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### Cooling Effect

Posted: Oct 05 2018 4:30am
Here's another thing that we can see and quantify from the log data, and that is the increased solar output we get on the panels from the cooling effect of passing air as we're riding. When you stop to take a break, you get some advantage that you can then perfectly orient the panels towards the sun. But it also allows the panels to get warmer than if you kept riding, and warmer solar panels have a less voltage and hence less power output.

Here's an example from a quick gas station stop. At first we orient orient the trike more ideally to be perpendicular to the sun direction and that immediately increases our power from ~360 watts to 378 watts. But then over the next 5-6 minute the goes back down to 357 watts as the roof heats up.

Here's another example where we stopped just for 5 minutes, and the solar power went from 313W to 300W.
SolarWattsVsHeating2.jpg (158.33 KiB) Viewed 3609 times
These aren't huge numbers but they are noticeable. Looking at some random examples I can find in our log data the solar output seems to drop by about 5% within 5-10 minutes of stopping. A fun theoretical question is whether the energy needed to actively cool the panel would be more or less than the energy gained from increased output.

Not that you want to spend too much time on your solar ebike trip stopped. But if you are stopped, is it worth running some small fans to keep the solar cells cool? Looking at these numbers I'd say probably not.

### Re: Cooling Effect

Posted: Oct 05 2018 3:30pm
justin_le wrote:
Oct 05 2018 4:30am
These aren't huge numbers but they are noticeable. Looking at some random examples I can find in our log data the solar output seems to drop by about 5% within 5-10 minutes of stopping. A fun theoretical question is whether the energy needed to actively cool the panel would be more or less than the energy gained from increased output.
This is consistent with my findings. It's good to see this in the empirical data. The thermal coefficient of power for Gen II SunPower cells is -0.35%/ºC so a 5% drop would correlate to a 14°C rise in cell temperature. In full sun with no airflow, cell temperature rise is typically 25-30°C above ambient so theoretically you could gain up to 10% if you could get the cell temperature down to ambient air temp. That doesn't sounds realistic with just fans and/or heat sinks but it does explain why you may notice a gradual 10% drop in power when you emerge from a cool garage directly into full sun.

In my modeled solar output, I initially failed to account for increased airflow over the solar panels from the travel speed of the bicycle. Anecdotally, I would see these drops in power when I stop but I didn't have enough logged data to quantify the effect. I looked at how wind speed in the weather data was used to calculate PV cell temperature (here's a paper on it). I found that at bicycle speeds, the power gain from increased airflow over the solar panels peaks at 5-7% but the annual average is in the range of 1-3%. I now use a 2% adder in my model when the bicycle is moving.

For anyone considering active or passive solar cell cooling solutions which will add weight and complexity to your project, keep in mind that you will not get 5% more Wh per day. The peak gains only apply when plane of array (POA) irradiance is around 1000 W/m^2 (cloudless conditions, solar noon +/- ~3 hrs). Earlier and later in the day and whenever there's any cloud cover and any time your panel isn't oriented perfectly you're getting less. Even on very sunny days, a significant portion of your daily Wh are accumulated under these conditions.

Solar cell temperature is a function of irradiance. At 500 w/m^2 (very bright overcast conditions or poor solar panel orientation) your cells are only heated half as many degrees over ambient air temperature meaning that your 5% cooling gain becomes a 2.5% gain. If you were getting 10 extra watts in full sun from your 200 watt panel, you will only get 2.5 extra watts at half sun (2.5% of 100 watts).

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

Posted: Oct 05 2018 5:36pm
justin_le wrote:
Oct 05 2018 3:37am
I applied a 15 day moving average to make it possible to compare with typical weather data
We had a friend who's involved in tracking migratory animals recently share us this program here
https://www.movebank.org/node/6607 which would let you extract the actual weather info for an location at any time in the past, instead of using 'typical' data. I haven't looked into it in any detail but if we could upload the GPS data for a trip and get back a set of cloud cover, wind speed and direction data for each point, that would be amazing.
Somebody else is interested in weather data along a path and they're creating tools to do that? Cool.

Typical meteorological year (TMY) data is a good choice for modeling average output of a system over 10, 20, 30+ years or predicting average daily Wh for Ushuaia in January. When analyzing trip logs, actual weather data for the same dates would be a better choice. Unfortunately, the PVWatts API I'm using for my modeling tool does not have an option for using custom weather data files.

Converting weather data into solar output watts can be done with other tools, or even from scratch by deriving cell temperature and irradiance from weather data, but it's not trivial. For example, most weather data sources do not include physical measurements of direct and diffuse irradiance so they need to be extrapolated from other measurements. There are companies like SolarAnywhere who specialize in this but they're focused on small niches with big budgets like utility-scale solar installations. They even do some short-term solar forecasting to help with stuff like utility grid load balancing.

My current efforts were mostly low hanging fruit for me. The goal was to get a ballpark figure of average daily Wh for an arbitrary date range for any location to help with route planning. Log analysis using custom weather data may be a project to tackle down the road when I have some down time. Hey, maybe I could add some sensors to my bike to measure ambient temp, wind speed, irradiance... the Analogger has input pads for a thermistor!... then again, feature creep already has me months behind schedule so maybe not.

### Re: Cooling Effect

Posted: Oct 08 2018 8:32am
justin_le wrote:
Oct 05 2018 4:30am
A fun theoretical question is whether the energy needed to actively cool the panel would be more or less than the energy gained from increased output.
I have found myself visualizing liquid cooling sitting under my solar canopy, especially in parts of the world where the heat not be considered an excess as often as a gift...
Observing the data I think your numbers say you had some really good quality of cells (myself I am going to learn how to do surgery an fix one that of the 3 Chinese 100W I was able to afford...

Raf van Hulle is so secretive, if nobody had damaged his cells nobody would even know that he uses some extra high performance cells - Is there a data collection somewhere about the technology used by (especially the highly successful) participants?

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

Posted: Oct 08 2018 11:27pm
Would the use of peltiers in this case be of benefit? The cool side on the elements that need cooling, the warm side mounted with heat sinks and exposed to the passing air.

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

Posted: Oct 09 2018 12:30am
And where does the power to run the peltiers come from?

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

Posted: Oct 09 2018 11:45pm
a disparity in temperatures as in the case of an overheating motor and passing air of ambient temperature, a peltier will generate electrical polarity: seebeck effect.

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

Posted: Apr 15 2019 9:05pm
So @justin_le... Are you registered for the 2020 version ?
With a bit more preparation work and time I would definitely be supporting your solar bike

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

Posted: Apr 16 2019 3:55am
There must be an abundance of data form all those data Loggers.

Is this data available or does/did someone make a summary?

I would be interested in the following information for each vehicle and each day:

- Daily time riding on bike in hours
- Distance driven per day in km
- Time while bike is in charging mode (not driving) in hours
- Solar energy produced (Wh/day)
- Motor energy consumption (Wh/day)
- other energy consumption (Wh/day)
- Battery SOC at beginning of each day in Wh or % + battery SOC at the end of trip.
- (if available: Human energy pedalled in Wh/day)

This would be great to compare different vehicles and concepts and "race" strategies.

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

Posted: May 29 2019 2:32am
Cephalotus wrote:
Apr 16 2019 3:55am
There must be an abundance of data form all those data Loggers.
There IS an abundance of data, but just a shortage of time. I has one of our software co-op students working on parsing and organizing much of it (and also fixing/correcting a bunch of corruption that managed to make it into a lot of the data streams) but we didn't get to the final stage of organizing it before the term ended at the end of December.

With people deep in preparation for the 2019 event though there should be some extra motivation to get this out there soon so I will do my best!

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

Posted: Nov 27 2019 5:17pm
Cephalotus wrote:
Apr 16 2019 3:55am
There must be an abundance of data form all those data Loggers.
I was interested in exploring the data to see what guidance it may contain for selecting solar panel size and tilting vs. non-tilting mounting design choices for casual solar bike touring. Here's what I found:
Screen Shot 2019-11-27 at 1.50.18 PM.png (33.5 KiB) Viewed 2291 times
I excluded two riders who suffered major solar panel losses along the way and used solar watts per rider to allow (an imperfect) comparison of single riders and tandems. The linear trend line is a surprisingly close fit. You can pick your target daily distance and use the line to tell you what size solar panel you need or use it to predict your daily distance for a given solar panel size.

The 440 watt outlier is Stéphane Bertrand, who came in 4th place. I speculate that the lower-than-predicted daily distance is due to his below-average ratio of solar watt-hours to solar watts (3.3) and above average energy consumption of 7.5 Wh/km at a high average speed of 26.1 kph.

The 270 watt outlier is the tandem team of Bernard and Yann Cauquil with a 540 watt array on their tandem. The higher-than-predicted daily distance can be attributed to the best-in-class solar Wh/W ratio (3.9) and below-average 5.9 Wh/km per rider at an average speed of 23.9 kph.

Human Wh were not recorded so it's difficult to account for the pedaling contributions of stronger vs. weaker riders. More or less efficient vehicle designs, route selection, etc. also surely play a role but solar panel size appears to be a solid predictor of average daily distance.

Next, what is the best strategy for getting the most watt-hours from your solar panel? Four of the top five in this group used panel mounting strategies which allowed them to ride with the panel tilted. They averaged 3.7 Wh per day for each solar watt. The rest had panels which were always horizontal when riding and they averaged 3.3 Wh per watt. The average gain from riding with a tilted panel was 13%.
Screen Shot 2019-11-27 at 1.13.48 PM.png (26.9 KiB) Viewed 2291 times
Bernard Cauquil posted an analysis (original French, translated to English via Google) using data from a single day and concluded the gain was only 9%. I agree with his recommendation that it is far simpler to add 10% more solar panels and avoid the complexity of tilting mounts for summer touring. In winter, the gains from a tilt (manual or automatic) would be much higher.

I also looked for a pattern to quantify the advantage of a roof mounted solar panels versus trailers and other lower mounts which are subject to self-shading early and late in the day. I found no such correlation here. Some of the lowest Wh/W ratios were for roof panels whereas 7 out of the top 10 Sun Trip finishers used designs with some amount of self-shading.

I shared my spreadsheet with all the daily data. Anyone can download it in Excel or OpenDocument format using File > Download. If you log in with a Google account, you can also use File > Make a copy to save your own copy which can then be edited in the browser to do your own analysis. The data files prepared by Grin Tech are here.

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

Posted: Nov 28 2019 5:15pm
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?

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.

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.
Screen Shot 2019-11-29 at 10.26.46 AM.png (100.26 KiB) Viewed 2229 times

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

Posted: Nov 29 2019 1:47pm
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. :^)

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

Posted: Nov 29 2019 6:40pm
wturber wrote:
Nov 29 2019 1:47pm
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.
Screen Shot 2019-11-30 at 9.10.59 PM.png (150.96 KiB) Viewed 2157 times
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.

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

Posted: Nov 30 2019 8:55am
solarEbike wrote:
Nov 28 2019 5:15pm
.... 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:

https://ridefar.info/races/transcontine ... e/tcr-no7/

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

https://ridefar.info/

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

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

Posted: Nov 30 2019 4:42pm
Cephalotus wrote:
Nov 30 2019 8:55am
This website offers plenty of information about winning long distance races:
https://ridefar.info/
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.
Cephalotus wrote:
Nov 30 2019 8:55am
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.
71834619_398593584360493_973046110987905435_n.jpg (207.82 KiB) Viewed 2176 times

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

Posted: Dec 01 2019 4:01am
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.

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

Posted: Jan 31 2020 11:24am
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.