How to turn a 'bathtub' into a solar car

Its name says it all: the Quiet Achiever. No noisy bursts of engine thrust marked the recent pioneering trip across the Australian continent, at an average speed of 15 miles-per-hour.

The 2,553-mile journey from west to east took just 20 days, though it was scheduled to take 28. And the trip was relatively incident-free.

What makes the long drive across a vast and mostly arid, drought-stricken landscape a milestone is that the Quiet Achiever was solar-powered. And it was the longest solar-powered journey in the world - from the Indian Ocean at Perth to Sydney on the Pacific.

The trip was an idea long harbored by a well-known Danish-born Australian professional adventurer, Hans Tholstrup. His previous achievements include circumnavigating Australia by speedboat, motorcycling around the globe, and rafting across treacherous stormy Bass Strait between the Australian mainland and the island state of Tasmania.

Tholstrup describes his dream drive: It was ''performed to achieve yet another milestone in the progress of mankind. Solar power today has similarities with man's (earlier) dream to fly.''

He added: ''Too many people keep telling the rest of us that it can't be done. There's nothing that can't be done.''

With this attitude, he approached racing driver Larry Perkins, who is also an engineer, to design and build the vehicle. Mr. Perkins says, ''When we did all the sums, we reckoned we could design and build a vehicle which would do the journey across Australia . . . in the time allotted.''

They built it with $50,000 and secured sponsorship of an oil company, BP Australia. The project fitted in with the conservation message that oil companies have begun to spread.

When it hopped off the drawing board, the Quiet Achiever wound up looking like a bathtub on four bicycle wheels. It weighed 330 pounds and was topped by a board-like roof of 90 square feet that was filled with 20 shiny solar modules.

In maximum sunlight conditions, 33 volts can be produced. Power is transmitted from the modules to two standard 12-volt auto batteries, coupled to provide 24 volts. The batteries are a storage unit for the power; when fully charged they provide enough power to drive the vehicle for about 90 minutes without further power from the sun.

Tholstrup and Perkins took turns driving the one-person vehicle, beginning their trip last Dec. 19. Observers from the Confederation of Australian Motor Sport looked on to verify that only solar power was used.

There were a few snags: Thunderstorms early in the trip caused a few delays. Then came four sweltering days of 110 degrees F. weather. But the pioneers' progress was swifter than planned, thanks to plenty of sunlight.

According to Perkins, ''Even when there was no direct sunshine, the solar cells absorbed more than enough solar radiation to keep the batteries fully charged.''

The two men were surprised that the vehicle performed so much better than anticipated and that they had so few problems.

''We had no plans to follow, no previous mistakes to look at and learn from - yet in only eight months we designed and built a whole new machine,'' Tholstrup exclaims.

''Had all the roads been as smooth as the final 625 miles, we could have . . . completed the trip in two weeks,'' he adds.

One of the motives of the journey was to popularize solar power. Tholstrup and Perkins are now talking about organizing solar-powered car rallies.

Neither man believes the technology has reached the point where mass-production of solar-powered automobiles is imminent. But in a decade or so, they say, there could be considerable advances on their cramped rough-riding vehicle.

''There's not much doubt that in the near future solar power must come into demand for use in transportation,'' Perkins says.

Adds Tholstrup: ''Critics will say it's not possible for a high percentage of . . . transportation to use solar power energy. We do not disagree with this premise today, but that may not necessarily be so in the future.''

And before long, he says, ''Who knows, we may see vehicles as big as a jumbo jet running entirely on solar power.''