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alotria avatar image
alotria asked

MPPT advice for solar-bike

I am currently building an e-bike with solar panels attached on a trailer.

The idea is to charge the battery while driving. I should be able to charge and use the battery for the motor at the same time. I've never done any projects with solar panels before, so I am not quite sure which MPPT I should choose and if my components work together.


This is my setup:

Solar Panel: 2x Sun Power SPR-E-Flex 170w (Rated Voltage (Vmpp) 29.9V)

http://spectrum.sunpower.com/sites/default/files/uploads/resources/sunpower-flexible-panel-170W-6x8.pdf

Battery: 2x 6s 22.2V 16Ah 10c Discharge

Motor: 48V (max)1000w


I thought of using one of the SmartSolar charge controllers. https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-75-10,-75-15,-100-15,-100-20,-100-20_48V-EN.pdf

But I'm not sure which one to choose... Is the MPPT100/20-48V my only option (since i have a 48V Motor) or is it also possible to use something like the MPPT 75/15? Or is there even a better option?

And does it make sense to connect the two batteries in series to better match the voltage of the motor? And is a serial or parallel connection better for the solar panel?


Thanks in advance for helping me out.

Damian

MPPT Controllers
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spirou avatar image spirou commented ·

Just one question that I can't get ouf of my head. Assuming this will be for touring long distances over several days, weeks...unless you're riding at night, when do you charge the batteries? Yes, you would be extending the range (by a bit), but by the time you're done riding for the day there's also not much sun out. So in the end, why bother with solar panels if you still need to find a place to charge over night? And wouldn't it make more sense to just carry a spare battery to extend your range?

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alotria avatar image alotria spirou commented ·

Hi Spirou

You should actually be able to extend your range quite a bit with the solar panel, if it's a sunny day. You will at least double your pedal power.

Of course it's easier to just charge your bike during the night or during a brake, but then you are dependent on existing infrastructure. So I would say to solar bike is more something for an off-road / off-grid adventure. Especially if you travel long distances. And I'am also doing it for the fun of building it:) There is even a solar bike race from France to China:

https://www.thesuntrip.com


some cool projects you can find on youtube:

https://www.youtube.com/watch?v=bSMugd-wGD0&t=179s

https://www.youtube.com/watch?v=X78VCsYJjbA

These are super high-end builds, mine will not be as advanced yet.


Hope this helps:)

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spirou avatar image spirou alotria commented ·

I get the range extension, but you still end up with an empty battery at the end of the day and start with an empty one the next day. Unless you stop quite early in the afternoon or start late morning that is.

But then again, cycling in mid day heat is no fun but perfect for charging batteries while you rest in the shade of your panels so...

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3 Answers
launacorp avatar image
launacorp answered ·

2x 22,2= 44,4 so 48V is your choice if your batterys are stacked in series. But:


6S LiPo is 6x3,7V nominal and 6x4,2V fullcharged so 25,2V. 2x 25,2V in series are 50,4V fullcharged if the batterys are stacked in serial.


A 48V mppt can Charge up to ~58V (check Datasheet!) so you have to make sure that the bms can cut the connection from mppt if required. I personly don't know how you can setup the MPPT in software for your application but I think this could be set up in the software of the mppt.


For your panels you should think of this:


Connected in parralel you will never exceed a voltage of 22,9V and in series 45,8V. Both constellations won't work because you will never reach the Vbatt+5V to initiate charging process. You have to put 3 of this pv panels in series. The MPPT will converts your higher pv-voltage into the suitable voltage for you battery. But for a 100/20 you better don't put 4 of your panels in series because a cold panel can reach a higher voltage than given on Datasheet for 25°C! So 4 of these can overshoot the 100V of the mppt in unlucky conditions.

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Vance Mitchell avatar image Vance Mitchell commented ·

The panels in the link have a Voc of 34.6 and a Vmp of 29.4.

2 in series would have 10v over the battery voltage you mentioned, so should be workable.

3 in series would exceed the maximum input voltage of the controller.

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alotria avatar image
alotria answered ·

Thanks a lot for your reply.

It seems that what I need is a Boost-MPPT. Something like this:

https://genasun.eu/collections/genasun-lithium-mppts/products/genasun-gv-boost-8-lithium-50-4-volt-mppt

Or do you see the possibility to use the SmartSolar MPPT if i connect my batteries in parallel and connect the panels in series.

And then convert the 24v to 48v for the motor?

Is it always necessary to use a BMS or can you connect the battery directly to the SmartSolar MPPT?

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launacorp avatar image launacorp commented ·

I don't think a DC/DC boost converter is the best (and efficient) soloution but it could work (with some powerloss over the DC/DC).


A LiPo without bms is ABSOLUTY CARELESS and your Bike will burn faster than u can pronounce bms!


Pls, very very pls take care what u do! Get as much info's as you could. A LiPo is not a toy!


What I can give you at now is a notice to watch "greatscott" on YouTube. He's a professional and you can learn much abaout LiPo's, electrical Bike's but espacially basics about Electronic's.

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alotria avatar image alotria launacorp commented ·

ok, thanks for the advice:) I will be careful and also check out his youtube channel!


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coin3ip avatar image
coin3ip answered ·

I don't charge while riding, and don't plan on it at all. but maybe my experience making a 48V direct solar charging setup can help you..

I use the 100/20-48V to charge my ebike (kuberg freerider street. 4kW 48V 22Ah)
so, to match the specs of the charger (54.6V 10A), I use 2x340W panels in series (trinasolar HONEY+DE06M.08(II) - 30V / 9.9A ).
The setup is I think the simplest it can be.

You plug the MPPT directly into the battery (but again, I don't charge while I'm riding, so I don't know).

The 100/20-48V MPPT is super small and light, so it's perfect for ebikes. (it could be improved with an outdoor/waterproof version though ;) )
The 'next' 48V MPPT is the 150/45. I first used it (because the 100/20 wasn't out yet, or just didn't find it in the catalog cause it's a 'special one' with the 24V, but hard to find when searching for 48V) but was way too big and heavy, adding 3,5kgs of overspecd weight.

So, for the choice of MPPT, I'd strongly advice for the 100/20-48V, so.. don't overspec the battery. the preset for a fully charged 48V lipo battery is 56.7V. I have a li-ion battery and the seller told me to use this preset and would be perfectly ok. I've then sets the 'limits' the same as marked on the AC charger (54.6V 10A) of the battery.

Obviously it's two very different systems. Apparently, you're searching for long range on-road, and I'm all about off-road exploration, and don't mind at all having to stop for (at least) 2 hours every 30kms. ^^

But like the other before, I'd say try not to underspec your array. you'll put boost converter, making the system heavier and more complex without gaining performance. it's just a hack to make it all work and fit the trailer. I've also seen big trailers (on youtube) that fit 2 large 300W 24V panels quite like mine, so it's possible.

The thing is to choose panels that can get you the specs you need. And if you're like me and the panels don't exist, design them and try to have them built ^^

So, mine is a very big and heavy array (2x20kgs. 2x(1x1.7m) ) and 'could' fit on a long trailer, but wouldn't be a very practical option for me. So, I'm gonna have a similarly spec array made, using flexible (and then, foldable) panels to be carried on the pilot's back. it could bring the weight of the array down to 10-12kgs and a folded footprint of approx. 50x60x10cms.
There's no real option on the market for "high" voltage (48V) portable array. Or at least, I haven't found a suitable one yet. There's one south african company that makes a high amperage / low voltage array (2x22V 12A in parrallel), I'm gonna ask them if they've tried it in series (their proprietary connection option is clearly designed for parrallel :/ as it's "for" direct use of electric handled tools.. In series, it could bring it closer to my needed specs, but if I have to use 3 of their panels (in series), it would become too heavy to be carried on my back (but very easy, folded in a trailer - that's why I'm still considering the trailer option for me too, even though it would restrict me sometimes).

I went a bit far off topic in the end, sorry ^^


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alotria avatar image alotria commented ·

Super cool project! It's for sure a lot of fun to ride around with your bike:)

Do you have a project page where you post updates?

And thanks for all the detailed informations on your build. Since I want to be able to charge my bicycle while riding and don't want to have a super big trailer I'm a bit limited with my solar panels. As launacorp wrote in his answer I would need three 170w panels to get the desired voltage for the victron MPPT. But this would make a way too long trailer.

It's a bit unfortunate that my Motor and battery system is 48V. It would have worked better with a 24V system. But I already had the component from a previous e-bike build.

So the only solution for now seems to be using a boost MPPT...

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launacorp avatar image launacorp alotria commented ·

1 thing I have overlooked was, Vance Mitchell told, that your 2 pv panels DO work because they have Voc 34,6V. So just connect them in parallel and youre fine.


Pls make arrangements that your stacked batterys can be balanced against each other. U told that the batterys are 6S and 2x 6s is 12s... Perhaps u can find a 12S BMS on eBay etc. So the 2 packs are balanced against each other. Than youre project have a good chance to be a success.

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alotria avatar image alotria launacorp commented ·

I really appreciate your help:)

Shouldn't I connect the panels in serial to reach the desired voltage? Or why would parallel be better in my case?


Serial connection of my sunpower panels: http://spectrum.sunpower.com/sites/default/files/uploads/resources/sunpower-flexible-panel-170W-6x8.pdf

Voc: 2x 34.6V = 69.2V

Vmpp 2x29.4 = 58.8V


Like this I should reach the required Vbatt+5V

(12*4.2V+5V=55.4V) (max charge voltage)


Would I then be able to use the SmartSolar Charge Controller 100/20-48V?

https://www.victronenergy.com/solar-charge-controllers/smartsolar-mppt-75-10-75-15-100-15-100-20#downloads

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alotria avatar image alotria alotria commented ·

This is written in the specifications of the charge controller

1b) The PV voltage must exceed Vbat + 5V for the controller to start.

Thereafter the minimum PV voltage is Vbat + 1V

So this should work, right?


Max. PV open circuit voltage of the charge controller is 100V and I also would not exceed that.

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launacorp avatar image launacorp alotria commented ·

I am a hobbyist like u and therefore I like your project.


The 100 in 100/20 is your maximal pv voltage, the 20 is the maximum current to your battery's. The 48 specifies the 48V battery voltage of a 48V lead-acid battery (12V cells= 14,4V x4 14,X volts, some batterys need 14,5V or 14,8V so 14,ish Volts).


SSo I think an 100V/20A/48V mppt would be okay. If your batterys are full and you will use 1kW power on youre motor, the mppt could deliver 1kW of power (20Ax 48,ish volts) but your panels don't, so on this side you are safe in my opinion. But it's only the Charge-prower in best conditions. The real power comes from your LiLo's. The charge-power is mathematical against the power you pull from the LiPo's so 500W use of power on the motor and 200W be given by pv your LiPo's must deliver 300W.


I think the mppt is managble as accurate you need in software to define your LiPo's in max Charge-voltage but don't hit me if I am wrong! But for this usecase I have the requirement that u have a 12S BMS connected to your 2x 6S batterys. Sorry for my poor english but I am german :)


Moreover I think that your 48V motor will not be destroyed by maximal 50,4V of your battery bank (4,2V x 12cells). This 4,2V/cell are not long under this heavy load, then u have tolerances and so on. The maximum load on a motor is only at starting moment wen it has to move an pushes the wheigt of your vehicle.

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launacorp avatar image launacorp launacorp commented ·

Just a correct of my post a time ago, I meant connect them in series

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alotria avatar image alotria launacorp commented ·

Mein Deutsch ist wahrscheinlich auch ein wenig besser als mein Englisch;) Ich werde aber nochmals auf Englisch antworten, damit alle mitlesen können.


Thanks again. I will try it with the 100/20 48V MPPT. I should be able to define the exact charging voltage in the app.

I normally only use 200w-300w with the motor and never more than 600w-700w. (full throttle)

So I think I should be fine with the batteries. According to my calculations the max. output of the batteries is 710.4w. (2x 6s 22.2V 16Ah 10c ) 2*22.2*16*10=710.4w

To motor is rated up to 54.6V so this is fine as well.

Do you have any recommendations for the BMS?

I will keep you updated with my project!

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launacorp avatar image launacorp alotria commented ·

Schön, dass ich nicht alleine bin und es probiere international zu halten ;)


I have Unfortunately not a bms for u :(


If u have time, go and pick some in the internet and check them with a labor power adaptor if u have and a multimeter.


I have some 7S bms laying around but they doesn't help u :(


Just 4 fun:

Ich lebe im Westen Deutschlands, falls du dort auch heimisch bist, könnte man sich ja mal treffen, btw hier gibt's auch ein paar SEHR Interessante E-Bikes, die es sich zu Fahren lohnt, das kannst du mir glauben ;)


Als Anreiz: https://youtu.be/iBvH9n8QICU

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alotria avatar image alotria launacorp commented ·

Ist ja mega cool, baut ihr die? Und krass schnell! offroad geht ja ultra ab :P

Da komme ich natürlich gerne mal vorbei wenn ich mein Gefährt auch fertig gebaut habe:) Wo wohnst du denn genau?

Ich selber wohne in der Schweiz, in der nähe von Zürich. Falls alles gut funktioniert, sollte ich mit dem Fahrrad dann so 300-400km pro tag schaffen.

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coin3ip avatar image coin3ip alotria commented ·

also yes, I post updates "everywhere" ahah .. most relevant would be my patreon www.patreon.com/coin3ip and/or my website www.danslecoin.net :-)

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alotria avatar image alotria coin3ip commented ·

cool, i will check it out:)

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coin3ip avatar image coin3ip commented ·

Also I've check your sunpower panels and it seems OK in series, as they're both 30V. 5,6A is a bit low (for me), but as you'll have them constantly working on the trailer, it should be fine.. the MPPT 100/20-48V directly to the battery, and spec your battery around 55-57V fully charged..

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alotria avatar image alotria coin3ip commented ·

I will try that, thanks:)

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