Solar Trailer Technical Advise

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etmz   1 µW

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Solar Trailer Technical Advise

Post by etmz » Sep 02 2019 9:47am

Hello Everybody!

I am building myself a solar trailer for my e-bike for touring Europe next summer. I want something like the one in the picture below:

Image


It doesn't need to be a perfect setup. I don't want to break any records, nor spend all my money on it. I just like the freedom of touring without being bound to grid electricity all the time. I'm not the most technical dude, so I prefer to keep it simple.

I bought a bike trailer, solar panel (100 watts , but I will buy another one) and a boost charge controller (genasun GV-8 / 42v)
My bike has a bafang mid drive (250w) and at this moment I have a cheap aliexpress 36v (17.5 Ah) battery pack.

I have read how other people done this, and it seems I got two basic options :

1. Two batteries Probably the most simple setup. Just buy another cheap aliexpress battery pack, and charge 1 battery pack while I ride (or camp) on the trailer , while the other is connected to the motor and used for riding. I have come up with this list of advantages / disadvantages:

Advantages
  • double my range (if I am able to charge both packs on a campsite)
  • reserve battery (in case my cheap aliexpress pack blows up)
  • It's simple. Not much wiring and soldering
disadvantages
  • heavy. I have to drag along an extra battery
  • less efficient ? Power probably get's lost while charging (instead of the motor using it directly)
  • A bit more expensive, have to buy two batteries (but my batteries also last two times longer)
  • I have to manually switch the batteries / monitor my charging

2. Charge while riding (only 1 battery) I think most people do it this way, but it requires more work and technical expertise.

Advantages
  • Probably more efficient (power the motor directly from solar panels?)
  • No switching of batteries
Disadvantages
  • harder to build, more technical knowledge needed. Have to run wires all over my bike and open up my battery pack to make a connection(input port) for charging
  • I've heard it could mess up the BMS of my battery pack (resetting it all the time). Maybe my cheap aliexpress pack can't handle it very well? Then I probably have to buy an expensive battery.

That's what I could come up with for now. What do you people think about the list? What would your advise be?

I appreciate any input.

Thanks :)

Thomas.

john61ct   100 GW

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Re: Solar Trailer Technical Advise

Post by john61ct » Sep 02 2019 12:00pm

Plan to spend **a lot** more time sitting in the sun than riding.

Even if you stick to this idea for "Green PR" purposes, for practicality carry a quality charger capable of fast (up to 1C-rate) charging when a mains plug is available.

Ideally able to de-rate current when their circuit is not high amps, or when you have overnight, gentler rate extends pack lifetime.

Grin Satiator a top-notch example.

Back to panels - use fold-out "blanket" type so when you are stopped in a field for seven hours, you can deploy 300W or more.

Might not even need the trailer 8-)

etmz   1 µW

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Re: Solar Trailer Technical Advise

Post by etmz » Sep 02 2019 4:31pm

Thanks for your reply John.
john61ct wrote:
Sep 02 2019 12:00pm
Plan to spend **a lot** more time sitting in the sun than riding.
Sitting in the sun sounds good to me 8)
It's the journey that counts for me, not the distance I ride. If i can do 100km/60miles a day I be more than happy.

My calculations are :

I can ride about 100km/60miles on a full charge (with maximum pedal assist). There are 5+ good sun hours in a day during summer (even more when I go down south). 200w in solar should almost give me 1000w of charging during a day. I know my calculations might be on the sunny side, but I only need 600w for a full charge, shouldn't I be capabple of getting a full charge every day? If I cycle for about 5 hours everyday with an average speed of 20 km/h , I can relax in the sun for the rest of the day :D Sounds fine to me.

I read the guys doing the sun trip 2018 sometimes got 400km in a day. I think 100km a day should be possible for me, but I would be still happy with 50.

Even if you stick to this idea for "Green PR" purposes, for practicality carry a quality charger capable of fast (up to 1C-rate) charging when a mains plug is available.
Yes, that's a good idea. I should defenitly get a good/fast charger.

Btw, I'm not doign this for green-PR purposes. I would power my bike with a nuclear reactor if that would be the most practical and efficient solution :twisted:
I prefere my freedom to camp in nature anywhere I like, solar just seems the most efficient and durable solution for it.

Back to panels - use fold-out "blanket" type so when you are stopped in a field for seven hours, you can deploy 300W or more.

Might not even need the trailer 8-)

Yes, I have thaught about that, and it's certainly a way to do it.
But I understand that a 1 wheeled bob style trailer is a pretty efficient way to carry lugage. Packing everything on the bike itself doesn't really give me that much of an advantage as far of energy consumption. And when I do have a trailer, I have to option to charge while I ride... And I can still carry extra (non-foldable) panels that I can setup in a field when camping.

john61ct   100 GW

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Re: Solar Trailer Technical Advise

Post by john61ct » Sep 02 2019 6:08pm

If i can do 100km/60miles a day I be more than happy.

Maybe if you sit all day, and then pedal at night.

200W of solar will give maximum 800Wh of charge, and that is no shading so stationary, with the panel angled towards the sun, lots less if cloudy maybe 100Wh if rainy or trying to charge while riding.

How far that gets you I dunno, but stopping at a cafe for an hour can get you say 4 kWh.

etmz   1 µW

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Re: Solar Trailer Technical Advise

Post by etmz » Sep 03 2019 4:32pm

Then I will add some extra panels.
If these solar trip guys can make it to China, I don't see why I can't do some relax touring. Of course I will bring a charger and charge where I can.

Some preliminary testing I did with my solar panel, shows I should be able to get a full charge on a sunny day with 200 watts.

matmaxgeds   10 mW

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Re: Solar Trailer Technical Advise

Post by matmaxgeds » Sep 04 2019 7:59am

Try the google sheet here for planning the energy you are likely to generate: viewtopic.php?f=6&t=94721&p=1406135#p1408723

etmz   1 µW

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Re: Solar Trailer Technical Advise

Post by etmz » Sep 05 2019 9:26am

That's a great tool!
Many thanks for sharing!

It seems I get less range than I expected. I have have to make my setup more efficient (or increase my fitness :lol: ).

john61ct   100 GW

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Re: Solar Trailer Technical Advise

Post by john61ct » Sep 05 2019 10:21am

I think you're greatly underestimating the availability of shore power along your route.

Assuming you're willing to ask, people will be happy to help out, probably without charge, especially if you're a customer but also farmhouses, petrol stations etc.

Not hard to carry big enough charger(s) to get back to full in the time it takes to eat & have a coffee.

billvon   1 GW

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Re: Solar Trailer Technical Advise

Post by billvon » Sep 05 2019 11:11am

etmz wrote:
Sep 02 2019 9:47am
2. Charge while riding (only 1 battery) I think most people do it this way, but it requires more work and technical expertise.
I'd do that. Really not that hard. Connect the charge controller directly to the battery and you're done. If you want more charging, carry extra 50W panels and just spread them around when you stop.
--bill von

999zip999   100 GW

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Re: Solar Trailer Technical Advise

Post by 999zip999 » Sep 05 2019 12:39pm

They make folding solar panels. But look for a plug. Also cheap batteries can only take 2-3amp thru the bms. Good batteries can charge at 10amps when plugged in to wall socket. Some better bms can take 5-6amp if rated for it. Maybe a leaf or other car style battery. Is this your first ebike ? As it all about a quality battery. The controller is very little a problem as with most motors when use as rated. It's cheap batteries that cause problems. When buying a battery find what cell they are using a trusted vendor will know. If he says tesla like cell he doesn't know. Samsung R25 or Q30 or which exact cell. That's the difference between a cell from the 99cent store or a Duracell so to speak.

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parajared   10 kW

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Re: Solar Trailer Technical Advise

Post by parajared » Sep 06 2019 11:12am

I guess that sort of depends on how many whs you want to consume per day.

I personally find myself creeping into the 2k per day mark at times. You won't get a full 100 watts out of that trailer during the morning and evening which is probably the time you want to charge.

I would expect maybe 40-50w a bit after sunrise then slowly more and more flow until around 10:30 11ish to get the full 100 watts. It starts to peter off on you again around 2-3pm. The stowable panels would be good for this and might get you that 100 watts all day long.

Assuming you consume 2 kilowatthours of energy that would mean 20 hours of re-charge time per day @100w :roll:

billvon   1 GW

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Re: Solar Trailer Technical Advise

Post by billvon » Sep 06 2019 11:20am

parajared wrote:
Sep 06 2019 11:12am
I would expect maybe 40-50w a bit after sunrise then slowly more and more flow until around 10:30 11ish to get the full 100 watts.
Well, you'll never get the full 100 watts. You can probably count on 70-80 watts under ideal conditions from a 100 watt panel.
--bill von

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parajared   10 kW

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Re: Solar Trailer Technical Advise

Post by parajared » Sep 06 2019 11:40am

Well, you'll never get the full 100 watts. You can probably count on 70-80 watts under ideal conditions from a 100 watt panel.
Depends on the panel. I was pleasantly surprised to see my HQST 50w "flex panels" giving just a little more than 50 watts (measured at the wires)

john61ct   100 GW

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Re: Solar Trailer Technical Advise

Post by john61ct » Sep 06 2019 1:02pm

Already spec'd

100W of solar will give maximum 400Wh of charge, and that is with a

top-efficiency panel, nice and clean

sunny weather with no shading so IOW stationary

with the panel angled towards the sun

Lots less than that if cloudy, maybe 50Wh if rainy or trying to charge while riding.

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