World Solar Challenge: about the Cruisers

To illustrate the World Solar Challenge Cruiser-class scoring for 2017, here is the calculation for Kogakuin’s 2015 car (above). Disclaimer: this is, of course, my personal interpretation of the regulations.

Notice that Cruisers are not in a race this year – any arrival time during the 11:00 to 14:00 time window on Friday is OK.

Arrival time

Friday 11:35.
Inside window? YES

Energy efficiency

Battery capacity, Q = 14.855 kWh
Number of recharges, n = 1 (at Alice Springs)
External energy use, U = (n + 1) Q = 29.71
Person-km, C = 3022
Energy efficiency, E = C / U = 101.7
Highest energy efficiency, E* = 203.6 (Eindhoven)
Relative energy efficiency, E / E* = 0.4996


Practicality P = 51.75
Highest practicality, P* = 84.5 (Eindhoven)
Relative practicality, P / P* = 0.6124

Total Score

Total score, S = 80 E / E* + 20 P / P* = 39.97 + 12.25 = 52.22

This is a massively lower score for Kogakuin than was actually awarded in 2015. This year, the World Solar Challenge Cruiser Class is all about energy-efficiency, carrying passengers, and practicality. Expect to see the four-seat and five-seat Cruisers (like the Polish car below) running with every seat occupied.


18 thoughts on “World Solar Challenge: about the Cruisers

  1. Yes, I’m afraid that the Cruiser class has changed from a competition to an exhibition.

    Ever since the class began the organizers have placed an emphasis on their belief that big cars are more practical and this time they’ve simply extended that emphasis. In fact if battery sizes are similar and the number of charges is the same then a car that carries 5 people all the way cannot be beaten by a car that carries fewer people.

    It’s a shame that the Columbian team didn’t make it this time, they would have really made a mockery of the event – ie the best car is a bus.

    • Well, not an exhibition so much as a people-per-kwh competition.

      Of course, battery sizes are not similar and the number of charges is not the same, so there is some strategy in the extra people vs minimum charge tradeoff. That said, I think you are right about a car carrying 5 people.

      In fairness to the WSC organisers, I think Cruiser panels did need to get just a tiny bit smaller, since they were driving some odd-looking designs. Doing that would make almost all cars too slow, so more recharges and/or bigger batteries were needed. And that left efficiency as the only real ground for competition.

      It would have been interesting to toss out the 2-person rule, however. Could a Challenger-like entry top the efficiency score by carrying 1 person with a small battery and no recharges?

      • I’ve been pressing for 1 seat cruisers since 2013 but it doesn’t appear to be a popular idea. Given that about 75% of journeys are made with one person in a car it’s always seemed to me that a single seat car is the most practical. Of Course some distinction would need to be made between a Challenger like Nuon’s and a single seat Cruiser.

        Re the 5 seat cruiser – realistically, based on previous outings, the 5 seat cars are either going to be top on practicality or close to it so they will have scores of app18 to 20 for that aspect. A decent two seater can probably score around the same so, as we said, the race will be decided by person kilometres.

        If we imagine that one of the bigger cars carries 5 people all the way for a total of 15100km and uses 48kw/h( a good common denominator between 12 and 16kw/h batteries) that would equal 314km/kwh.
        For a two seat car to beat that they would have to use less than 19.2kwh so would have to do the whole journey without re-charging.

  2. Pingback: World Solar Challenge: about the Cruisers 2 | Scientific Gems

  3. Thank you for your really nice introduction in cruiser class scoring.
    In my opinion it is only logical that efficiency is the key to win the race, since the race is limited by the speed limit anyway. However, I’m also disappointed that the person-km play such a dominant role in the calculation of the score. The idea of a solar car race should always be: no battery charges from the grid. Nevertheless I don’t understand why they gave um the limitation of the battery for cruiser class. The rules should always be in line with the idea of a SOLAR car race. Wouldn’t it be more interesting to have a tight size regulation (of car & battery) and a bigger solar array or even extra loading panels for the after race hours? There are a lot more possibilities and I hope they will not tend to make the WSC to an exhibition but to a race of ideas. For this years competition it would be a lot more exciting, if they would publish each cars’ battery capacity and weight before the start.

    • Thank you for your comment. A few friends have said similar things. Some of the car weights we know, and MostDece will probably summarise those.

    • As we approach the third challenge with another new scoring idea it is clear that the organizers do not know how to deal with this class. All of the things that you suggest have been used in the two previous challenges and discarded.

      In fairness to the organizers though, how can you have a competition of ideals.
      The winning cars from Eindhoven are certainly not my idea of what is needed but they might well be yours. Neither of us is right or wrong!

      I’m not sure that it is valid to mention the speed limits when the target speed for the event is 40-43mph(66-70kph). This is the real mistake in my opinion if the idea is to prove the validity of solar power.

      Notwithstanding all of the above it is important to remember that whatever the results or whatever our thoughts the main thing is the challenge and the brilliance of all of the competitors. All in all, given that the challenge itself is so difficult, perhaps the event should be an exhibition in future rather than a competition.

      • One problem has been that Bochum more or less defined the Cruiser class, but only a handful of teams can build cars in that league. Eindhoven’s influence has pushed the class towards people-movers, and personally I think the class may have gone a little too far in that direction.

      • It would be interesting to know whether Eindhoven designed their cars to win the challenge or because that is how they think cars should be.
        Bochum never made a car to win the challenge (until now maybe) and it appears that other teams are more concerned with making their ideal vehicle than winning a competition.
        That’s why I suggested that the competition element is futile and perhaps it should just be a challenge and an exhibition.
        Obviously there could still be prizes but for design and innovation.

      • Going by what they said with Stella, Eindhoven designed their cars to be viable family cars rather than to win (although they did win).

      • I’m inclined to believe that, and that they were fortunate that their design best met the criteria of the competition and looks likely to do so again.
        I’m also inclined to believe that, with a few exceptions(Kogakuin and Tehran last time), most teams will favour their ideals over the demands of the competition.
        So if this speculation is anywhere near the truth, that the “best” team achieved their position, in part, by good fortune and that other teams are not trying to “win”, then what is the point of having a competition element?

  4. @Nigel STE (Solar Team Eindhoven) really had a internal battle during the brainstorming sessions (almost 50/50) prior to the design sessions. But Stella Lux came out as “we want to build a human carier”.
    Unable to find the video at this time, but is is somewhere online.

    Since the WSC has set a time frame for finishing and average speed looks to be going down (can’t calculate that: -solar cells + longer boat tale) i’m also disapointed.
    I’m more looking for a Solar car (not a single seater) which has the practicality of a modern road car.
    So i.m looking for:
    – seating position to the road and surroundings
    – real seats (been in Stella Lux, and being 50+, i can’t imagine my back and arms wouldn’t be sore after 150-200km)
    – airconditioning (heared that they where working on that)
    – reallife average speed
    and so on, and so on

    • The 2015 Bochum car had nice comfy seats. As to speed, several of the 2015 Cruisers seemed to be designed either as city cars (where average speed is lower anyway), or for fewer than 8 hours driving per day (giving more charging, and therefore allowing higher speeds).

    • Found it: starts at 3:30 and going on till 5.23.
      You can even see a sketchup/mockup of a 2 seater challenger
      It is in Dutch, nothing found with subtitles

    • Ollie
      Thanks for the reply. As I said, we will all have different ideas about what sort of car we want.
      I have always thought that real life speeds are important so I agree that it’s a shame that it is a time trial this time.
      It seems that the real problem is that the teams are asked to design cars that are practical for everyday use but the cars are then tested by a challenge that is far from everyday.
      So we will find out that next time we want to carry 5 people for 3000km across a continent the most efficient car to do it would (probably) be a Stella type car. Unfortunately any team that has not designed a car to fulfil that task will not win the challenge but how do you compare apples and oranges?

      I repeat that none of this debate should detract from what teams have done, indeed it can only be wholly admirable that they are determined to make their own idea of the “best” car.

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