The American Solar Challenge Cruiser class is a contest for multi-person solar vehicles, powered by 5 square metres of silicon solar cells (or 3.3 m2 of multi-junction cells), with the option of recharging from the grid. The contest is not actually a race – cars must get to the finish line within 53 hours elapsed time (not including the 45 min checkpoint times, which means maintaining an average speed of 33.3 mph or 53.5 kph), carrying as many people as possible, and drawing as little power from the grid as possible. Scoring is roughly as per WSC 2017. It is always difficult to explain race-type events that are not actually about “first over the line,” which is why I developed this “cactus diagram” last year:
For each car, the first coloured bar indicates the number of person-kilometres, which is basically just a weighted average of the number of people in the car. This is expressed as a percentage of the best value. You can see that Eindhoven won here, with an average of a little over 3 people in the car.
The second coloured bar indicates external energy use, which is the size of the battery multiplied by the number of times it was charged from the grid (counting the pre-race charge). External energy use is bad, so this bar is drawn pointing downwards. It is expressed as a percentage of the worst value, and you can see that Eindhoven won here again, because of its small battery.
The overall energy efficiency score (the third coloured bar) is the first bar divided by the second bar, scaled to a maximum of 80%. We then add on the practicality score (grey bar), scaled to a maximum of 20%. This gave Eindhoven an overall score of 100% last year, which was a convincing win.
In a recent rule revision (13.3.A), ASC Cruiser scoring this year will be modified with a time penalty on the energy efficiency score, similar to next year’s WSC rules. Cruisers that do not complete the entire course will receive an energy efficiency score of zero (13.3.B).
The diagram below shows an alternate view of Cruiser scoring (scaled differently, and ignoring practicality):
Here cars are scored based on the assumption that all cars run fully loaded (which doesn’t usually happen) and that they recharge from the grid at every opportunity (which generally does). Coloured triangles show values for the top WSC 2017 Cruisers, and black triangles show values for Cruisers at ASC this year (although the values for PrISUm and Minnesota may be out of date). On these assumptions, the score is just the number of seats in the car divided by the battery capacity, and is shown as coloured numbers.
What generally happens, of course, is that because of clouds, or mountains, or other factors, some Cruisers can’t keep up with the required pace. This means that they have to turf out passengers (rest assured, this does not happen while the vehicle is in motion). That is reflected on the chart by the triangles shifting downwards. The dashed lines show this happening for WSC 2017. Notice that Eindhoven could drop two people and still retain a huge lead in the scores, while Bochum could drop two people and stay just ahead of Team Arrow.
For ASC this year, PrISUm appears to have the advantage, if it can climb those mountains with four people in the car. The Cruiser class is all about people-carrying ability. On the flat, that means aerodynamics. In the mountains, motor power and regenerative braking ability will come into play. It promises to be an exciting contest!
See also my annotated ASC teams list and information page here.