My Sun Trip Bike, Back to Back Tandem Trike with Rowing Generator, Pedals, +Solar

My last post offered some conclusions about building a solar bike for casual touring but what does the data say about strategies for winning The Sun Trip 2020?

Max out your solar array
For single riders, the 2018 rules allowed up to 450 solar watts deployed while riding. The 2020 rules no longer specify a wattage limit and only impose a 2.50 m² limit. You'll need to max this out using a custom solar array made with Sunpower Gen III bin Le1 Maxeon cells at 3.63 watts/bare cell. At 125mm x 125mm per cell plus 1mm gap between cells, you can build 2 panels consisting of 6 x 13 cells for a total of 2.48 m² and a whopping 566 watts (excluding encapsulation losses).

Your panel voltage will be too high for a boost charge controller with your nominal 36V or 48V battery so you might want to split into 4 panels. Also, the 2020 rules dropped the words "Solar cells surface is measured from cell to cell, not counting the outer panel borders but including the gaps between cells" so you might want to check with the organizers to get some clarification about how they handle the border measurements.

Use a tilt tracker
Forget what I said about solar tilt not being worth the trouble for casual touring. The difference between 1st and 2nd place in The Sun Trip 2018 was 13%. You'll need the additional 13% a tilt mechanism can provide.

Don't ride a tandem
While there are some theoretical weight savings and aero advantages of two riders sharing the same vehicle, the solar allowance per rider is much lower for tandems. Consider that not a single tandem team made it to Guangzhou in the final rankings with the "100% solar" badge next to its name... possibly because none of them were participating as if they were in a race.

Pedal your butt off
Extrapolating from the #2 ranked rider's 8 hours and 46 minutes per day, you'll need to average 10 hours of riding per day if you want to win. No time to stop and smell the roses. Also, don't bother with carrying the additional 1.50 m² of solar panels you're allowed to deploy only when stopped. You won't be standing still long enough during daylight hours to offset the extra weight.

Pace yourself
Mickaël and Stéphane had almost identical vehicles (short wheel base recumbents with both solar roof and solar trailer) and covered the same total distance along a similar route. However, Mickaël finished 5 days faster despite having 2.6% less solar energy per day. He covered more distance per day not by riding faster and harder but by riding slower and longer. Using the Grin Motor Simulator, I get about 5% more range by riding at 24.8 kph instead of 26.1 kph. If we pretend all other factors are equal, the remaining extra daily km come from additional human Wh from that extra hour of pedaling.

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Cool. Thanks for the analysis. This provides a stark contrast to my much higher Wh/mi consumption in my city e-bike commuting.

I think the tortoise would feel validated by these results. :^)
wturber said:
Thanks for the analysis. This provides a stark contrast to my much higher Wh/mi consumption in my city e-bike commuting.

Same here. It took me a long time to figure out what kind of Wh/mi to expect for solar touring. It's different from everyday local riding where a bigger battery will easily solve your range problems.

So what does the average Sun Trip look like? I pulled out a few figures based on what I found interesting and where there was enough data to tell a story. I figure this is a good reality check for anyone planning a solar bike adventure. If your solar panel size and daily distance expectations are far outside this baseline, you may need to re-evaluate some of your assumptions. Unlike simple back-of-the-envelope solar calculations, these numbers include all those pesky, hard-to-quantify factors which usually get left out of the simple calculations: available sun, shading along the route, headwinds/tailwinds, rough roads, terrain, stationary vs. mobile charging differences, rest days, etc. The bar charts show the number of data points and their distribution in each category.

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DISCLAIMERS: The Sun Trip 2018 had over 30 participants. There are only 13 log files. Two of those had fewer than 20 travel days so I excluded them. Two of the remaining bunch had problems with their solar panels in route so I excluded them from some of the solar performance metrics. I also added several riders using publicly available information about their panel size, travel days and total distance without any detailed logs about solar production. Some of these numbers look like they don’t add up (solar Wh divided by solar W doesn’t match solar Wh/W). I think it’s mostly because of the way I combined them using simple averages instead of weighted averages to account for differences in distance and because there are gaps in the data and possibly because of my (questionable?) decision to treat tandems on a per-rider basis. The discrepancies are on the order of 5-10% so I think that’s pretty good for a rough approximation.
solarEbike said:
.... what does the data say about strategies for winning The Sun Trip 2020?

If you manage to ride 200km/day on average you will be in the top 10, maybe top 5, if you manage to ride 250km/day you are in the range of the winner, so someone who rides 300km/day should be able to win.

The TCR Europe 2019 had a distance of 4000km and 40.000hm crossing the alps and was won in a bit more than 10 days, so almost 400km/day with no motor at all.
Btw, it has been won by a woman and if I understand that correctly on her first ultra endurance bike race:

This website offers plenty of information about winning long distance races:

Okay, we are talking about 10 days vs 45 days, but still the 250km/day don't look so impressive any more.

There are three differences between suntrip race and the TCR

1. Suntrip race bikes are much heavier
2. Suntrip race bike have a much higher air resistance
3. Suntrip racers are forced to stop for 10h per night.

So I assume the winning strategy for suntrip is:

1st: ride as long as you can. Ideally you would ride 12-13h per day in your allowed 14h time frame. This isn't the samllest bit of fun and has nothing to do with travellling and seening other countries. For me it wouldn't work either. 6h/day on real bike time is okay for me and I assume that I could do 8h/day if I have various positions for my hands and a good saddle. For 8h riding time I would need 10-11h, in reality much more if I want to see something of the country I travel through and if I want to eat real food.

So if you want to win you have to manage to ride 11-12h/day within your allowed 14h time frame.You have to use a bike that will not destroy you when doing it for 40days+ I know I can not do it on my standard e-bikes

2nd: At an average speed of 25km/h you have a significant amount of distance when you need to ride faster than 30km/h and air resistance becomes very important. You have to optimize air resistance as much as you can. This includes air resiatsance of you solar generater and of your gear, too, of course. I see lots of potential from the 2018 participants here.

3rd: Use as much solar power as you can without sacrificing to much on #2nand practicability

4th: Don't miss the optimal route (that includes the weather)

5th: Keep your body healthy so it can produce maximum power output (maybe more important than #5). Problem will be to find good food, which collides with priority #1

6th: keep the weight low, especially with hub motors.

most important: your bike must survive the trip or at least be easily repairable on the road.


I assume that a velomobile with a ~500W solar generator will win the Suntrip 2020
Cephalotus said:
This website offers plenty of information about winning long distance races:
Okay, we are talking about 10 days vs 45 days, but still the 250km/day don't look so impressive any more.

Great resource, thanks. I look forward to reading more of it.

If we're looking for ultra long distance self-supported bikepacking comparisons, perhaps there's also something to be learned from Jonas Deichmann's recently completed self-supported 18,000 km trip in 72 days 7.5 hours. He averaged 250 km/day, unencumbered by Sun Trip rules requiring him to carry solar panels and motor or about riding after dark.

Perhaps the winning strategy is to use the smallest allowed solar panel size (0.75m²), distribute it on the bike for optimal aerodynamics regardless of solar generation penalty and couple it to the smallest possible motor with no battery?

If I were the betting type (I'm not), I'd bet on whoever comes closest to matching your guidelines instead of mine. :D

Cephalotus said:
I assume that a velomobile with a ~500W solar generator will win the Suntrip 2020

I don't know if you were just speculating or you already know but it looks like there's already a velomobile in the mix: @canton_veut_on_peut.

Yepp, I have seen that solar velomobile before.

An efficient velomobile needs around 200W for riding at 45km/h. Maybe 300W if you include the solar generator incl. mounting.

A 500W solar generator is able to produce 2500Wh on a okayish day, so in theory you are able to use 250W battery power for 10 hours a day.

I assume that 350-400km per day on flat terrain could be possible with this setup.

A minimal setup could be interesting for a very strong rider who is willing to tide 50 days with a rather minimal setup.
75cm x 100cm at maybe 150W mounted at the rear rack would have low resistance when done right. Weight should be low at that position. Shadow from rider could be a problem, so I would not expect much solar production. Maybe 500Wh on an okayish day.

You could use that for going uphill while riding without motor in the flat.

How much power does the logging eqipment, GPS, navigation device, solar charger and motor controller in standby consume? If its 10W we are talking about 140Wh lost every day.

Nontheless, a strong and determined ridee might be able to ride 200km a day which could give you a goid position.

Do you know how much GaAs modules do cost? A 200W+ panel should be possible at 0.75m2, but are we talking abot 5000 Euro or about 50,000 Euro here?

For traveling with a solar ebike I would use a rather small solar setup. Maybe 150W to 200W solar an a small trailer, a 2000Wh battery and a charger.

I can travel ( != race) 120 to 150km a day using 1000Wh, so recharging in good weather need only to happen every 3 to 4 days.
In bad weather I prefer not to ride anyway :)

If there would be no rules in suntrip sleeping during the day charging from unshaded solar modules and riding at night with the modules packed away would be an interesting option.
hi all. I feel so grateful for all the brainstorming that has been done so far for 2020 edition.
The velo in the picture must belong to Jean-Marc Dubouloz. There's another WAW registered, another Quest, and probably a third WAW to be confirmed.
I'll be the one in the Quest.
Calculations aside, the biggest problem seems to be the frequent breakdowns and flat tyres.