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Title: Evaluation of Methods to Correct for IR Loss in Eppley PSP Diffuse Measurements

Authors:
; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy Solar Energy Program
OSTI Identifier:
1121000
DOE Contract Number:
AC36-08GO28308
Resource Type:
Conference
Resource Relation:
Conference: Optical Modeling and Measurements for Solar Energy Systems: Proceedings of the Conference, 26-28 August 2007, San Diego, California; Proceedings of SPIE Vol. 6652
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 47 OTHER INSTRUMENTATION

Citation Formats

Vignola, F., Long, C., and Reda, I. Evaluation of Methods to Correct for IR Loss in Eppley PSP Diffuse Measurements. United States: N. p., 2007. Web.
Vignola, F., Long, C., & Reda, I. Evaluation of Methods to Correct for IR Loss in Eppley PSP Diffuse Measurements. United States.
Vignola, F., Long, C., and Reda, I. Mon . "Evaluation of Methods to Correct for IR Loss in Eppley PSP Diffuse Measurements". United States. doi:.
@article{osti_1121000,
title = {Evaluation of Methods to Correct for IR Loss in Eppley PSP Diffuse Measurements},
author = {Vignola, F. and Long, C. and Reda, I.},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

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  • The IR loss in diffuse measurements made by thermopile pyranometers is examined. Diffuse measurements are used for the study of IR losses to minimize the effects of beam irradiance and therefore much of the cosine response error influences. Specifically, diffuse measurements of an Eppley PSP pyranometer are compared to those made with a Schenk Star pyranometer. Eppley B&W and Star type pyranometers suffer minimal IR loss because the reference and receiving junctions of the thermopile are at the same thermal level. The difference between diffuse values can be attributed to calibration and cosine response errors as well as IR loss.more » Therefore it is necessary to separate out the various sources of error and examination of the differences over various times of the year can help, at least for systematic errors. Several methods of correcting for IR loss will be examined. First subtracting out the average nighttime offset during the day will be tested. Next an extrapolation between early morning and late evening offsets will be tested. This should help eliminate the IR offset in both the morning and evening, but underestimate the IR losses during the rest of the day. Correlations of the remaining IR losses with temperature, relative humidity, and irradiance will be evaluated. In addition, the IR losses will be studied both for clear days and for totally overcast periods. Pyrgeometer measurements will also be compared to the estimated IR losses. The above measurements and comparisons will help quantify the magnitude and variation of the IR losses.« less
  • A method has been developed to estimate IR radiative losses using solar radiation and meteorological data without the need for pyrgeometer data. The modeled IR radiative losses are not as accurate as that obtained using pyrgeometer information, but 95% of the modeled IR radiative losses are with a few W/m2 of the actual IR radiative losses. Currently this method is limited to having a least some period when pyrgeometers measurements are available. More testing and evaluations are needed at a number of locations to test the general applicability of the model developed.
  • Simple single black detector pyranometers, such as the Eppley Precision Spectral Pyranometer (PSP) used by the Atmospheric Radiation Measurement (ARM) Program, are known to lose energy via infrared (IR) emission to the sky. This is especially a problem when making clear-sky diffuse shortwave (SW) measurements, which are inherently of low magnitude and suffer the greatest IR loss. Dutton et al. (2001) proposed a technique using information from collocated pyrgeometers to help compensate for this IR loss. The technique uses an empirically derived relationship between the pyrgeometer detector data (and alternatively the detector data plus the difference between the pyrgeometer casemore » and dome temperatures) and the nighttime pyranometer IR loss data. This relationship is then used to apply a correction to the diffuse SW data during daylight hours. We developed an ARM value-added product (VAP) called the SW DIFF CORR 1DUTT VAP to apply the Dutton et al. correction technique to ARM PSP diffuse SW measurements.« less
  • The necessity of establishing the traceability of dose measurement in brachytherapy [sup 192]Ir sources is realized by physicians and researchers in the medical field. Standard sources of various shapes such as [open quotes]hairpin,[close quotes] [open quotes]single pin,[close quotes] [open quotes]thin wire,[close quotes] and [open quotes]seed[close quotes] for calibrating ionization chambers in hospitals are being demanded. Nominal activities of not only these source products but also the standard sources have been so far specified by [open quotes]apparent[close quotes] values. Determination of [open quotes]absolute[close quotes] activity by an established means such as 4pi-beta-gamma coincidence counting is not practical because quantitative dissolution ofmore » metallic iridium is very difficult. We tried to determine the [open quotes]absolute[close quotes] activity by a calorimetric method in a fully nondestructive way.« less
  • The kinetics of phase transformations, including diffusion-controlled precipitation, are frequently well described by the Avrami equation. The authors have presented methods for deriving Avrami parameters in cases where data are missing for early times. The first method involves re-plotting the experimental data for a series of shifts, [Delta]t, of the time origin (neglecting data falling earlier than the new time origin); calculating X(t), fraction of material transformed, vs. t for each [Delta]t; fitting the Avrami equation to X(t) to derive [tau] and m values; plotting the values as a function of [Delta]t; and extrapolating to [Delta]t = 0 to obtainmore » the best values. A second, faster method may, at times, be suitably accurate: the authors use the 2-exponential simulation to approximate the data over the entire time range from 0 to [infinity]. They then calculate X(t) and carry out an Avrami fit to X(t) to determine [tau] and m values in fair agreement with those of the lengthier first method. A caveat is in order: The methods of the present paper should be applied with caution.« less