The blog recently showed an Alpaero Exelec electric motorglider to which Francis Marlier of the ultralight club of Alsace, France, had taped 66 square feet of solar cells. The Sunexelec that resulted has enhanced endurance, managing up to four-hour flights, although Francis does not indicate how much of that is soaring flight and how much powered.
He reports, “Using SUNPOWER C65 solar cells which are encapsulated in modules of 20 or 15 cells. The total weight per wing of these modules is about 3 kilograms (6.6 pounds).
“I have used special 3M adhesive tape to fix the modules [which are 0.8 millimeters (3/64-inch) thick] directly on the wing skin. Special covers are put on the wings that I remove just before the take-off. During the flight there is no risk to damage the epoxy resin.”
His airplane has a 60 Volt, 30 Amp-hour battery pack measuring 30 x 30 x 20 centimeters (11-13/16 x 11-13/16 x 7-7/8 inches) to power the Eck/Geiger HPD 13.5 brushless motor.
He had used a Swift motorglider “as a prototype to test solar cells and a solar charger,” showing the experimental nature of the enterprise and the careful exploration of the problems involved.
It would be interesting to see glide tests showing the effect of the solar cells on the airfoil and its flight efficiency. The fact that Francis keeps his wings covered before flight shows that any benefit to range and endurance comes from the in-flight activation of the cells. Other solar-powered craft have wings designed for integration of the solar cells, so the “after-market” addition on the Sunexelec is an interesting experiment.
We can hope for even thinner solar cells and greater efficiency in the future. Congratulations to Francis Marlier for a worthy exploration of new technology.