World Solar Challenge: solar cells

Part of the rule changes for the 2017 World Solar Challenge was a change to allowable solar cell array areas. In the Challenger class, the limits became 4 m2 for silicon and 2.64 m2 for multijunction gallium arsenide (in the Cruiser class, 5 m2 and 3.3 m2, which is the same ratio). Depending on the efficiencies of the two technologies, we therefore get the following comparison:

There are two important caveats, however. First, the cars in the World Solar Challenge will be getting pretty hot. The performance of multijunction GaAs degrades less with heat than that of silicon, so this increases the benefit for GaAs beyond that shown in the chart. For example, if we assume a 24%/35% efficiency combination for Si/GaAs, with temperature coefficients of power of 0.4%/0.2%, then the red dots in the chart show a GaAs advantage above about 43°C.

Secondly, the use of a 2.64 m2 GaAs array allows teams to build a smaller (and hence more aerodynamic) car, as Nuon and Punch have done. This increases the benefit for GaAs even further. Consequently, the five favourites (Nuon, Twente, Tokai, Michigan, and Punch) are all capable of winning the race, but the teams that switched to GaAs might have made a good move.

Update – the graph below clarifies the temperature-dependence for the two technologies (assuming a 24%/35% efficiency combination for Si/GaAs, and temperature coefficients of power of 0.4%/0.2%):


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World Solar Challenge head to head: Australian Challengers

The World Solar Challenge is an exciting race to find the best solar car in the world. That makes for serious competition between countries. But there are also some interesting contests within countries. The most obvious is between Nuon (3) and Twente (21), who came first and second in the Challenger class last time.

Within Australia, Western Sydney (15, Unlimited 2.0, above) did very well in 2015, coming 10th in the Challenger class. Adelaide University (7, Lumen II, below) did not do quite so well back then (coming 21st), but have learned a lot about building solar cars from the experience. Potential competitors Clenergy Team Arrow (who came 8th in 2015) have switched to the Cruiser class, while newcomers ANU are still on their initial learning curve. Who will be Australia’s leading Challenger in 2017?


World Solar Challenge head to head: Japan

The World Solar Challenge is an exciting race to find the best solar car in the world. That makes for serious competition between countries. But there are also some interesting contests within countries. The most obvious is between Nuon (3) and Twente (21), who came first and second in the Challenger class last time.

Within Japan, Tokai University (10, Tokai Challenger, above) has a long tradition of excellence in the Challenger class, winning in 2009 and 2011, and coming at least 3rd since then (see chart at top). Their elegant new car is radically different from anything else in the competition, and looks fast.

Kogakuin University (88) raced in the Cruiser class in 2015, with an innovative design that almost won. This year, they have an equally innovative car in the Challenger class (Wing, below). Can Kogakuin take over the leading Challenger role in Japan? Can their car win against the equally streamlined Tokai vehicle? Or will Goko or Nagoya make a dramatic leap upwards from their 14th-place and 16th-place finishes in 2015? Only time will tell.


World Solar Challenge head to head: Sweden


Flag image by Tage Olsin

The World Solar Challenge is an exciting race to find the best solar car in the world. That makes for serious competition between countries. But there are also some interesting contests within countries. The most obvious is between Nuon (3) and Twente (21), who came first and second in the Challenger class last time.

Within Sweden, JU Solar Team (46, Solveig, above) did well in the Challenger class in 2015, coming 15th. But fellow Swedes MDH (22) have joined the competition, with a very interesting-looking car (MDH Solar Car, below). Which of the two will be the best Swedish team in 2017?


World Solar Challenge: doing media right

I’ve often pointed out that a solar car team is more like a startup company than anything else. A little like the early days of Google, really. The main product (the solar car, the search engine) is a gigantic money sink, and any cash coming in relates to something else (sponsorship, advertising). Overall success requires multiple skill sets working together. In particular, making sponsorship work requires an excellent media team (as well as a car fast enough to generate lots of good news). A number of teams have a track record of doing this well – Twente, for example, and Punch.


Deufol Technics packs Punch’s car and gear yesterday

An important example of sponsorship relates to transport. Here, the team acts as a kind of giant billboard for a tricky logistics problem handled well. This year, Punch provided a textbook example of superb media handling on this topic:

‘Voor mij is het de eerste keer dat ik voor zo een uitdaging sta,’ zegt logistiek manager Pieter Galle uit Leuven. ‘Het batterijpakket versturen is de grootste uitdaging voor het team. De batterijcellen die wij gebruiken zijn vaak niet toegelaten op vluchten. Om deze toch te kunnen versturen moeten er veel veiligheidsmaatregelen getroffen worden. Gelukkig heeft DHL Global Forwarding, in samenwerking met Deufol als verpakker van de goederen en batterijen alles tot in de puntjes kunnen regelen, zodat wij ons met het team volledig op het wereldkampioenschap konden concentreren.’” (Translation: “‘It’s the first time I’ve faced a challenge like this,’ says logistics manager Pieter Galle from Leuven. ‘Transporting the battery pack was the biggest challenge for the team. The batteries we use are often forbidden on flights. To be able to send them, many safety measures need to be taken. Fortunately, DHL Global Forwarding, in cooperation with Deufol our packer, has managed all the details, making it possible for us to focus our attention on the world championship.’”)

And Pieter Galle wasn’t just engaged in hyperbole there – transporting lithium battery packs really is tricky. In 2015, and again this year, there have been horror stories involving battery packs. I should also point out that some good photos really help the sponsorship game too, like these from Twente this year, or this one from Michigan, or this one from Nuon in 2015:


Nuon’s 2015 flightcase being loaded (photo: Jorrit Lousberg)

Another important sponsorship category relates to the team’s university. Here Western Sydney provides an excellent example, with their 2015 car being part of a major university rebranding exercise:


Western Sydney University’s 2015 car (photo: A. Dekker)

Michigan always does a great job of this during the American Solar Challenge. Their media team generates local news coverage everywhere they go. And the University of Michigan can afford to take the long view. If a 12-year-old boy or girl somewhere in rural America gets excited by the car, and decides to study engineering at Michigan one day, that’s a win. And not just for the university – if the sponsorship money keeps rolling in, the cars keep rolling on, and the fans can keep watching.


World Solar Challenge head to head: UK

The World Solar Challenge is an exciting race to find the best solar car in the world. That makes for serious competition between countries. But there are also some interesting contests within countries. The most obvious is between Nuon (3) and Twente (21), who came first and second in the Challenger class last time.

Within the UK, Cambridge University (12, above) has spent several years trying to make their series of teardrop-shaped cars succeed. The new rules may help with this. Meanwhile, Durham University (20) have improved their 2015 car (DUSC, below), and are ready to make it zoom. Who will be the fastest British Challenger this year?


World Solar Challenge head to head: USA Cruisers

The World Solar Challenge is an exciting race to find the best solar car in the world. That makes for serious competition between countries. But there are also some interesting contests within countries. The most obvious is between Nuon (3) and Twente (21), who came first and second in the Challenger class last time.

Within the Cruiser class, the University of Minnesota (94 this year, Eos II, above) has been the only US entry since 2013, and held its own both times (see chart at top for 2015 results). This year, however, Iowa State University (PrISUm) has entered the class as well (9, Penumbra, below). Both teams have very nice-looking cars. Which of the two will be the biggest challenge to Eindhoven and Bochum?