Solar Impulse grounded following 'irreversible' battery damage

The Solar Impulse 2 (Si2) plane has been grounded in Hawaii after successfully completing the eighth, and most grueling, leg of its around the world journey. Damage to certain parts of the four 70 liter lithium polymer batteries, attached to the plane’s wings, is said to be irreversible, with repairs and replacements expected to take several weeks.

The batteries were developed with Solvay, Kokam and Bayer Material Science, and have been optimized to 260 watt hours per kg. Combined, they can store 164,580 watts of power, and weigh 633 kg – one-quarter of the aircraft’s total weight.

Due to the damage, the team will not be able to embark on the ninth (from 13) leg of its mission – to achieve the first round-the-world solar flight (35,000 km, 18,000 km of which has been covered) – until at least the beginning of August.

"During the first ascend on day one of the flight from Nagoya to Hawaii, the battery temperature increased too much due to over insulation," said the Solar Impulse team in a statement released.

"And while the Mission Team was monitoring this very closely during the mission leg, there was no way to decrease the temperature for the remaining duration of the flight as each daily cycle requires an ascend to 28’000 feet and descend for energy management issues," it continued.

Si2 began it record-breaking attempt this March 9 in Abu Dhabi. The next leg will see it flying around 4,707 km, from Hawaii to Phoenix. The plane, which is also equipped with 17,248 of SunPower’s monocrystalline solar cells, has an average speed of just 70 km/h.