Solar Impulse 2 circumnavigates globe using solar and NMC only

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The sky could literally be no limit to the potential applications for Kokam’s Ultra High Energy nickel manganese cobalt batteries that on July 26 successfully helped to land the first round-the-world fuel-less aircraft, the Solar Impulse 2, in the UAE.

The solar-powered aircraft, crewed by two pilots, Bertrand Piccard and Andre Borschberg, arrived safely in Abu Dhabi on July 26. It had flown 40,000 kilometres to get there, using solar power by day and by night, strapped to its wings, four of Kokam’s lithium batteries.

The voyage had not all been plain flying. After taking off from Abu Dhabi in March 2015, with a scheduled finish date of August the same year, the batteries overheated in the longest leg between Japan and Hawaii, and in July the plane was forced to stop while they were replaced and a cooling system fitted. This took nine months.

Speaking to Batteries International on August 31, Ike Hong, vice president of power solutions at Kokam (and also company founder J Hong’s son), said that although the batteries had not in fact suffered any damage, the company had no choice but to replace them since “1% risk is too much”.

The flight resumed from Hawaii in April 2016 when it flew to California, followed by New York City, across the Atlantic Ocean to Spain, then Egypt for its final leg to Abu Dhabi in July.

Industry leaders” who Hong would not name were interested in Kokam’s NMC batteries because of their unique offering, he said.

They are looking for a lot more challenge,” he said. “They need better, lighter technology, and we are continually developing our batteries to meet the need.

Our batteries are already being used in space, the military, submarines, torpedoes— they are never going to be super commercialized, but no other battery manufacturer makes anything similar, and we want to differentiate ourselves.”

Hong said one of the main applications for the Ultra High Density NMC batteries was unmanned flying machines — or drones — because while there were cheaper alternatives, they did not offer the same return on investment.

They are more expensive to make than Chinese batteries, which are 30%-40% cheaper and used a lot in drones. But ours offer 40%-50% more flying time. Other batteries have to be replaced after 60 times of use, whereas ours have a life cycle of a couple of hundred,” he said.

For the Solar Impulse 2, made by the Swiss firm of the same name, the batteries were a stage further developed than those used on the aircraft’s predecessor in 2010, the Solar Impulse 1.

For the Solar Impulse 1, the cells were 87 Ampere hours per cell. On the Solar Impulse 2, we developed 150 Ah cells. The capacity was almost double, but the weight was not,” said Hong.

Weight is still a key issue. To fly for hundreds of hours without landing is a real challenge. Industry progress will come from much lighter but very high-energy lithium batteries. As this is achieved, greater possibilities for non-stop solar-powered flight open up.”