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29th 2002f June 2002
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  Solar Cars - Peter Pudney

Date:June 14, 2002
Time:7:00 pm.
Place:WEA, 223 Angas Street, ADELAIDE
Presenter:Mr Peter Pudney

The Darwin to Adelaide Solar Car Race is the world's supreme solar powered car event. While the race starts in Darwin, the administration and organization is centred here in Adelaide and a main participant in this organization and in at least two of the competing teams is Dr Peter Pudney from the Centre of Industrial and Applied Mathematics at the University of South Australia who spoke to us at our June meeting.

As well as the Darwin to Adelaide races Peter has been involved with smaller events held around the world and several Austalian tours arranged to test the cars under Austalia's extreme climatic and road conditions. Peter's main interest is in the cars Aurora RMIT 101 (RMIT and 101 Collins Street are major sponsors) and Ned (Ned being named after the narrow windscreen slit's resemblance to Australia's famous outlaw, Ned Kelly's, helmet).

Peter started his presentation with some "holiday snaps" of his 24 day around Australia solar car trip which showed some of the conditions the car had to handle. The car held up well in all respects, except that the special, low rolling-friction, tubeless tyres were puncturing at a rate of up to 3 times a day!

Peter then moved onto the technical aspects of designing solar cars such as the Aurora to win races - Aurora has won one World Solar Challenge (the race from Darwin to Adelaide), and has been the top Australian team every year (exept the year they crashed).

As Peter stated, solar cars are essentially a solar array converting sunlight into electricity, an electical energy storage system, and a motor or motors driving one or more wheels. Steering, suspension, getting the driver in and out of the car, and driver comforts are simple and minimal. The design emphasis is put into solar energy conversion efficiency and wiring, aerodynamics, weight reduction, motor energy conversion efficiency, energy storage/retrieval efficiency, tyre-to-road rolling friction reduction, and winning.

Amazingly, motor efficiencies using Australian CSIRO motors is over 98% and really give designers no more scope for improvement. Similarly, electrical storage using lithium secondary cells is over 90% efficient and their light weight gives only very limited scope for improvement.

From this point in Peter's talk it started to become evident where a mathematician can make all the difference between winning or losing. Even a few percent improvement in design or operation can give you the edge over your rivals. The main areas for design improvement are solar cells, cell wiring configuration, and aerodynamics all within the race rules. Attention to detail is all important.

Solar cell sunlight-to-electrical energy conversion efficiencies are presently about 20% for silicon and up to 27% for multilayer Gallium arsenide. This delivers about 1.4 kilowatts peak for Aurora using space-grade silicon cells compared to the winning Dutch team's much more expensive gallium arsenide cells' 1.8 kilowatts.

Peter showed several parallel/series solar cell wiring configurations that reduce the effects of shaded cells. This is a problem where shaded cells overheat and risk damage or fire if wired in series with illuminated cells. Careful wiring configurations can minimize the problem. Peter examined a variety of configurations that finally resulted in a practical, static solution that is now used in Ned. The parallel/series wiring scheme is almost essential on Ned because it has a highly curved panel whereas the flatter Aurora RMIT 101 uses a more conventional wiring scheme.

The special tubeless, treadless, soft rubber tyres used by nearly all solar racing cars are designed to reduce rolling friction to a minimum, but unfortunately are very prone to puncture on Australian rough roads. Nevertheless, changing puntured tyres is still a better choice than using tougher, slower tyres. There is not much that can be done to improve things here.

Aerodynamics becomes the dominant factor above about 60 kph and increases rapidly at higher speeds. This is where good design gives real gains. Peter has used mathematical modelling and wind tunnel tests to prove the current design shape for Ned. Nearly all cars use essentially the same shape now so that, apart from the colour, all solar racing cars look much the same - and no more tilting panels!

Aurora is actually a little different, as Peter pointed out, because it has one front wheel and two rear wheels while all other cars use two wheels at the front and one or two at the rear. Aurora's wheel configuration makes steering and suspension a little simpler, avoids wheel alignment problems, and has proven itself in race conditions.

Many questions relating to the solar cars, electric cars generally, boats, gophers, the Segway, and even the Australian electric skate board were discussed for some hour or more.

Many thanks, Peter, for your well-illustrated presentation and the very best of luck in all future solar car events.

. . . Rick Matthews

Rick has put up some pictures taken at the last Solar Car Race. Also found www.wsc.org.au and www.unisa.edu.au/solarcar which may be of interest.