To get through the night, the propellers are powered from lithium-sulphur batteries which are topped up during the day.
"A lot of effort has gone into power storage and light-weighting the systems," explained Mr Kelleher. "Lithium sulphur is more than double the energy density of the best alternative technology which is lithium polymer batteries.
"They are an exceptional performer. We've worked with the Sion Corporation. They've had them in development for years. We're actually the first application in the world for them."
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This would see the biggest plane in history take to the sky, powered by the sun and capable of carrying a 450-kilo (1,000lb) payload.
US commanders say the design must be able to maintain its position over a particular spot on the Earth's surface uninterrupted for five years.
