KEYWORDS: Calibration, Radiometry, Humidity, Meteorology, Data modeling, Temperature metrology, Error analysis, Solar energy, Systems modeling, Solar energy systems
When an Eppley Normal Incident Pyrheliometer is calibrated against an Eppley Hickey Frieden Absolute Cavity
Radiometer, the instrument systematically deviates from the absolute cavity readings. The reason for this deviation is
not understood. Comparisons are made between one pyrheliometer and an absolute cavity radiometer on selected clear
days over a period of 8 months in Eugene, Oregon. The ratios of the readings from the two instruments are correlated
against wind speed, pressure, temperature, relative humidity, beam intensity, and zenith angle to determine if any of
these parameters statistically influence the calibration process. Wind speed, pressure, beam intensity, and air mass are
shown to be statistically significant factors in determining the responsivity of the normal incident pyrheliometer. The
results of these tests are evaluated and discussed. Use of air mass instead of zenith angle is proposed for calibration
reports.
Thermopile pyranometers exhibit IR radiative losses that affect global and diffuse shortwave measurements made with
first class thermopile based instruments. Pyrgeometers can be used to measure the sky temperature and are used to
calculate the pyranometer's IR radiative losses. Few solar monitoring sites are equipped with pyrgeometers necessary
to account for the IR radiative losses associated with the pyranometers. High quality data from the Solar Radiation
Research Laboratory (SRRL) at the National Renewable Energy Laboratory are used to test and further develop a
model for the IR radiative losses without the use of pyrgeometer data. The various methods for obtaining IR radiative
loss values are compared and contrasted using the SRRL data. A simple scaling method is proposed and tested to
adjust the non-pyrgeometer based correlation models to sites with different sky temperature characteristics.
KEYWORDS: Clouds, Satellites, Solar energy, Satellite imaging, Solar radiation, Solar cells, Earth observing sensors, Vegetation, Solar radiation models, Receivers
A simple, affordable and efficient multifaceted system with technical software programs, "Kosmos 3M", was developed
for taking images of the Earth from NOAA satellites and for handling this images and analyzing many geographical and
meteorological parameters. Technical software programs have been developed that utilize the "Kosmos 3M" Receiver
system. Basic capabilities of the multifaceted "Kosmos 3M" system include: receiving signal from NOAA satellites;
digital processing of space images with geographical fixing, superposition of maps of cities and coordinate grid; finding
of geographical coordinates at any point of space image; finding of temperature of underlying surface at given points;
finding of albedo (reflection coefficient) at any point of space image; finding of upper boundary of clouds (cloudiness);
forecasting of dangerous weather phenomena; defining wind fields in cyclones; precipitations forecast; measuring
distances between given points; measuring surfaces (areas); and forming of electronic library of images of the Earth.
Work is underway to use the "Kosmos 3M" cloudiness images to estimate the incident solar radiation values for
evaluating terrestrial solar energy performance in real time. Such kind of system would have a wide variety of uses from
the classroom to the field.
KEYWORDS: Infrared radiation, Solar radiation models, Data modeling, Atmospheric modeling, Humidity, Solar radiation, Meteorology, Sensors, Domes, Temperature metrology
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.
The IR loss in diffuse measurements made by thermopile pyranometers is examined. Diffuse measurements are used for
the study of IR losses because diffuse irradiance is much smaller than the total irradiance and hence the IR effects can be
more clearly seen. Specifically, diffuse measurements of an Eppley PSP pyranometer are compared to those made with a
Schenk Star pyranometer. Pyranometers with black and white or star type junctions 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. This is a preliminary study over one month
when pyrgeometer data are available. Examination of the differences at various times of the year and at more than one
location is necessary to generalize the findings in this report. Several methods of correcting for IR loss are examined.
First subtracting out the average nighttime offset during the day is tested. Next an extrapolation between early morning
and late evening offsets is tested. This should help eliminate the IR offset in both the morning and evening hours, but
underestimate the IR losses during the rest of the day. Next, correlations of IR losses calculated using pyrgeometer
measurements with temperature, relative humidity, and irradiance are evaluated. Initial results show that it should be
possible to use more commonly available measurements rather than prygeometer data to estimate IR loss for Eppley PSP
pyranometers.
Conference Committee Involvement (3)
Optical Modeling and Measurements for Solar Energy Systems III
2 August 2009 | San Diego, California, United States
Optical Modeling and Measurements for Solar Energy Systems II
13 August 2008 | San Diego, California, United States
Optical Modeling and Measurements for Solar Energy Systems
26 August 2007 | San Diego, California, United States
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