ASC 11: Leadership


Nuon Solar Team celebrates their 2017 WSC win (photo: Anthony Dekker)

Ernest Hemingway famously said that “war is fought by human beings.” It’s the same with solar cars – they are built and raced by human beings. Or, as Solar Team Twente likes to say, they are “powered by human energy.

There are many aspects to this human side of solar car racing. I’ve written before about how little things like team clothing contribute to team cohesion. A diversity of skills is important if a team is to succeed. During the race, nutrition is one of the things necessary to keep people working at top efficiency. But today, I want to talk about team leadership.

Engineering leadership is critically important, although surprisingly little is written about it. Tracy Kidder produced a fantastic, almost ethnographic, description of real-world engineering in his 1981 book The Soul of a New Machine, but even that book has the actual leadership happening mostly in the background.

A century earlier, Leo Tolstoy opened his novel Anna Karenina with the words “Happy families are all alike; every unhappy family is unhappy in its own way” (“Все счастливые семьи похожи друг на друга, каждая несчастливая семья несчастлива по-своему”). That is true also for solar car teams. Many things have to be done right if a team is to succeed, but doing one thing badly is enough to stop a team in its tracks.

A team leader must, first of all, motivate team members to do their best – it is no accident that all the solar car team leaders I’ve met have been really nice people. A team leader must make sure that the overall problem of building, racing, and finding sponsorship for a solar car is broken down into manageable pieces, and that the right person is in charge of each piece – this is the essence of engineering.

A solar-car team leader must also have – and promote – a clear vision of the car that the team is going to build. It is possible to have a world-class suspension, a world-class body, world-class solar cells, and world-class everything else, and still fail, because the components were designed under different assumptions, and don’t actually fit together to make a world-class car.

A team leader must keep an eye on the critical path as well. Building a solar car for a race is one of the most challenging kinds of engineering project – one where the delivery date is fixed in stone. What project managers call the critical path is the sequence of activities which, if they take any longer than planned, are guaranteed to delay project completion. Generally, the schedule for building and testing a solar car doesn’t leave much room for that kind of schedule slippage.

One perennial question with solar car team leaders is how long it takes them to realise that there is a problem requiring the team to either (a) change the way it operates or (b) pull out of the competition. Each year, I am reminded by somebody or other of Napoleon’s 1812 invasion of Russia, summarised so well in the famous data visualisation above (by Charles Minard).


Napoleon’s death march (painted by Illarion Pryanishnikov)

Napoleon began his invasion with 422,000 men, and reached Moscow with only 100,000 survivors. This was not enough to do anything, so he turned around and went home again, losing most of his remaining troops to cold and skirmishes in the process. I have often wondered at what point Napoleon realised that his plan was not working the way that it was supposed to. In a similar way, there is always a solar car team that begins a last-minute “death-march,” working until 3:00 AM each night, desperately trying to finish their car. The early hours of the morning are not a good time to be making safety-critical engineering decisions, and teams which leave it so late to panic generally don’t do very well.

But enough of Napoleon. Let us listen to some men and women who know how it’s done (translations from Dutch are my own best attempts):

Olivier Berghuis, Solar Team Twente (2017): “As team leader you are the one ultimately responsible for the success of the project. That means that you have to keep a close eye on the progress of the project’s technical, communication, and financial aspects. The mood of the team and the personal development of each team member are also critically important important responsibilities of the team leader.” (“Als teamleider ben je eindverantwoordelijk voor het slagen van het project. Dat betekent dat je de voortgang van het project op technisch, communicatief en financieel gebied in de gaten moet houden. Daarnaast is de sfeer binnen het team en de persoonlijke ontwikkeling van elk teamlid een zeer belangrijke verantwoordelijkheid van de teamleider.”)

Shihaab Punia, University of Michigan (2016): “… build the best possible team and team culture …”


Photo: Jerome Wassenaar

Irene van den Hof, Solar Team Twente (2015): “I think that I am a good listener for my teammates. I try to put a lot of emphasis on that. Everyone is young and inexperienced, and that can sometimes cause problems, but together we are indeed a team, and everyone has to reach the finish line – I make sure of that.” (“Ik denk dat ik heel goed kan luisteren naar mijn teamgenoten. Daar probeer ik ook veel aandacht aan te besteden. Iedereen is jong en onervaren en dat kan voor problemen zorgen, maar samen zijn we wel een team en iedereen moet de eindstreep halen, daar zorg ik ook voor.”)

And it’s worth repeating the excellent insights from Rachel Abril, who was on the Stanford solar car team for four years (“Go fast, but not recklessly fast. Test it. Test it again. Test it more. Use failure as a foundation for success.”):


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ASC 9: Aerodynamics

For both the Challenger class and the Cruiser class, solar car racing is to a large extent about aerodynamic drag. That’s overwhelmingly what the hard-earned solar energy is being wasted on, and therefore it’s what teams need to concentrate on minimising. The drag force on a car is given by the equation:

F = ½ Cd A ρ v2

Breaking that down, v is the speed of the car, ρ is the density of air (about 1.2), A is the frontal area of the car, and Cd is the drag coefficient, a number which indicates how aerodynamic (and therefore, how energy-efficient) the shape of the car is. For Challengers, minimising Cd allows the speed v to be increased, while for Cruisers (for which the average v is essentially given), minimising Cd allows non-solar energy use to be minimised. Of course, minimising frontal area is important too (and that is the motivation behind asymmetric Challenger cars).

To give a feeling for the all-important Cd, here are some vehicles with values ranging from 0.19 to 0.57:


Drag coefficients for a selection of vehicles. Clockwise from top left: 0.57 – Hummer H2 (photo: Thomas Doerfer); 0.30 – Saab 92 (photo: “Liftarn”); 0.26 – BMW i8 (photo: “youkeys”); 0.19 – General Motors EV1 (photo: Rick Rowen)

Because Cd is so all-important, it is the one thing that solar car teams are really secretive about. Challengers generally have values under 0.1. With no need for practicality, they chase their way towards the impossible goal of Cd = 0, trying to come up with the perfect race car, which will slice through air like a hot knife through butter:


Nuon’s 2005 car, Nuna 3, with Cd = 0.07 (photo: Hans-Peter van Velthoven)

Cruisers, on the other hand, have to balance aerodynamics with practicality. Bochum’s early SolarWorld GT had Cd = 0.137:


Bochum’s 2011 car, SolarWorld GT, with Cd = 0.137 (photo: “SolarLabor”)

Eindhoven’s recent Stella Vie, with its sleek aerodynamic shape, does much better than that (but they won’t say how much better):


Eindhoven’s 2017 car, Stella Vie (photo: TU Eindhoven, Bart van Overbeeke)

I understand that Sunswift’s 2013–2015 car eVe had Cd = 0.16. Appalachian State (Sunergy) have stated that their newly-built ROSE has Cd = 0.17. PrISUm’s Penumbra has a higher value (Cd = 0.2), because of the blunt end which they chose for practicality reasons (although they did do a few clever things to reduce the impact of that blunt end). I’m not aware of the Cd values for other ASC cars.


Appalachian State’s beautiful ROSE, with Cd = 0.17 (image credit)


ASC 8: About Cruiser Practicality

The American Solar Challenge Cruiser class is a contest for multi-person solar vehicles, each 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 on time, carrying as many people as possible, and drawing as little power from the grid as possible.

Cars are also scored partly on practicality. This can mean different things. Eindhoven’s 2015 car (Stella Lux), for example, was designed as a four-person family car, and the team took photos of it doing family things like shopping, going on holiday, and picking children up from school. A big feature was that, for an average family in the Netherlands, the car would produce more electricity than it used. The car scored 84.5 for practicality at the 2015 World Solar Challenge.


Eindhoven’s Stella Lux (photos: TU Eindhoven, Bart van Overbeeke 1, 2, 3, 4 – click to zoom)

Bochum’s 2015 car (ThyssenKrupp SunRiser), on the other hand, was a luxury two-person sports car, with leather seats and an incredibly beautiful interior. It was an almost perfect example of the car it was trying to be, and scored 80.5 for practicality (far higher than the next car, which scored 63.5).


Bochum’s ThyssenKrupp SunRiser (photo: Anthony Dekker)

One of the highest WSC 2017 Cruiser practicality scores went to PrISUm for their four-seat Penumbra, which was intended as the kind of practical SUV that you might take on a fishing trip. The car has plenty of room for carrying your esky, tackle box, etc. PrISUm deliberately made some aerodynamic compromises in order to achieve their practicality goal, and the car scored 79.8 for practicality at WSC 2017.


PrISUm’s Penumbra (composite image)

This year at ASC, PrISUm’s Penumbra is again a strong contender. Minnesota (UMNSVP), Appalachian State (Sunergy), and Waterloo (Midnight Sun) are entering two-person solar sports cars, while Onda Solare from Italy seems to be inspired by Eindhoven (see my annotated teams list). It promises to be an interesting field.


Solar cars – From the Outback to the Oregon Trail

As I watch the lead-up to the American Solar Challenge next July, above are the entries that previously raced in the World Solar Challenge in Australia last year. Left to right from the top, they are Michigan (came 2nd), Iowa State University / PrISUm (raced in the Cruiser class), Western Sydney (came 6th), Illini (participated in the Adventure class), Principia (raced, but trailered after 2390 km), and Minnesota (raced in the Cruiser class).

Several different approaches are visible here to building a car for both races. It’s easier to do so in the Cruiser class, for a start. Illini chose to build their car for the ASC and race it non-competitively in Australia. Principia built their car for both events (unveiling it at FSGP 2017). Michigan and Western Sydney built their cars specifically for the WSC, and may have to adapt the cars for the American race (last ASC, Michigan had to modify their car, and then incurred a daily 6-minute race penalty because the modifications made the car too wide).

My ASC race information page will be updated from time to time with information on the progress of these and all the other teams.


Solar car team composition

The chart above shows 2017 team composition for the Eindhoven and Bochum solar car teams (divided by study major, not team responsibility). Not surprisingly, electrical and mechanical engineering students are the core of both teams (about half in each case) Yet there is also considerable diversity, because the business side of a solar car team requires other skills too. The Bochum team also includes a media unit, which explains the large “other” category (one of the team photographers is a biology student, for example).

The chart was constructed by parsing web pages, which may have introduced errors (also, I guessed a bit with the German words). But the main point stands – solar car teams require a diverse set of skills.


The Bochum car (photo: Anthony Dekker)


WSC: final Cruiser results

Based on the official results, the chart below (click to zoom) shows the final scores for the WSC Cruiser class. Each team has three coloured bars: first the number of person-kilometres, which should be large (black icons show occupied seats and white icons empty seats), then the energy usage, which should be small (number of charges, which is 6 in each case, times battery capacity), and finally the overall efficiency score, which should be large again (it is the ratio of those first two numbers). The rule for the efficiency score bar is: first bar divided by second bar, then scale so that the largest result is 80%. The scaled practicality scores out of 20 (grey bars) are then added. Eindhoven is the clear winner, with Bochum second.

The chart below (click to zoom) shows the raw practicality scores for all Cruisers (finishing, non-finishing, and non-starting).