Geneva - The sun-powered plane Solar Impulse 2 will be grounded for months in Hawaii to carry out battery repairs, after completing nearly half of an unprecedented round-the-world flight, the project said Wednesday.
"Irreversible damage to certain parts of the batteries will require repairs which will take several months," it said in a statement.
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The team said last week that battery temperatures in the innovative craft had surged during a gruelling, five-day journey from Japan to Hawaii, and there was no way to cool the battery packs once the aircraft was in flight.
There had been hope that repairs could be completed by next month, but the statement said fixes will take until "early spring 2016."
A spokeswoman for the project separately told AFP that it was possible the battery packs needed to be replaced entirely if the existing system could not be repaired.
"We don't know yet if we have to change everything or if we can repair (the existing material)", but any new parts would have to be produced by the project, she said.
"It's not like you can order them," as the craft is unique, she added.
Not a 'technical failure'
The aircraft has been flown by Swiss businessman and pilot Andre Borschberg, 62, who has already set a new record for the longest solo plane flight.
His 118-hour journey across the Pacific smashed the previous record of 76 hours and 45 minutes set by US adventurer Steve Fossett in 2006.
His partner, Swiss aviator Bertrand Piccard had been scheduled to pilot the next leg of the journey from Hawaii to Phoenix, Arizona.
The Solar Impulse 2 team said the battery overheating during the long flight across the Pacific Ocean was not caused by "a technical failure" or "a weakness in the technology."
Instead, the problem was a failure to fully anticipate the quick rate at which battery temperatures can rise in tropical climates.
"The Solar Impulse engineering team will be studying various options for better cooling and heating processes for very long flights," the project said.
The aircraft took off from the United Arab Emirates (UAE) earlier this year powered by 17,000 solar cells, with the project aimed at promoting the use of renewable energy.
Its wingspan is longer than a jumbo jet but its weight is roughly the same as a car thanks to its light construction.
A series of setbacks
Once repairs are completed, the plane is expected to cross the United States, stopping in New York before a trans-Atlantic flight to Europe.
From there, the pilots plan to make their back to the point of departure in Abu Dhabi.
The battery damage is the latest in a series of hitches.
Borschberg experienced a problem with one of his eyes, which forced him to cut short his flight over Asia and return to Switzerland for several days.
The plane was also not supposed to land in Japan, but bad weather en route from Nanjing in China to Hawaii forced a diversion at the start of June.
Solar Impulse 2 was stranded in Japan for nearly a month, with the crew scouring long-range forecasts for a favourable weather window.
"Setbacks are part of the challenges of a project which is pushing technological boundaries to the limits," the project said Wednesday.