Driven by Challenges

Solar Team Eindhoven has won the World Solar Challenge Cruiser Class four times with their Stella family of solar cars (see montage of team photos above). The team’s home base, Eindhoven University of Technology (TU/e) is one of the best technical universities in the world (Times Higher Education rated it #64 in 2017, but that really doesn’t do it justice). So what do engineers do after building the world’s best solar family car?

In 2019, Liselotte Kockelkoren-Graas (account manager of the 2015 team) reconnected with five other former members of Solar Team Eindhoven, in a documentary produced by D2D Media. The six episodes of this beautifully filmed documentary (in Dutch with English subtitles) can be accessed via this playlist.

Liselotte and the other highlighted team alumni are working on some of the coolest engineering projects in the world, in some really cool places (see table and montage below). This list says something about the superb teaching that TU/e offers, the high-tech industry hub in which TU/e is located, and the close links that TU/e (wisely) maintains with its industry neighbours.

Who Now at Where
Liselotte Kockelkoren-Graas (2015 team) Innovation Lead / Senior R&D Engineer, Vanderlande Eindhoven area, NL
Arjo van der Ham (2013 team) Co-Founder / CTO, Lightyear Eindhoven area, NL
André Snoeck (2013 team) Researcher, MIT Megacity Logistics Lab Boston area, US
Patrick Deenen (2015 team) Senior Business Process Analyst, Nexperia & PhD student, TU/e Manchester, UK & Eindhoven, NL
Wouter van Loon (2013 team) Escalation Project Lead / Strategic Business Planner, ASML Taipei, TW & Eindhoven area, NL
Jessie Harms (2017 team) Graduate Intern Eindhoven area, NL & Ahmedabad, IN

Among the things I learned from the documentary Driven by Challenges: exciting things happen when your suitcase vanishes down a belt in an airport, and my beard grows at 5 nanometres per second. It was great to see that the careers of Solar Team Eindhoven alumni are progressing many orders of magnitude faster than that.

Harp strings and design

Having previously blogged about the mathematics of the harp, I thought I might say some more about harp design issues. It’s an interesting question that involves both physics and human factors. For simplicity, I’m going to talk about just one string, one playing the note A at 440 Hz. Of course, a real harp will have between 21 and 46 other strings.

The physics of vibrating strings gives us Mersenne’s laws, which tell us that the frequency of a string of length L is (1 / 2L) √ T / μ , where T is the tension force on the string (in newtons), and μ is the density per unit length of the string (in kg per metre).

The diagram below shows the required tension force (in newtons) for a nylon string of various lengths and diameters to play the note A at 440 Hz (click to zoom). A newton corresponds to roughly the gravitational force on 100 grams.

The first, and most obvious, design factor is that too much tension causes the string to break. Setting a design limit of 90% of the expected breaking strength means that the string must be less than 560 mm in length. Interestingly, this limit is independent of the diameter of the string.

The string must also be playable. A string that is too floppy or too tight cannot be effectively played. A rough guide is that the tension should be at least 35% of the expected breaking strength, which means that the string must be at least 350 mm long. Additional limits, which I’m ignoring here, relate to how much room the string needs to vibrate.

Thirdly, the frame can only take so much. If the frame of a 40-string harp is built to withstand 10,000 newtons (roughly the gravitational force on 1000 kg), then the average string has a limit of 250 newtons. This restricts us to the design space on the diagram outlined in red.

Finally, a harp has levers or pedals which shift the strings to be sharp or flat (the basic harp strings correspond only to the white keys on a piano). Those devices set further limits on the design space for strings.

A modern electric lever harp (photo: Athy)

It is interesting to relate this to my other interest, that of solar cars. They are vehicles, which means that they must hold a driver (and new guidelines on World Solar Challenge driver space have just been announced). They are solar, which means that their upper surface must hold a solar panel of specified size. And they race, which means that their aerodynamic drag must be as low as possible. This necessitates a variety of compromises, just as with the design of a harp. The problem is much more complex however; the space of possible solar car designs has many more dimensions than two.

World Solar Challenge Anthropometrics

The World Solar Challenge has recently previewed the 2021 regulations. This has included a standard mannequin (“PVC Pat”), which must be able to fit into all car cockpits. The idea here is that a less cramped cockpit will reduce driver fatigue (at least to some extent).

For comparison, here are some body measurements from the standard 1988 ANSUR dataset of anthropometric measurements on 1,774 male and 2,208 female U.S. Army personnel (but scaled to a 50% male, 50% female population). Click the images to zoom. It can be seen that the new cockpits will be able to comfortably hold most people, with the exception of long-legged men, or men that are more broad-shouldered than average. “PVC Pat” also has a fairly small head.




Emerging solar car teams

Here is a brief list of emerging solar car teams. We wish them all the very best as they plan for their first race, especially in these difficult times. Please notify me in the comments of other new teams aiming at major races.

CO  Universidad Nacional de Colombia, Medellín (Hydrómetra) 

Challenger – this team has a background in boat racing, but are building a car for iESC.

picture credit (click image to zoom – OLD PIC)

MX  Universidad Autónoma del Estado de México Solar Racing Team (Hyadi) 

Two-seat cruiser (car: Quetzal 2) – this new team from Mexico are planning to build a great-looking Cruiser. They hope to attend the World Solar Challenge.

picture credit (click image to zoom)

PL  PUT Solar Dynamics (Poznań University of Technology) 

Two-seat cruiser – they are making good progress on construction. This (Polish) video describes their project. They had originally hoped to race at WSC 19.

Left: credit / Right: credit (click images to zoom)

SA  Alfaisal Solar Car Team 

Classic symmetric challenger (car: Areej 1) – they originally registered for ASC 2018 and WSC 2019, but withdrew from those events. Their car name is a pun: AREG/Areej is an acronym for Alfaisal Renewable Energy Group but also means “the scent of a flowery garden” in Arabic. Their car appears complete.

Left: credit / Right: credit (click images to zoom)

US  Bradley University 

Challenger – I am not sure of the status of this team.

US  Comet Solar Racing team (UT Dallas) 

Challenger – I am not sure of the status of this team.

US  Grand Valley State 

Symmetric challenger – they appear to have gotten started by being given Poly Montreal’s Esteban 8. Their team number (616) is the telephone area code for Grand Rapids, Michigan.

picture credit (click image to zoom)

US  KU Solar Car 

Monohull challenger (car: Astra) – they are raising funds for construction. The render they have posted shows a monohull design, 1.3 m wide. They completed their battery pack in March. Their team number (785) is the telephone area code for northern Kansas.

picture credit (click image to zoom)

This page last updated 13:33 on 16 May 2020 AEST.

How solar is that solar car?

Above (click to zoom) is a chart showing WLTP-standard solar-only driving ranges for the three solar cars from my last post (battery ranges not shown here):

  • Solar Team Eindhoven’s Stella Era, winner of the BWSC Cruiser class
  • Lightyear One, a commercial solar car from the Netherlands
  • The Sion electric vehicle from Sono Motors

These solar-only driving ranges are marked on a smoothed distribution of electric vehicle driving patterns reported in this paper (distance driven per vehicle-day on days when the vehicle was driven).

The sleek Stella Era has a solar-only range more than 4 times the mean 70 km driven. On more than 99% of trips, Stella Era can operate solar-only, and, on average, its solar panel produces substantial excess electricity which can be donated to other vehicles.

Lightyear One has a solar-only range less than the mean 70 km, but is still able to operate solar-only on 57% of trips.

The less expensive Sion is able to operate solar-only on 19% of trips, and has a useful solar boost to its battery the rest of the time.

So you want to buy a solar car?

Above (click to zoom) is a chart showing WLTP-standard driving ranges for four electric vehicles (brown for battery range, yellow for the boost due to solar panels). The four cars are:

  • Solar Team Eindhoven’s Stella Era, winner of the World Solar Challenge Cruiser class (not for sale, of course)
  • Lightyear One, a commercial solar car from the Netherlands which incorporates considerable know-how from solar car racing
  • The Sion electric vehicle from Sono Motors
  • The non-solar Tesla Model 3 Long Range

The sleek Stella Era has almost double the range of the Tesla, in spite of having a much smaller battery pack. This is due to the Dutch racing car’s extremely aerodynamic shape and light carbon-fibre construction. Lightyear One comes about as close to the performance of Stella Era as you would expect a normal-looking production car to come (and is about two and a half times as heavy).

The rather boxy Sion has a much smaller range than Lightyear One (but, at an expected €25,500, is much cheaper). Which solar car would you choose?

World Solar Challenge 2019: even more charts

Adding to my earlier list of World Solar Challenge distance/speed plots, here are 8 more (mostly circulated previously on Twitter). Night stops and notable events are marked on the bottom of each chart in a highlight colour. Control stops are in black.

Michigan traditionally comes third in the World Solar Challenge. They were third again this year. Their chart shows no drama, just fast, steady racing.

Control stop times for Michigan: Katherine: Sunday 12:29:00, Daly Waters: Sunday 16:08:02, Tennant Creek: Monday 12:13:30, Barrow Creek: Monday 15:14:24, Alice Springs: Tuesday 10:02:07, Kulgera: Tuesday 13:42:10, Coober Pedy: Wednesday 10:25:19, Glendambo: Wednesday 14:21:01, Port Augusta: Thursday 9:14:26, Adelaide: Thursday 14:56:00.

Western Sydney, in their beautiful car Unlimited 3.0, battled electrical issues, motor problems, and a wind gust that finally took them out. They still found time to help out Sonnenwagen Aachen on the road south. The photograph in the chart is mine.

Control stop times for Western Sydney: Katherine: Sunday 12:55:00, Daly Waters: Sunday 16:59:06, Tennant Creek: Tuesday 11:51:31.

There was no such drama for ETS Quebec (Éclipse), just steady consistent driving, finishing as best Canadian team, 2th North American team, and 9th in the world. That’s why they received my consistency gem.

Control stop times for Éclipse: Katherine: Sunday 13:27:04, Daly Waters: Monday 8:55:47, Tennant Creek: Monday 16:08:23, Barrow Creek: Tuesday 11:13:27, Alice Springs: Tuesday 16:10:27, Kulgera: Wednesday 11:59:00, Coober Pedy: Thursday 9:48:25, Glendambo: Thursday 13:56:55, Port Augusta: Friday 9:32:09, Adelaide: Friday 14:21:48.

Swedish team Jönköping University (JU) also had plenty of drama. They were forced to stop under cloudy skies with a flat battery and they needed an overnight repair. But they still finished tenth!

Control stop times for JU: Katherine: Sunday 12:51:56, Daly Waters: Monday 8:07:49, Tennant Creek: Monday 14:31:05, Barrow Creek: Tuesday 9:41:27, Alice Springs: Tuesday 14:13:37, Kulgera: Wednesday 12:39:00, Coober Pedy: Thursday 9:53:47, Glendambo: Thursday 13:51:40, Port Augusta: Friday 10:04:55, Adelaide: Friday 14:44:20.

Antakari had a smooth and largely uneventful race, apart from a couple of stops of a few minutes each. The GPS track shows them hunting around for a good campsite each night. They finished 7th (just ahead of NITech).

Control stop times for Antakari: Katherine: Sunday 13:15:43, Daly Waters: Monday 8:56:38, Tennant Creek: Monday 15:06:40, Barrow Creek: Tuesday 9:55:51, Alice Springs: Tuesday 14:17:59, Kulgera: Wednesday 10:34:05, Coober Pedy: Thursday 8:45:34, Glendambo: Thursday 12:58:06, Port Augusta: Friday 8:33:08, Adelaide: Friday 13:07:11.

Nagoya Institute of Technology (NITech) also had a smooth and largely uneventful race, finishing 8th (just behind Antakari).

Control stop times for NITech: Katherine: Sunday 12:56:50, Daly Waters: Monday 8:06:31, Tennant Creek: Monday 14:42:02, Barrow Creek: Tuesday 9:38:31, Alice Springs: Tuesday 14:40:56, Kulgera: Wednesday 10:22:50, Coober Pedy: Thursday 8:45:20, Glendambo: Thursday 13:01:29, Port Augusta: Friday 8:38:35, Adelaide: Friday 13:24:10.

The team from Durham University crossed Australia on solar power, in spite of minor electrical problems (they are the first UK team to do so for many years). Unfortunately they only managed around 2830 km, not quite reaching Adelaide. In the past, cars have been permitted to drive on Saturday mornings, whereas this year, cars had to cease driving on Friday evening. Judging from the graph, Durham might not have realised this for the first few days.

Control stop times for Durham: Katherine: Sunday 14:26:58, Daly Waters: Monday 10:34:22, Tennant Creek: Tuesday 9:39:42, Barrow Creek: Tuesday 13:45:32, Alice Springs: Wednesday 10:53:29, Kulgera: Wednesday 15:59:45, Coober Pedy: Thursday 14:36:36, Glendambo: Friday 10:01:30, Port Augusta: Friday 14:42:19.

Swedish newcomers Chalmers Solar Team managed two control stops, but were slowed significantly by the hilly terrain in the first part of the route. They therefore trailered at around 735 km.

Control stop times for Chalmers: Katherine: Sunday 14:56:54, Daly Waters: Monday 12:49:32.

World Solar Challenge 2019 Revisited: some additional charts

Revisiting the World Solar Challenge, the chart below shows distance/speed plots for seven WSC teams (for other teams I was either missing some GPS data, or did not have access to explanatory social media). Distances shown are road distances (not geodesic), while speeds are estimated from distance and time information (because speeds were not included in the GPS data that was kindly supplied to me). As a result of data limitations, the compulsory 30-minute stops at Katherine etc. are shown by sharp speed dips, but not necessarily ones that drop all the way to zero.

Vattenfall (3) had a devastating battery fire; Top Dutch (6) were the best new team, finishing 4th; Agoria (8) won the Challenger class; Twente (21) tragically crashed while in the lead; Sonnenwagen Aachen (70) were one of two teams to come back from a serious crash and still finish; Blue Sky (77) were the 11th and last Challenger team to reach Adelaide on solar power; and Kogakuin (88) were the other team to recover from a major crash.

Night stops in the chart above are marked in red. Photos are from their tweet posted minutes before the fire and from a tweet posted shortly afterwards.

Control stop times for Vattenfall: Katherine: Sunday 12:19:21, Daly Waters: Sunday 15:59:21, Tennant Creek: Monday 11:45:23, Barrow Creek: Monday 14:51:01, Alice Springs: Tuesday 9:30:33, Kulgera: Tuesday 12:51:41, Coober Pedy: Wednesday 8:39:31, Glendambo: Wednesday 12:40:58, Port Augusta: Wednesday 16:44:32.

The chart shows Top Dutch’s multiple stops just out of Tennant Creek with battery problems. Top Dutch finished 4th, and won the WSC Excellence in Engineering Award.

Control stop times for Top Dutch: Katherine: Sunday 12:16:27, Daly Waters: Sunday 15:57:03, Tennant Creek: Monday 12:12:55, Barrow Creek: Monday 15:28:35, Alice Springs: Tuesday 10:39:32, Kulgera: Tuesday 14:41:40, Coober Pedy: Wednesday 12:00:43, Glendambo: Wednesday 15:48:50, Port Augusta: Thursday 10:47:39, Adelaide: Thursday 15:30:00.

Night stops in the chart above are marked in blue. Agoria had a virtually perfect race, winning the Challenger class. Visible in the chart after Coober Pedy is the 80 km/h speed limit imposed by the WSC on Wednesday morning after wind gusts caused multiple crashes.

Control stop times for Agoria: Katherine: Sunday 12:17:04, Daly Waters: Sunday 16:05:54, Tennant Creek: Monday 11:55:56, Barrow Creek: Monday 14:56:40, Alice Springs: Tuesday 9:46:28, Kulgera: Tuesday 13:10:50, Coober Pedy: Wednesday 9:22:36, Glendambo: Wednesday 13:05:06, Port Augusta: Wednesday 16:51:59, Adelaide: Thursday 11:52:42.

Twente’s tragic crash (due to a strong wind gust) occurred at about 2165 km from Darwin, just before Coober Pedy. Photos are from a tweet posted the day before the crash and from a tweet posted shortly afterwards. I was one of the people that signed the car after the crash. Twente won the Promotional Award, for their excellent media.

Control stop times for Twente: Katherine: Sunday 12:08:43, Daly Waters: Sunday 15:32:39, Tennant Creek: Monday 11:33:01, Barrow Creek: Monday 14:31:33, Alice Springs: Tuesday 9:17:16, Kulgera: Tuesday 12:40:40.

Sonnenwagen Aachen stopped for five hours to repair their car on Wednesday, just before Coober Pedy, after the car was blown off the road (their first priority was the driver, of course). There was another stop between Glendambo and Port Augusta, due to a broken shock absorber that had been damaged in the crash (Western Sydney Solar Team kindly helped get them back on the road). Sonnenwagen Aachen finished 6th. They also won the Safety Award and and the Spirit of the Event Award (for not giving up).

Control stop times for Sonnenwagen Aachen: Katherine: Sunday 12:27:34, Daly Waters: Sunday 16:09:06, Tennant Creek: Monday 12:17:32, Barrow Creek: Monday 15:12:27, Alice Springs: Tuesday 9:52:06, Kulgera: Tuesday 13:31:00, Coober Pedy: Wednesday 15:08:20, Glendambo: Thursday 9:35:27, Port Augusta: Thursday 14:49:06, Adelaide: Friday 10:03:48.

Blue Sky (Toronto) had several brief stops of a few minutes (including for electrical issues on Monday), but no particularly dramatic events. They were also slowed somewhat by clouds on Wednesday morning. Blue Sky finished 11th (the last Challenger team to reach Adelaide on solar power).

Control stop times for Blue Sky: Katherine: Sunday 12:49:29, Daly Waters: Monday 8:03:38, Tennant Creek: Monday 14:42:34, Barrow Creek: Tuesday 9:54:44, Alice Springs: Tuesday 14:23:40, Kulgera: Wednesday 11:00:30, Coober Pedy: Thursday 10:34:55, Glendambo: Thursday 15:01:18, Port Augusta: Friday 10:53:25, Adelaide: Friday 15:47:10.

Kogakuin was forced to stop with an overheated motor just after Katherine. They also crashed twice due to strong winds. The second, more serious, crash was due to a mini-tornado or willy-willy just before Glendambo (see their report here), and required overnight repair in town on Wednesday night. Kogakuin finished 5th. They won the CSIRO Technical Innovation Award, for their hydropneumatic suspension. Their dramatic after-race video is here.

Control stop times for Kogakuin: Katherine: Sunday 12:18:43, Daly Waters: Monday 8:03:13, Tennant Creek: Monday 13:16:26, Barrow Creek: Monday 16:15:52, Alice Springs: Tuesday 11:03:53, Kulgera: Tuesday 14:32:15, Coober Pedy: Wednesday 12:04:23, Glendambo: Thursday 9:45:18, Port Aug: Thursday 14:18:47, Adelaide: Friday 9:53:00.

For comparison, here is the distance/time chart I did before. In that analysis, higher means slower, and the arrival times (in Darwin time) can be read out on the right:

Farewell to the World Solar Challenge

This ends my World Solar Challenge 2019 coverage. I will begin covering the American Solar Challenge in a few months. Meanwhile, regular science content resumes.

Summary of WSC additional awards:

  • CSIRO technical innovation award: Kogakuin, for their hydropneumatic suspension.
  • Safety award: Sonnenwagen Aachen, who crashed.
  • Spirit of the Event award: Sonnenwagen Aachen, for not giving up.
  • Promotional award: Solar Team Twente, for their excellent media.
  • Excellence in engineering award: Top Dutch, for their wonderful car.