The Cambridge University Eco Racing team (CUER) has unveiled designs for its latest solar powered racing car. Codenamed ‘Daphne’, the prototype is being developed to take part – and with any luck win – the 2013 World Solar Challenge, an arduous 3,000km road race from north to south Australia in cars powered by the sun.
The race attracts all comers – from big-budget international teams to glorified hobbyists. CUER has competed in the bi-annual race twice – in 2009 and 2011 – both times finishing in relatively lowly positions.
This year, spurred on by dreams of that elusive first victory, the team decided to go back to the drawing board, developing a new two-wheeled design they were convinced was going to win next year’s race. But in June disaster struck when the rules governing the designs of competing cars were changed, at a stroke eliminating 36 of 37 teams’ vehicles, CUER’s included.
Since then the team has been feverishly working on a new design that fulfils all the new race rules but still gives them what they are confident will be the winning edge. With rivals on multi-million dollar budgets (compared to Cambridge's £500,000) the team realised they couldn’t hope to win by emulating these other teams' designs. “The only thing we can do is be smarter and build something technologically better, that works under a different set of constraints and assumptions about how to win race,” says team engineer Oliver Armitage.
The design the team have come up with for Daphne, unveiled at the end of last week, is certainly striking to look at. It is only at a concept and development stage, but models and visualisations of the prototype show a sleek, tear drop-shaped design with a rack of angled PV modules mounted under a clear, tapering canopy.
The key to the design is its shape, which is as aerodynamic as is achievable within the parameters of the new rules. The team’s boffins have also developed a computer code to predict how any shape would perform if smothered in solar panels. This allowed them to calculate the most efficient way of mounting the PV panels on the most aerodynamic shape possible.
Beyond the shape of the car, another crucial element is, of course, the PV units themselves. Whereas CUER’s old car Endurance used silicon cells arranged on a flat ‘table-top’ body, this time, with a bigger budget, the team has opted for triple junction gallium arsenide modules, as used on spacecraft.
“The cost of getting anything up in to space is dependent on how much it weighs, so it’s crucial to have the most efficient cells possible,” says CUER’s chief engineer Peter Mildon.
Mildon explains that by absorbing a broader spectrum of the sun’s light, the Azur gallium arsenide cells achieve about a 35% efficiency compared to the 22% rates of their silicon counterparts. The cells are coated with a “micro-pyramid” encapsulant, which minimises the solar energy lost through reflection. A further innovation designed into Daphne’s solar ‘engine’ is a mechanical tracking system that allows the car’s driver to adjust the position of the cells throughout the day and capture the sun’s full rays, increasing the unit’s efficiency by about 20%.
Although collectively the amount of power this solar unit will produce is only minimal when compared, say, to the requirements of a household appliance, the car should be able to hit top speeds of 130km/h, Australia's speed limit. The team hopes it will be able to average 92km/h, although they have calculated an 82km/h average should be sufficient to win the race. “Daphne will be 98% efficient, allowing us to exceed speeds of 82km/h, all on the equivalent power of a hair dryer,” says CUER team manager Keno Mario-Ghae.
Solar Power Portal hopes that the new car, once finished, will perform rather better than its predecessor Endurance did on the day of Daphne’s launch. Although now in retirement, the old race vehicle was wheeled out to give the gathered journalists a chance to experience the simple pleasures of solar powered travel.
It was a bright and sunny day in Cambridge, but the team member with the right knowledge of how to wire up its PV modules without liveing the whole car was not to hand, meaning it had to run on the limited power stored in its batteries. Aware the juice might not last long, SPP was the first of press pack to have go, somehow squeezing into the cramped bucket seat that serves as the Endurance cockpit.
After fiddling various with switches, alarmingly labelled “Ready”, “Steady” and “Go”, and with a bit of a shove from CUER team members, we were off – not quite at 92kmh, but maybe close to nine. A few startled pedestrians and cyclists were forced to scurry out of the path of the oncoming contraption, bemused looks on their faces. A concern for SPP was whether the car might veer off and end up in the River Cam.
Despite the sluggish performance of Endurance, the CUER team are confident their new design will give them the race winning formula. Their sponsors – a local syndicate of high net worth investors – are also apparently confident too, granting their support only on the basis that they were backing the ‘winning design’.
But while the team members are inspired and motivated by their design and clearly posses the brains to pull it off, there will be any number of unpredictable factors – weather, bush fires, errant kangaroos – beyond their control. What happens if some disaster strikes and the team fail to fulfil their dream?
At the very least the team hopes that some of the technology developed for Daphne could have some future application in energy efficient cars. “When petrol starts to become even more expensive, you will start to see why the World Solar Challenge, and why things like having suspension that’s 10 times lighter because it’s made of a composite rather than springs, are important,” says Mario-Ghae.
But ultimately the team are realistic that despite all their preparations something could go wrong on the day and that if it does it won’t be the end of the world. “We are a bunch of students,” says Mildon. “We could mess this up. If we come in six minutes behind the winner, we’ll have performed well.”
Clearly, though, they would rather win.