We have lift-off: Solar Impulse begins round-the-world journey

The world’s first solar-powered circumnavigation attempt began today as the Solar Impulse 2 (Si2) aircraft took off from Abu Dhabi at 07:12 local time this morning.

Swiss pilot Andre Borschberg was entrusted with commencing the historical first leg of a journey that is expected to take five months as the solar-powered plane heads eastwards over India, Burma, China, the Pacific Ocean, the U.S., the Atlantic, southern Europe and back to Abu Dhabi some time around late July.

Fitted with 17,248 SunPower monocrystalline solar cells across the aircraft’s 72-meter wingspan, tailplane and fuselage, the Si2 is entirely powered by the sun, storing excess energy in its four lithium ion batteries attached two to a wing.

Over the course of the 35,000km journey, Borschberg will share piloting duties with fellow Swiss aviator and Solar Impulse founder Bertrand Piccard, swapping in and out approximately every five days. Both pilots trained themselves to sleep in short, 20-minute sessions, using yoga and meditation techniques to ensure that they are as sustainably energetic as the plane itself.

A dedicated ground crew will guide the plane, with the journey relayed to interesting onlookers via the Solar Impulse website. "I am confident we have a very special aeroplane, and it will have to be to get us across the big oceans," said Borschberg.

Carrying the solar message

In November, pv magazine heard how Piccard wants the journey to carry the message that solar energy – and all forms of renewables – can carry the world into a new era and finally do away with our dependence on fossil fuels.

While the Si2 aircraft itself is not intended to ever carry passengers, its aim is to inspire people to think differently about how the world consumes energy.

The aircraft will manage an average speed of just 70 km/h, but Piccard is confident that the message the plane carries will propel an altogether faster adoption of clean technology.

"I had this dream 16 years ago of flying around the world without fuel [Piccard was the first man to circumnavigate the globe in a hot air balloon], just on solar power," he said. "Now we’re about to do it. The passion is there and I look forward so much to being in the cockpit."

Solar innovation

In creating an aircraft capable of circumnavigating the globe powered purely by the sun, the Solar Impulse team had to think creatively about nearly every single aspect of the aircraft.

The solar and battery technology used was already widely available; it was the rest of the plane that has had to play catch up. SunPower’s cells are 135 microns thick, bringing much-needed flexibility and lightness to the aircraft, which weighs just 2.3 tonnes (around the same as a large passenger car).

"The solar cells cover a total area of 250 square meters, delivering a combined power output of 45 kWp,” Borschberg told pv magazine in November. “The system uses MPPT to create a direct current of 300 volts, which is fed to the four DC motors and li-ion batteries."

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

According to Piccard, storage represents the plane’s chief inefficiency – but also its most achievable goal for improvement. "The batteries we have used have been specially developed for optimal maintenance but are still 10 times heavier than kerosene. I would imagine that we are still 20 years away from attaining parity on this point, but the hope is that Si2 can inspire better efficiencies and lighter batteries."

Solar storage makes the Si2 journey possible, despite the limitations to weight, speed and thrust the technology currently brings to the table. Piccard added, however, that the only way to push the envelope on solar-powered flight was to be able to fly at night, safely: "We have only recently been able to fit the Si2 with battery storage ample enough to achieve this," said Piccard.

The first leg of the journey is a short 12-hour, 400 km stint to nearby Oman, where Borschberg will land to enable the ground crew to administer inaugural, post-first-leg tests on the aircraft. The second leg sees Si2 fly across the Indian Ocean to Western India.

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