Science

Solar plane may help green energy take off

By James Maynard , Jun 19, 2013 08:45 PM EDT
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Solar impulse, an aircraft powered by the Sun, is nearing the end of a cross-country trip, landing at Dulles International Airport in Washington DC on June 16. The HB-SIA touched down in the second-to-last stop on a long tour across the country. The plane was piloted by Bertrand Piccard from Cincinnati, and the aircraft will next be flown to New York City, under the command of Andre Borschberg.

This solar-powered airplane is different from most of its predecessors in that instead of having solar cells being applied over the surface of the plane's wing and horizontal tail, the cells are the skin itself. Although the HB-SIA has a wingspan about equal to that of a 747, the plane only weighs 3,500 pounds.

The challenge in keeping the plane airborne lies not with the aircraft itself, but the people who fly it. The plane is slow - just 44 MPH, so the journeys are long. Because the weight of the aircraft had to be kept at a minimum to power the plane with sunlight, there is no bathroom. Pilots must also wear face masks, since the cabin is unpressurized. The longest anyone has ever stayed in the plane so far is 26 hours. A successor to the Solar Impulse craft is already being built.

"The seat is like a really bad economy seat on an airliner. The next version will be like a good business-class seat," Gregory Blatt, a managing director of Solar Impulse, the company based in Lausanne, Switzerland, which built the craft, said.

It is believed that the next generation aircraft from Solar Impulse, known as the HB-SIB, will allow the pilot to stay aloft for five or six days at a time. People flying the plane will be able to move around the cabin and the aircraft will have an autopilot.

But to fly a heavier craft is going to mean more efficient solar cells, better engines, and several other improvements over the current design. The engines aboard the current craft are more than 90 percent efficient, which is better than most engines on the ground. The 11,628 solar cells provide 22.7 percent efficiency. That new technology could lead to advances in renewable energy storage systems, more eco-friendly vehicles and homes.

"This wonderful achievement, this engineering marvel, touches four really critical areas for the Department of Energy." Ernest Moniz, Secretary of Energy, said. The Secretary was referring to solar power, energy efficiency, electrical storage and advanced materials.

One of the goals of the HB-SIB will be circumnavigating the world on solar power - a task set for 2015. To do that will require engines running at 94 percent efficiency or better.

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