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CLOUDY SKY VERSION OF BIRD'S BROADBAND HOURLY
CLEAR SKY MODEL
SOLAR 2006July 8-13, 2006 Denver, Colorado
Renewable Energy Key to Climate Recovery
Daryl R. MyersNational Renewable Energy Laboratory
1617 Cole Blvd Golden CO 80401
NREL/PR-581-40115
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Disclaimer and Government License
This work has been authored by Midwest Research Institute (MRI) under Contract No. DE-AC36-99GO10337 with the U.S. Department of Energy (the “DOE”). The United States Government (the “Government”) retains and the publisher, by accepting the work for publication, acknowledges that the Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for Government purposes.
Neither MRI, the DOE, the Government, nor any other agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe any privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the Government or any agency thereof. The views and opinions of the authors and/or presenters expressed herein do not necessarily state or reflect those of MRI, the DOE, the Government, or any agency thereof.
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AcknowledgmentsThe pioneering work of Dr. Richard Bird has stood the test of time, and still reverberates in the solar modeling community.
Dr. Richard E. Bird✭ 1 February 1942
–✝ 18 April 2002
This work is but an editing of his contribution.
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Based on observed cloud cover data
Using a SIMPLE model
Produce “all sky” modeled hourly solar radiation
Objective:
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Bird’s Clear Sky Model
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8760 Hour Clear Sky Profile (Climatological Aerosol, Water, Ozone)
and Real Data
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The (Long Standing) Problem--CloudsCloud Type?
Layers?
Height?
Thickness?
Density?
Distribution?
“Fuzzy” and AI Models: Require “training” with real data
Empirical: Measured solar data and cloud information
Stochastic:Need statistics!
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Nielsen’s Irradiance Vs CC Reported by Ehnberg
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Zenith angle (90 - elevation)
Glo
bal I
rr. W
.m-2
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2 Octa
3 Octa
4 Octa
5 Octa
6 Octa
7 Octa
8 Octa
Nielsen, L., et al. Net Incoming Radiation Estimated from Hourly Global Radiation and/or Cloud Observations. Journal of Climatology, I, p. 225-272, 1981 Ehnberg, J.S.G., and M.H.J. Bollen, Simulation of Global Solar Radiation Based on Cloud Observations, Solar Energy Vol 78, p. 157-162, 2005
Normalization
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Normalized Cloud Transmittance Vs Z and CC
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Zenith Angle
Tra
nsm
issi
on r
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to C
C=0
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1 Octa
2 Octa
3 Octa
4 Octa
5 Octa
6 Octa
7 Octa
8 Octa
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45° Z Normalized CC Transmittance
y = -0.0112x2 - 0.0016x + 1.0041
R2 = 0.9955
0.00
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0 1 2 3 4 5 6 7 8
Cloud Cover, Octa
Mea
n R
elat
ive
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tanc
e
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Let’s Try It with Real Data: 30 Sites, 2 Years Measured CC & Solar Data
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National Climatic Data Center Integrated Surface Hourly (ISH) Online Data
• http://lwf.ncdc.noaa.gov/oa/mppsearch.html• http://www5.ncdc.noaa.gov/cgi-bin/script/webcat.pl• http://hurricane.ncdc.noaa.gov/pls/plclimprod/poemain.accessrouter?datasetabbv=DS3505
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Excel Model Implementation
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FORTRAN Program Process 30 SitesINPUTSINPUTSLatitudeLongitudeYearMonthDay HourPressureAerosol OD @ 550 nmAOD @ 380 nmTotal Water VaporTotal OzoneAlbedo
Total Cloud Cover (8ths)
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Hourly Mean Errors(ANNUAL)
MBE 23 Wm-2
-80 Wm-2 <MBE<+60 Wm-2
RMS ~ 133 Wm-2
MBE ~ - 7%, -32%<MBE<+17%
RMS ~ 40%
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Mean Bias and RMS Monthly Hourly Averages 30 Sites
100
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130
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160
170
180
190
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Site
Wm
-2 R
MS
-400
-350
-300
-250
-200
-150
-100
-50
0
50
100
Wm
-2 M
BE
RMS
MBE
MBE PERCENTAvg = - 7%
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1999 Albany NY
Bird All Sky Model Results
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Day of Year
Irrad
ianc
e W
/m2
G*tGN
Measured Global Hz
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0 30 60 90 120 150 180 210 240 270 300 330 360
Day of Year
Irra
dian
ce W
/m2
Global
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June 1999 Albany NY
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Albany 1999 Monthly Mean Hourly Bias Errors
MeasuredMonthly Hr Mean
ModeledMonthlyHr mean
MBE % of MEAS
Jan 45.4 40.4 -12.3Feb 99.0 91.1 -8.6Mar 133.0 157.0 15.3Apr 204.5 187.5 -9.1May 230.5 242.0 4.7Jun 271.2 266.9 -1.6Jul 269.2 260.0 -3.5Aug 214.7 210.3 -2.1Sep 173.8 164.5 -5.7Oct 99.6 91.6 -8.7Nov 75.7 77.9 2.7Dec 55.7 31.6 -76.3
TOTAL 1872.3 1820.9 -2.8
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Seasonal Bias Errors (1999-2000)? From ?
NSRDB Daily Aerosol Optical Depth “Annual
Sine Curve”
Climatological (Long Term) Water Vapor
&Imprecision in
Model
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Compare NSRDB/METSTAT Data and Cloudy Sky Model Results
• Selected 30 Years of Hourly Global Hz Irradiance, Total CC (10ths)
• Convert CC 10ths to Octas• Compute Bird Clear Sky Irradiance
– USE NSRDB (daily) aerosol, (hourly) water vapor
• Modify with Cloud Transmittance• Compare with NSRDB Results
– Remember: NSRDB hourly data are STATISTICAL for 95% of NSRDB—hour by hour matching is unlikely; but MONTHLY MEANS agree well with measured data
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Mean Difference 1.6 Wm-2
Std Dev±93 Wm-2
Mean Difference -8 Wm-2
Std Dev±88 Wm-2
Port Arthur Texas & Evansville Indiana Hourly Simulation 30 Years
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Modeled Global Horizontal G*tGN
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• Very simple model to implement!
•Average -7% MBE (max ~ 25%) and 40% RMS errors
• Realistic model hourly solar radiation profiles
•Based on cloud cover observations for a wide variety of sites...
Summary