Solar Energy and Zo power

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

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
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

5
Solar flux Atacama - September
3
4
5
6
7
Sol
6
Solar flux Atacama - October
Sol 10
Sol 11
Sol 12
Sol 13
Sol 14
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
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
9
Zoë electrical load energy logged data
10
Solar input energy from array logged data
11
Energy balance logged data
12
Energy required per day
Issue Available electrical power on Zoë
marginal for expected locomotion and science loads
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

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

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