Textured Solar Arrays for Enhanced Low-Angle Light Collection on High-Altitude Pseudo-Satellites |
Robert F. McCarthy1, Chris Youtsey1, Ray Chan1, Ian Witting1, Paul Stevens2, Steve Tate2, Noren Pan1 1MicroLink Devices, Inc., Niles, IL, United States /2Voltitude, Farnborough, --, United Kingdom |
High Altitude Pseudo-Satellites (HAPS) are fixed wing, heavier-than-air solar electric aircraft that operate continuously for multiple months in the stratosphere. They are energy self-sufficient, highly automated, low signature, with low vulnerability to attack. MicroLink Devices’ inverted metamorphic (IMM) multi-junction epitaxial lift-off (ELO) solar cell technology is the basis for advanced thin-film solar panels for Aalto and BAE Systems; the world leaders in this new platform. During ELO, light-sensitive semiconductor layers having only a fraction of the thickness of human hair are peeled from a growth substrate. After processing, solar cells achieve conversion efficiencies >30% (1-sun AM0) with an array specific power of >1500 W/kg. Currently, year-round operation is possible between +/- 40° latitude and only seasonally beyond this range. To expand HAPS utility, MicroLink developed a textured top sheet to enhance light collection when the sun is lower in the sky. Production and qualification involved ray tracing models, identification of a film supplier (3M), selection of a material (fluoropolymer), and estimation of the expected benefit for a solar powered HAPS aircraft. Reliability tests performed and passed include UV exposure, handling, dust collection and cleaning, thermal cycling, damp heat exposure, film adhesion, and outdoor power collection. Textured arrays were successfully integrated onto a scale HAPS model produced by Voltitude and flight tested. The results show significant increases in light collection at 80° zenith angle from 60% to 90%, improving power generation at high latitudes and sunrise/sunset. Textured arrays “extend the day” over 40 minutes at 40° latitude for a HAPS aircraft with 10% extra total daily power, lengthening their usable range and/or reducing requirements for heavy, expensive batteries. Replacing MicroLink’s current planar top sheet with textured fluoropolymers is projected to offset over 130g of battery per 1 kW of solar array, allowing for larger HAPS payloads. |