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

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


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


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?


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


Simulation – activity schedule

Activity

• Components

Power

(W)

Hibernation

• Core CPU 5

Plan

• Hotel 120

Traverse

• Locomotion

• Hotel250

120

Fluorescence

• Locomotion

• Hotel & science

100

120


Simulation – Atacama – 2 m2 panel

Date: 9/1/04

Date: 9/30/04

Insolation vs. time Panel Power vs. time Battery Energy vs. time


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


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


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


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)


Solar panel – issues

Schedule

design finalization

diode procurement

fabrication

Spares

Testing

Pittsburgh sun in spring insufficient

Arizona testing before shipment limited


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


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


Action items

Solar array

Finalize design

Procure bypass diodes

Fabrication detailing

Power tracker

Finalize solar panels and power system parameters

Procure


Solar power point tracker – Biel MPPT


Insolation – Atacama 03 field data


Insolation – Atacama 03 field data - summary

Average available energy per day: 6335 Wh/m2/day

Std dev: 212 Wh/m2/day


Solar panel – cell response


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

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

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