloudless sky conditions, unstable sky conditions with some clouds or cloudy sky conditions. The classification criteria described by the standard have been enhanced for an easier application, establishing additional radiometric conditions, especially for unstable sky conditions with some clouds. Detailed criteria are based on CENER’s experience in solar collector testing and on the experimental CENER BSRN station (Baseline Surface Radiation Network) measurements and total sky camera images. In this study, several calibration coefficient results have been analyzed in order to validate the three different methodologies regarding the sky conditions mentioned before. The calibration coefficient can be slightly different depending on the sky conditions and the calibration methodology; therefore global solar irradiance measurements can differ too. The influence of this dependency has been evaluated in order to estimate the monthly and yearly global solar irradiation.
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the influence of sky conditions on the standardized calibration of Pyranometers and on the measurement of global solar irradiation
Energy Procedia, 2014Co-Authors: Xabie Olano, Fabienne Sallaberry, Alberto Garcia De JaloAbstract:Abstract Global solar irradiance measurement is used for applications such as verifying satellite measurements, studying the distribution and variation of the received radiation or estimating the energy yield of solar plants. This measurement is directly influenced by the reference calibration coefficient of the field pyranometer used. The radiometer calibration laboratory of CENER is accredited by ENAC (Spanish National Accreditation Body) since 2010 according to ISO 9847:1992 for the calibration of field Pyranometers via comparison to a reference pyranometer. The accreditation's scope covers calibrations “type Ia” (outdoor horizontal calibrations for meteorological and resource measurements, part 5.2.2, annex B.2). For the outdoor calibration, the methodology takes different sky conditions into account: stable cloudless sky conditions, unstable sky conditions with some clouds or cloudy sky conditions. The classification criteria described by the standard have been enhanced by CENER for an easier application, establishing additional radiometric conditions, especially for unstable sky conditions with some clouds. Detailed criteria are based on CENER's experience in solar collector testing and on the experimental CENER BSRN station (Baseline Surface Radiation Network) measurements and total sky camera images. During laboratory activity, several calibration coefficient results have been analyzed in order to validate the three methodologies regarding the before mentioned sky conditions. The calibration coefficient can be slightly different depending on the sky conditions and the calibration methodology; therefore global solar irradiation measurements can differ too. The influence of this dependency has been evaluated in order to estimate the monthly and yearly global solar irradiation.
Richard A Hansell - One of the best experts on this subject based on the ideXlab platform.
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a novel nonintrusive method to resolve the thermal dome effect of Pyranometers radiometric calibration and implications
Journal of Geophysical Research, 2011Co-Authors: Sichee Tsay, K M Lau, Richard A Hansell, James J Utle, J W CoopeAbstract:[1] Traditionally the calibration equation for Pyranometers assumes that the measured solar irradiance is solely proportional to the thermopile's output voltage; therefore, only a single calibration factor is derived. This causes additional measurement uncertainties because it does not capture sufficient information to correctly account for a pyranometer's thermal effect. In our updated calibration equation, temperatures from the pyranometer's dome and case are incorporated to describe the instrument's thermal behavior, and a new set of calibration constants are determined, thereby reducing measurement uncertainties. In this paper, we demonstrate why a pyranometer's uncertainty using the traditional calibration equation is always larger than a few percent, but with the new approach can become much less than 1% after the thermal issue is resolved. The highlighted calibration results are based on NIST traceable light sources under controlled laboratory conditions. The significance of the new approach lends itself to not only avoiding the uncertainty caused by a pyranometer's thermal effect but also the opportunity to better isolate and characterize other instrumental artifacts, such as angular response and nonlinearity of the thermopile, to further reduce additional uncertainties. We also discuss some of the implications, including an example of how the thermal issue can potentially impact climate studies by evaluating aerosol's direct radiative effect using field measurements with and without considering the pyranometer's thermal effect. The results of radiative transfer model simulation show that a pyranometer's thermal effect on solar irradiance measurements at the surface can be translated into a significant alteration of the calculated distribution of solar energy inside the column atmosphere.
