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1. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Harnessing the Sun:
Extend Your UAV’s Endurance with GaAs Solar Power
Chris France
MTS, Product Development
April 29th, 2015

2. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Presentation Outline
2
‣ Solar energy 101:
• How solar cells work
• Comparing solar technologies
• Different solar environments
‣ Solar for UAVs
• Alta Device’s AnyLight™ Technology
• Photon Recycling
• System Considerations
‣ Case Studies
• Puma UAV
• Cyclopes-C
AeroVironment
Solar Puma

3. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Solar Energy 101
3

4. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Science of a Solar Cell (Photovoltaic)
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‣ Photo-voltaic:
• Light → electricity
• A semiconductor device
(diode) that absorbs light to
energize electrons that are
extracted as current
• Material properties
determine:
- Amount of light absorbed
- Voltage produced by solar cell
- Energy lost at high temperature
- Sensitivity to environment
(moisture, UV, heat, light, etc.)
- Ability to be thin, light and flexible
[2]
For details, see: http://www.altadevices.com/technology-videos.php

5. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Band Gap – Tradeoff Between Voltage & Current
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‣ The fundamental solar material
parameter is band gap
• Low band gap PV
- Absorb most light, but low cell voltage
- Silicon (single & multi-crystalline)
• Medium band gap PV
- Optimum balance of absorption and
voltage
- GaAs, CdTe, amorphous Si
• High band gap PV
- Only absorb high energy light (blue → UV)
- CdS, InGaP, AlGaAs
- Only used in multi-junction cells
Low
Bandgap
High
Bandgap
Absorption
(current)
↑ ↓
Potential
(voltage)
↓ ↑
[3]

6. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Major Solar Technology
6
‣ UAV application require:
1. Flexible material that can easily be integrated into the wing,
2. High efficiency solar due to limited surface area,
3. Lightweight material to maintain payload capability
‣ Thin-film GaAs is the only solution to fit all 3 criteria!
10% 12% 14% 16% 18% 20% 22% 24% 26% 28% 30%
Organic
•Flexible
•Moisture
sensitive
•Low cost
(theory)
•Low
efficiency
a-Si
•Flexible
•Low
cost
•Low
efficiency
CIGS
•Flexible
•Emerging
thin-film
tech.
•Moisture
sensitive
•Low cost
(theory)
CdTe
•Rigid
•Established
thin-film tech.
•Cost
competitive
µc-Si
•Rigid
•Cost
competitive
•Very
common
material
c-Si
•Rigid
•Industry
standard
solar
material
GaAs
•Flexible
•Emerging
thin-film tech.
•World
record
efficiency
•1 W / gm
•Great
temperature
coefficient
•Well
established in
space
environment

7. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Click to edit Master title styleSolar environments
‣ Terrestrial Solar
• Solar irradiance or insolation
• 1000 W/m2
• Wide spectral distribution
• 300-2500nm
• Varying angle
• sun and UAV move
• Varying intensity
• sunny, clear sky 600 - 1000 W/m²
• sunny, partly cloudy 300 - 600 W/m²
• cloudy, fog 100 - 300 W/m²
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http://en.wikipedia.org/wiki/Solar_insolation
‣ Solar for UAVs
• Unique because solar power
plant always moving
• Solar surfaces directly facing
the sun = More power
• More solar power at higher
altitudes
• Shading based on craft
orientation

8. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Solar for UAVs
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9. Confidential and Proprietary Information of ALTA Devices, Inc. a company
GaAs – The Benchmark Solar for Efficiency
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Pros:
‣ GaAs has been the industry
standard in single- and multi-
junction space qualified solar
• Robust to moisture, radiation and
UV
• Highest efficiency technology
• Great temperature coefficient
(minimal power loss at high temp)
• Ideal band gap for terrestrial solar
Cons:
• Cost: GaAs
wafers are >200x
more expensive
than Si
• Rigid: Single
wafer technology
like c-Si (also
heavy)
3J GaAs solar cells on MidSTAR-1 satellite[wikipedia]

10. Confidential and Proprietary Information of ALTA Devices, Inc. a company
And the data to prove it
10
4J Records
GaAs Based
3J Records
GaAs Based
2J Records
GaAs Based
1J Records
GaAs
Alta Devices

11. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Alta Devices’ AnyLight™ Power Technology
11
‣ Alta Devices is the leader in thin-film GaAs technology
• Goal:
- Bring the efficiency of GaAs to a broad market
• Technique:
- Develop highest throughput GaAs MOCVD reactor in the world
- Transfer solar film from wafer template to flexible light-weight carrier
– Reuse the expensive wafer
– Utilize efficient light-trapping of thin-film to beat thick-film GaAs 1J efficiency!
- Develop flexible product sizes to fit broad customer base

12. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Photon Recycling in AnyLight™ Power Technology
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Reflection
Radiative
recombination
Strong external fluorescence
ThinFilmcell
Photon
recycling
• Single-crystal thin films provide new solar cell design opportunities
• Minimizing optical and electrical losses is key to high performance
• Maximize absorption of incident sunlight
• Maximize external fluorescence yield
• Minimize non-radiative recombination
• Minimize loss of recycled photons

13. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Click to edit Master title styleSystem Considerations
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‣ Voltage Conversion
• Voltage from solar can range from 0.3V (aSi) to 1V (GaAs)
• Need multiple cells in series to match electrical system voltage
• Series connection multiplies voltage
• Parallel connection multiplies current
• Use diodes to protect against leakage currents / shading
• Max power point tracking (MPPT) increases system efficiency across
wide-range of illumination
‣ Energy Storage
• Needed to use power when sun may not be shining
• Commercial solar uses the grid as a giant battery
• Mobile solar needs something local!
• Li-ion, Li-Polymer batteries – already used on non-solar UAVs

14. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Click to edit Master title style
‣ Flexibility / Weight
• Crystalline silicon is thick (>200um), heavy and not flexible
• Thin-film technologies can use a flexible substrate
• Weight driven by metal or glass substrate and encapsulation
‣ Encapsulation requirements
• Depends on environment and material
• Product lifetimes:
– Rooftop solar - 25 year outdoor exposure
– Indoor appliances - 2 year indoor product
– UAVs - X number of landings?
• Some solar constructions are inherently moisture sensitive (CIGS, CdTe, organic)
– GaAs is not
‣ Layout considerations
• Fill the wings with as much solar as possible
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Material Considerations for UAVs

15. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Case Studies
‣ 2-4x Increase in Endurance
‣ AV: Puma
• Application: Hand Launched Military
UAV
• ~160 W of thin film GaAs solar on wing
• 2-3 hr → 8 hrs
‣ Aerial Vista: Cyclopes – C
• Application: Anti-poaching (WC-UAV
Challenge)
• 60 W of thin film GaAs solar on wing,
and control surfaces
• 6 hr endurance → 10 hrs
• Come see an example at the Alta booth
15

16. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Thanks for listening!
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17. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Supplemental Material
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18. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Click to edit Master title styleAdditional Resources
‣ Alta Devices: www.altadevices.com (homepage)
• UAV Application Info: www.altadevices.com/applications-uavs.php
• YouTube Channel: www.youtube.com/user/altadevicesvideos
‣ AsiaTech Drones: www.asiatechdrones.com/
• Manufacturer of the Cyclops-E used in this presenation
‣ sUAS: http://www.suasnews.com/
‣ PV Education dot org: www.pveducation.org
• All you ever wanted to learn about solar and more
‣ Sustainable Energy: Without Hot Air:
http://www.withouthotair.com
• Free, e-textbook on sustainable energy
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19. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Click to edit Master title styleReferences
1. http://www.altadevices.com/pr-2013-08-12.php
2. https://www.youtube.com/watch?v=HWBVi0FcrdM
3. http://solarcellcentral.com/limits_page.html
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20. Confidential and Proprietary Information of ALTA Devices, Inc. a company
ASIATECH DRONES – CYCLOPS E
A solar UAV example:
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21. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Which UAVs are best for solar?
21
‣ Fixed-wing UAVs
• Have large surface area and require less
power to remain airborn
‣ Many wing sizes can provide useful
power
‣ Must consider many factors:
• Battery voltage
• Use conditions
• Payload
• Available wing area
• Desired flight extension time
‣ Alta Deivces’ product engineers can
help optimize a solar design to your
UAV
Example Layouts:

22. Confidential and Proprietary Information of ALTA Devices, Inc. a company
AsiaTech Drones Cyclops E – Specifications
22
‣ Manufacturer’s Specs:
• Cruise Speed ~ 32 knots
• Max speed ~ 110 kph
• Stall speed @5.1 lbs ~ 12 knots
• Climb Rate > 2000 ft/min
• Wingspan ~ 101 in
• Wing area ~ 598 sq in
• Fuselage Length ~ 52 in
• Materials:
- EPO Foam - Wings, Fuselage and Tail
- Carbon Fiber - Tail boom, Wing spars and Tail
support components
- Plywood - Internal structure & support
- Wood, Plastic – Misc. parts
‣ Additional Configuration:
• Assuming a 6S (25.8V) 5.5Ah LiPo battery
• ~ 3lbs additional payload with battery
‣ 2.56m wingspan high-efficiency fixed-
wing airframe
‣ Wing shape allows for easy solar
integration
‣ AsiaTech Drones is a sponsor of
wcUAVc and University of British
Columbia Aerodesign team

23. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Basic Layout and Power Calculations
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Assumptions for Cyclops-E:
• Large wing area for cells
• Optional area:
- V-tail
- Large control surface on wing
• 6S (25.8V) LiPo battery
- 18V when discharged
• 2A draw at cruise
• 15A draw at take-off
Required Info:
 Dimensioned top-down schematic
 Hold-out areas
 High curvature
 Movable / detachable parts
 Wiring difficulties
 Battery voltage
 Battery capacity
 Average power consumption or flight time
‣ Find usable solar area on UAV:
• Mostly flat, horizontal surfaces
• Avoid shading from fuselage / tail
• Must be able to route wiring back to
battery area
‣ Estimate flight-time gains:
• Based on power draw of UAV
• Usable solar area

24. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Detailed Layout and Design
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‣ Design:
• String length determined by
system voltage
- Advanced charging electronics
allows more flexibility in string
length
• Fit maximum number of panels
on surface to maximize power
• Might require larger holdouts if:
- Protection diodes in panel
- Certain types of lamination
methods used
– See pg 20
‣ Result:
• Product design specs:
- Size and number of matrices
- Diode install / wiring plan
- Lamination method that works
with customer integration
Conservative: 41W
Aggressive: 51W
Aggressive w/ flaps: 61W

25. Confidential and Proprietary Information of ALTA Devices, Inc. a company
Cyclops E – Conservative 41W Design
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‣ Range extension estimate
• 2 A cruise for 2 hrs = 4 Ah.
- 1.5Ah remaining for take-off and climb
– @ 15A draw, that is 6 min of climb
- Reasonable estimate?
• This solar array produces > 1.5A of
current.
- Cruising consumption dropped from 2 to 0.5A
- 4 Ah / 0.5A = 8h is the new cruising time!
• Since the 2A @ 25.8V is ~50W the more
aggressive configuration could sustain
flight without battery draw.
‣ 26 cell strings
• Voc=27.0 V
• Vmp=23.6V
• Assuming blocking
diode
‣ Require at least 2
bypass diodes
• Can be placed on
outer strings on wings.
Qty Size Power Notes
2 26x2 10.2 W
2 26x1 5.1 W
2 26x1 5.1W Split in
3
Total: 40.8 W
Solar BOM: