Life in the Atacama Carnegie Mellon

Insolation of the Atacama Desert

Michael WagnerJames TezaJuly 28, 2003

Life in the Atacama Carnegie Mellon

Weather / Solar Station PurposePerform environmental measurements in the field for science and engineering purposesMeasure insolation to understand solar power available to a roverMeasure solar spectra quantitatively to predict ATJ performance in the fieldCharacterize Si and ATJ solar cell performance to aid design of new rover solar panel

Life in the Atacama Carnegie Mellon

Solar Measurement Station

Periodically performed measurements of•Global insolation •Solar Irradiance spectra•ATJ and Si solar cell behavior

ATJ CellsSi Cells

Spectrophotometer PTUPyranometer

Life in the Atacama Carnegie Mellon

Insolation - ExperimentalImplementation• 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

Life in the Atacama Carnegie Mellon

Insolation Results - Overview

Life in the Atacama Carnegie Mellon

Insolation Results – Clear Days

Life in the Atacama Carnegie Mellon

Insolation Results – Cloudy Days

Life in the Atacama Carnegie Mellon

Insolation Results – Total Daily Energy

Average available energy per day: 20.9 MJ/m2/dayStd dev: 5.3 MJ/m2/day

Life in the Atacama Carnegie Mellon

Spectrophotometry – Motivation

Need to predict efficiency of ATJ cells in AtacamaSpectral response of ATJ cells (efficiency) differs from Si responseSpectral content of insolation dependent on air mass and other factors

Emcore ATJ - Spectral response vs. Wavelength

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200 400 600 800 1000 1200 1400 1600 1800 2000

Wavelength (nm)

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ctra

l res

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/W)

GaInP2InGaAsGe

Life in the Atacama Carnegie Mellon

Spectrophotometry – ExperimentalOcean Optics SD2000 spectrophotometer•Spectral range:•200 – 850 nm (master channel)•520 – 1100 nm (slave channel)

•Cosine corrector disks both channelsInstrument pointed at sun via PTU using solar ephemeris

Life in the Atacama Carnegie Mellon

Spectrophotometry – Typical Results

11:49 am 5:01 pm

Life in the Atacama Carnegie Mellon

Spectrophotometry – AM1.5 Standard Spectrum

Life in the Atacama Carnegie Mellon

Spectrophotometry – Results

Acquired spectrophotometric data in fieldProblems observed in data

•Shift between channels•Dark current may change wrt time and temperature

Insufficient IR range to cover ATJ responseFurther work :

•Improve calibration - dark current and drift

•Apply results to ATJ spectral response model

Life in the Atacama Carnegie Mellon

Solar Cell Characterization – OverviewSi 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 cellsCorrelated maximum power per unit area of horizontally oriented cells to measured global insolation to obtain efficiencyTemperature of cells acquired

Life in the Atacama Carnegie Mellon

ATJ Results – Efficiency: Power vs. Insolation

Typical plot of normalized maximum power versus measured insolation (horizontal orientation)

Life in the Atacama Carnegie Mellon

Solar Cell Characterization - Results

Cell typeATJ Si

Efficiency 26.6 % 6.4 %

Std Dev 1.93 %(7 % error)

3.61 %(56% error)

Life in the Atacama Carnegie Mellon

Solar Cell Results - SummaryATJ – 26.6% measured efficiency with respect to measured global insolationSi - efficiency undetermined experimentallyTemperature effect on efficiency possibleFurther work -

•Validate measurement methodology•Improve measurement implementation and acquire additional field data (if required)

•Refine response model

Life in the Atacama Carnegie Mellon

SummaryInsolation •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

Life in the Atacama Carnegie Mellon

Additional slides

Life in the Atacama Carnegie Mellon

ATJ Results – Typical Solar Cell IV Response for One Day

Life in the Atacama Carnegie Mellon

ATJ Results – Typical Maximum Power for One Day

Life in the Atacama Carnegie Mellon

Solar Cell Results – Efficiency

Date

slope R slope R11-Apr-03 bad PV data bad PV data12-Apr-03 0.2622 0.9999 0.0651 0.958913-Apr-03 0.2893 0.9946 0.0072 0.276114-Apr-03 0.2575 0.9932 0.0539 0.958115-Apr-03 0.2471 0.9950 0.0366 0.957416-Apr-03 0.2935 0.9879 0.0326 0.890417-Apr-03 0.2606 0.9399 0.1233 0.872018-Apr-03 0.2518 0.9976 0.0523 0.963519-Apr-03 0.2592 0.9632 0.0726 0.898520-Apr-03 0.2957 0.8992 0.0764 0.787221-Apr-03 analysis failed 0.1277 0.909022-Apr-03 analysis failed23-Apr-03 analysis failed24-Apr-03 0.2446 0.9994 0.0655 0.975425-Apr-0326-Apr-0327-Apr-03

Average 0.2661 0.0648std dev 0.0193 0.0361

Horizontal orientation ATJ - string 3 Si - cell 1