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Solar Energy and Zoë power

Solar Energy and Zoë power. Life in the Atacama 2005 Science & Technology Workshop January 6-7, 2005 James Teza Carnegie Mellon University. Zoë Power in 2004. Advanced Triple Junction solar array Cell efficiency 23.3%, system efficiency 21.7% Area 2.4 m 2 Batteries

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Solar Energy and Zoë power

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  1. Solar Energy andZoë power Life in the Atacama 2005Science & Technology WorkshopJanuary 6-7, 2005 James TezaCarnegie Mellon University

  2. Zoë Power in 2004 • Advanced Triple Junction solar array • Cell efficiency 23.3%, system efficiency 21.7% • Area 2.4 m2 • Batteries • Lead acid (used to Oct 14) • 1000 Wh • Li polymer (Oct 14 through 18) • total 3k Wh • Power management and distribution (PMAD) system • Monitored of power system parameters • bus voltages and currents • solar input currents • load currents (locomotion and hotel) • Load switching hardware in place but not operational • Acquired insolation data at weather station NASA Ames Research Center /Carnegie Mellon

  3. Zoë power system - overview HOTEL DC/DC SOLAR ARRAY 1 MPPT 1 PMAD CONTROL & LOGGING PMAD SWITCHING BATTERY 1 AND CONTROLLER LOCOMOTION (FRONT) COMPUTING SENSORS SOLAR ARRAY 2 MPPT 2 COMM BATTERY 2 AND CONTROLLER LOCOMOTION (REAR) SCIENCE INSTRUMENTATION NASA Ames Research Center /Carnegie Mellon

  4. Do we have enough energy available? • Weather station logged solar radiation data each minute • Sensor • Thermopile, spectral range: 305 to 2800 nm • Data logged to disk within station • Station located within about 10 km of science site B, 20 km of site C NASA Ames Research Center /Carnegie Mellon

  5. Solar flux – Atacama - September Sol 3 4 5 6 7 NASA Ames Research Center /Carnegie Mellon

  6. Solar flux – Atacama - October Sol 10 Sol 11 Sol 12 Sol 13 Sol 14 NASA Ames Research Center /Carnegie Mellon

  7. Solar energy in Atacama • Available solar energy per day for flat collector using logged data • Average: 2.52 x 107 J per day (period 9/8/04 through 10/9/04) Sol 10 11 12 13 14 Sol 3 4 5 6 7 NASA Ames Research Center /Carnegie Mellon

  8. Available electrical energy on Zoë • Calculations based on logged data • ATJ panel area 2.4 m2, Cell efficiency – 23.3%, MPPT efficiency – 97% • Array network efficiency (diode) – 96% • Average: 1.35 x 107 J per day (period 9/8/04 through 10/9/04) Sol 10 11 12 13 14 Sol 3 4 5 6 7 NASA Ames Research Center /Carnegie Mellon

  9. Zoë electrical load energy – logged data NASA Ames Research Center /Carnegie Mellon

  10. Solar input energy from array – logged data NASA Ames Research Center /Carnegie Mellon

  11. Energy balance – logged data NASA Ames Research Center /Carnegie Mellon

  12. Energy required per day Issue: Available electrical power on Zoë marginal for expected locomotion and science loads NASA Ames Research Center /Carnegie Mellon

  13. Issues with logged data • Weather station data contained gaps • Spectral mismatch of solar sensors and solar cells • Spectral response of ATJ cells about 450 to 1600 nm • Thermopile data from the weather station may over estimate available insolation • PMAD data log contained gaps • Start of day charging was typically not logged • PMAD time stamps incorrect • Initial PMAD logs (before site C) corrupt NASA Ames Research Center /Carnegie Mellon

  14. 2004 results • Positive • ATJ solar arrays performed as expected • Lithum polymer batteries appeared to perform well • - typically ended day at 60 to 77 % of full charge • Negative • Power available marginal for expected loads (computing and FI) • PC104 stacks not as robust as hoped • PMAD, weather station and state estimator all experienced faults • Electrical system several faults • Softstart relay failure at start of mission • PMAD problems during Site B – faulty connection • PMAD logging not automatic – missing data • PMAD switching not implemented – hardware exists (mostly) but not software • PMAD power backup – implementation faulty and unreliable • Li polymer cell balance is critical for extended operation NASA Ames Research Center /Carnegie Mellon

  15. 2005 Issues • Power switching required to fulfill objectives • Complete PMAD hardware implementation • PMAD Software design • Robust system - extensive testing • Consider lower power options – if any • Mission scheduling to maximize insolation and minimize load • Li battery testing and spares • Better battery model for planning extended operation NASA Ames Research Center /Carnegie Mellon

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