How good is Tokai really?

There were those who thought Tokai had a terrific advantage over the competition in 2009 because of their awesome GaAs solar array, and they thought that the new regulations would level the competition and take away Tokai’s supremacy. Reality now proves them wrong. Apparently there must be something more to it.

Lightyears ahead of the rest?

Why is Tokai so good?

Let’s do some numbers based on Day 3 results. Tokai departed Wauchopa at 08:00 and reached Kulgera – 667 km down south – at 16:02, having stopped twice at the 30-minute control stops along the road. So – with 7:02 hours driving – they averaged at 95 kph.

Nuna 6 departed at 08:08 and arrived at 16:37 – thus having averaged 89 kph. This 6 kph difference with Tokai leads to a gap of about 30 minutes between the two cars.

Since this race is about energy, let’s do some energy calculations. I will take this site as example – you can calculate power consumption based on weight and aeroshape.

A typical solar car weighs in at 230 kg (150 kg + 80 kg driver) and has a CdA (a measure for aero drag) of 0.09.

Fill this in on that site and look at the resulting tables: 89 kph leads to a consumption of 1315 W. Nuna drove for a total of 7:30 hours, so total energy consumed on this 667 km stretch is 1315 x 7.5 = 9.9 kWh.

As a reference, Nuna used the equivalent energy of 6 hours vacuum cleaning to travel 600 km at normal commuting speed.

Tokai’s 95 kph with the standard specs lead to a consumption of about 1550W and since they drove for 7 hours, their consumption amounts to 1550 x 7 = 10.9 kWh.

In other words, to create a gap of 30 minutes to Nuna, Tokai had to consume 1 kWh of energy more than Nuna 6, or 10% more energy.

Obviously, energy flows into the car via the solar panel, but where does it go to? First of all, there are losses from solar panel to electric motor, like in the motor controller and other electronic equipment required for operating the solar car.
Secondly, the aerodynamic shape requires energy – the shape of the car is important but also surface smoothness.
Thirdly, there is rolling resistance, related to the type of tire and the weight of the car pushing on those tires. Less weight decreases rolling resistance.

So, let’s see how good Tokai needs to be to be able to spend 10% more energy create that 30-minute gap.

Keep in mind that 1% of energy consumption is about 12W, similar to a small lightbulb.

A 10 kg lighter car leads to 1.5 % less energy consumption.

5 % improvement in aerodynamics lead to 2 % less energy consumption. 5% is the difference between a clean car nose, and one which has flies on it, or other irregularities. So the car needs to be as smooth as possible at all times. Small things have great impact.

If your panel is able to give a mere 2% more solar power, the car has 2% more energy to spend.

If you are able to make your electronics between panel and motor just 1% more efficient, there is a direct relation and you’ll have 1% more energy to spend.

Let’s talk a bit about the battery. A typical solar car battery can hold 5kWh energy. Solar cars take into account what energy the sun delivers and what they can take out of the battery. Battery energy level is called State of Charge (SOC), and you may finish a Race Day with a certain percentage of SOC. Suppose you have 2 similar cars – if one drives faster on a race day, he will have covered more distance but will have less Battery SOC.

Now suppose Tokai has taken more out of its battery SOC than Nuna, when rolling into Kulgera. Let’s say that number is 3.5% of the total Energy Consumption, which comes down to 0.35 kWh. On a battery with 5 kWh capacity that’s 7% SOC less than Nuna, which is really not that much.

In short, for Tokai to gain 30 minutes on Nuna, they need to have taken 7% more out of their battery, have a car that weighs just 10 kg less, have an aero that is just 5% better (which could already be achieved with keeping the car smooth and clean), a panel that can power 2 small lightbulbs more and a little more efficient electronic system.
That totals the 10% of energy that Tokai got to spend to increase their lead by 30 minutes.

Is Tokai that mystical energy powerhouse that people claim it to be?

No. It’s all in the small numbers as described above. A little bit better here, and a little bit better there can already lead to fantastic results.

Tokai’s technology is not lightyears ahead but just a few lightbulbs in every area.

Tokai is not magic, not supernatural, not sent from the future and they don’t overpower their competitors with special technology.

They are just a very good team with great attention to detail. And that’s how you win races.

23 thoughts on “How good is Tokai really?

  1. Interesting article :) The last 2 phrases say it all.

  2. Excellent article. There is, however, one other possible scenario that matches the current race results and that is Tokai drawing and extra kWH from their batteries compared to Nuon (all else being equal). Perhaps Nuon is saving energy for the cloudier SA racing.

    That said, I think you’re right!

  3. Hi,

    Good article! But remember that tokai buys a solar array, buys batteries and more and let it put together. For example nuon makes the most of the car by itself, which has the consequence that its never that good as bought. But you do get a lot of experience and learn a lot from it. That is the most important goal of the race.

  4. @cpheineman: Are you saying Tokai bought the victory (that is to say, if they win, it isn’t over yet)? That’s a steep claim. That’s more or less the same as the reproaches the Nuna got from certain corners in the years that they won, and now they’re not winning because they ‘only’ built the car themselves?

    And the most important goal of the race is ‘getting a lot of experience and learning a lot from it’, you say. That’s not what I heard Siebe say when I visited the Twente team during their wind tunnel tests. I clearly heard him say the goal was to win.

    I don’t understand your comment. Can you elaborate, please?

  5. @chheineman

    I kind of agree with you. I think the winner or top teams are comprised of three things: their ability to procure the most advance technology (60%), reliability/team dynamics (20%), strategy (15%), and luck (5%). There are clear advantages and disadvantages to this and maybe it would be good to compare it F1 or something.

    It would be interesting to see the data (car specs vs winning rank) from these races and draw the conclusions from there.

  6. And where is this solar car dealership that Tokai has discovered?

  7. Great article D. Nuna does spend a lot of attention to details and remember they finished equal on the first day. but seeing the situatuion they are driving through i would say keep it in one piece and enjoy the ride.

  8. @FN: it’s in Tokyo. You can buy Bronze Packages, that’ll get you third, Silver Package, that’ll get you second, and the Gold Package was somehow sold out recently. Probably back on sale in 2013.

  9. The reason why Tokai leads is the sponsor. My Japanese wife told me they are sponsored by Panasonic. Besides some money, they they deliver top of the shelf solar cells. During the flash test there are very good cells. 0.1% of the top Wp.
    Those cells went to the Tokai solar car.
    The other teams just buy cells, hoping for some quality.
    Besides PV Panasonic makes batteries. And they sponsored with the top of the shelf quality. Minimal losses in storage and consumption. Those cells went to Tokai.

    Please explain. Do you mean Panasonic designed the car and not the students?

  10. So, if it is this easy, why aren’t the other teams doing this? Being excellent in all of these areas, is a great job. Of course is 30 minutes after three days of racing nothing, but on the other hand, it is all what Twente needed at the beginning of the race.

  11. Dear,

    Please, don’t get me wrong. It is very hard to race 3000 km thru the dessert, with any car. The tokai team does a great job in this.
    About their car, if a specialized company makes the complete solarpanel It has less losses than maked by students.

    And, with or without winning as goal, the biggest thing about this race is gaining experience and learning. As Hans tulstrup had in mind by untaking this challenge.

    Please correct me if I’m wrong

  12. @cpheineman,

    Did panasonic make the solar panel or did they just provide the cells for the students to hand-assemble onto their car? Just like Nuon.


    Why wouldn’ you be able to buy a batch of top 0,1% solar cells fromt Sunpower? It will cost you top $$$$, but I don’t see why they wouldn’t do that.

  13. Dear Anne,

    in 2009 Sharp was the main sponsor of Tokai and they provided the top shelf of the solar car (we spoke with some teammembers of the 2009 team of Tokai), including MPPT’s and solarcells. I guess (and therefore am not sure) it is the same this year, and if it results in winning (like in 2009) why wouldn’t do that again?

  14. @ myself

    I can’t find any facts about who made the solarpanel. the cells are from panasonic, but i can’t find who assembled it. So, could anyone provide some info about it?

  15. @Anne – just a correction there. The Nuon Solar Team does not hand-assemble the solar cells on the car. The cells are bought, and then laminated in Germany according to student design and what they get back are panels of, say, 600x300mm in size which are placed on the car by the students.

    @cpheineman: I think Panasonic/Sanyo laminates it for them.

    The thing is, with this project: if you can do it yourself, do it – if you can’t, don’t mess it up and let someone else do it. This is as much of a management project than it is a tinkering/engineering project.

    If Hans T. created this race for people to build their own car with their bare hands – then the WSC has evolved out of this. The WSC is something that is created to win, and it has quite a bit of prestige now – so teams should find all means necessary to gain that prestige by winning it. That’s how a race works. If that means co-operating with other parties to get this project moving, then so be it.

    I myself am proud of the fact we – as a team with 11 students back in 2003 – co-operated with no less than 77 companies (both sponsor and non-sponsor) to get something beautiful as Nuna 2 on her wheels and bring her to victory.

  16. @diederik

    That’s right, and i agree: if you can do it yourself, do it. It you can’t, let someone else do it. In 2009 we worked with 150 companies… but the assembly we did ourself, the solarsells were laminated by somebody else, but put together by ourself (on the top of the car) incl all the elektronic parts. Even made our own electronic circuits.

    We will see.

  17. my team told me i should should tell you:

    Everything i write, say or do, i do out of personal opinion. So it doesn’t reflect the opinion Solar Team Twente.

  18. From an ex sunswift team member(Wsc 2007) now living in Holland: I think what has been missed in these discussions is mention of the size of the teams bank accounts. It is clear that the teams that have money to spend or good sponsors have an advantage, if they also have the discipline and design skills to match. Less time building=more money spent=more time for detailed design work.
    If students don’t want the first hand experience of not only designing, but manufacturing with their own hands, then so be it, but surely victory is sweeter if it comes from your own hands. In saying this, I think what Wsc have done with silicon vs gallium has been awesome at leveling the field.

    I wish the two Dutch teams all the best of luck. But GO SUNSWIFT!

  19. Smithy! What on earth are you doing in Holland?
    I can tell you personally: closing a sweet sponsordeal (money or in-kind) is definitely rewarding as I closed it with my own hands… It’s not that we live near a river of euros and just stick our hand in it if we need something done.

  20. Not saying that. Also not saying its not extremely rewarding to secure awesome sponsorship. I suppose it’s 50% of the battle. I guess regardless, the Wsc need to continue to make decisions to continue the advancement of technology.
    I’m in holland to experience your lovely weather, your extremely flat and extnsive bike tracks, and mainly to follow my partner so she can do her postdoc. Better learn some of your language too!