solar energy and zoë power life in the atacama 2005 science & technology workshop january 6-7,...

Solar Energy andZoë power

Life in the Atacama 2005Science & Technology WorkshopJanuary 6-7, 2005

James TezaCarnegie Mellon University

Life in the Atacama 2005 Science/Technology Workshop

2 NASA Ames Research Center / Carnegie Mellon

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) systemMonitored of power system parameters• bus voltages and currents• solar input currents• load currents (locomotion and hotel)

Load switching hardware in place but not operationalAcquired insolation data at weather station



SOLARARRAY 1

Zoë power system - overview

MPPT 1

BATTERY 1AND

CONTROLLER

LOCOMOTION(FRONT)

SOLARARRAY 2 MPPT 2

BATTERY 2AND

CONTROLLER

LOCOMOTION(REAR)

HOTELDC/DC

COMPUTING

SCIENCEINSTRUMENTATION

SENSORS

COMM

PMADCONTROL &

LOGGING

PMADSWITCHING



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



Solar flux – Atacama - September

3 4 5 6 7Sol



Solar flux – Atacama - October

Sol 10 Sol 11

Sol 14Sol 13

Sol 12



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 3 4 5 6 7

Sol 10 11 12 13 14



Available electrical energy on Zoë

Calculations based on logged dataATJ 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 3 4 5 6 7

Sol 10 11 12 13 14



Zoë electrical load energy – logged data



Solar input energy from array – logged data



Energy balance – logged data



Energy required per day

Average Power (W)

Time per day

(h)

Energy per

day (Wh)

Energy per

Day (MJ)

Locomotion 260 6 1560 5.62

Hotel 215 10 2150 7.74

Spectrometer 14 2 28 1.01

FI 114 2 228 0.82

Hibernation

(estimate)

14 14 196 0.70

Total 15.0

Issue: Available electrical power on Zoë marginalfor expected locomotion and science loads



Issues with logged data

Weather station data contained gapsSpectral mismatch of solar sensors and solar cellsSpectral response of ATJ cells about 450 to 1600 nmThermopile data from the weather station may over estimate available insolation

PMAD data log contained gaps Start of day charging was typically not loggedPMAD time stamps incorrectInitial PMAD logs (before site C) corrupt



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



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

solar energy and zoë power life in the atacama 2005 science & technology workshop january 6-7,...

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