TECHNOLOGY AREAS: Air Platform, Materials/Processes

OBJECTIVE: Develop and demonstrate an integrated photovoltaic (PV) module for Unmanned Aerial Vehicle applications

DESCRIPTION: Unmanned Aerial Vehicles (UAV) are primarily used for military applications which include both reconnaissance and attack missions. A major problem for electrically powered UAVs is limited mission longevity caused by re-chargeable battery systems. Most UAVs that are currently in use are electrically powered and typically use a collection of lithium-based batteries. Advantages of Li-ion batteries are high energy storage densities (in the range 140-160 W A hr/kg), high performance, and ready availability. Intrinsic limitations such as having to dismount the battery unit for charging via an external source, and battery weight and weight distribution are factors that reduce mission longevity.

The purpose of this STTR effort is to develop an integrated thin-film photovoltaic module that is conformal, lightweight and provides an electric power source for small UAVs such as the Raven. If successful, these PV modules should extend mission longevity by providing an energy source, possibly reduce the weight of air platforms (i.e. UAVs), and reduce battery charging constraints.

Proposed systems should be highly conformal (i.e.10-20% stretchable and flexible to a radius of curvature <8 mm) and provide sufficient energy output to replace current lithium ion polymer battery (~ 4 ampere hours capacity, 25 VDC and 100Whr power output). Thin-film solar cells composed of Silicon, Gallium Arsenide, Organic are likely candidates, but others would be considered provided that the resulting system can be conformally wrapped around curvilinear and non-curvilinear surfaces (i.e., ellipsoid surfaces), and are lightweight (<0.25 lbs). Ideally, the resulting system would be of such light weight that it would substantially reduce the weight and improve weight distribution (i.e. aerodynamics) of current UAV designs. In addition, proposed photovoltaic modules should be thin (<80 microns thick), be able to cover a large area (~0.2 m2) and show > 10% solar efficiency. A successful outcome at the end of this project is to develop and demonstrate a conformal integrated photovoltaic module charging system for powering small UAVs.

PHASE I: Demonstrate a thin-film photovoltaic module with 10% solar efficiency, >10 % mechanical stretchability, high voltage output (> 25V) over an area of 1 cm x 1 cm. Identify a plan for and possible routes for achieving the desired performance metrics for replacing Li-ion polymer batteries.

PHASE II: Scale up fabrication of high quality photovoltaic modules to one square meter and demonstrate electrical performance under ideal (Air Mass 1.5 illumination) and non-ideal conditions. Integrate cells with UAV and provide high quality photovoltaic modules for testing.

PHASE III: Conduct field testing to demonstrate and validate the conformal photovoltaic module. Transition and integrate the system for small UAV applications.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The development of conformal, lightweight PV modules is not limited to only military applications/market. Commercial applications could include portable power for wearable electronics, cell phones, sun umbrellas and vehicles.

REFERENCES:
1. Kim J. Y., et al. (2007, July 13). Efficient Tandem Polymer Solar Cells Fabricated by All-Solution Processing. Science, 317(5835), 222-225.

2. Kim, D.H., Ahn, J.H., et al. (2008, April 25). Stretchable and Foldable Silicon Integrated Circuits. Science. 320(5875), 507-511.

3. Baca, A.J., et al. (2009). Compact Monocrystalline Silicon Solar Modules with High Voltage Outputs and Mechanically Flexible Designs. Energy Environ, 3, 208-211. DOI: 10.1039/b920862c.

KEYWORDS: Photovoltaics; Flexible Photovoltaics; Unmanned Aerial Vehicles; Portable Power Sources; Organic Solar Cells; Wearable Electronics

** TOPIC AUTHOR (TPOC) **

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