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Solar Impulse CEO Andre Borschberg sits in the cockpit before takeoff early Saturday morning.

(Credit: Solar Impulse)

Solar Impulse pilot André Borschberg had more than 12 hours of solo flying in the cramped cockpit of a solar-powered airplane left, but he was not about to start keeping time.

"I don't count the hours. If you could the hours, that's the wrong way to go about it because you say 12, 11, 10 and start to count down," he said during an in-flight phone interview with CNET on Saturday during his eighth hour of flight. "I try to enjoy each moment. I really try to appreciate where I am, what I am doing. I'm not in a hurry because I cannot land early. So, time is not so much an issue, so important, it's more the way to get to the destination, which is very interesting."

The co-founder and CEO of the team behind the Solar Impulse HB-SIA plane, is certainly taking an interesting way to get to his destination, John F. Kennedy Airport in New York. The airplane he's flying, developed and built in Switzerland, doesn't need use any fuel. Instead, it has 12,000 solar cells built into its wings that charge lithium batteries, enabling the plane to fly both day and night for up to 26 hours.

Borschberg took off early Saturday at 2 a.m. PT from Washington Dulles International Airport and was scheduled to land after 11 p.m. PT. This is the is the last leg of a coast-to-coast tour of the United States. The plane started its journey at Moffett Field in Mountain View, Calif., on May 3, in hopes of promoting clean technology. It has also made stops in Phoenix, and Dallas.

Borschberg said the toughest challenge so far has been responding to weather conditions, particularly in central Texas and in Missouri, where tornadoes have afflicted the areas. The slender aircraft weighs, 3,527 pounds, about the same as a midsize car but has a wingspan of 208 feet, matching that of a jumbo jet.

Borschberg said he has had no doubts in the solar technology would hold up since the team knows exactly how much energy the plane can get from the sun and how much it will need to store to get it through a flight. The plane can climb to 35,000 feet.

"There are no limits. The only limit is the pilot...To cross oceans and to make very long flights, we need entertainment for the pilots to stay alert and in good shape, many days and many nights," Borschberg said. Solar Impulse plans to address some of these issues with a new plane that should be ready by the end of this year.

The solar-powered plane set a world record in late May, when it broke the record for the longest distance flown by a solar-powered aircraft. Borschberg flew the aircraft 1,541 kilometers (957 miles or 832 nautical miles), beating the previous record of 1,116 kilometers (602 nautical miles), also set by Borschberg when he flew the Solar Impulse from Switzerland to Spain in May 2012.

The Solar Impulse crew wants the flights to prove that solar-powered technology is capable of long-term use. Already, the materials used for the plane, including insulation materials for the batterires and the batteries themselves, can be used for every day applications, Borschberg said. The seat insulation is light weight and ideal for cars or homes while the batteries can go into cars and other transportation.

As he soared over the Atlantic Ocean coastline just north of Atlantic City at 8,000 feet in the air, Borschberg could see people out on the beach enjoying the long holiday weekend. But, he had no inkling to join them. He was reveling in his moment of flight.

"Very often, we are extremely stressed and pushing to get things done very quickly, so this is a totally different situation when you sit in this airplane," he said. "If you don't have any fuel, time is not a problem."

You can follow on with Borschberg's journey, and monitor its battery levels and other stats, on the Solar Impulse's site.