WSC 2023 Challenger Wrapup

It's been a week TWO WEEKS THREE WEEKS since the awards ceremony, so let's wrap this up.

Chart via Scientific Gems

Similar concept to above, but inverted and with granular data rather than just control stop times
Adapted from work by Jelmer van de Wiel

Quick recap: Over the last two days of the event, there wasn't any movement among the top four. Twente closed the gap to Innoptus from 33 minutes at Erldunda in the middle of Day 3 down to 16 minutes at Coober Pedy on the morning of Day 4, and then 14 minutes at Glendambo... and then back up to 30 minutes at Port Augusta before the end of Day 4, and that was that. Speed limits drop soon after PA and catching up becomes extremely difficult, barring your competition breaking down. A second consecutive win for Innoptus proves that 2019 was not a fluke: The have what it takes to win even without their two biggest competitors wrecking out or burning down. And second place is still a great result for Twente, besting their third place finish from 2015!

As of the last update on this blog it still looked like anyone's race among the top 3, but afterward Delft slowed down dramatically relative to the top two; basically taking them out of contention for the win. They managed to stay on the podium and finish in 3rd, however. It's worth noting how big of an upset this is, historically: Other than coming in 2nd to Tokai in 2009 and 2011, and the DNF due to the fire in 2019 (after a super tight battle for the lead...), Delft has won every other WSC they've entered - 2001 through 2007 and 2013 through 2017, seven victories. At 2 hours and 18 minutes, this was their second biggest margin of loss: only 2009 was larger at 2 hours and 49 minutes. Talking with some team members after the race, it didn't sound like they had any critical issues this year - they just think that they've taken the catamaran design as far as it can go, and this year proved that the monohull design concept had more performance potential than they thought.

Behind Delft, Michigan was slowly catching up over the last two days, but they were just too far back to close the gap - Michigan was still an hour behind at Port Augusta, and had to be content with 4th place. Speaking with the team after the event, they were pretty sure they could have finished 3rd if they hadn't botched the hot lap - starting at the tail end of the grid put them 40 minutes back at the start line, and overtaking all of the teams certainly ate up more time. It's very easy to picture them being ahead of Delft at Port Augusta if they'd started up in the top 10. On the other hand, Michigan also had a lot more unplanned side-of-the-road pauses than Delft, so they can't blame their 4th place finish purely on starting position - Delft just ran a cleaner race! I wonder if this is a visible result of Delft finding races to attend in 2021 and 2022, whereas Michigan has not had to deal with the pressures of a competition since 2019.

Just Delft and Michigan, for clarity
You can see a lot more little stops peppered around on Michigan's line

Sonnenwagen rolled on the last day of the event, in a situation that sounds eerily similar to their 2019 accident: in a situation with high crosswinds from the right, the team passed by an oncoming road train - which blocked the crosswind momentarily - and then lost directional stability in the combination of the sudden return of the crosswind and the wake of the road train. Fortunately the driver was largely unhurt and able to walk away from the crash, and the car appeared to mostly suffer only cosmetic damage to the structure. The team claims that they could have continued, but it rolled entirely over and the regs this year state that if the car rolls it's automatically removed from the event.

Tokai finished 5th, around two and a half hours after Michigan. It might have been a tight competition for 4th with Michigan, but Tokai suffered some sort of suspension failure over a cattle grid in the late afternoon on Day 4. This put them on the side of the road for about two hours, and momentarily behind Top Dutch. But they were able to repair the car and regain their 5th place position quickly, finishing a comfortable hour or so ahead of Top Dutch's 6th place finish.

1st to 6th was a seven hour spread overall, and then we had a five hour gap back to 7th place, followed by less than a two hour spread between 7th and 11th! That's where the real action on the road was this year and I kind of wish I'd been back there to see more of it.

JU ended up on top of that group, prevailing in a tight multi-day battle with Kogakuin and Durham. 7th is also a best-ever finish for JU, ahead of their 8th place finish in 2017. Kogakuin finished in 8th, while in 9th was a surprise interloper - Western Sydney! WSU had been spending most of the race further back with Blue Sky, Goko, and αCentauri, but they got the car working the way they wanted to (or found the accelerator pedal?) sometime on the fourth day and made a breakaway ahead. At one point I was wondering if they'd be in contention for 7th! Even if they ultimately couldn't come out on top of this group of teams, it still had to be satisfying to finish on a strong note instead of in limp-mode. In 10th was ETS Eclipse from Canada, who also staged a late-race comeback, abet in not as dramatic fashion as WSU. And at the tail end of this group in 11th was Durham - completing WSC without trailing for the first time, on what I believe is their fifth attempt. A big congratulations to them!

It's really interesting to contrast the paths the teams took to this tight finishing group. Kogakuin started up front - on pace with the likes of Top Dutch, Tokai, and Michigan - until they progressively fell off-pace after Dunmarra. Meanwhile WSU was frankly on a not-finishing-the-race pace all the way through Alice Springs, and these two teams finished side-by-side 8 minutes apart.

Rounding out the finishers a little over an hour back from the 7th-11th group was the αCentauri team in 12th.

Of the teams that failed to finish, Sonnenwagen Aachen was the first to get past Port Augusta, so they received 13th place. 14th and 15th were Goko and Blue Sky - unfortunately they were about 60km shy of finishing the event by the 5pm cutoff on Day 6.

The last car still out driving at the end of Day 6 was Chalmers - they simply refused to put the car in the trailer until the race was really truly over. Earlier in the race they missed a control stop cutoff and were listed as "no longer competing" on the race map. Did they give up? No! They kept driving, and made the cutoff for the next control stop, and WSC changed their race map dot back to green! In the end they made it past Port Augusta and to within 260km of the finish. They actually made it past where Sonnenwagen wrecked - if WSC counted driving distance between control stops in the final rankings, Chalmers would have been ranked 15th, over Sonnenwagen in 16th. Never give up, never surrender! I would have nominated Chalmers for the spirit of the event award if I could!

No one behind Chalmers made it past the midpoint of the event. AUSRT called it between Barrow Creek and Alice Springs, Halmstad ended their race between Tennant Creek and Barrow Creek, Wakayama put it in the trailer between Dunmarra and Tennant Creek, ITU and ANU ended their race after Katherine, and Arrow and TUCN didn't even make it as far as the first control stop.

Overall this was a really clean year for the Challengers, which was a welcome change from 2019. Given that this year was the first run of the new 3-wheel regs, I doubt we'll see any huge shakeups in the formula for 2025, absent two possible areas: Active aerodynamic devices, and battery size.

Innoptus's big "secret weapon" - and winner of the innovation award - was their big retractable and steerable fin. They claimed it allowed them to reduce drag and improve the stability of the car in crosswinds. Post-race, the top teams seemed pretty unanimous - they don't want to see devices like this banned in 2025, they all want a chance to experiment with active aero devices themselves - but we'll see how the WSC technical staff feels about it.

On the battery front, WSC limits battery capacity by regulating the weight rather than by kWh, but they've reduced the allowed weight over the years as batteries have gotten better: we were allowed 35kg of Lithium-Ion batteries in 2003 and 2005, 30kg in 2007, 25kg in 2009, and 21kg in 2011 and 2013. These weights corresponded to about 5kWh of capacity. Then the weight was dropped to 20kg in 2015, and... that's where it's stayed. Lithium battery technology isn't advancing as fast as it was in the 2000s, but it is still advancing, and in 2023 the top team's battery capacity has crept past 8kWh and is knocking on 9kWh. 

Meanwhile, over that same timespan we've cut the array size way down. We've gone from "literally as many solar cells as you can fit on a car 1.8m wide x 5m long x 1.6m high, of any kind" in 2003 and 2005 (in practice ~8m² of dual- or triple-junction gallium), to 6m² of any array chemistry 2007-2009, to 6m² of silicon cells 2011-2013, to 4m² of silicon cells 2017-2023. Essentially, cars are making half as much array output as they did ~20 years ago - but they're also half the size, and much lighter and lower drag.

The long and short of it is that we've gone from the energy in the battery on the start line being about ~10% of the total available energy over the race 2003-2013, to being over 30% of the available energy in 2023. This doesn't feel great to some of the teams - it's supposed to be a solar car race, not an EV race. Given that the cars are also lighter and much lower drag than they used to be, that increase in battery capacity represents a lot more time/distance that teams can just punch through bad weather without slowing down. It's also changed strategy a lot - back in the day, we'd need to get pretty far down near the bottom of our ~5kWh battery packs every evening, so that we wouldn't "waste" any of the energy we'd gather from our ~1.8-2kW solar arrays by pointing them at the sun in the evening and following morning. But when the batteries are 8kWh and the arrays are sub-1kW? Teams will never get close to filling it in an evening and morning charge, they can hold a lot more energy in reserve.

The TL;DR is that everyone agrees that the batteries need to shrink, it's just a question of how much. The conservative answer is that we should just get back to ~5kWh or so - but this still leaves us with "proportionally" more battery storage relative to solar collector output and aero drag than we used to have. The aggressive answer is that we should shrink the batteries down to ~2.5-3kWh to be proportional again, but that might cripple the weaker/slower teams... it'll be interesting to see what WSC decides.

I had a ton of fun this year, and really reminded myself how much I love solar racing. Hopefully I'll be able to cover WSC 2025 more like I did 2015 and 2017.

Stay tuned for a recap and some thoughts on the Cruiser class.