The aircraft will fly powered only by the rays of the sun.

Sim, isso está dito no seguinte trechos das linhas 3-4: "...powered by nothing but the rays of the sun."

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According to information gleaned from the text, the challenge consists of designing a light-weight plane that will be able to circle the earth using only a solar battery rather than their hated fossil fuel

Parte do projeto Solar Impulse é usar bateria carregável pelo sol. 

If the Solar Impulse project goes to plan, in 2011 a gangly aircraft with the wingspan of an Airbus A380 and the weight of a compact car will attempt to circle the globe in about a month at an average speed of 43 m.p.h.......