World Solar Challenge 2019 Regulations

The 2019 Bridgestone World Solar Challenge begins in about 12 months, so this is a good opportunity to summarise changes in the regulations since 2017 (disclaimer: I may have missed something – don’t base your team strategy on what I say!).

General

There are clarifications for several regulations, including signage, licence plate visibility, braking configurations and occupant cell loads. All team members must be in Darwin and registered by 17:00 on October 10th (1.19.2) and, once scrutineering commences, all participating teams must base themselves, and their solar cars, at the Hidden Valley Motor Sports Complex (3.10.2).

Li-ion ‘18650’ cells are deemed to have a cell mass of 47.6 g, which means that at most 420 such cells are allowed for Challenger cars (2.5.4).


Li-ion ‘18650’ cells (photo: Lead holder)

Ground sheets

The use of ground sheets generated some controversy in 2017. They now may not be used at control stops at all (3.26.4) and their use is restricted at other times (3.18.2).

Cruisers

There are multiple changes to the Cruiser rules:

  • No more than four solar car seats may be occupied while driving (2.12.6).
  • Cruiser solar cars must be equipped with a specific kind of on-board ac charger (for use at Tennant Creek and Coober Pedy only). Usage will be metered (2.5.20, 4.4.6).
  • Cruisers must arrive at Tennant Creek (stage stop), Coober Pedy (stage stop), and Adelaide (finish) at specified times. Penalties are imposed for average speeds below about 74.5 km/h, with exclusion below about 60 km/h for the first stage and 72.2 km/h for the second (4.4.2, 4.4.5). This will be tough, given that the winning Cruiser in the American Solar Challenge averaged only 48.6 km/h!
  • Cruiser scores will be calculated by S = D / E × P × 0.99(l + d), where:
    • D is the number of person-km
    • E is the nominal external energy use in kWh (initial battery charge plus recharges)
    • P is the practicality score of the car
    • l is the total lateness at staging locations, in minutes
    • d is the number of demerit points received by the team

PrISUm’s 2017 Cruiser Penumbra (photo: Anthony Dekker)


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Solar Car World Rankings Revisited


Nuon at WSC 17 (photo: Anthony Dekker)

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:

Rank Previous Team WSC17 ASC18 ESC18 Sasol18
1 1 NL  Nuon Solar Team 1 1
2 ↑ 3 NL  Solar Team Twente 5 1
3 ↓ 2 US  University of Michigan 2 2
4 4 BE  Punch Powertrain Solar Team 3 6
5 5 JP  Tokai University 4 2
6 ↑ DE  Sonnenwagen Aachen P 3
7 ↓ 6 AU  Western Sydney Solar Team 6 1
8 ↑ 18 CH  Solar Energy Racers 3
9 ↓ 8 HU  Kecskemét College GAMF (Megalux) 4
10 ↓ 7 JP  Kogakuin University 7
11 ↓ 9 SE  JU Solar Team 8
12 ↓ 10 US  Stanford Solar Car Project 9
13 ↑ ZA  Tshwane University of Technology (TUT) 4
14 ↓ 11 CL  Antakari Solar Team 10
15 ↓ 13 CA  University of Toronto (Blue Sky) 11
16 ↓ 14 CA  ETS Quebec (Eclipse) 3
17 ↓ 15 JP  Nagoya Institute of Technology 12
18 ↓ 12 ZA  North West University P 5
19 ↑ FR  Eco Solar Breizh 7
20 ↓ 17 CA  Poly Montreal (Esteban) 4
21 ↓ 19 US  Massachusetts Institute of Technology 5

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.


Michigan at WSC 17 (photo: Anthony Dekker)


Solar Car World Rankings


Nuon at WSC 17 (photo: Anthony Dekker)

Here is my personal world ranking of the top twenty Challenger-class solar cars. 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 (SASOL 16, ESC 16, WSC 17, and ASC 18). There is as yet insufficient data to rate Cruiser-class teams (apart from the actual WSC 17 results: 1 Eindhoven, 2 Bochum, 3 Arrow).

Rank Team SASOL16 ESC16 WSC17 ASC18
1 NL  Nuon Solar Team 1 1
2 US  University of Michigan 2 2
3 NL  Solar Team Twente 1 5
4 BE  Punch Powertrain Solar Team 2 3
5 JP  Tokai University 2 4
6 AU  Western Sydney Solar Team 6 1
7 JP  Kogakuin University 7
8 HU  Kecskemét College GAMF (Megalux) 3
9 SE  JU Solar Team 8
10 US  Stanford Solar Car Project 9
11 CL  Antakari Solar Team 10
12 ZA  North West University 4 P
13 CA  University of Toronto (Blue Sky) 11
14 CA  ETS Quebec (Eclipse) 3
15 JP  Nagoya Institute of Technology 12
16 TR  Istanbul Technical University (ITU) 7 P
17 CA  Poly Montreal (Esteban) 4
18 CH  Solar Energy Racers 8
19 US  Massachusetts Institute of Technology 5
20 TR  Dokuz Eylül University (Solaris) 9

Note that, for ESC 16, the 3rd, 4th, and 5th place cars were all Bochum Cruisers and are therefore not listed here, while 6th was Onda Solare, which is now also a Cruiser team. The letter P marks cars that participated in WSC 17, but did not finish, and thus were not ranked. It must also be said that 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.


Michigan at WSC 17 (photo: Anthony Dekker)


ASC 40: Reflections

Well, I have blogged about the results of the American Solar Challenge, and produced this summary chart (click to zoom):

I would like to supplement that with some general reflections (as I did in 2016). First, let me complement the ASC organisers on the choice of route. It was beautiful, sunny, and challenging (but not too challenging). Brilliant planning!


The beautiful ASC route (picture credits: 1, 2, 3, 4, 5, 6, 7, 8)

Second, the FSGP/ASC combination worked well, as it always does. Teams inevitably arrive at the track with unfinished and untested cars (App State had never even turned their car on, I am told). The FSGP allows for testing of cars in a controlled environment, and provides some driver training before teams actually hit the road. The “supplemental solar collectors” worked well too, I thought. I was also pleased at the way that teams (especially the three Canadian teams) had improved since 2016.


Supplemental solar collectors for Poly Montreal (picture credit)

If one looks at my race chart at the top of this post, one can see that the Challenger class race was essentially decided on penalties. This has become true for the WSC as well. It seems that inherent limits are being approached. If experienced world-class teams each race a world-class car, and have no serious bad luck, then they will be very close in timing, and penalties will tip the balance. For that reason, I would like to see more transparency on penalties in all solar racing events.

I was a little disappointed by the GPS tracker for ASC this year. It was apparently known not to work (it was the same system that had failed in Nebraska in 2016), but people were constantly encouraged to follow teams with it anyway. It would almost have been better to have had no tracker at all, instead just encouraging teams to tweet their location regularly.

Cruiser Scoring

I though Cruiser scoring for ASC 2018 was less than ideal. A great strength of the ASC Challenger class is that even weak teams are sensibly ranked. This was not entirely true for the Cruisers. I would suggest the following Cruiser scoring process:

  • Divide person-miles (there’s no point using person-kilometres if everything else is in miles) by external energy input, as in existing scoring
  • Multiply by practicality, as in WSC 2019 scoring (for this purpose, it is a good thing that practicality scores are similar to each other)
  • Have a target time for Cruiser arrival (53 hours was good) but no low-speed time limit – instead, calculate a lateness ΔH (in hours) compared to the target
  • Convert missing distance to additional lateness as if it had been driven at a specified penalty speed, but with no person-mile credit (the ASC seems actually to have done something like this, with a penalty speed around 55 km/h)
  • Multiply the score by the exponential-decay term e−ΔH/F, where F is a time factor, measured in hours (thus giving a derivative at the target time of −1/F)
  • Scale all scores to a maximum of 1

The chart below applies this suggested process to the ASC 2018 Cruisers, for various choices of penalty speed and time factor F, drawing a small bar chart for each choice. Sensible choices (with a grey background) give each car a score of at least 0.001. It is interesting that all sensible choices rank the cars in the sequence Onda Solare, Minnesota, App State, and Waterloo.

Applied to the WSC 2015 finishers (with a target of 35 hours), penalty speed is obviously irrelevant. A time factor of F = 10 preserves the rankings awarded in that event, while higher time factors would have put Bochum in second place. In that regard, note that regulation 4.4.7 for WSC 2019 is equivalent to a very tough time factor of around 1.66 hours.

Of course, another option would be to return to the additive scoring systems of WSC 2013 and WSC 2015, and this has been suggested.

Strategy

I have posted about basic Challenger strategy. This race illustrated the fact that Cruiser strategy can be more complex. First, it is inherently multi-objective. Teams must carry passengers, drive fast, and conserve energy. Those three things are not entirely compatible.

Second, even more than in the Challenger class, the Cruiser class involves decision-making under uncertainty. In this event, teams could build up a points buffer early on (by running fully loaded without recharging, planning on speeding up later if needed). Alternatively, and more conservatively, teams could build up a time buffer early on (by running fast and recharging, in case something should go wrong down the track). Both Minnesota and Onda chose to do the former (and, as it happened, something did go wrong for Minnesota). In the Challenger class it is primarily weather uncertainty that requires similar choices (that was not a factor in this wonderfully sunny event).

Third, even more than in the Challenger class, psychological elements come into play. Onda were, I think, under some pressure not to recharge as a result of Minnesota not recharging. In hindsight, under the scoring system used, Onda could have increased their efficiency score by recharging once, as long as that recharge made them faster by at least 3 hours and 36 minutes (not that it mattered in the end, since all teams but Onda were given a zero efficiency score).

Together, factors such of these underscore the need to have a good operations analyst on the team, especially in the Cruiser class.

Media Coverage Summary


ASC 30: A Milestone

One of my eagle-eyed readers has pointed out an interesting milestone – Italian team Onda Solare has competed in solar car races on all six continents not covered in ice. I believe that they are the first team to do so.

  • North America: this event, the 2018 American Solar Challenge
  • South America: the Carrera Solar Atacama (coming 2nd in the Evolución class in 2016)
  • Europe: the European Solar Challenge (coming 6th in 2016) and the Albi Eco Race (winning in 2017)
  • Africa: the Moroccan Solar Race Challenge (wnning in 2016)
  • Asia: the Abu Dhabi Solar Challenge (coming 10th in 2015)
  • Australia: the World Solar Challenge (coming 10th in 2013)

Well done, Onda Solare!


ASC 18: Convoys


A typical convoy (click to zoom, photo of solar car by Jorrit Lousberg)

Solar cars in the American Solar Challenge each form part of a convoy – a typical convoy is shown above. The lead (front) escort vehicle must travel 500 metres or less ahead of the solar car, with headlights on and roof-mounted amber lights flashing.

The chase (rear) escort vehicle follows directly behind the solar car, also with roof-mounted amber lights flashing, and bearing a sign that says “CAUTION: SOLAR CAR CARAVAN AHEAD.” Both escort vehicles must carry safety equipment such as first aid kits and fire extinguishers. The chase (rear) escort vehicle typically also houses the team’s Decision-Making Unit (DMU), who plan the strategy for the race.


Left: Michigan’s lead and chase vehicles for the 2010 American Solar Challenge (credit). Right: interior of Nuon’s chase vehicle for the 2011 World Solar Challenge (credit).

The truck (or car with a trailer) rides further behind (at least 1 km). It carries equipment and provides the ability to transport the solar car in the event of a breakdown.


Left: Michigan’s semi-trailer driving down the Stuart Highway in the 2011 World Solar Challenge (photo: Marcin Szczepanski). Right: Calgary’s road crew truck from the 2005 North American Solar Car Challenge (photo: James Tworow).

The (optional) scout vehicle rides well ahead (at least 1 km), checking out road conditions and potential hazards. There may also be additional vehicles, like media cars, or a weather car watching for clouds an hour or so ahead of the solar car. All the cars in the convoy stay in touch using CB radio. It takes a whole team to race a solar car! Here are some team descriptions of their convoys:

This post has been adapted and updated from a previous one.


ASC 16: Tires


Tire on Bochum’s 2017 car (photo: Anthony Dekker)

In response to my Challenger strategy post, someone asked “what about tires?”

Yes, the rolling resistance of tires is a factor with solar cars. As tires rotate, the rubber in them flexes, and some energy gets lost this way. For a top Challenger class car, with good tires, about 85% of the solar energy is lost through aerodynamic drag, and about 15% through tires. That’s why my simple car model considered only aerodynamic drag.

The force required to overcome rolling resistance is g = 9.8 times the weight of the car times a tire-specific coefficient (ranging from 0.002 for an expensive solar car tire to 0.01 for a typical car tire). For a top Challenger class car, car and driver together will weigh around 250 kg. For a four-person Cruiser, it’s more like 800 kg – about triple. Bearing in mind that Cruisers often have tires with a higher coefficient of rolling resistance, this means that rolling resistance becomes quite significant with Cruisers. That is why Cruisers will sometimes turf out passengers to cut their energy use – even when running on a flat road. Climbing the mountains, overcoming gravity will come into play, and that uses up even more energy.


In ASC race news, I have updated my information page and teams list with news about day 1 of scrutineering.