It has a wingspan of almost 72.4 meters—four meters greater than that of a Boeing 747-8I—yet it weighs just 2,300 kg, roughly the same as an SUV. Its top speed is a distinctly modest 43 kt (80km/h), yet it can stay aloft virtually indefinitely, with only the endurance of its pilot the limiting factor.

So what lessons can Solar Impulse 2 (Si2), a solar-powered aircraft designed to showcase the benefits of pollution-free flight, have for the future of commercial aviation?

The aircraft, which completed a round-the-world trip July 26, 2016, that began and ended in Abu Dhabi, operates by converting sunlight through more than 17,000 solar cells on its upper surfaces into electricity that is stored in four high-voltage lithium polymer batteries. It collects up to 340 kilowatt-hours of solar energy a day and generates more power than it uses during hours of daylight, allowing it to draw power from those batteries to its four motors during the hours of darkness, until the sun is powerful enough the next morning to start the recharging process again. 

The brushless, sensorless motors, each generating 17.4 horsepower (13.5 kilowatts), are mounted below the wings, and fitted with a reduction gear limiting the rotation speed of a four-meter diameter, two-bladed propeller to 525 revolutions per minute.

This technology will not replace commercial aviation and is not meant to. Rather, the flight aims to demonstrate clean technologies and renewable forms of energy.

However, some of the systems on board will potentially translate to the commercial sector.

Creating an aircraft the size of Si2 while keeping its weight to the absolute minimum to ease the strain on its motors called for not only innovative design but also the use of new materials.

The latest developments in carbonfiber are likely to find their way in some form into commercial airliners. Si2’s structure uses sheets of the material weighing only 25 grams per square meter, or three times lighter than paper. 

Similarly, a new type of insulating material used on the aircraft may have uses in the commercial sector. The high-density foam, designed to provide insulation from extreme temperatures during flight, has very thin pores, high rigidity and structural strength while remaining lightweight—lighter than Styrofoam. 

With the aircraft being so light and relatively fragile, telemetry is vital for the controllers to know what the aircraft is doing at any moment in time. Bad weather along Si2’s proposed flightpath was enough for the mission control center in Monaco to postpone or abort a flight. 

The aircraft contains some 10,000 sensors that generate data covering everything from the temperature of individual groups of solar cells to strain gauges on the control surfaces, with critical sensors sending data 10 times a second to the controllers.

Current airliners, of course, already send data—particularly for maintenance purposes—via the Aircraft Communications Addressing and Reporting System (ACARS), but Si2 transmits an unusually large quantity of data.

Communications, including those for the telemetry, are provided by SITAONAIR using the Inmarsat SwiftBroadband-based satellite communications link. “Providing global and reliable connectivity for this aircraft is absolutely fundamental for operational and critical navigation purposes, from nose-to-tail,” SITAONAIR CEO Ian Dawkins said.

“This data is comprised of messages from the 10,000 plus sensors covering the aircraft from cockpit data, voice communications over IP and also from live streaming video when [the pilot] talks to the media via his GoPro camera onboard,” Dawkins said.

The aircraft has generated seven gigabytes of background IP data and 2,500 minutes of streaming IP data since initial departure from Abu Dhabi on March 8, 2015.

Perhaps the technology of most interest to the airline world, however, given the disappearance of Malaysia Airlines MH370 March 8, 2014 over the Indian Ocean, is the tracking system used on board Si2.

“If we’re out of radar range we check the aircraft’s position’ via GPS through the satellite,” flight director Michael Anger said. “The primary telemetry system is Inmarsat, but as back-up, we use Iridium. This transmits the major data such as battery temperature and altitude, every one to two seconds. With that, we also get position data.” The Iridium system weighs just 200 grams, Anger said.

“The tracking system is designed by Swisscom and can be used by the commercial industry; I wonder why such a small box with Iridium technology isn’t standard an all aircraft around the world,” Anger said.

In terms of pilot aids, meanwhile, the extremely long flight times of some of Si2’s sectors led to the adoption of an electrocardiogram to monitor the pilot’s fatigue and vigilance level. The size of a matchbox, it immediately transmits a warning to ground controllers if a problem with the pilot is detected. Given the phenomenon of pilots on commercial flights falling asleep at the same time, a modification of this system could provide a timely warning in such circumstances.

There are more devices waiting in the wings that may have applications to commercial aviation, but they remain shrouded in secrecy. “There’s one thing I can think of,” mission engineer Yves Heller said, piquing interest among assembled journalists touring the mission control center in June. “But I’m probably not allowed to speak about it…”.