The two races can’t be compared directly, however. The Carrera Solar Atacama has a greater elevation range (sea level to 3415 m, compared to 296 m to 2585 m for this year’s ASC). The CSA is south–north, rather than east–west, and takes place around 20° closer to the equator, on average. More dramatically, however, this year’s ASC allowed 2 m2 supplementary solar panels during static charging (see image below). This made the ASC a faster race.
What I have done instead is compare the average speed for each segment against the approximate average climb rate, using the information provided in Punch’s wonderful infographics (see their social media: ). The corresponding datapoints for WSU were calculated in exactly the same way, and linear regression was applied for each team (see lines on the chart at the bottom of this post). The flatter line for Punch shows that they were less affected by the steep climbs. This is presumably due to their fancy new motor, which has a half-speed/double-torque mode. This Mitsuba motor was built by Nomura Co to Punch’s requirements.
Below is my personal world ranking of the top 21 Challenger-class solar car teams (revised with new data from an earlier list). It was produced entirely algorithmically by using linear regression on historical data to build mappings between WSC rankings and those of other races, and then applying those mappings to the results of four recent events (WSC 17, ASC 18, ESC 18, and Sasol 18). For example, this is the mapping between Sasol placings and WSC placings. It was used to map all Sasol 18 teams to expected WSC placings:
There is as yet insufficient data to rate Cruiser-class teams (apart from the actual WSC 17 results: 1 Eindhoven, 2 Bochum, 3 Arrow). But here is the table of Challengers:
Note that Cruiser teams like Eindhoven, Bochum, and Arrow are excluded from the list. The letter P marks cars that participated in WSC 17, but did not finish, and thus were not ranked at the time. It must also be said that Western Sydney, Eclipse, Esteban, and MIT should probably be ranked higher than they are here – the algorithm is not taking into account the dramatic improvement in ASC teams this year. However, good ESC and Sasol performance has bumped up Aachen, SER, Eco Solar Breizh, and South Africa’s new champion team, TUT.
This component of iESC counts for 20% of final points. On mean times, Cruisers were 2.1 seconds faster in the Chicane than Challengers. The revised chart below (click to zoom) reflects the scoring (which, it must be said, has Bochum bringing home the bacon so far). Times shown are the best out of qualifying, semi-final, and final times. See also this excellent video.
Tokai, who came 4th at WSC 2017, will race against Nuon at SASOL this year (photo: Anthony Dekker)
In further solar car racing news, preparations are continuing for the SASOL Solar Challenge in South Africa (September 22 to 30). Defending champions Nuon and Japanese team Tokai will attend this event, along with local teams, such as North-West University.
The Belgian car, Punch 2, which came 3rd at WSC 2017, will be challenging Twente at iESC this year (photo: Anthony Dekker)
Missouri’s new car, Independence, was unveiled on 18 April (picture credit)
Five teams are attending with cars that raced at WSC 2017 (including one Australian team), although these cars will require adjustment to satisfy ASC rules. Seven other teams had existing cars (including one Russian team). The remaining teams have been building new cars.
Poly Montreal’s new car, Esteban 9, was unveiled on 23 April (picture credit)
Recently unveiled cars for the ASC include Missouri S&T (18 April), Poly Montreal / Esteban (23 April), and Georgia Tech (24 April). There are 17 cars still to be unveiled.
Georgia Tech’s new car, SR-2, was unveiled on 24 April (picture credit)
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.
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%):
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.