Keeping cool, Swedish style

It’s a good question, say the battery suppliers to the Swedish institutions racing in this month’s Bridgestone World Solar Challenge, when asked how electric vehicles should be optimised to work in Australian conditions.  

Especially when Sweden is lucky to see maximum summer temperatures of about 25 degrees. 

In contrast, temperatures in Katherine, 350 kilometres south of Darwin, are forecast to hit 40°C on Sunday, the first day of the event. Cabin temperatures could be a further 20 degrees above that – posing a unique physiological challenge to their drivers. And many EV batteries operate best at temperatures below 45°C.

A solar car on a race track
JU Solar Team’s car ‘Axelight’ at Hidden Valley Raceway. Credit: Eclipse Solar team via Instagram

While every team – whether from Australia, America, Asia or Europe – will operate in the same conditions during this 3,000km endurance test, the Swedes are perhaps the most unaccustomed to the testing heat of Australia’s Top End.  

Sweden is disproportionately represented in the event – three of its universities have teams – and outside of Australia, Japan and the Netherlands, no other country has as many entries. Sweden, of course, has a proud heritage in automaking – Volvo and Saab both hail from the Scandinavian nation.  

That might explain some of the appeal of a challenge promoting both automotive development and renewable tech innovation.  

But it’s difficult to simulate 40-degree-plus conditions in the limited facilities afforded to university teams, so seeking ways to cool both driver and battery is essential.  

Halmstad University has landed on a brutal solution: taking its smooth bodywork, puncturing it and connecting a hose to the cabin to capture air as it speeds down the Stuart Highway next week.  

Its temperature simulations for its battery are, also, conservative. As a low-budget team competing in the event, it doesn’t have the luxury of building a $1 million+ vehicle like other competitors. It’s also a young team that failed to finish its first and only world race in 2019. To enhance its chances of finishing, it’s not looking to run its car into the ground, so to speak. 

Solar team crews inspect their car
Halmstad University inspects their car. Credit: Oskar Zetterström

“We did it,” says Alexander Kullenderv, the team’s technical manager of puncturing the hull with a hose, “because it’s safe.” 

“You get a lot of air [into the cabin], but we know it’s not efficient, we’d rather have a lot of cooling than to overheat the car. It’s about reliability because we want to make it to the finish line.” 

Cooling the driver and the battery will be crucial across the nine legs of the event’s Challenger class though. 

Johannes Söderberg worked on the aerodynamic shape of the Jönköping University entry. Making sure the car remains as ‘aero’ as possible while taking advantage of the air rushing past the vehicle as a passive cooling measure has been an important part of the JU team’s strategy. 

Its solution was to adapt the wheel casings – the shroudlike structures that house the car’s wheels. Whereas Halmstad punched vents into its external body to allow airflow, air whipped up from the road into JU’s wheel casings is ventilated inside the cabin via PVC pipes to the driver and battery. It’s an elegant solution that doesn’t compromise the aerodynamics of the car.

The wheelcovers of the ju team
The wheelcovers of the JU Solar car vent cooling air inside the cabin. Credit: Supplied, JU Solar Team

“For the ventilation system we have a nozzle from the wheel enclosure – around the whole wheel – and in the back enclosure, we have a pipe so the air gets tunnelled into the pipe and sprayed onto the driver,” says Söderberg.  

“But we have an active ventilation cooling system as well with a fan that could actually blow even more air on the driver.” 

The battery pack – mounted behind the driver’s cockpit, also has both passive and active ventilation. JU’s battery is also lithium-ion phosphate – which reaches lower heat levels than a typical lithium-ion counterpart. Though their battery is insulated, an overheating signal from the management unit will engage a fan system to bring the cell temperature down. 

JU is the more experienced of the three Swedish teams and hoping to push the frontrunning Dutch, Belgian and American teams during this year’s event, which sets off to Adelaide on Sunday.

For their compatriots, completing the 3000km Darwin-Adelaide journey without breaking down is a priority. 

Doing so will require careful battery management and monitoring on the road. But how to best prepare for Australia’s scorching inland conditions when you’re stuck in comparatively cool Sweden?

“We were a bit more focused on estimating what the temperatures could be like. We tried really hard to estimate what would be the thermal capacity of the pack,” says Avanish Raj, who manages the high voltage systems of Chalmers University’s car.  

Chalmers relied on modelling temperature changes to understand how their car’s battery would perform. If the ambient temperature jumps 10 degrees – how does it impact the optimum operating temperature for the battery pack?  

“It was a lot of modelling – rough modelling.” 

A solar car with its canopy raised is monitored by four men.
Raj, Styrefors Sparby and their electrical crewmates monitor their systems in the pitlane at Hidden Valley Raceway, Darwin. Credit: Felix Christensson

His collaborator on the Chalmers electrical system, Anton Styrefors Sparby, says the lack of data from previous events means this year’s team will be trailblazing for future challenges in both Australia and Europe.  

Whereas some competitors have dozens of solar challenges worth of experience, Swedish teams have comparatively little. Before the event, the best they can do is push the limits of the car’s drive cycle to determine possible operating thresholds for the car’s electrical system. 

“We’ve been running a more extreme kind of drive cycle to simulate the battery rise over ambient [temperature] and using the university facilities to do these kinds of somewhat simulated experiences,” Styrefors Sparby says. 

“However a lot of it is based on assumptions. I get the feeling that the Swedish teams tend to err on the side of expecting it to be hotter than it [might be].” 

But conditions might well be hotter than would usually be expected for the Top End, right through to the Adelaide finish. With both El Niño and a positive Indian Ocean Dipole affecting the continent, most Australians are expecting a hotter and drier spring and summer period. So a conservative approach to temperature management may improve the prospects of these Swedish outfits, even if their goal is to simply finish the race. 

At least for the drivers, and across all the teams, ice vests will be deployed to help to keep the human element of the car cooler, for longer.  

And as Styrefors Sparby says, at least the Swedish drivers have tried to acclimatise to the hot and humid temperatures by sitting in a sauna.

That’s how you train to keep cool, Swedish style. 

The Bridgestone World Solar Challenge gets underway in Darwin on Sunday 22 October.

Subscribe to ultramarine from riaus

Cosmos is a Media Partner of the 2023 Bridgestone World Solar Challenge Follow our coverage.

Please login to favourite this article.