SunSPEC4 is a solar car engineered, manufactured and raced in Australia by a bunch of Singapore Polytechnic students.
THE World Solar Challenge (WSC) is a biennial race for electric cars with solar power. It’s more of a road rally, though, because the challenge starts in Darwin, Australia and ends in the southern city of Adelaide – a total distance of 3000km in six days.
Competing cars travel on public roads and, hence, are bound by Australian highway code and traffic regulations. There are also strict rules on the technical specifications/limitations of the participating cars.
Singapore Polytechnic (SP) has been constructing its very own solar racecars for the event since 1999. Up till 2013, the WSC cars were all single-seaters.
Last year’s challenger created by SP was a totally new, ground-up redesign bearing no resemblance to any previous version.
Called SunSPEC4, the SP solar car was to compete in a different, more advanced category from its predecessors – the Cruiser Class of the World Solar Challenge. To qualify, the contender must prove to be a practical passenger vehicle that’s usable in urban conditions, and have room for a couple of occupants plus some luggage.
The competitors come from universities all over the world, including Cambridge University and the Massachusetts Institute of Technology, and Singapore’s 2015 entry was the only one from a polytechnic.
The two-seater SunSPEC4 (whose name is short for “Singapore Polytechnic Engineering Cluster, version 4”) is a full carbon-fibre-bodied four-wheeler with electric motors driving the rear wheels. The main objective of the new configuration is to optimise efficiency without compromising performance. To this end, SunSPEC4 is 100 percent more powerful than its 2013 predecessor.
Each rear wheel is driven by a built-in 2kW brushless DC motor. There is no issue of transmission losses since the drive is direct. The 16- inch wheels themselves are ultra-lightweight, with aluminium hubs, and made from carbon fibre composites.
These wheels are shod with Bridgestone Ecopia tyres manufactured specifically for solar racecars. They are 95mm wide, with an aspect ratio of 80. Once pressurised to nearly 5 bar, these tyres roll with less resistance than anything you could ever find at any tyre shop in Singapore.
Suspending each wheel is a double-wishbone system, with all the A-arms and relevant component parts machined from aluminium. The dampers are the adjustable telescopic type.
The suspension design was undertaken by the SP students engaged in the project. They even did the machining work themselves.
As you can guess, SunSPEC4’s powertrain consists of plenty of wiring, electrical switchgear and a battery pack. All of it looks like the innards of a regular electric vehicle.
What is unusual is the roof, which is actually a solar panel, specially constructed in a curved form so that it maintains the aerodynamics of the car’s body.
Supplementing the roof panel is a smaller set of solar cells on the front of the vehicle, just below the windscreen. With clear skies and bright sunlight, the solar cells can produce 1.1kW of power, which is sufficient to keep SunSPEC4 cruising at 70km/h on flat ground. While it may seem as simple as wiring up the cells to the motors, the reality is far more complex.
A control system needs to manage the energy flow so that the lithium-ion storage cells can continue to be charged by the sun, whether the car is stationary or on the move. The control system also needs to provide the 122 volts to the motors when called to do so.
Hence, the students had to develop their own power management system, one that would optimise performance and energy consumption.
The 3000km race allows grid charging only once at the halfway point, so how the energy is consumed and replenished at all other times is a highly critical factor.
The long and arduous road to building the solar car took a nasty turn when a fire totally destroyed a 95-percentcomplete SunSPEC4. Eight months of effort literally went up in smoke.
What happened after that is an incredible tale of perseverance, determination and pure spirit.
With barely eight weeks to the race, the team members, led by Steven Chew, senior lecturer in SP’s School of Electrical and Electronic Engineering, embarked on what seemed like an impossible task: building another SunSPEC4 from scratch, in time to appear at the start line Down Under.
The new solar car was ready in four weeks, and with Singapore Power sponsoring the airfreight, SunSPEC4 and its team made it to Darwin!
The race itself was not without incident, although there were just two main issues that caused problems.
One was a persistent wheel misalignment that was fixed more than once, while the other was a malfunctioning battery contactor that would cut off electrical supply.
In the end, SunSPEC4 finished the solar race, but was only driven over half the total distance.
Due to technical problems, it was carried on a trailer when the need arose over the rest of the race distance. SunSPEC4 is Singapore Polytechnic’s first Cruiser Class car for the WSC. It was put together by the students, with technical supervision and advice from their school lecturer and team manager, Chew.
“All in all, it was a very intense and extremely challenging project – designing and building a practical, family-oriented solar car that is able to travel 3000km with only one grid charging in between,” he said.
Chew added: “We may not have managed it this time, as it was our first two-seater solar EV, and the design and handling are very different from that of a Challenger-class vehicle. However, we hope to come back with a much better car for the 2017 WSC.”
Hopefully, the polytechnic’s next solar car will be able to undergo wind-tunnel tests, at least in scale model form.
More importantly, it should be given a special permit for cordoned-off road tests in Singapore that would enable the team to evaluate the car at road speeds, instead of being restricted to Singapore Polytechnic’s 400m running track.
“With clear skies and bright sunlight, the solar cells are sufficient to keep sunspec4 cruising at 70km/h on flat ground.”
