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Performance Projections for Solar Array Power Options on the Lunar Surface

Performance Projections for Solar Array Power Options on the Lunar Surface. Julie Anna Rodiek and Henry W. Brandhorst, Jr. Space Research Institute Auburn University, AL Mark J. O’Neill ENTECH, Inc., Keller, TX Michael I. Eskenazi ATK-Space.

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Performance Projections for Solar Array Power Options on the Lunar Surface

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  1. Performance Projections for Solar Array Power Options on the Lunar Surface Julie Anna Rodiek and Henry W. Brandhorst, Jr. Space Research Institute Auburn University, AL Mark J. O’Neill ENTECH, Inc., Keller, TX Michael I. Eskenazi ATK-Space

  2. What’s NASA’s Approach?(Shana Dale, December 2006) • A Lunar outpost at the South Pole • Cost-effective • Abundant sunlight for solar power (>70%/month) • Cuts down on energy storage • Incremental build-up based on PV • Resources • Allows development and maturation of ISRU • Possible source of H2 from H2O • Flexible • Achieves many science objectives South Pole

  3. System Overview • Solar Array requirements for lunar power • High efficiency • Lightweight • High packaging density • Withstand broad temperature swings • Determine temperature effects of arrays on lunar surface considering • Array orientation • Surface treatments • Stretched Lens Array (SLA) • Refractive photovoltaic concentrator • Developed by ENTECH, Inc. • Converts solar energy into useful electricity with an efficiency >27% • Refractive approach superior to reflective • Shape errors • Ease of manufacture • Slope error tolerance

  4. Space Fresnel Lens Photovoltaic Concentrator Evolution Launched in 1994: Mini-Dome Lens Array on PASP+ Provided Best Performance and Least Degradation of 12 Advanced Solar Arrays Stretched Lens Array Invented in 1998 Launched in 1998: SCARLET Array on Deep Space 1 Performed Flawlessly for 38-Month Mission on First Spacecraft Powered by Triple-Junction Cells Developed in 1999-2000: Flexible-Blanket Version of Stretched Lens Array (SLA) Developed in 2003-2006: SLA on SquareRigger with Unprecedented Performance Metrics Developed in 2001-2002: Rigid Panel Version of SLA

  5. SLA on SquareRigger Performance • Stretched Lens Concentrator Array on SquareRigger • 8X concentration level • >80 kW/m3 stowed power • >300 W/m2 areal power • >300 W/kg specific power • High voltage (>600 V) • Cost-effective: (50-75% savings in $/W) compared to planar solar arrays • 85% fewer solar cells than planar arrays • SquareRigger platform • Lightweight • Rigid This module can produce 3.75 kW and weighs only 10 kg.

  6. SLA on SquareRigger Deployment

  7. Lunar Design Constraints • Temperature cycling • 100 – 400 K swing overnight • SLA lens thermal cycle tested • Limited heat loss mechanisms • Gravity 1/6th of earth’s • Environmental conditions • Surface reflectivity/albedo • Radiation (solar flares) • Micrometeoroid bombardment • SLA tested and no lens tearing or electrical arcing with 1000 V • Environmental contamination • Dust electrostatic charging • Abrasiveness • Extended night duration

  8. Temperature and Power Analysis • Array temperature dependent upon location on lunar surface • Lunar polar region with high daylight • Equatorial location during the day • Solar array heat transfer model • Solar radiation • Lunar surface temperature radiation • Aluminized blanket • Paint array backside white • Reflected sunlight off lunar surface • Albedo • Radiation to space from array

  9. Variation of Power with Temperature • Advanced triple-junction solar cells • Using the BOL cell temperature coefficients • Assumes lunar temperature range and no radiation damage • Location on surface affects operating temperature • Irradiance • Surface albedo

  10. SLA Solar Cell Temperature Variation • Worst case conditions • Ground shadowing effect not included • Temperature reduced by cosine of longitude angle • Maximum power loss • 27 % at noon • 8 % at sunrise/sunset

  11. Array Temperature Reduction • Methods of lowering array temperature • Include ground shadowing effect of the array on lunar surface temperature • Reflective blanket on lunar surface • Infrared reflector • Thermal control coating on the back of radiator • Cell temperature falls to approximately 109 ºC at solar noon on equator when including these temperature lowering features: • 80% reflective solar reflector sheet • 80% reflective white thermal control coating on back of radiator • 17 % solar cell power loss

  12. Conclusion • SLASR is an option for all lunar sites chosen for exploration • Future Research Opportunities • SLA design modifications for lunar application • In depth Temperature vs. Power analysis • Evolution of thermal models for both SLASR and planar arrays based on • Ground cover/albedo • Solar position • Surface location

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