Fly towards the Future with Renewables!

By Daniele Pagani


“The future belongs to renewables!”: this is not anymore a mere statement, but a reality, thanks to the pioneers behind the Solar Impulse project.

For those readers who never heard about this project, the Solar Impulse 2 was the first plane which was able to fly around the world without using a single drop of fossil fuel. Instead, it used a fuel which is clean, available in endless amounts and is the source of any other type of fuel and energy on Earth: the sun.

The idea of solar planes is not new and it has already been experimented in the 1970s, with the AstroFlight Sunrise, which was the first unmanned aircraft powered by solar power. But, unlike the Solar Impulse, it was not able to fly during the night.

The Solar Impulse project started in 2002, when a feasibility study was commissioned to the Ecole Polytechnique de Lausanne (Switzerland), which was the first step for the realization of the project; it took more than six year to move from the idea-stage to a fully functional model, the Solar Impulse 1, which was presented on the 26th of June 2009 in front of 800 guests. The plane had a wingspan of 63 m and a weight of 1'600 kg.

Approximately one year later, the Solar Impulse 1 made its first night flight, proving that it was possible to fly also if the sun was not available. This was the beginning of a series of test flights at an international level: in 2011, the aircraft flew to Paris and Brussels, following the invitations of the European Commision and Parliament, where it met 150'000 fans in only three days. The following year, the plane travelled to Morocco, covering 6'000 km without using any fuel. The next step was to travel across United States (2013), for a distance of 5'650 km.




In April 2014, the Solar Impulse 2 was presented to the public. The prototype has a 72 m wingspan (more than a Boeing 747), a weight of 2'300 kg and it is equipped with a number of last-generation technologies: the power is provided by 17'248 solar cells with an efficiency of 22,7% (efficiency of regular cells: ca. 16%), which are only 135 µm thick (like a human hair) and, therefore, ultralight. The electricity produced powers four 17,4 HP electric engines, with an efficiency of 97%, which is a considerable improvement both in comparison with standard electric engines (η=80-92%) and with thermal engines (η=30%). The extra electricity is stored in four lithium polymer batteries, with a density of 260 Wh/kg and a total mass of 633 kg, which allow the plane to fly also during the night. Furthermore, to save energy, the aircraft is not equipped with conventional lights, but with LED technology.

The entire plane is made of composite materials, such as carbon fiber, which reduce the weight without decreasing the strength. A bee-nest structure allows the plane to have layers of carbon material weighting only 25 g/m2 (three times lighter than paper).

The cockpit has only 3,8 m3 of space available and it is equipped so that the pilot can fly for an entire week without the need of stopping. The thermal insulation is done by using a special foam, which has pores that are 40% smaller than the conventional ones, therefore making it very strong an lightweight at the same time.

The plane can fly up to 8'500 m, but during the night descends at 1'500 for saving energy. The maximum speed is 70 km/h, and it takes off at 44 km/h.

The two pilots, Bertrand Piccard (58) and André Borschberg (63), have flown alternately for 40'000 km for almost 17 months, 10 of which were a stop in Hawaii due to overheating of the batteries. The pilots, who were constantly supported by a team of 90 people (engineers, scientists, technicians and media responsible) flew in 17 legs, from and to Abu Dhabi (UAE):


Path Pilot Date Duration Distance Energy Produced
Abu Dhabi-Muscat Borschberg 09.03.2015 13h 1m 772 km 383 kWh
Muscat – Ahmedabad Piccard 10.03.2015 15h 20m 1'593 km 304 kWh
Ahmedabad – Varanasi Borschberg 18.03.2015 13h 15m 1'170 km 428 kWh
Varanasi – Mandalay Piccard 18.03.2015 13h 29m 1'536 km 397 kWh
Mandalay – Chongqing Piccard 29.03.2015 20h 29m 1'450 km 440 kWh
Chongqing – Nanjing Piccard 20.04.2015 17h 22m 1'241 km 325 kWh
Nanjing – Nagoya Borschberg 30.05.2015 44h 9m 2'852 km 958 kWh
Nagoya -Honolulu Borschberg 28.06.2015 117h 52 m
7'212 km 2'409 kWh
Honolulu – S.Francisco Piccard 21.04.2016 62h 29m 4'086 km 1'121 kWh
S. Francisco – Phoenix Borschberg 02.05.2016 15h 52m 1'113 km 480 kWh
Phoenix – Tulsa Piccard 12.05.2016 18h 10m 1'570 km 445 kWh
Tulsa – Dayton Borschberg 21.05.2016 16h 34m 1'113 km 460 kWh
Dayton – Lehigh Valley Piccard 25.05.2016 16h 49m 1'044 km 391 kWh
Lehigh Valley – New York Borschberg> 11.06.2016 4h 41m 265 km 0 kWh
New York – Seville Piccard 20.06.2016 71h 8m 6'765 km 1'388 kWh
Seville -Cairo Borschberg 11.07.2016 48h 37m 3'745 km 808 kWh
Cairo – Abu Dhabi Piccard 24.07.2016 48h 37m 2'694 km 917,9 kWh


To understand how important is this result, a conventional van (same weight as the Solar Impulse 2) would need more than 3'300 liters of fuel to cover the same distance. This data should explain how extraordinary is what the Solar Impulse team achieved.

With their adventure, the team showed that renewable energy is the future for any application and, although at the moment it is not possible to use solar power for commercial aircrafts, that does not mean that it will not be viable in the future.



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