24th-SPRAT-Sept-2016

© 2016 Mark O’Neill, LLC
Mark O’Neill, LLC
P.O. Box 2262
Keller, TX 76244-2262 USA
817-380-5930
markoneill@markoneill.com
www.markoneill.com
Space Photovoltaic Concentrator Using Flat Glass/Silicone Fresnel Lenses, 4-Junction
IMM Cells, Graphene-Based Radiators, and Articulating Photovoltaic Receivers
Mark O’Neill, MOLLC, Keller, Texas
A.J. McDanal, AJMLLC, Emory, Texas
Henry Brandhorst, Carbon-Free Energy LLC, Auburn, Alabama
Brian Spence, Deployable Space Systems, Inc., Goleta, California
Shawn Iqbal, Deployable Space Systems, Inc., Goleta, California
Paul Sharps, SolAero Technologies, Inc., Albuquerque, New Mexico
Clay McPheeters, SolAero Technologies, Inc., Albuquerque, New Mexico
Jeff Steinfeldt, SolAero Technologies, Inc., Albuquerque, New Mexico
Michael Piszczor, NASA-GRC, Cleveland, Ohio
Matt Myers, NASA-GRC, Cleveland, Ohio
NASA SPRAT XXIV
Cleveland, Ohio
September 22, 2016

© 2016 Mark O’Neill, LLC Slide 2
Background

Launched in 1994: Mini-Dome Lens
Array on PV Array Space Power Plus
(PASP-Plus) Provided Best
Performance and Least Degradation
of 12 Advanced Solar Arrays
Launched in 1998: Solar Concentrator Array with
Refractive Linear Element Technology
(SCARLET) 2.5 kW Array on Deep Space 1
Performed Flawlessly for 38-Month Mission on
First Spacecraft Powered by Triple-Junction Cells
Developed in 1999-2000:
Flexible-Blanket Version of
Stretched Lens Array (SLA)Developed in 2001-2004:
Rigid Panel Version of SLA
Refractive Concentrators for Space Power – A
Long Heritage of Success with 1 Glitch
Stretched
Lens Array
Invented in
1998
Developed in 2003-2014: Ultralight SLA
(>300 W/m2, >350 W/kg, >80 kW/m3)
Launched in 2011: SLA Technology
Experiment (SLATE) on TacSat 4
Demonstrated Less than ½ the
Degradation Rate of One-Sun Cells
During First 6 Months on Orbit
Before Lens Mechanical Failure
(Problem Now Solved)

Basic Building Block of New Concentrator
New 10 cm x 10 cm Flat
Color-Mixing Fresnel Lens
Comprising a Single Sheet of
50 µ CMG Glass with 100 µ
Tall Silicone Prisms Molded
onto the Bottom Glass
Surface Forming Two 4X
Line-Focus Lenses
4-Junction IMM Cells with
Optimized Grid Pattern for 4X
Concentration Profile and
Appropriate Encapsulation
and Front and Back Shielding
for Mission Requirements
25 µ Graphene Sheet Waste
Heat Radiator with 25 µ
Silicone Coating on Both
Sides to Enhance Emittance

New Lens

New Color-Mixing Lens Design Approach Minimizes
Chromatic Aberration Loss in 4-Junction IMM Cell
● Old Approach from SCARLET Period (1996)
Used Color Mixing by Each Pair of
Neighboring Prisms.
● New Approach Uses Color Mixing by Each
Triplet of Neighboring Prisms with Better
Mixing.
● Old Chromatic Aberration Model for 2-
Junction Cells Has Been Extended to 4-
Junction IMM Cells Assuming a Conservative
500 ohms/square resistance between
junctions.
● Alex Haas (SolAero) and Sarah Kurtz (NREL)
Were Consulted about this Resistance Value
and this Extended Model. Both Thought 500
ohms/square Is Conservatively Large.
● Chromatic Aberration Power Loss for this
Case < 1%.

Three New Types of Robust Lenses
Transparent
Film
Superstrate
with
Silicone
Prisms
50 Micron Ceria-
Doped Microsheet
Glass Superstrate
with Silicone Prisms
Embedded
Metal Mesh
Silicone
Lens
All Three Lens Types Have Been
Measured to Have a Net Optical
Efficiency of Over 90% for Zero Beta
Angle. A Combination of the Glass and
Mesh Approaches Is Also Under
Consideration
Patent
Pending

New Lens Design with Articulating Receiver Enables
Single-Axis Tracking with ± 50˚ Beta Angle Tolerance
A video showing more views is available at www.markoneill.com/movies.html
Patent Pending
50º Beta
Receiver
Position
0º Beta
Receiver
Position
Lens
Outdoor Measurements for Lens with 50 micron
CMG Superstrate and 100 Micron Silicone Prisms
Focusing Onto 4-Junction IMM Cell

Simple Method of Following Articulation Path
Photos Clockwise from Above
Showing Increasing Beta Angle
Accommodation with Offset 4-Bar-
Linkage Rotation. 0º Beta Above,
25º Beta Upper Right, 50º Beta
Lower Right.

Electroformed Mesh Suggested by Geoff Landis
Offers Many Advantages
● Only 50 microns thick
● 97% open area
● Border can have
features such as
alignment holes for
assembly into carbon
fiber peripheral frame
or graphene
peripheral frame

New Strengthened Material Approaches Save
Mass and Make More Robust Lens

Radiation Testing of Lens Materials

Photograph of 8 Samples After High-Energy Proton
Exposure (Very Little Optical or Mechanical Change)
25µ PET
(Mylar)/100µ
Silicone
100µ Glass
Mesh
Embedded
in 200µ
Silicone
25µ Colorless
Polyimide/
100µ Silicone
50 Micron
CMG/100µ
Silicone
25µ FEP
(Teflon)/100µ
Silicone
25µ ETFE
(Tefzel)/100µ
Silicone
200µ
Monolithic
Silicone
100µ Aluminum
Mesh
Embedded in
200µ Silicone
Tested at Auburn University at 2.7 MeV protons through backside at 5x1012 p+/cm2

Spectral Transmittance Before and After High-Energy Proton
Exposure (2.7 MeV proton through backside at 5x1012 p+/cm2)
CMG Superstrate/Silicone Aluminum Mesh Embedded in Silicone

Photos of Low-Energy Proton Samples Tested by
Scott Messenger in Japan

AFRL Measurements of Transmittance Before and
After Low-Energy Proton Exposure

The Low-Energy Proton Samples Were Uncoated –
A UVR Coating Would Minimize Surface Damage
● Degradation Was Minor Except at the Highest Dose
of 1E16p+/cm2 of 30 keV Protons
● The UV-Rejection Coating Which We Have Used Successfully on
Silicone Lenses Since PASP+ in 1994-95 Would Intercept Most of
the Low-Energy Protons and Protect the Silicone from Damage
● We Therefore Think the Silicone Lens with Embedded Metal Mesh
Is Viable with the UV-Rejection Coating

New Graphene Radiator

Graphene Described in the Nobel Prize Press
Release from 2010
● “In our 1 m2 hammock tied between two trees you could place a weight
of approximately 4 kg before it would break. It should thus be possible
to make an almost invisible hammock out of graphene that could hold a
cat without breaking. The hammock would weigh less than one mg,
corresponding to the weight of one of the cat’s whiskers.”
Source: Scientific Background on the Nobel
Prize in Physics 2010 -- GRAPHENE
compiled by the Class for Physics of the
Royal Swedish Academy of Sciences --
October 5, 2010

Radiator Material Considerations (Patent Pending
for Space PV Concentrator with Graphene Radiator)
● Until recently, the best radiator material from thermal, mass, and strength
considerations was composite sheet made with carbon fiber fabric, and
the second-best material was aluminum sheet with an oxide coating to
improve emittance.
● Recent developments in graphene sheet have brought this new radiator
material to the forefront. As shown in the table below, graphene offers
unprecedented thermal, mass, and strength properties.
Material
Effective
Thermal
Conductivity, k
(W / m-K)
Density, ρ
(kg / m3)
Tensile
Strength
(MPa)
k/ρ
(W-m2 / kg-K)
Carbon Fiber
Composite Sheet
240 1,750 1,500 0.14
Aluminum Sheet 200 2,700 200 0.07
Graphene Sheet 1,600 2,200 100 0.73

Graphene Is an Atomic-Scale Hexagonal Lattice
Made of Carbon Atoms
Angstron Materials Thermal Foil
● In-Plane Thermal Conductivity:
1500-1700 W/(m-K)
● In-Plane Electrical Conductivity:
12,000 S/cm
● Tensile Strength: 100 MPa
● Max Operating Temperature: 400 C
in air
● Density: 2.2 g/cc
● Thickness: 25 µm and 40 µm
● < 10¢/cm2 Retail for 1 Sheet
Andre Geim and Konstantin Novoselov at the
University of Manchester won the Nobel Prize in
Physics in 2010 "for groundbreaking experiments
regarding the two-dimensional material graphene."

Strengthening the Graphene Sheet and Adding
Emittance-Enhancement Silicone Coating
An Aluminum Mesh Has Been
Added to the Graphene Sheet
Using Silicone as Both
Adhesive and Emittance-
Enhancement Coating for
Graphene Sheet

Graphene Emittance With and Without Silicone
Coating (AFRL Measurements)

Figures from Pending Patent

Graphene Sheet Will Work Well for Line-Focus
and Point-Focus Concentrators
5 cm Wide Line Focus 25 µ Thick 10 cm x 10 cm Point Focus 40 µ Thick

New IMM Cell

New 4-Junction IMM Cells in 3-Cell Receiver Circuit
SolAero Produced a Trial Run of Cells with Average 1-Sun AM0 Efficiency of 31% for Total
Cell Area Including Busbar and Tab-Covered Area. On Active Area Basis, Average 1-Sun
Cell Efficiency Would Be 33%. At 4X Concentration, Average Cell Efficiency Would Be 35%.

Concentrator Test Module for Ground and Lear Jet
Testing

Test Module Sketch

Module Under Outdoor Test

Integration of New Flat Lens Architecture into
Deployable Space Systems’ SOLAROSA Platform

Flat Lens Engineering Development Unit (EDU)
with Lenticular Springs
Kevlar straps with lenticular
springs
• Straps carried in tension. Lens bonded to
Kevlar straps.
• Lenticular springs hold lens deck up off of
cells. Small lanyard sets deployment
position of lenticular springs.
• EDU unit developed to investigate
kinematics and potential for safe stow.

Flat Lens Engineering Development Unit (EDU)
with 4-Bar Linkage
Deployable 4-bar linkage:
• Integrated with 4-bar linkage to deploy
lenses off of cell deck.
• Lenses bonded to small brackets at
corners
• Small springs and hard-stops in cell-deck
brackets set max deployment of lens-deck

Effect of New Lenses and Radiators on Specific Power

Lens + Receiver + Radiator Areal Mass Density for
Heavily Shielded Receiver
4.00 X 3.03 X
5.00 cm Cell Width 1.45 cm
Receiver
Width
1.65 cm
Major
Subsystem
Element
Element
Area per
sq.m.
Aperture
Thickness Density
Mass/
Aperture
Subtotals:
Mass/Aperture
(sq.m.) (cm) (g/cu.cm.) (kg/sq.m.) (kg/sq.m.)
Lens 50 micron CMG/50 micron Silicone 1.000 0.010 1.790 0.179 0.179
Radiator Silicone-Coated Graphene Radiator 1.000 0.005 1.420 0.071 0.071
CMG Microsheet Cover Glass 0.330 0.008 2.550 0.063
Cover Glass Adhesive 0.330 0.003 1.030 0.009
IMM Cell 0.330 0.001 5.300 0.017
Glass Carrier 0.330 0.008 2.550 0.063
Thermally Conductive Adhesive 0.330 0.005 1.500 0.025
0.427 kg/sq.m.
Aperture Width
Total Areal Mass Density:
Areal Mass Density for 4X Line-Focus SLA with Glass/Silicone Lens, Graphene Radiator Sheet,
and Photovoltaic Receiver Elements for IMM Cell with 150 micron (6 mil) Equivalent Cover Glass
Shielding Front and Back
Geometric Concentration Ratio Physical Concentration Ratio
Receiver 0.177
New 92% Lens with New 35% Cell with Reasonable Knock-Down Factors Should Yield About 380
W/m2 Areal Power Density for Higher Earth Orbits. With Lens + Receiver + Radiator Mass Shown
Above, About 900 W/kg for the New Concentrator Blanket Is a Realistic Target. This Does Not
Include Harnesses or Deployment and Support Structure – Just the Three Key Blanket Elements.

Conclusions and Acknowledgement

Conclusions
● Robust New Lens Has Been Developed for Future Missions
♦ 5.0 cm Wide Flat Lens for 4.2X Geometric Concentration Ratio (GCR)
♦ Leading Material Approach: Ceria-Doped Glass Superstrate Supports Silicone
Prisms
♦ Alternate Material Approach: Embedded Mesh Supports Silicone Lens
● New 4-Junction IMM Cell Has Been Developed, Improving Efficiency and
Reducing Mass
● New Graphene Radiator Has Been Developed, Improving Performance
and Reducing Mass
● New Articulating Receiver Approach Has Been Validated, Enabling
Single-Axis Sun-Tracking
● Test Module Has Been Developed for Ground and Lear Jet Testing
● Lens + Radiator + Photovoltaic Receiver Combine for ≈ 900 W/kg
● New SOLAROSA Platform Provides Deployment and Support

Acknowledgement
● The Authors Gratefully Acknowledge that the Work Reported in this
SPRAT XXIV Presentation Was Funded by the NASA SBIR Program
(Phase I and Phase II Contracts) with Mark O’Neill, LLC

24th-SPRAT-Sept-2016

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