Solar powered plane set to circumnavigate the globe

In 1903 two audacious young men set human kind into a new era with their bold attempt at flight. They were the Wright brothers, and their pioneering invention, which got of the ground for all of three seconds, now allows people to seamlessly travel around the world in hours rather than weeks.

It is through bold dreams that challenge the impossible that man reaches new heights. And a team of European scientists now dreams of a new era; pollution-free flight. Aircraft emissions are a significant contributor to climate change, and the continuing explosion in air traffic volumes as more people gain access to flight means this will only grow. For Australian’s, taking an overseas holiday to Europe or the US is enough to blow your carbon footprint right off the scale.

Flight is a particularly difficult activity to make emissions free. The advent of the aeroplane had as much to do with the development of reliable and powerful engines as it did with Bernoulli’s equations and aerodynamics. That is because in order to fly you need a powerful, lightweight and reliable source of propulsion to give you lift, and that is exactly what the jet engine gave us.

If you sit a jet engine and all of the fuel required to power it on one side of a scale, and an equivalently powerful electric motor and batteries on the other you’d see one almighty tilt with batteries at the bottom. Principally this is due to the storage medium for energy. On a kilo for kilo basis one kilo of petrol contains massively more energy then can be stored in a one kilo battery. And this is a very significant problem that inhibits the development of many electric machines such as the electric car and aircraft. Now to add a little more spice to an already red hot problem, imagine having to power the aircraft using solar cells and charge batteries to use when the sun doesn’t shine.

This is exactly what one man has in mind. A plane powered by solar energy that flies continuously, day and night, around the circumference of the world “ the Solar Impulse. Fortunately, our dreamer Bertrand Piccard, has some experience in bold endeavours, being the first man to pilot a balloon non-stop around the world.

So far the Solar Impulse team has ticked the first box, building a prototype that flew successfully for 350 meters. The aircraft being developed are unique, with colossal wingspans to accommodate the thousands of solar cells needed, as well as the lift and aerodynamic efficiency to fly at low speeds with small amounts of power. Their first prototype, HB-SIA, has a wing span the size of an Airbus A340 and a power output of 6kW “ roughly the same amount used by the Wright brothers Flyer. Once this first prototype goes through its paces the HB-SIB will be made, with a wingspan the size of an Airbus A380. It is hoped that this plane will be ready to circumnavigate the globe in the year 2012.

The aircraft works by using its massive array of 12,000 solar cells to fly during the day whilst charging its batteries and gaining height. Although the flight will take place near the equator where there are 12 hour days, it is estimated that with cloud cover and low sun angles at dawn and dusk the solar impulse will only have 8 hours of full solar charge time a day (see the Solar Impulses proposed flight path here). The team selected 130 micron monocrystalline silicon PV cells for their capacity to combine lightness and efficiency. Although more efficient cells exist and are used in space, the added weight of these cells would penalize the plane during night flight.

Night flying is the most crucial and challenging phase. In order to retain enough energy the plane carries 400kg of batteries, which is more than one quarter of the planes total weight. However, electrical energy is not the only form of energy stored. By gaining height during the day and slowly gliding it down during the night the plane also stores potential energy. Along with the immense challenge of energy are several others, including building a plane with the wingspan of an A380 that weighs only 1500kgs “ an amazing materials engineering and structural design feat.

The plane also has a highly sophisticated central control system which will enable the pilot to make the optimum flying decisions. There aren’t very many comforts for the pilot on board though, and due to these restrictions the flight will not be non-stop. Several momentary stops are planned in order to change pilots, but as Piccard points out it took 60 years from the first aircraft to make it around the globe to the first non-stop circumnavigation.

With an average flying speed of only 70km/h this plane is no lightning bolt, but the race is about endurance, not speed. And the symbolism here is clear, solar energy too is about endurance “ the endurance of our planet. As Piccard says, œthe pilot will be equipped with a parachute if all goes awry, “but our world doesn’t have any such protection. So although the Solar Impulse may not be pushing Boeing 747’s out of Qantas’ fleet today it is the start of a new era. œIf we go back into history, when the great Wright brothers got their first plane to fly a distance of 200 meters in 1903, could they have imagined that 66 years later, two men would walk on the moon?

Kobad Bhavnagri
Solar Energy Consultant
Solar Choice Pty Ltd

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