Around the world in 23 days

Image credit: Frederic Legrand - COMEO /

The return of Solar Impulse 2 last week heralded a significant moment in the history of renewable energy. Manned by Swiss pilots Bertrand Piccard and Andre Borschberg, the 2,300 kg carbon-fibre aircraft completed a round-the-world voyage using only clean energy and broke 19 aviation records in the process.

Their 43,041km journey was split into 17 stages, including a record-breaking five day non-stop flight from Japan to Hawaii. The adventure ended where it began, in Abu Dhabi, to the jubilation of the 90-strong Solar Impulse team and countless supporters worldwide.

But just how do you circumnavigate the world using only green energy?

Firstly, it takes a lot of research. Piccard first had the idea for an emissions-free round-the-world flight in 1999, after his successful non-stop balloon trip around the world with Briton Brian Jones. Feeling guilty about the amount of fuel needed to power the voyage, he dreamed up the idea for Solar Impulse. This spirit of innovation and adventure is in Piccard’s blood, whose father and grandfather have equally impressive record-breaking histories – the former made the first trip to the deepest part of the ocean and the latter rode the first balloon into the stratosphere.

The Solar Impulse project was officially founded in 2004 by Piccard and fellow pilot Borschberg and after the design, testing and construction of numerous prototypes, Solar Impulse 2 took its first maiden flight 10 years later in 2014. The wider Solar Impulse team is made up of 30 engineers, 25 technicians and 22 mission controllers.

Solar Impulse 2 weighs no more than a car and has a wingspan of a Boeing 747. More than 17,000 solar cells collected energy from the sun during the day and kept the plane’s propellers and electric engines powered at night. But it wasn’t always a smooth flight.

Whilst the flight hours only equated to 23 days, the actual mission lasted around 16 months as the pilots contended with poor weather conditions and a problem with the batteries overheating after the five day non-stop flight on leg 8 of the tour. The engineers in the Solar Impulse 2 team were then tasked with studying different options for cooling and heating processes for long flights.

According to Piccard these setbacks only added to the adventure, which also saw the pilots face the day-to-day challenges of wearing oxygen masks to breathe at high altitude and only being able to sleep for 20 minutes at a time.

Despite breaking 19 aviation records, the project is unlikely to have any significant implication on the commercial aerospace industry, as Matchtech Aerospace Manager, Ben Birch explains:

“Whilst the achievements of these pilots will go down in history and the engineers involved will forever hold these memories dear, the practical implications for the commercial aerospace industry are minimal. Unfortunately, at its current scale, Solar Impulse is too small and too slow to meet the demands of the commercial industry. Simply scaling up the solar panels would still not be enough to take a commercial aircraft and its payload on its journey at speed.

“The aerospace industry is, however, involved in and committed to improving fuel/energy efficiency so battery-cell and regenerative (think F1’s KERS) technology is an area that is being further explored. The sun still has another part to play – helping us to grow crops for Bio-Fuels. Plant bio mass fuels can give up to 80% reduction of aircraft CO2 emissions.”

The Solar Impulse 2 pilots are now setting their sights on the next challenge: unmanned solar drones. Whilst this concept isn’t completely new - solar-powered drones are already being used by the UK forces abroad to undertake surveillance and provide telecommunications services - the innovative pair are actually more interested in the use of drones for environmental purposes including agriculture, weather forecasting and environmental management (e.g. forests and oceans).

Regardless of the outcomes of their future endeavours, the team behind Solar Impulse 2 have made history and certainly brought the power of renewables into the spotlight once more.

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