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Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Solar array design
Life in the Atacama Design ReviewDecember 19, 2003
J. TezaCarnegie Mellon University
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Solar Panel - requirements
Provide energy through day of mission (full sun) plus charge battery for night operation
Light weight
Robust
Low wind profile
Easily removable
Transportation, safety, access
Minimum shadowing
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Solar Panel - design
Emcore ATJ cells Efficiency > 23%
Panel area: less than 2.5 m2 ModularEase of assembly / disassemblySimplify design and fabricationSpares
Orientation Fixed – simplicity, can’t demonstrate gain of pointed panel offsets complexity and losses of actuationHorizontal – simplicity, symmetry, lower wind profile
Can this design provide sufficient power?
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Simulation
Schedule load over typical mission day
Simulate insolation for location and time
Matlab simulation of sun position, airmass attenuation, integrated over wavelength
Compared insolation against SBDART and Atacama 03 field data (error < 6% for insolation > 300 W/m2)
Model system energy• cell efficiency (empirical)• panel area• MPPT efficiency
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Simulation – activity schedule
Activity
• Components
Power
(W)
Hibernation
• Core CPU 5
Plan
• Hotel 120
Traverse
• Locomotion
• Hotel250
120
Fluorescence
• Locomotion
• Hotel & science
100
120
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Simulation – Atacama – 2 m2 panel
Date: 9/1/04
Date: 9/30/04
Insolation vs. time Panel Power vs. time Battery Energy vs. time
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Simulation – Atacama – 2.5 m2 panel
Date: 9/1/04
Date: 9/30/04
Insolation vs time Panel Power vs time Battery Energy vs time
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Simulation – Atacama - Results
Date Panel area (m2)
Panel energy / day
(Wh)
Margin
(Wh)
9-1 2 2863 69
9-1 2.5 3579 785
9-30 2 3467 673
9-30 2.5 4335 1541
Load energy / day : 2794 Wh
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Solar panel – configurations
Cells per module 6 x 16 = 96 6 x 16 = 96 8 x 20 = 160
Modules 8 9 6
Panel – total cells 768 864 960
Effective area (m2) 2.04 2.30 2.55
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Solar panel – design strawman
6 modules
160 cells / module
dimensions: 58 cm x 85 cm
20 cells per string yielding 46 volts at MPP
8 cells parallel yield 2.8 A Isc max at 1000 W/m2
Panel
effective area 2.5 m2
geometric area 2.62 m2
Power from panel • 1000 W/m2 and 23.4% efficiency • 97.5 W / module• 585 W total
Weight estimate: 8 kg total
(including cell encapsulation, lamination and wiring)
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Solar panel – issues
Schedule
design finalization
diode procurement
fabrication
Spares
Testing
Pittsburgh sun in spring insufficient
Arizona testing before shipment limited
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Solar – power trackers
PurposeElectrically couple solar array to battery / DC busOperate at or near maximum power point of solar array
VendorsBrusa / Solectria – analog, complex, geared for lead acidAERL – buck converter with temperature dependent model of panel IV characteristic (not a true MPPT), simpleBiel – digital controlled, efficient, solar race technologyOthers – typically not suitable for this application• Consumer; designed for lead acid (Morningstar)
Reliability, do not support Li technologies, not flexible• Industrial; designed for lead acid (Trace)
Over built - do not support Li technologies
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Solar power point tracker – Biel MPPT
Biel School of Engineering and Science (Switzerland)
NG Maximum Power Point Tracker
Boost converter
Tracks maximum power point
Power capacity 800 W
Can bus interface
Issues – reliability, support, programming
Cost $780
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Action items
Solar array
Finalize design
Procure bypass diodes
Fabrication detailing
Power tracker
Finalize solar panels and power system parameters
Procure
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Solar power point tracker – Biel MPPT
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Solar power point tracker – Biel MPPT
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Insolation – Atacama 03 field data
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Insolation – Atacama 03 field data
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Insolation – Atacama 03 field data
Carnegie MellonLife in the Atacama, Design Review, December 19, 2003
Insolation – Atacama 03 field data - summary
Average available energy per day: 6335 Wh/m2/day
Std dev: 212 Wh/m2/day