Solar plane extends stay

The Solar Impulse 2 — the plane attempting to be the first to fly around the world powered by the sun — will winter in Hawaii.

The crew of the record-breaking aircraft, which had hoped to fly to the mainland in August, has decided to keep the plane on Oahu at least until April.

Because repairs to the plane’s batteries won’t be finished until August, it makes it difficult for the Solar Impulse to complete the remainder of its journey as daylight hours get shorter moving into fall.

"Between the vision and its implementation, there are numerous challenges to be met," said Swiss pilot Andre Borsch­berg on Tuesday via Twitter.

The Solar Impulse landed in Hono­­lulu on July 3 after Borsch­berg broke the rec­ord for the longest solar flight with his five-day journey from Nagoya, Japan. The Hono­lulu landing completed eight legs of the 13-leg around-the-world venture.

The Solar Impulse team said Tuesday it would postpone the second half of its journey until spring because leaving Hawaii in August would push the plane’s Atlantic crossing to Europe into the fall.

The 17,000 solar cells of Solar Impulse need long days to fully charge the batteries to successfully power the plane for eight to 10 hours without the sun.

On Saturday the crew originally said the plane could not leave the island for two or three weeks because of the time needed to repair the batteries.

The crew has to order new battery elements, wait for the elements to be shipped and test them before attempting the flight. The batteries overheated during the 118-hour flight to Hawaii from Japan.

On Tuesday the organizers determined that the delay for repairs made it too risky to attempt the rest of the journey this year.

The plane will be kept at the University of Hawaii Hangar 111 at the Kalaeloa Airport, where it has been since landing.

Some members of the Solar Impulse 2 crew will stay in Hawaii with the plane.

Borschberg and Solar Impulse co-founder Ber­trand Piccard, who take turns flying the single-pilot plane, were in Hawaii on Tuesday and will meet with media Wednesday to discuss their plans.

Borschberg’s flight to Hawaii from Japan set solar aviation rec­ords for distance (4,480 miles) and duration (117 hours and 52 minutes) and set the duration rec­ord for a solo flight without refueling, the organizers said.

The batteries overheated during the first ascent on Day 1 of the flight to Hawaii. The battery temperature increased too much due to over-insulation, the crew said.

Several battery parts were damaged, more than the crew had on hand. The team has about 100 replacement elements, when more than 200 were damaged.

The energy collected by the solar cells is stored in lithium polymer batteries. The batteries are insulated by high-density foam and mounted in the engine housing, with a system to control charging thresholds and temperature.

Weather has been a challenge for the Solar Impulse in its race to beat the shorter days of fall as the plane was grounded in Nanjing, China, for more than 39 days and in Nagoya for more than 27 days due to weather.

The combination of a wingspan the size of a commercial airliner wingspan with the weight of a car makes the aircraft vulnerable to bad weather. The crew had to time each flight to match favorable weather conditions.

Since leaving Abu Dhabi, United Arab Emirates, in March, the plane has traveled to Muscat, Oman; Ahmed­­­a­­bad and Vara­­­nasi, India; Mandalay, Myan­mar; Chongqing and Nanjing, China; and Nagoya.

ENLARGE PHOTO.