Transcript Insolation of the Atacama Desert

Insolation of the Atacama
Desert
Michael Wagner
James Teza
July 28, 2003
Life in the Atacama
Carnegie Mellon
Weather / Solar Station Purpose
Perform environmental measurements in the
field for science and engineering purposes
Measure insolation to understand solar power
available to a rover
Measure solar spectra quantitatively to predict
ATJ performance in the field
Characterize Si and ATJ solar cell performance to
aid design of new rover solar panel
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Solar Measurement Station
Periodically performed
measurements of
•Global insolation
•Solar Irradiance spectra
•ATJ and Si solar cell
behavior
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Si Cells
ATJ Cells
Spectrophotometer
PTU
Pyranometer
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Insolation - Experimental
Implementation
• Kipp and Zonen CM3
Thermopile pyranometer
• 303 – 2800 nm range (50%)
• +/- 2.5% non-linearity
• 180 degree sensitivity
• Time constant 18 sec
• Sensor oriented horizontally
for global insolation
• Acquired measurement
every minute
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Insolation Results - Overview
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Insolation Results – Clear Days
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Insolation Results – Cloudy Days
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Insolation Results – Total Daily Energy
Average available energy per day: 20.9 MJ/m2/day
Std dev: 5.3 MJ/m2/day
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Spectrophotometry – Motivation
Need to predict
efficiency of ATJ
cells in Atacama
Emcore ATJ - Spectral response vs. Wavelength
1.2
GaInP2
InGaAs
Ge
Spectral response
of ATJ cells
(efficiency) differs
from Si response
Spectral response (A/W)
1
0.8
0.6
0.4
0.2
0
200
400
600
800
1000
1200
Wavelength (nm)
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1400
1600
1800
2000
Spectral content of
insolation
dependent on air
mass and other
factors
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Spectrophotometry – Experimental
Ocean Optics SD2000 spectrophotometer
•Spectral range:
•200 – 850 nm (master channel)
•520 – 1100 nm (slave channel)
•Cosine corrector disks both channels
Instrument pointed at sun via PTU using solar
ephemeris
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Spectrophotometry – Typical Results
11:49 am
5:01 pm
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Spectrophotometry – AM1.5 Standard Spectrum
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Spectrophotometry – Results
Acquired spectrophotometric data in field
Problems observed in data
• Shift between channels
• Dark current may change wrt time and temperature
Insufficient IR range to cover ATJ response
Further work :
•Improve calibration - dark current and drift
•Apply results to ATJ spectral response model
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Solar Cell Characterization – Overview
Si and ATJ cell arrays tested in field
Cell IV response acquired with insolation
•various orientations (horizontal and pointed to sun)
•various times of day
Computed instantaneous maximum power of cells
Correlated maximum power per unit area of horizontally
oriented cells to measured global insolation to obtain
efficiency
Temperature of cells acquired
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ATJ Results – Efficiency: Power vs. Insolation
Typical plot of normalized maximum power versus
measured insolation (horizontal orientation)
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Solar Cell Characterization - Results
Cell type
ATJ
Si
Efficiency
26.6 %
6.4 %
Std Dev
1.93 %
3.61 %
(7 % error)
(56% error)
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Solar Cell Results - Summary
ATJ – 26.6% measured efficiency with respect to
measured global insolation
Si - efficiency undetermined experimentally
Temperature effect on efficiency possible
Further work •Validate measurement methodology
•Improve measurement implementation and
acquire additional field data (if required)
•Refine response model
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Summary
Insolation
•Observed 900 W/m2 peaks (mid day)
•Observed decrease in peak insolation over time
•Total daily energy averaged 21 x 106 J/m2/day
•Cell characterization
•Efficiency: ATJ 26.6%, Si undetermined
•Performing additional testing
Spectrophotometery
•Spectral distribution shift observed over day
•Calibration and drift issues to be addressed
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Additional slides
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ATJ Results – Typical Solar Cell IV Response for One
Day
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ATJ Results – Typical Maximum Power for One Day
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Solar Cell Results – Efficiency
Date
11-Apr-03
12-Apr-03
13-Apr-03
14-Apr-03
15-Apr-03
16-Apr-03
17-Apr-03
18-Apr-03
19-Apr-03
20-Apr-03
21-Apr-03
22-Apr-03
23-Apr-03
24-Apr-03
25-Apr-03
26-Apr-03
27-Apr-03
Average
std dev
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Horizontal orientation
ATJ - string 3
Si - cell 1
slope
R
slope
R
bad PV data
bad PV data
0.2622
0.9999
0.0651
0.9589
0.2893
0.9946
0.0072
0.2761
0.2575
0.9932
0.0539
0.9581
0.2471
0.9950
0.0366
0.9574
0.2935
0.9879
0.0326
0.8904
0.2606
0.9399
0.1233
0.8720
0.2518
0.9976
0.0523
0.9635
0.2592
0.9632
0.0726
0.8985
0.2957
0.8992
0.0764
0.7872
analysis failed
0.1277
0.9090
analysis failed
analysis failed
0.2446
0.9994
0.0655
0.9754
0.2661
0.0193
0.0648
0.0361
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