Insolation of the Atacama Desert

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

2. 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 Carnegie Mellon

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

4. 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 Carnegie Mellon

5. Insolation Results - Overview Carnegie Mellon

6. Insolation Results – Clear Days Carnegie Mellon

7. Insolation Results – Cloudy Days Carnegie Mellon

8. Insolation Results – Total Daily Energy • Average available energy per day: 20.9 MJ/m2/day • Std dev: 5.3 MJ/m2/day Carnegie Mellon

9. 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 Carnegie Mellon

10. 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 Carnegie Mellon

11. Spectrophotometry – Typical Results 11:49 am 5:01 pm Carnegie Mellon

12. Spectrophotometry – AM1.5 Standard Spectrum Carnegie Mellon

13. 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 Carnegie Mellon

14. 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 Carnegie Mellon

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

16. Solar Cell Characterization - Results Carnegie Mellon

17. 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 Carnegie Mellon

18. 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 Carnegie Mellon

19. Additional slides Carnegie Mellon

20. ATJ Results – Typical Solar Cell IV Response for One Day Carnegie Mellon

21. ATJ Results – Typical Maximum Power for One Day Carnegie Mellon

22. Solar Cell Results – Efficiency Carnegie Mellon