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Zephyr solar plane soars to new flight record, but details on thin-film PV remain scarce
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Despite decent coverage elsewhere in the media, no mention of the light but mighty Zephyr has appeared so far this week in the PV-Tech news section, which has me a bit taken aback.
After all, the solar-powered aircraft, which stayed aloft for more than 82 hours over the US Army's Yuma (AZ) Proving Ground and shattered the existing record (albeit unofficially) for sustained unmanned flight in late July, is manufactured by a British company, QinetiQ (pronounced "kinetic"). I would have thought that a UK-based publishing concern with a keen interest in photovoltaics would want to show some post-imperial pride!
No matter, I guess the Yank will have to pick up the slack for the preoccupied Londoners this time.
I contacted QinetiQ, hoping to get some details about the "amorphous silicon solar arrays no thicker than sheets of paper that cover the aircraft's wings" mentioned in the press release. After an exchange of several emails, company spokesman Douglas Millard phoned to let me know that such specifics as the PV manufacturer, conversion efficiency of the panels, panel lamination method used, total number of cells, and total system electrical output cannot be disclosed at this time, so as not to give away any "competitive advantage."
Millard did let on that the solar component was from a "commercially available" source, reiterating the paper thinness and flexibility of the array. He also said the solar power generated "was sufficient to power the aircraft during the day and to store enough energy in the lithium-sulfur batteries" for the night.
In addition to finding ways to reduce the overall mass of the carbon-fiber surveillance and communications prototype craft--now a svelte 30 kg, or 66 pounds--the project team wants to "achieve multiple charge and discharge cycles over the course of the day," an enhancement which would come through continuously improved PV and battery systems.
Since a-Si TFPV, although robust and reliable, does not boast the highest conversion efficiencies, it would seem that when suitable, ultralightweight polymer, high-efficiency CIGS panels come along, they might be candidates for future generations of the aircraft.
For now, a nagging question remains: Which commercially available, a-Si plastic flex PV panels adorn the Zephyr's high-flying wings?
The list of companies that offer such a line of products is not long. My best guess? PowerFilm Solar.
Although I cannot get confirmation from QinetiQ or PowerFilm, the Ames, IA-based company (formerly known as Iowa Thin Films) has been rolling out sheets of amorphous silicon-on-polymer PV for years. Its product line includes panels specifically tailored for use in remote-controlled aircraft--the RC7.2-75. available with or without pressure-sensitive adhesive.
Weighing just 0.3 ounces with a thickness of only 0.2 mm (8 mil, otherwise known as paper thin), the 270 X 90 mm panels push out about 100 mA @ 7.2 volts. That's not a lot of juice, but when combined in an array of the type integrated into Zephyr's wings, the RC panels could supply enough power to sustain the unmanned aerial vehicle's high-altitude, long-duration flights.
QinetiQ's Millard told me that "once they can come forward" with technical details on Zepyhr's solar PV array, "they'll get back to me." Since "they" (AKA the company) reside deep inside the military-industrial complex, I won't be holding my breath in anticipation of such revelations happening any time soon.
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