Over The Horizon

Driving into the Sun

The results of the World Solar Challenge car race show that solar-powered vehicles have come a long way in just over ten years. The first long-distance solar car journey in 1982 saw the vehicle travel at 23 kilometres per hour; the latest models were doing three times that and clocking qualifying times of over 120 km/h.

Fifty-five cars, with a total value of more than $25 million, lined up for the 3,000-kilometre race from Darwin to Adelaide. In amongst the hi-tech entries from Japanese manufacturers, European universities and Australian high schools was the Philips Solar Kiwi team from New Zealand.

Line honours went to the Dream car, of Honda's R&D department, which hit an average speed of 85 km/h. The New Zealanders were 15th overall, but first in the private entry class, ahead of their nearest rivals by 300 kilometres. Stewart Lister's team also got the award for the best team spirit for the second year running. The Philips Solar Kiwi had less than half the battery capacity of the winning vehicle, at 1.63 kW/h, and a top speed 40 km/h rather than the 130 km/h which the Dream car could manage.

Technical progress in solar design has been rapid, partially spurred on by the demands of the Solar Challenge. Aerodynamics has been one area, with teams keen to reduce drag and improve stability as much as possible. Stability is an important safety point, as each car had to be able to survive being overtaken by the dreaded Northern Territory Road Trains. These monster trucks are equivalent to three 18-wheelers and, when travelling in the opposite direction on a narrow two-lane highway at 80 km/h, they can be a major aerodynamic hazard.

Tyres came under scrutiny, particularly given the hot road conditions --  temperatures on the Stuart Highway reached over 70^oC. Michelin worked with one team to develop a tyre that reduced rolling resistance by 30%.

The major focus was on improving motor design and efficiency. Honda, NTU, and Biel independently developed slow revving, highly efficient motors which sat inside the cars' drive wheel hub. This enabled them to have a motor speed of 950-1500rpm. The NTU design had a claimed efficiency of 96%, with only 2% loss in the trackers and power management systems. A typical family car, in comparison, is around 20% efficient.

The photovoltaics that power the cars have improved markedly, particularly in cost. Five years ago, cells cost around $40 a watt, but are now available for $10/W. Solar researchers say that $2/W is achievable. The eight-square-metre panels used in the cars cost from $15,000 to $1.2 million.

Battery technology has always been a limiting factor in solar power utilisation, and race observers were disappointed that progress in this area has not matched other developments. There have been some small energy density improvements, and one team trialled gallium-arsenide batteries, but the bulk of the storage side continues to remain with conventional lead-acid batteries.

As race organisers said, "The World Solar Challenge may not provide immediate solutions to the problems of rapidly depleting oil reserves and the environmental cost of individual automobility. It does provide a vehicle for the further research and development of alternative transport that will one day result in a viable alternative to the internal combustion engine." They're on their way.