Solar array design

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Solar array design

• Life in the Atacama Design ReviewDecember 19,
  2003
• J. TezaCarnegie Mellon University

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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

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Solar Panel - design

• Emcore ATJ cells
• Efficiency 23
• Panel area less than 2.5 m2
• Modular
• Ease of assembly / disassembly
• Simplify design and fabrication
• Spares
• Orientation
• Fixed simplicity, cant demonstrate gain of
  pointed panel offsets complexity and losses of
  actuation
• Horizontal simplicity, symmetry, lower wind
  profile
• Can this design provide sufficient power?

4
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 300 W/m2)
• Model system energy
• cell efficiency (empirical)
• panel area
• MPPT efficiency

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Simulation activity schedule
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Simulation Atacama 2 m2 panel
Date 9/1/04
Date 9/30/04
Insolation vs. time
Panel Power vs. time
Battery Energy vs. time
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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
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Simulation Atacama - Results
Load energy / day 2794 Wh
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Solar panel configurations
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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)

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Solar panel issues

• Schedule
• design finalization
• diode procurement
• fabrication
• Spares
• Testing
• Pittsburgh sun in spring insufficient
• Arizona testing before shipment limited

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Solar power trackers

• Purpose
• Electrically couple solar array to battery / DC
  bus
• Operate at or near maximum power point of solar
  array
• Vendors
• Brusa / Solectria analog, complex, geared for
  lead acid
• AERL buck converter with temperature dependent
  model of panel IV characteristic (not a true
  MPPT), simple
• Biel digital controlled, efficient, solar race
  technology
• Others 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

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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

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Action items

• Solar array
• Finalize design
• Procure bypass diodes
• Fabrication detailing
• Power tracker
• Finalize solar panels and power system parameters
• Procure

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Solar power point tracker Biel MPPT
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Solar power point tracker Biel MPPT
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Insolation Atacama 03 field data
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Insolation Atacama 03 field data
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Insolation Atacama 03 field data
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Insolation Atacama 03 field data - summary
Average available energy per day 6335
Wh/m2/day Std dev 212 Wh/m2/day
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Solar panel cell response
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Solar panel Cells

• InGaP/GaAs/Ge cell with Si bypass diode
• Cell dimensions 4 cm x 6.9 cm (nominal)
• Cell area, effective 26.6 cm2
• Cell area, geometric 27.3 cm2