Most electric-powered aircraft are currently at the experimental stage and still a long way from widespread freight or passenger use. However, electric power does seem likely to play a part in the aerospace industry of the future.

Solar power holds promise for the aircraft industry

There are currently lots of ventures to develop electric cars, some of which will draw partly on solar power. A number of entrepreneurs are also looking to use electric energy to power another major form of engine-driven transport, namely the aeroplane, but there they are coming up against considerable barriers. Top of the list is the weight. For an equivalent mass, batteries provide far less power than a jerry-can of petrol, so an electric plane has to carry a greater load than its kerosene-fuelled cousins. But then a heavier plane consumes more energy…and so on ad infinitum. Add the weight of the pilots(s) and passengers and the plane might not even be able to get off the ground. The risks involved are enough to give one very cold feet. When an electric vehicle breaks down, it is usually a mere nuisance, but when the same happens to a plane the consequences could be fatal. This is why so far most trials have been made with gliders carrying no passengers. However in 2013 two Swiss pilots achieved what had seemed impossible. They crossed the United States coast-to-coast in a fully solar-powered aeroplane called Solar Impulse 1.

Solar-powered flight proven

Solar Impulse 1 left San Francisco in early May that year and landed at Kennedy Airport, New York, two months later, having stopped at Phoenix, Dallas and Washington on the way. Project leaders Bertrand Piccard and André Borschberg took turns in the one-man cockpit throughout the adventure. This pioneering exploit was made possible by the advanced technical features of the plane, which took Piccard and Borschberg four years to design and two to build. Their plane is the same size as an Airbus A340, but its weight is just 1% that of the commercial airliner. It draws its power from the solar panels which cover its wings and the upper side of the cabin. Surplus energy gathered during the day is stored in the batteries to enable it to continue flying at night. The plane had previously completed successful solar-powered flights from Switzerland to Spain and Morocco in 2012, thus becoming the first solar-powered aircraft to link two continents. Having proved that solar energy is a viable means of powering aeroplanes, the duo now intend to continue with their experiments. At the end of February they plan to set out from Abu Dhabi to attempt the first round-the-world trip in a solar-powered plane, the upgraded Solar Impulse 2. Their schedule envisages 25 days’ flying over five months, at a speed of between 50 and 100 km/h, with a dozen stopovers.

Facts and figures on Solar Impulse 2’s odyssey from French press agency AFP

This plane has clearly not been designed as a commercial carrier but its achievements are nevertheless encouraging others to attempt similar feats. Last April, California-based Solar Flight posted a video on its website featuring a first solar-powered plane carrying a passenger in addition to the pilot. The plane was designed by a team of European engineers. Once it has attained altitude it can fly with its engine turned off, in glider mode.



Electric-powered planes in the near future?

Promising though these experiments undoubtedly are, these aircraft are still a long way from meeting the needs of the flying public, and it is difficult to imagine a large airliner powered entirely by photovoltaic energy in the near future. A more realistic aim in the near term is to develop hybrid models, such as the Sun Flyer, developed by Colorado-based Bye Aerospace. The Sun Flyer is powered by electric batteries, which must be charged on the network when the plane is on the ground. When in flight its solar panels then provide some extra autonomy. Sun Flyer can stay airborne for just two hours on its batteries, but this can be extended to three or four hours when the sun is shining. It also has a propeller which works like a windmill, providing some further additional power. The plane is small, but the company says that in the next five to ten years the basic design could be applied to larger aircraft. Cheaper, quieter, cleaner, and needing less maintenance than combustion-engine aeroplanes, this plane has a number of features that are likely to attract entrepreneurs and investors.

Meanwhile companies in other areas of the transport sector are also becoming increasingly interested in electric-powered mobility. In the automobile industry, we recently reported on Ubitricity, a company which seeks to provide infrastructure enabling electric vehicle owners to charge up their vehicles anytime, anywhere. The railway sector, already electric-powered for a long time, is also looking to use photovoltaic energy. Some years ago Belgium’s national railway company experimented with running a train on solar energy collected by solar panels installed on the roof of a long tunnel. Last but not least, electricity provides a range of options for powering scooters and personal transporters.

By Guillaume Renouard