1. Life in the AtacamaCarnegie Mellon Insolation of the Atacama Desert Michael Wagner James Teza July 28, 2003

2. Life in the AtacamaCarnegie 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

3. Life in the AtacamaCarnegie Mellon Solar Measurement Station Periodically performed measurements of Global insolation Solar Irradiance spectra ATJ and Si solar cell behavior ATJ Cells Si Cells Spectrophotometer PTU Pyranometer

4. Life in the AtacamaCarnegie Mellon 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

5. Life in the AtacamaCarnegie Mellon Insolation Results - Overview

6. Life in the AtacamaCarnegie Mellon Insolation Results – Clear Days

7. Life in the AtacamaCarnegie Mellon Insolation Results – Cloudy Days

8. Life in the AtacamaCarnegie Mellon Insolation Results – Total Daily Energy Average available energy per day: 20.9 MJ/m 2 /day Std dev: 5.3 MJ/m 2 /day

9. Life in the AtacamaCarnegie Mellon 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

10. Life in the AtacamaCarnegie Mellon 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

11. Life in the AtacamaCarnegie Mellon Spectrophotometry – Typical Results 11:49 am 5:01 pm

12. Life in the AtacamaCarnegie Mellon Spectrophotometry – AM1.5 Standard Spectrum

13. Life in the AtacamaCarnegie Mellon 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

14. Life in the AtacamaCarnegie Mellon 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

15. Life in the AtacamaCarnegie Mellon ATJ Results – Efficiency: Power vs. Insolation Typical plot of normalized maximum power versus measured insolation (horizontal orientation)

16. Life in the AtacamaCarnegie Mellon Solar Cell Characterization - Results Cell type ATJSi Efficiency26.6 %6.4 % Std Dev1.93 % (7 % error) 3.61 % (56% error)

17. Life in the AtacamaCarnegie Mellon 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

18. Life in the AtacamaCarnegie Mellon Summary Insolation Observed 900 W/m 2 peaks (mid day) Observed decrease in peak insolation over time Total daily energy averaged 21 x 10 6 J/m 2 /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

19. Life in the AtacamaCarnegie Mellon Additional slides

20. Life in the AtacamaCarnegie Mellon ATJ Results – Typical Solar Cell IV Response for One Day

21. Life in the AtacamaCarnegie Mellon ATJ Results – Typical Maximum Power for One Day

22. Life in the AtacamaCarnegie Mellon Solar Cell Results – Efficiency