“THIS is a live laboratory,” says battery scientist David Rand. He’s here in Darwin, capital of Australia’s Northern Territory, and the lab he’s talking about is this year’s . In it, the fastest solar-powered cars race from Darwin to the sleepy city of Adelaide in the south, hitting speeds of more than 100 kilometres per hour.
Cars making it to the end will have travelled 3000 kilometres through the red deserts into the woodlands of South Australia (see diagram). The designs, particularly a more realistic type of car taking part for the first time this year, will one day make an impact far beyond this one race.
Rand, from the CSIRO in Melbourne, is scrutinising car battery packs to make sure they comply with the rules. He has been to every race since it began in 1987. It has been a great testing ground in that time, he says. “Whether it’s photovoltaics, composites, suspension, tyres, motors, batteries – you’ve got to try things out under arduous conditions,” he says.
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This is as arduous as it gets. The race cuts the driest inhabited continent in half, starting here in the tropical savanna at the end of the five-month dry season.
Right now we’re in a large warehouse while eight of the fastest solar cars are being dismantled and put back together. The entire landscape is a fire scar. At the start of the highway green shoots are emerging from black stumps and the smell of ash sits heavily in the hot, thick air. The sun is burning my skin.
Rand confirms that a race favourite, Tokai Challenger from Japan’s Tokai University, has exactly 21 kilograms of lithium ion batteries, the allowable limit that lets cars drive when clouds or hills block sunlight. He waves them on to have their roadworthiness checked at the next station. As they move on, the other race favourite, Dutch Nuna7, rolls in behind them.
The two cars are formidable competitors. Tokai has won the event twice in a row and intends on making it a hat-trick. Delft University of Technology won the race four times in a row with the first four versions of its But they dropped to second place behind Tokai in the last two races.
The exact designs are a closely guarded secret but the Tokai Challenger has several new tricks. For one thing, the efficiency of the solar array has been tweaked, upping its efficiency from 22 per cent to 22.5 per cent. Tiny changes can make all the difference, says team member Hideki Kimura.
“Nuna7 has high-end paint sealant that reduces air drag by stopping dust from sticking to the paintwork”
But Nuna7 might have bettered Tokai’s solar efficiency, at least with some of its cells. While the Nuna team is using the same cells as many of the other teams, half of them have a secret coating to boost efficiency over the long dusty journey. Nuna7 has high-end paint sealant that reduces air drag by stopping dust from sticking to the paintwork.
“You cannot hold the car any more because it’s slippery,” says Allard Lambers, Nuna7 team manager. He lets me touch the surface and the lack of friction almost makes the car feel wet.
Teams are allowed 6 square metres of silicon solar cells or half the amount of the enormously expensive, but super-efficient, gallium arsenide cells. Nuna7 stretched the rules to put 5.9 square metres of silicon cells on the car, and a set of 3600 gallium arsenide cells inside, along with a solar concentrator to charge the battery when it is stationary – a design tweak that will prove crucial.
“Always people push boundaries. That’s what we’re about,” laughs event director Chris Selwood. “But that’s bloody clever.” He tells me the race organisers will have to think carefully about whether to allow that kind of thing next time. All the other favourites calculated that the best strategy would be to use silicon rather than gallium arsenide cells.
“They basically all design the same car. The only way they can win is minute gains,” says Keno Mario-Ghae, team manager for the University of Cambridge’s car, Resolution. “So we sat down and thought we have to beat them with an idea that’s inherently better and radically different.”
“The rear of Resolution is clear, with most of the solar array inside fitted to a system that tracks the sun”
Its car is definitely different. Opting for the smaller gallium cells let it design a tiny bullet-shaped car – different to the wide table-top designs of the others. What’s more, the rear of Resolution is transparent, with most of the solar array inside fitted to a system that tracks the sun.
“You lose about 5 per cent of the light through the canopy but you gain about 20 per cent by tracking the sun,” says Mario-Ghae. And with solar cells that can reach 35.4 per cent efficiency, the team had what they hoped would be a winner – until disaster struck.
Driving at 85 kph on a public road in Darwin the car rolled over, slid 50 metres on its side and down an embankment. “It behaved as it was modelled to in a crash. But the car is only designed for one crash.”
Unable to fix it, the team bowed out of the race the next day, the first victim of the brutal live laboratory.
Back inside the warehouse, computer engineer Dave Snowden is marching around with a clipboard between a new class of cars racing for the first time this year: the Cruiser Class. The cars in this group must be able to pass the requirements for being registered in their home country and carry more than one person. Unlike the Challenger class, they look a lot like real, albeit futuristic, cars.
Eight teams designed cruisers, including one from Eindhoven University of Technology, the Netherlands. Its four-seater family car is nicknamed “the bus” because of its square shape.
“You could drive to work in one of these things,” Snowden says. “The point of this class is to move closer to reality.”
Technology developed for the race in the past is now being put to use in more efficient solar roof panels, he says. Another example is the motors first used in the 1999 race – they’re being studied by the US Defense Advanced Research Projects Agency, which wants to put them in high-altitude UAVs that could in some instances replace satellites.
The Cruiser Class should assuage even the most neurotic person’s “range anxiety”, he says. “These cars carry as much battery energy as the bottom of the line Tesla, and drive more than 3000 kilometres.”
A few days later, on 6 October, the cars are flagged off from Darwin’s Parliament House. No revving engines. No smoke. Just a slow, efficient acceleration towards the other end of the continent.
Quickly the race leaders make their break, with Tokai Challenger and Nuna7 leading the pack the whole way. But Nuna7’s clever ploy with the solar concentrator means the battery can almost fully recharge during the mandatory stops. This means Nuna7 can continue through rain at the end of the race, while Tokai grinds to a brief halt. That interlude gives Delft University its fifth win, as it rolls over the finish line three hours ahead of Tokai, after four gruelling days on the road. They are already planning for the next race in 2015, says the team’s Leslie Nooteboom. “I’m hoping that we’ll be one step ahead again and come with new innovations that the other teams haven’t heard of at all yet.”
This article appeared in print under the headline “Cool run in the sun”
