Can a solar powered plane make it around the entire Earth? That’s what two Swiss pilots are finding out at the moment – and it’s all in the name of renewable energy.

André Borschberg and Bertrand Piccard are the two pilots flying the groundbreaking Solar Impulse 2 plane around the world. It uses 17,000 solar cells to power itself by nothing other than the Sun, with this electricity being used to power propellers. 

This all comes at a bit of a cost, though. Solar cells are not yet very efficient, so the plane has a rather modest top speed of 138 km/h (86 mph). And as for the pilots, they must do without many comforts as they fly for up to five days alone at a time. 

The plane recently completed the ninth leg of its round-the-world trip from Hawaii to California after a nine-month delay, with the pilots taking it in turns to fly the single-seater plane. We caught up with Bertrand while he was flying that leg, interviewing him live over the Pacific Ocean, to see what life is like on board Solar Impulse 2.

You can watch the interview below.

 

“I’m very comfortable, I have to say,” Bertrand said when we asked how he was feeling. It’s quite an unusual flight, to say the least. So stripped down is the plane that it only has a very basic autopilot system, so for the majority of the flight, he must remain in control. The plane also needs to constantly switch between high altitude, where it can gather as much sunlight as possible, and low altitude, which is its power-saving mode.

To keep himself awake, Bertrand is afforded short 20-minute “catnaps,” a similar technique to sailors on solo round-the-world voyages. “It is important to keep the energy of the pilot up, not only the energy of the airplane,” Bertrand explained. “I’m using self-hypnosis, which is a way to disassociate your mind and your body, so the body can sleep, but the mind stays alert.”

In order to utilize as much solar power as possible, the plane is as wide as a jumbo jet, but as light as a car. This can make it quite difficult to control, and very susceptible to turbulence. If the worst came to the worst, and Bertrand had to bail, he has a lifejacket and an inflatable raft that would keep him safe in the ocean until rescue arrived.

“It’s very different [to flying a regular plane],” he said. “The price to pay to fly on solar power day and night is to have an airplane that’s extremely big and extremely light, which means it’s sensitive to turbulence and difficult to handle if you have a lot of wind.” It’s this latter reason that the plane has often been delayed on flights. If the wind is too high, it is not safe to take off.

^{André Borschberg, left, and Bertrand Piccard after the successful crossing of the Pacific Ocean. Solar Impulse}

And what’s life actually like inside the cockpit? Well, it might not be for everyone. For starters, there’s no heating, so the pilots have to wrap up well to keep themselves warm. For food, they have a strict diet to adhere to, which includes things like mashed up food, quinoa, and even a few more exciting items like mushroom risotto.

As for personal hygiene, things get a bit… interesting. To keep themselves clean, the pilots simply use a wet tissue. And to go to the toilet, well, there’s a flap that opens a hole in their seat. We think you can get the picture.

You might be thinking, why would anyone put themselves through all this? Well, both the pilots are trying to show the benefits of solar power, in a world that they say needs to shift towards using renewable energy.

“Solar Impulse is not going to transport 200 passengers any time soon,” Bertrand admits. “But I guess in 10 years time, there would be short or medium-haul airplanes that will transport 50 people on electric, not necessarily solar, but will be plugged in on the ground with electric batteries. It can be done also for cars, lots of technology for houses, smart grids. So the technologies are here. Solar Impulse is a flagship of these technologies.”

Whether Solar Impulse will truly be this game-changer remains to be seen. But perhaps testament to its success is that, shortly after speaking to IFLScience, Bertrand spoke live to United Nations General Secretary Ban-ki Moon at a meeting of more than 170 countries to sign the Paris climate agreement, which also just happened to be Earth Day.

The plane has a few more stops planned in the U.S. before it flies back to Europe, and ends the round-the-world trip in Abu Dhabi later this year, where it began in March 2015. For now, Bertrand is just happy to be back in the air again.