Night flights powered by the sun
30 June 2009
Four years of development work are now coming to a head for the prototype plane of the Solar Impulse project, intended to achieve flight around the world using only solar power.
Some people are driven to do dangerous things basically because the boundaries that determine most people’s mundane lives are too narrow for them. Life without danger is no life at all, as many of them find to their cost at a tragically young age. These are the people that swim vast distances, climb great heights and circumnavigate the earth in a host of uncomfortable and unlikely ways – and we all admire their courage and dedication, while sometimes wonder about their intellect. Their contribution to society is to make life interesting.
Other people have equally flamboyant targets, but their targets do bring with it benefits for the human race – ‘One small step for mankind...’ moments (as we shall hear about endlessly in the coming months). One such project is resurfacing after a period in development. It is the Solar Impulse project intended, ultimately, to achieve flight around the world using only solar power. Four years of development work are now coming to a head and the prototype plane, the catchily named HB-SIA, is nearly ready to take its first cautious test flights, hence the interest in the press. This plane will not actually be the one to tackle long-distance flights. Its successor, the HB-SIB, should be ready to fly the Atlantic in 2012 if the prototype lives up to expectations.
Bertrand Piccard is the name of the project leader and pilot. This was the man who ballooned around the world in 1999 and, presumably spurred on by the thrill of survival, came up with the idea of Solar Impulse. There are some serious technological issues involved in the construction and propulsion of this plane. One of which is that weight must be kept to an absolute minimum (about 1500 kg) if it is to be able to fly continuously at night using only the stored solar energy from the previous day. The consequence of this is that much of the structure is of carbon sheet, stretched to such an extent that you would need a micrometer to measure its thickness (literally). While I am sure that this is unfeasibly strong, anyone who has experienced severe turbulence in an aeroplane is not readily going to trust their safety in a storm to something so apparently flimsy. When I say anyone, I do not of course include the adventurers of this world like Bertrand Piccard.
Beyond the engineering materials used in constructions, the project stated at its outset that it intended to add to human knowledge in terms of energy use. Here is an extract from the Solar Impulse website: “The message we want to share is that it is essential to develop new technologies to allow our society to reduce its energetic consumption. As it is almost unthinkable that people will accept to diminish their life standards, we must develop efficient equipments that consume less, as well as alternative sources of energy and first of all solar energy.”
Personally it has always seemed obvious to me that solar energy will ultimately be the way forward. There is an endless amount of clean and continuous energy raining down on earth, even if we have to compensate for, or get above, clouds in order to obtain it. It also doesn’t sit under the topsoil of any particular nations, so it could also reduce global tensions. How to harness this energy source is a maturing technology, but one that is still far from solving mankind’s energy problems. The photovoltaic cells used by Solar Impulse have an efficiency of 20% and are made of silicon mono-crystalline of a fine thickness. Higher performance technologies exist that offer output nearer 30%, but these come with a weight penalty that made them unsuitable for this project.
Again I revert to my position of cowardice as the thought of relying on fragile power panels that cover the upper surface of the wings, presumably which will flap about a bit due to their 61 m span, seems bordering on the suicidal. But if the project does succeed in developing a practical balance of weight, performance and achievability, it could make huge strides in the development of portable solar power.
In terms of paving the way towards a solar powered aviation industry, it seems hard to imagine. But then I am sure the Wright Brothers couldn’t have predicted that their legacy would be the daily bedlam that exists at Heathrow and thousands of other airports round the world – and the Wright Brothers historic first manned and self-powered trip was only 106 years ago. So beyond the individual technological improvements that emerge, perhaps this is the dawning of a new era!
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