A NEW SILICON PHOTOVOLTAIC PYRANOMETER FOR MEASURING SOLAR IRRADIANCE IN METEOROLOGICAL AND SOLAR RESOURCE APPLICATIONS
T. Thomas*, D. Johnson, D. Heinicke, R. Peterson, P. Morgan, J. Wurm, D. McDermitt, G. Burba, and B. Biggs LI-COR Biosciences, Lincoln, NE, USA. *[email protected]
INTRODUCTION REFERENCE LI-200 PYRANOMETER
REFERENCES
NEW LI-200R PYRANOMETER
PERFORMANCE OF NEW vs OLD DESIGNS: LATEST RESULTS
LI-COR solar radiation measurements:
• Designing solar radiation sensors for over 40 years
• Sensors used at thousands of locations around the world
• Used for solar resource assessment, photovoltaic efficiency
monitoring, meteorological and agricultural studies
Silicon photovoltaic design advantages of LI-200 Pyranometer:
• Low-maintenance, proven field performance [2, 3]
• Lower cost than thermopile designs
• Lower sensitivity to dust and dirt compared to thermopile designs
• Response time less than 1μS (2m cable terminated into 147 Ω load)
In unobstructed daylight conditions, LI-200 Pyranometer compares well
with thermopile pyranometers [1, 2, 3]
LI-200: silicon photovoltaic detector, fully cosine-corrected miniature
head, current output directly proportional to solar radiation
New Design Azimuth Response
Cosine response is corrected well up to 82° angle of incidence*
Detachable sensor head
Easy removal for calibration w/o unwiring
Larger drain for improved water shedding
High-speed, fully cosine corrected
Designed for continuous monitoring
μA and mV (with adapter) output
Sensitivity typically 90μA per 1000 Wm-2
Errors were below 1% in new LI-200R over 360° at 45°elevation
New Design Cosine Response
[1] Biggs, William W. (1984). Principles of Radiation Measurement. LI-COR, Inc. Lincoln, NE [2] Kerr, J. P., Thurtell, G. W., & Tanner, C. B. (1967). An integrating pyranometer for climatological observer stations and mesoscale networks. Journal of Applied Meteorology, 6(4), 688-694. [3] Weiss, A., & Norman, J. M. (1985). Partitioning solar radiation into direct and diffuse, visible and near-infrared components. Agricultural and Forest meteorology, 34(2), 205-213.
In 1:1 comparison, new LI-200R performed well vs reference LI-200 at 1 minute intervals with no averaging
Irradiance from new LI-200R and reference LI-200 sensors. Values represent an average of 5 pyranometers.
New Design Output vs. Reference Irradiance Response Daily Irradiance
Photo: Aaron Deschane
The LI-200SA Pyranometer spectral response along with the energy distribution in the solar spectrum. [1, 2]
The sensitivity of new LI-200R sensors as a function of angle of incidence
Azimuth errors for a set of 5 new LI-200R sensors at 45˚ angle of incidence
Under unobstructed daylight conditions, new LI-200R pyranometer compared well with reference LI-200 *A sensor without an accurate cosine correction can give a severe error at low solar elevation angles. The cosine error at angle 0 is the
percent difference of the ratio of the measured output at angle 0 and normal incidence (angle 0°) as compared to the cosine of angle 0
New LI-200R performed well vs reference LI-200 (data for 1 minute intervals with no averaging)
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Open base with head removed
Closed base with head removed
Overall view
y = 0.0789x + 0.0628 R² = 0.9999
0
10
20
30
40
50
60a
Current (μA) output from new LI-200R sensors as function of reference LI-200 irradiance (Wm-2)
Irradiance from new LI-200R sensors plotted against irradiance values from reference LI-200 sensors
0
100
200
300
400
500
600
700
800
AM7:37:00
AM11:37:00
PM3:37:00
Reference Irradiance
New Irradiance
Time
Example of one day 0°
20°
40°
60°
80°
100°
120°
140°
160°180°
200°
220°
240°
260°
280°
300°
320°
340°
A B C D E
+1% error
-1% error
+5%
+4%
+3%
+2%
-2%
-3%
-4%
-5%
+1%
-1%
Reference Sensor: Irradiance (Wm-2)
y = 0.0774x - 0.0097 R² = 0.9998 =
y = 0.0742x - 0.0013 R² = 0.9999
0
10
20
30
40
50
60
0 500 1000
c y = 0.079x + 0.0086
R² = 0.9998
0 500 1000
=
0
100
200
300
400
500
600
700
0 100 200 300 400 500 600 700
New
Se
nso
r: Ir
rad
ian
ce (
Wm
-2)
Reference Irradiance (Wm-2)
y = 0.997x - 0.089 R² = 0.999
3615 data points per each of 5 sensors
Detachable head
Detachable base
Leveling plate
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