Sunexelec – Recharging in Flight

The Club d’Ultra Léger d’Alsace is a group of French enthusiasts in Strasbourg, on the German border about halfway between Luxembourg and Switzerland. They have been building ultralight aircraft since 1983, tackling technological innovations such as carbon fiber leading edges, motorization, electrification, and now solar power. They were the first to motorize a Swift, and with one of their craft electrically powered, mounted strips of photovoltaic cells to the upper wing surface.  Finding that worked to boost battery duration, the group went on to mount 6.1 square meters of solar cells on an Alpaero Exelec, an ultralight self-launching sailplane.

Sunexelec soaking up some rays before taking flight

After making 60 flights on battery power between May and April of this year, the group installed the solar cells on the wings, flying 18 times on solar assist between May 21 and July 20. These included eight launches in which the solar cells recharged the airplane’s LiFePO4 batteries during the flight, making the possibility of endless cross-country flight a realizable goal. Club members documented an average power of 1,000 Watts from the solar array, giving a recharge current of 15 Amps.

This could be the least expensive solar-powered airplane in the world, with the base airplane selling for about 25,000 euros ($31,000), and the electric motor, controller and 40 Amp-hour batteries adding approximately 10,000 euros ($12,400). Note that these are estimates based on recent price lists. Thin film solar cells are dropping in cost, with Flexible Energy Inc. forecasting manufacturing prices of $1.00 per square foot soon. That would make the 66 square feet of solar cells on Sunexelec a real bargain, although one can count on spending more at today’s rates.

Sunexelec wing high above Alsace countryside

A self-launching, self-recharging sailplane for under $50,000 is an inexpensive way to go flying, though. As battery weights and costs decrease and solar cells become a commodity item, we will see more ultralight and light sailplanes being converted, since the prospect of truly free flight will appeal to many.

{ 2 comments… add one }

  • Brent 08/16/2012, 10:26 pm

    Looks like GREAT idea to me….Hope it makes it to market before my flying days end, age I mean.

  • Thomas Boyle 08/17/2012, 5:48 am

    I’m actually surprised this is taking so long. Unlike all these battery-power-only airplanes, an electric touring motorglider capable of level flight under solar power (solar tourer) actually makes sense if you run the numbers. I think the idea of a solar tourer is especially appealing: it would offer (almost) the silence and simplicity and, for want of a better word, natural-ness of glider flight, with a new flight mode not available to gliders – the ability to “cruise” in straight flight above the lift band (and above the clouds).
    This is not a solar tourer, however, it is a solar-recharging battery-operated self-launch sailplane, not capable of sustained level flight under solar power. Given the Exelec’s posted data, and assuming the L/D degrades to 25:1 with solar panels on the wing, and assuming a prop efficiency of 80% and an electric system efficiency of 88%, it would need 3.6kW from the solar panels for level flight – but delivers only 1kW. Nothing wrong with that, but not quite what seizes my imagination. A more urgent question, though: what kind of composite is that Exelec wing made of? IIRC, most composites have to be painted white, lest they overheat and soften in the sun. Those solar cells look awfully like… black. They must get very, very hot, no? Is there a solution to that?

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