Insolation of the Atacama Desert

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Insolation of the Atacama Desert

• Michael Wagner
• James Teza
• July 28, 2003

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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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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
• Spectral response of ATJ cells (efficiency)
  differs from Si response
• 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
1149 am 501 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
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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