World Solar Challenge: Challenger dimensions

MostDece has written a superb blog post on the WSC challengers. Based on that, I’ve updated my previous post on dimensions. The infographic above (click to zoom) shows the reported length and width of 16 WSC cars (Challenger class only, this time). The widest car (at 2.05 m) is the South African car from NWU (below), but of course that includes the outrigger wheels. The narrowest is the long narrow bullet car from Michigan. There are also short zippy little cars from Nuon, Principia, and Punch.

Update: The chart below clusters cars with similar length/width combinations. NWU is a visible outlier. Below NWU, we have big cars (ITU, MDH, Adelaide, Aaachen, JU – over 1.6 m wide and at least 4 m long), short catamarans (Nuon, Principia, Punch – 1.55 to 1.6 m wide and at most 3.5 m long), narrow catamarans (Nagoya, Stanford, Twente, WSU – 1.38 to 1.5 m wide and at least 4 m long), and monohulls (Tokai, Kogakuin, Michigan – at most 1.2 m wide and over 4.9 m long):

Update: Unfortunately, the two charts above reflect incorrect information from the Stanford team. The Stanford car is actually substantially wider.


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%):

World Solar Challenge: the favourites

I will need to re-do this at some point, but the poster below shows the favourites (based purely on 2015 performance) for the 2017 World Solar Challenge (click to zoom). There is a very interesting mix of designs this year! For more details, see my annotated list of teams.

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 car sizes

The infographic above (click to zoom) shows the reported length and width of eight World Solar Challenge cars. The widest car (at 1.8 m) is that of the Swedish MDH Solar Team (although this car has large bites taken out of each side). The two family Cruisers from Eindhoven and Lodz (dashed lines) are also quite wide, and take full advantage of the maximum allowed length of 5 m.

The Belgian Punch Powertrain Solar Team has produced a very short zippy Challenger class car (illustrated), and Nuon’s car (not shown) seems of a similar size. In contrast, Michigan has a long narrow bullet car, powered by GaAs solar cells. Twente, using Si cells, has a substantially longer car than Punch, but a narrower one. It will be very interesting to see how these differences play out in the race, come October.

June 21 in Solar Cars

June 21 was an eventful day in solar-car racing. The Belgian team revealed their zippy new car:

Nuon Solar Team set a world record, clocking up 882 km in a 12-hour track session.

Eindhoven have also unveiled their new car, and it’s gorgeous! It lacks the “tunnel” of their previous vehicle, and this allows them to seat a family of five:

More World Solar Challenge progress

The open road is calling teams for the 2017 World Solar Challenge, and JU Solar Team (battery box ready for shipping), Lodz Solar Team (battery box), Nuon Solar Team (world record attempt), Solar Team BE (unveiling Punch 2), and Singapore (dashboard design) are hearing that call.

In other news, Solar Team GB have pulled out of the race, and Eindhoven are due to unveil their car in a few hours.