Solar Impulse II grounded in Hawaii - Battery overheat

Solar Impulse II Stalls Out in Hawaii

Juliet Van Wagenen

[Avionics Today 07-15-2015] The round-the-world flight of Solar Impulse II, a completely solar powered aircraft, has been suspended until early spring 2016 due to irreparable damage to the aircraft’s batteries, which overheated during flight. The solar-powered airplane will stay in Hawaii until early spring 2016.

Solar Impulse II on its flight from Nagoya, Japan to Hawaii, U.S. Photo: Solar Impulse

Following the longest and most difficult leg of the round-the-world journey, which lasted 5 days and 5 nights, Solar Impulse will undergo maintenance repairs on the batteries due to damages brought about by overheating. During the first ascent on day one of the flight from Nagoya to Hawaii, the battery temperature increased due to a high climb rate and an over insulation of the gondolas. Despite the mission team’s close monitoring of the aircraft, there was no way to decrease the temperature for the remaining duration as each daily cycle requires an ascent to 28,000 feet and descent for optimal energy management.

Overall the airplane performed well during the flight, according to a statement released by Solar Impulse, which noted the damage to the batteries is not a technical failure or a weakness in the technology but rather an evaluation error in terms of the profile of the mission and the cooling design specifications of the batteries. The team did not properly anticipate the temperature of the batteries in a quick ascent/descent in tropical climates.

Irreversible damage to certain parts of the batteries will require repairs that will take several months. In parallel, the Solar Impulse engineering team will be studying various options for better cooling and heating processes for very long flights.