Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Solar array design Life in the Atacama Design Review December 19, 2003 J. Teza Carnegie Mellon University

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Solar Panel - design Emcore ATJ cells Efficiency > 23% Panel area: less than 2.5 m 2 Modular Ease of assembly / disassembly Simplify design and fabrication Spares Orientation Fixed – simplicity, can’t demonstrate gain of pointed panel offsets complexity and losses of actuation Horizontal – simplicity, symmetry, lower wind profile Can this design provide sufficient power?

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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/m 2 ) Model system energy cell efficiency (empirical) panel area MPPT efficiency

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Simulation – activity schedule Activity Components Power (W) Hibernation Core CPU5 Plan Hotel120 Traverse Locomotion Hotel Fluorescence Locomotion Hotel & science

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Simulation – Atacama – 2 m 2 panel Date: 9/1/04 Date: 9/30/04 Insolation vs. time Panel Power vs. time Battery Energy vs. time

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Simulation – Atacama – 2.5 m 2 panel Date: 9/1/04 Date: 9/30/04 Insolation vs time Panel Power vs time Battery Energy vs time

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Simulation – Atacama - Results DatePanel area (m 2 ) Panel energy / day (Wh) Margin (Wh) Load energy / day : 2794 Wh

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Solar panel – configurations Cells per module6 x 16 = 96 8 x 20 = 160 Modules896 Panel – total cells Effective area (m 2 )

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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 I sc max at 1000 W/m 2 Panel effective area 2.5 m 2 geometric area 2.62 m 2 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)

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Solar panel – issues Schedule design finalization diode procurement fabrication Spares Testing Pittsburgh sun in spring insufficient Arizona testing before shipment limited

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Action items Solar array Finalize design Procure bypass diodes Fabrication detailing Power tracker Finalize solar panels and power system parameters Procure

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Solar power point tracker – Biel MPPT

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Solar power point tracker – Biel MPPT

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Insolation – Atacama 03 field data

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Insolation – Atacama 03 field data

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Insolation – Atacama 03 field data

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Insolation – Atacama 03 field data - summary Average available energy per day: 6335 Wh/m 2 /day Std dev: 212 Wh/m 2 /day

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Solar panel – cell response

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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 cm 2 Cell area, geometric: 27.3 cm 2