The aCentauri Solar Racing team from ETH Zurich recently competed in a race for solar-powered cars. Gebrüder Weiss was its main partner and sponsor for the venture. Frank Haas talked to Alexandr Ebnöther and Gian-Leo Willi about their special solar vehicle and what some of their findings mean for the future of mobility.

You’re studying at ETH Zurich and took part in the Bridgestone World Solar Challenge – a race covering 3,000 kilometers (1,864 miles) from Darwin to Adelaide through the Australian Outback. You finished in twelfth place out of a total of 32 teams. Are you pleased with the result?
Alexandr Ebnöther: Yes, we are. Our aim was just to complete the race, so there was a huge sense of relief and excitement at the finish. However, we also know there’s still room for improvement, and we can’t wait to get our “race heads” on again.

The race wasn’t so much a sporting event as a research project for you. What did you learn from the expedition across Australia?
Gian-Leo Willi: For us it’s all about efficiency and looking for ways to squeeze out extra gains. We want to find out how to take mobility to the next stage and make it more sustainable, which can also include improving aerodynamics, for example.

So to win this sort of race you’re better off working on the aerodynamics of the car than the motor’s performance?
Ebnöther: Yes. Efficiency will also make cars in general fit for the future.

Now, though, you’re working on a custom-built miniature car. Can your findings here also be applied to normal cars?
Ebnöther: You wouldn’t go shopping in our car, of course; it would be far too uncomfortable. It’s more about the little things we try out – how to save another watt or so here and there. Or how you can also charge a car while it’s on the move and not just at a specific location. These little details ultimately make a big difference. The mobility transformation is a process made up of many small steps.

“Efficiency will also make cars in general fit for the future”

Your car weighs just 188 kilograms, i.e., far less than a standard passenger car. If we’re trying to make cars universally more efficient, don’t they all need to be much lighter?
Willi: That would require special production processes and a change in design philosophy – less powerful engines and motors, better aerodynamics, efficient drivetrains and so on. Our solar car is made of a material used in space rockets, which can also be found in motor racing cars and other high-tech applications. In reality, we’re not just looking to test out technologies, but materials too.

What materials did you use here?
Ebnöther: The main structures are mostly made from carbon fiber. This material combines low weight with high strength – it’s stronger than steel or aluminum, for example. Carbon-fiber body parts are far lighter than equivalent components made of aluminum or steel. But I think our vehicle is still too heavy for a solar car.

Why isn’t carbon fiber used in conventional cars?
Ebnöther: It is already used to some extent, however carbon parts are more complicated to manufacture. A lot of human input is required and that is both time-consuming and expensive. Aluminum injection molding, on the other hand, is a process that can be automated far more easily.
Willi: To be honest, the manufacture of carbon-fiber parts isn’t particularly sustainable either. The upshot is that, at the moment, carbon is mainly used when every last gram counts. However, tests are also being conducted with natural fibers, which could potentially replace carbon fibers.

What sort of natural fibers are we talking about?
Ebnöther: They’re usually flax fibers, and the manufacturing method and the way they work are exactly the same as for carbon fibers. The fibers are impregnated in epoxy resin, which holds them in position, while the fibers themselves absorb the forces at play. So flax fibers are very similar to carbon fibers, yet they are more energy efficient to produce and come from renewable raw materials. On the other hand, the material is a little more flexible; it expands more. This means you need more natural fibers than carbon fibers to achieve the same level of strength.

The materials list for your car also includes paint. Why is that important?
Ebnöther: The car has to look good – that matters not least for marketing. But first and foremost, paint plays an important part in the car’s aerodynamics, as the smoother surface created by it reduces air resistance. There are even so-called sharkskin paint finishes that are inspired by nature and contain nanoparticles designed to give the surface a special grooved structure for lowering aerodynamic drag. This sort of paint can be applied to an aircraft’s fuselage, for example, or the hold of a ship to increase efficiency. For our solar car, though, we used a standard type of paint that could also be applied to a normal car.

So an unpainted car would use more fuel?
Ebnöther: It depends on the specific use. In Formula 1, many of the teams don’t use any paint at all to make the car lighter. And that makes sense, because an F1 car needs to accelerate and brake extremely quickly, so weight is an prominent factor here. Our car, on the other hand, accelerates far more slowly. We performed a sensitivity analysis to find out which factor – weight or aerodynamics – is more influential in our case. The aerodynamics turned out to be much more important, so we used paint.

How much does the paintwork typically weigh?
Ebnöther: Of course, this depends on the vehicle and the paint used. The paint on our car weighs around ten kilograms.

Besides carbon fiber and paint, what other special or completely normal materials did you use?
Ebnöther: A solar car of this type has some areas of specialization, such as the driver’s cockpit. This was made of fiberglass to allow radio waves for communications to pass through.

And who needs to do the communicating?
Ebnöther: We drive in convoy. There’s a lead car ahead of the solar car, and then there’s a chase car following it. The chase car is the brains, as it were; that’s where the whole strategy comes from. The solar car itself is brimming with sensors for measuring things like solar radiation. So that we’re able to continuously adapt our strategy, we have to know how much energy the car’s receiving, what the status of the battery is, etc., at any given moment. This information must be constantly communicated and we need radio contact to be able to tell the driver, ‘Hey, drive at 80 kilometers an hour instead of 75 (50 miles per hour instead of 47) because we’ve got more sun’ or even, ‘Watch out, there’s a pothole coming up!’. It’s a constant back and forth.

Speaking of energy, the solar panels on your car measure a total of four square meters (43 square feet) in size. Is that enough to power a normal electric motor?
Willi: Our electric motor was purpose designed for this race. In the end, we were driving on an average of 1,000 watts – that’s less than a standard toaster needs. So we can drive at 80 kilometers per hour (50 miles per hour) on the power of a toaster! We should point out, though, that the solar cells supplied by our sponsors are very efficient. Not surprisingly, solar cell manufacturers are constantly striving to improve the efficiency of their product. It’s a really fascinating field of research.

As things stand, a regular car can’t yet be recharged using just solar panels, can it?
Ebnöther: No. There are, of course, solar cells with an extremely high level of efficiency. Gallium arsenide cells, for example, are resistant to radiation and their uses include generating energy for satellites in space. But even with such advanced materials, the limited surface area of a car would be insufficient to supply the amount of energy needed for the high power consumption involved. Having said that, research is also being carried out on transparent solar cells for car windows.

“There’s no one solution for everything – it’s always a combination of various factors”

The tires are another interesting point. Did you use special tires?
Ebnöther: Yes, we did. We’re talking here about the Bridgestone World Solar Challenge, so our tires were supplied by Bridgestone. They were made from 70 percent recycled material but still had very low rolling resistance, which is crucial for efficiency, of course.

Moving on from the individual parts, let’s finish by coming back to the big picture: how should we go about making mobility sustainable?
Willi: It’s difficult to single out one specific thing. The question of where savings can be made is one that affects not just vehicles and transport, but society as a whole. There’s no one solution for everything – it’s always a combination of various factors. Needless to say, this is an interdisciplinary field, where everyone involved has to do their bit. For our part, we work on building cars to be as efficient as possible. But at the end of the day, those cars also have to be used wisely by people.

What’s next for your solar car?
Ebnöther: It’s going racing again, this time in the iLumen European Solar Challenge. This is a 24-hour endurance event for solar cars that takes place every two years at the Circuit Zolder former F1 track in Belgium. So that’s our next big date in the racing diary.