Monday, June 6, 2016

2017 World Solar Challenge Regulations Posted!

Regulations for the 2017 World Solar Challenge have been released; check them out!

Here's an overview of what's changed:

Major Changes:

WSC has done some (much needed) reorganization of the regs - in my opinion, they're much easier to read than the 2015 regs. Thanks for including a table of contents!

Car Size (2.2): Bigger! 

Reg 2.2.1 states that the car, while driving, must fit in a rectangular prism 5m long, 2.2m wide, and 1.6m high. This is significantly up in width from previous years (1.8m wide since at least 2001), and also reverses the 2013-2015 shrink in length (down to 4.5m long).

Also in 2015, cars had to fit within the bounding box at any time while driving or charging, but the later stipulation has been dropped from the 2017 regs - there is no longer a bounding box on the charging configuration.

Solar Collector (2.4): Smaller!

Reg 2.4.2: Solar array sizes are down across the board - the Challenger class is allowed 4m2 of aperture when using silicon cells, and the Cruiser class is is allowed 5m2 - both down from 6m2 in 2015.

There are some interesting changes to the other cell types - 2011 though 2015, teams were allowed only 3m2 of cells if they chose to use something other than silicon; 50% as much. As a result, pretty much everyone used silicon cells. But this year, the proportion of allowed multijuntion cells is 66% that of silicon, and the proportion of allowed thin-film is 89% that of silicon! Expect to see teams start to experiment with different array types again.

Note that the heading on reg 2.4 is not "Solar Array", it is "Solar Collector". The wording of 2.4.2 makes some implications, but 2.4.4 makes it extremely clear: concentrators such as reflectors or lenses are counted in the allowed aperture area of the solar collector. So no using lenses or mirrors to increase the effective aperture of your solar collector, as many teams have been trying for the past several races. And 3.18.3 explicitly bans the use of ground sheets to increase irradiance while statically charging.

Although the bounding box for the charging configuration is gone, reg 2.4.7 confirms that all devices used for solar charging must be carried within the solar car - including stands, supports, and cables.

An aside: I love the combination of larger bounding box + smaller array; it greatly frees up the aerodynamic design space. Teams are no longer constrained to a rectangular planform if they want to fit the full array! Expect to see wildly divergent design strategies from different teams at WSC in 2017.

Safety (2.10):

This new section mostly includes stuff that was found elsewhere in the 2015 regs - (2017) 2.10.1 corresponds with (2015) 2.23.1 and 2.23.3, while (2017) 2.10.3 corresponds with (2015) 3.1.7. But 2017's 2.10.2 is brand new, and requires each team to "engage a professional engineer, who must certify that the solar car is designed and constructed using sound engineering practice, and is roadworthy and fit for purpose." Certification from the PE is referred to specifically ("approved by the certifying engineer") in several other sections. This will be a big deal for some teams. Teams, if you're reading this, consult with a PE early! A good one is not just going to rubber-stamp your car after you've built it.

A quick scan through the document reveals that the battery protection system, driver/passenger occupant cell, safety belts, occupant ventilation/cooling, brakes, and tires all MUST be approved by the certifying engineer.

Occupant Cell (2.11):

This section is largely new - compare to section 2.4 in the 2015 regs. Impact survivability requirements (2.11.5) are both more numerous and more strict, and calculations must be certified by a PE. Notably, 2.11.4 specifies that no point on an occupant's helmet may lie within 50mm of the boundaries of the occupant cell. Although a forward roll hoop is not expressly required, I think this regulation will strongly push teams towards both a forward and rear roll hoop. The requirement for 50mm of of energy absorbing material on either side of the occupants in 2.11.6 is also an interesting addition, which appears to partially mimic reg 7.3.E.1 from the 2016 ASC regulations.

Stability (2.20):

This is an entirely new section, defining a figure-8 and slalom course that the cars must be able to complete. The courses and times are lifted straight out of the American Solar Challenge requirements - see section 7.9 of the ASC 2016 regs.

Control Stops (3.26):

There are some big changes to how control stops are operated. To summarize, the arriving driver, alone, may reconfigure the car from driving configuration to charging configuration before control stop timing starts. One the control stop clock has started, no team member may touch the car (although the car can reconfigure itself). After the control stop is over (30 minutes), the departing driver alone may reconfigure the car from charging configuration to driving configuration.

I think these rules are hilarious, and I love them. They're very clearly intended to eliminate the zoo at control stops, and be easy to inspect and enforce. It also forces teams to build simple and robust array starts that are quick and esay to assemble - that is, if they want to normalize the array at checkpoints. Bravo, WSC. 

However, I think WSC wrote some of these regs too narrowly and maybe inadvertently opened up some silly loopholes. The big one is 3.26.7: "Teams may not spray water on the solar collector during the 30 minutes of the control stop." At first blush, this looks reasonable, but to a devious cheaty solar car team member's mind, it's way too narrowly defined. I've already heard teams musing about spraying alcohol or other coolants on the array during control stops. I've also heard teams discussing "what constitutes 'spraying', anyway? What about squirting water on the array? Dribbling water on the array?"

I did a quick scan through the document to see if there's anything that would prevent teams from using coolants other than water. 3.18.3 states that "External devices intended to increase the irradiance on the solar collector must not be used at any time." but coolants aren't actually increasing the energy flux onto the array itself, like lenses or reflectors do, so I don't think this rules out other coolants. Similarly, 3.28.1 mentions that ambient temperature water may be sprayed onto the car from a hand-operated pump, but does not specify that this is the only coolant allowed, nor that this is the only allowed application method. This is a reversal of the wording in 2015, where reg 3.27.6 stated that ONLY coolant allowed would be ambient temperature water, ONLY applied by use of a hand-operated spray.

I think this is an error on WSC's part, and I'd expect a regs bulletin to be issued clarifying this at some point in the future.

Cruiser Class:

Running down Cruiser Class regs changes in one location:
  • 2.4.2: Cruiser Class is allowed 5m2 of silicon solar cells, and the same proportions of other cell chemistry as in Challenger. This is down from 6m2 in 2015.
  • 2.5.2: Total allowable battery mass is unrestricted (!!!) for Cruiser cars.
  • 3.13.5: Cruiser Class cars must complete dynamic scrutineering with all seats occupied.
  • 3.18.2: Cruiser Class cars may recharge from external sources at any time except during control stops. 
  • 3.27.10: If a Cruiser team elects to not charge from an external source overnight then all work on the solar car must cease and the car must be secured to the satisfaction of the observer, despite reg 2.5.16.
4.4 is where the meat of the Cruiser Class changes are detailed. The format of the Cruiser Class has changed significantly. For starters, the Cruiser race is now run over a fixed time period. All Cruisers must arrive in Adelaide between 11:00 and 14:00 on the 6th day of the race (4.4.1). No credit will be given for arriving before the target time window (4.4.5), and teams arriving after the target time window will not be ranked (4.4.6).

The Cruiser class will be run in a single stage - no forced overnight stop in Alice Springs.

The new scoring equation detailed in 4.4.3 is very interesting. One of the four factors from the 2013 and 2015 regs (elapsed time) is eliminated as detailed above, and the two remaining performance based factors - person-km and energy usage - have been rolled into a single "energy efficiency" factor. This is defined as person-km divided by energy usage; both factors calculated in the same way as in previous years. Energy efficiency is 80% of the score, and practicality is 20% - compare this to 18.87% for practicality in 2013, and 10% in 2015.

Generally speaking, I like the new format a lot. The fixed arrival time means that teams are all equally ready for practicality judging; no worrying about stragglers - and it'll be a good spectacle when they all parade in together. The new scoring equation results in a much more complex and non-linear design space, as carrying more people or using less grid energy has a multiplicative effect on the energy efficiency score. I suspect we'll see a lot of 4-seat cars, and although it's tough to fit more people than that and still stay within the load ratings of solar car tires, I'm very curious to see if anyone tries a 6+ seat car with very low rolling resistance "real car" tires like those found on the BMW i3.

The amount of margin to carry in the battery is also very important, because the cost of screwing up strategy is far higher in Cruiser class. In the Challenger class, if strategy is screwed up, oh well - the team may drop back a place or two, but they'll still finish close to where they were going to anyway. In Cruiser, if a team misjudges and has to charge up off the grid an extra time, it results a giant step-function on their score. There's also a lot of very tight risk vs reward calculations on how tight to cut the arrival window... Cruiser is a very complex optimization problem this year - moreso than in the past - and I'm kind of fascinated by it.

That said, I'm really disappointed in the solar array size for the Cruiser class. The reduction in array size is fine for the Challengers as they've been edging up in speed, but most of the Cruiser class really struggled to finish even with with 6m2. The reduction in array + emphasis on more passengers is going to make the Cruisers even more dependent on grid energy than they already were. Early rumors seemed to indicate that the Cruiser's arrays would be increased to 8m2 for 2017, which sounded a lot more reasonable to me.

I still don't like how vague and subjective the practicality judging is, and I especially don't like that it's an even larger part of the score than it was in the past two runnings of the Cruiser class, but I'm probably just yelling into the void about this.

Minor Changes:

Entry Fees (1.14):

Fees are up quite a bit across the board; roughly 30%.

Drones (1.28):

The regs note that all UAV flights must comply with relevant Australian regulations as well as be approved by the event organizer.

Dimensions (2.2):

Reg 2.2.3 is a little interesting - "The fully-laden solar car must be able to drive off a road with a 50 mm vertical edge drop without any part of the body touching the ground." See also reg 3.24.1 - "No team vehicle may stop on the road except in an emergency or when required by traffic conditions. Stopping on the road so that you can lift your car off the road is dangerous, and will attract a penalty determined by the Clerk of the Course." The second sentence there is new for 2017; I'm guessing there were some shenanigans with the catamaran cars scraping their bottoms on the shoulder drop-offs in 2015...

Reg 2.3.4 refers to future International Solarcar Federation (ISF) events and regulations, and requires Challenger cars to provide internal space for up to 2m2 of supplementary array, although that won't be utilized at WSC 2017. There's no mention of how this space will be measured, so I'm assuming this space will be left up to the teams to justify and this is a reg without teeth to back it up. That said, the mention of ISF is very interesting, and combined with the stability regs in 2.20 that are borrowed from ASC, perhaps we're seeing some subtle indications of closer collaboration between race organizers in the global solar car community. This is a very good thing!

Energy Storage (2.5):

No major changes; the allowed Challenger Class battery mass (2.5.1) for Li-Ion, LiPo, and LiFePO4 are all unchanged at 20kg, 20kg, and 40kg, respectively. LiS is a new addition, at 15kg. NiMH and Lead-Acid have been dropped from the main list (presumably due to few teams using them) although teams can still contact the organizers if they want to use them or other unlisted battery chemistry (2.5.2).

LiS appears very compelling at that allowable mass, although they are not in widespread commercial use yet so procurement may be harder.

Vehicle Identification (2.6):

The angles which one can see the license plate from are much more strictly specified in 2.6.2. This reg also defines a "flat vertical surface... at the rear of the solar car" to which the license plate will be mounted. This may be specifically disallowing putting the plate on the back of the roll cage inside the driver's canopy? 

Signage (2.7):

Largely the same. The front 600mm x 150mm area now has the clarification "...must not overlap with the solar collector. Part of the front signage area must be further forward than every part of the solar collector", which is likely in response to Twente's shenanigans in 2015.

Seats (2.12):

A stipulation has been added in 2.12.2 that seats must face less that 10 degrees off from the direction of travel.

Egress (2.15):

In addition to demonstrating un-assisted egress (2.15.1) during inspection, 2.15.4 states that during the event, occupants must exit the solar car without assistance. Does this mean that, even for the Challenger cars, the driver must get out before the team removes the top of the car? This probably won't be an issue with the smaller cars we'll be seeing this year (especially if they're still catamarans), but this is an interesting little addition.

Cooling and Hydration (2.16):

2.16.1 states that the driver ventilation and/or cooling system is one of the many things that must be approved by the certifying engineer, and 2.16.2 specifies that the driver must be provided with 2L of drinking water. Both of these were simply described as "must be adequate" in the 2015 regs (2.5.1).

Forward Vision (2.17):

This reg specifies that the driver must be able to read 75mm high letters in the forward vision, not just "be able to see" as stated in the 2015 regs (2.6.1). It also defines forward vision as 100 degrees right and left of the direction of travel, not simply "every forward angle" as in 2015.

Brakes (2.21):

There's a lot of new stuff here this year. As in past years, cars are required to have redundant brake systems. The reg this year (2.21.2) specifically states "The solar car must be equipped with independent primary and secondary mechanical braking systems, so that if the primary system fails the secondary system can still stop the solar car." However, 2.21.5 states that "the primary braking system must apply mechanical braking effort to all road wheels" (emphasis mine). So teams can't have one brake system act only on the front wheels and another act only on the rear wheels, as some teams have split their redundancy in the past.

Required deceleration remains the same as in previous years, although WSC has added another (lower) requirement (2.21.9) for the secondary brake system alone if the primary has failed.

WSC has expanded the parking brake requirement (2.21.10) to all entries; in 2015 only the Cruiser class needed a parking brake.

Tires (2.22):

The tread depth requirement from 2015 (2.11.3) has been eliminated. As I detailed in an old post, the tread depth regulation was introduced in 2009 but basically neutered in 2015, and I'm not surprised to see it gone this year. Tire technology has advanced a lot in the past decade, and the tires teams use will continue to be far better than the old ones, even with this regulation eliminated.

Reversing (2.23):

All solar cars must be able to be driven backwards, not just the Cruiser class as in 2015.

Lights (2.24):

Solar cars are now required to have side turn indicators, in addition to front and back. The requirement for UNECE or SAE/DOT compliant lights is expanded to all classes of solar cars, not just the Cruiser class as in 2015.

Horn (2.25):

There is now a required sound pressure level - 105 dB at 2m away from the horn.

Instrumentation (2.26):

Teams are now required to display a minimum of information to the solar car driver - speed, whether the turn signals or hazard flashers are operating, and any warnings from the battery protection system.

Automatic Functions (2.27):

It addition to requiring cruise control to turn off when the brakes are touched, any "automatic driving function" must deactivate on any manual input. This appears to be a preemptive regulation in case any teams implement self-driving functionality.

Electrical Safety (2.28):

2.28.10 requires a main battery fuse or circuit breaker, which shockingly appears to NOT have been required previously?

Safety Equipment (3.5):

Teams are now required to carry sand and a spade, in addition to a fire extinguisher. Similar to above, I'm a little shocked this wasn't required before - an ordinary fire extinguisher isn't doing to do shit when 20kg of lithium batteries ignite.

Energy Collection (3.18):

3.18.3 now very specifically mentions that ground sheets may not be used to increase irradiance on the array while charging, so presumably no more of this from teams will be tolerated.

Penalties (3.31):

The minimum penalty for Challenger class cars (3.31.2) is now 30 minutes, up from 10 minutes.

A new penalty policy for Cruiser class cars is detailed in 3.31.3. Rather than serving a time penalty, Cruisers will have penalties applied to their energy efficiency score.

It appears that only the Clerk of the Course can issue penalties in 2017, instead of Red-Shirt Officials as in the past.

WSC has adopted a "three strikes and you're out" policy with penalties (3.31.4).


Arrays are smaller, while allowed car sizes are bigger. I think this is a great thing, and will really shake up how teams design their cars. It's going to be an exciting time to be a solar car aerodynamicist!

The 2015 bounding box for the car while array standing is eliminated, but they've kept the 2013/2015 requirement that any and all equipment required for array standing must be carried within the car.

Control stop rules have been changed - all reconfiguring from driving to charging and back must be performed solely by the driver, and only before the control stop starts/after it ends. No touching the car - period - for the full 30 minute duration of the stop, including array spraying. The new setup and water-spraying constraints do not apply to end-of-day stops. This should be very easy for WSC to consistently enforce across the entire race, and hopefully quell complaints about checkpoint shenanigans.

LiS batteries are potentially compelling. The use of multijuntion GaAs arrays and especially thin-film GaAs arrays are potentially compelling. Hopefully we'll see a lot more variety of batteries and arrays, instead of nearly every team using Panasonic 18650 LiIon batteries and Sunpower silicon solar cells.

Big changes to the Cruiser Class - it's now an efficiency challenge over a fixed length of time, and the scoring dramatically emphasizes carrying more passengers. Practicality is also more important than it was in 2013 or 2015.

There are some subtle indications that WSC is working with the organizers of other solar car races to move towards more cross-compatible regulations, which I think is a very good thing.

Generally speaking, I think these regs move in a lot of good directions, and I'm excited to see what teams bring to Australia in 2017!


  1. Some good insights there! It will be interesting to see the 2017 race unfold.

  2. I really like the information provided in this article and I really like the way you have explained each and everything so well. Very well done with the article, hope that you will continue to do posting

  3. Really nice article!! I am glad to read your post, pretty informative.

  4. Wsc released our design by mistake, they took it down. But you have given it away, we have now put a hit out on you with the local wildlife. Enjoy the drive, see you soon. Love, WSU.

    P.s Goko Highschool is amazing. *licks car*