35w Array and 60v MPPT Question

[Block]

Hey everyone,

I have an ebike that I'm going to build some new cargo boxes for. I was weighing the idea of putting some PV panels on the box lids.


There are some small 60v mppt boost units that have decent reviews and documentation, an important note is their minimum input voltage starts at 12v-17v.

My weekly commute is 51km/31mi, 0.95kwh total. I can fit 10 of these Maxeon cells, creating a 35.5w array, which PVwatts estimates weekly 0.62kwh on average at my latitude with 0 degree tilt. This is assuming the bike is in the sun at all times, which is -mostly- correct. Front box is 10”x10”, rear is 20”x10”.

The question: Are these Maxeon cells (linked above) really only 0.6v? 10 cells in series would really only get 6v? Would anyone have different cell recommendations to get up to ~17v for the mppt to turn on? I’m assuming this is like the “12v panels” that can output upwards of 20v. Let me know if there’s any other info I can provide.

Thanks

 

[sunshine_eggo]

"12V" panels are 36 cell. Vmp of about 18V, Voc of about 22V

"24V" panels are 72 cell. Vmp of about 36V, Voc of about 44V

So yes, solar cells are about 0.5Vmp each.

 

[sunshine_eggo]

Suggest an off-the-shelf 25W:

Newpowa 10W 20W 30W 50W Solar Panel 12V Battery Maintain for Marine RV Trolling | eBay

30W Mono: 4.98Ibs. 50W Mono: 7.72lb. 10W Mono: 2.2lbs. 20W Mono: 3.31lbs. Our goal is to provide you quality solar products, with reasonable price. For Large solar system, do not connect solar module/panel with battery directly.

www.ebay.com

 

[sunshine_eggo]

The question: Are these Maxeon cells (linked above) really only 0.6v? 10 cells in series would really only get 6v? Would anyone have different cell recommendations to get up to ~17v for the mppt to turn on? I’m assuming this is like the “12v panels” that can output upwards of 20v. Let me know if there’s any other info I can provide.

They don't put out power at 20V, or they put out very very little. They put out their peak power at their Vmp - around 18V, and it drops off rapidly as the voltage increases.

 

[meetyg]

Hey everyone,

I have an ebike that I'm going to build some new cargo boxes for. I was weighing the idea of putting some PV panels on the box lids.
View attachment 195856

There are some small 60v mppt boost units that have decent reviews and documentation, an important note is their minimum input voltage starts at 12v-17v.

My weekly commute is 51km/31mi, 0.95kwh total. I can fit 10 of these Maxeon cells, creating a 35.5w array, which PVwatts estimates weekly 0.62kwh on average at my latitude with 0 degree tilt. This is assuming the bike is in the sun at all times, which is -mostly- correct. Front box is 10”x10”, rear is 20”x10”.

The question: Are these Maxeon cells (linked above) really only 0.6v? 10 cells in series would really only get 6v? Would anyone have different cell recommendations to get up to ~17v for the mppt to turn on? I’m assuming this is like the “12v panels” that can output upwards of 20v. Let me know if there’s any other info I can provide.
View attachment 195857
Thanks

Are you thinking of building a DIY panel from these raw cells?
If so, first I need to warn you that it's a pain in the butt to work with them. They are very fragile, and hard to solder. You will need to encapsulate them somehow.

I did build a panel from scratch from these cells. Actually I had a minimum voltage requirement for my DIY project, but with limited space, so I used third-cut Maxeon cells. You can get them on Aliexpress half-cut or third cut. These still give you 0.6v per cell, but less amperage (third-cut give around 2 amps per cell @ 0.6v). This allowed me to series enough cells to meet my minimum voltage requirement.

But, if you aren't that strict about weight/size, I would recommend you work with mono-crystaline cells that already have an epoxy like coating on them. You can get these mini-panels on Aliexpress at various voltages and just string them in series.

 

[Block]

Hey, thanks all for the advice on this - sounds like building a panel is more than just slapping a bunch of cells together. Tons of stuff needed like bypass diodes, the glass protector, and the delicate soldering mentioned, all to get a sub-par panel (with my craftsmanship at least).

I wanted to use raw cells so I could fit the custom footprint, but now I’m finding more ~10”x10” panels, which seems like the ideal size for a 30w+ array without getting unwieldy.

I could do 3 of these


or 3 of these


All in series(?), so I get to the 17v minimum input for the mppt boost converter. Open to more than amazon, it's just what keeps popping up in google.

 

[Block]

Parts arrived - Here’s the new wiring diagram for the build this weekend. Roast it, before I roast myself.


At first I was planning to run the panels in series, but the open circuit voltage of these Renogy 10w panels is 21.6v, meaning 3 of them in series is 64.8v (the inverter cuts off over 55v). I could also arrange the panels in parallel, but wouldn’t they barely work in low light conditions, since the inverter LV cutoff is 18v? I'll test them in both configurations.

Inverter specs:

Panel specs:

 

[Block]

Working pretty good so far.

I’m taking a solar installer course, and did an analysis on the bike panels. Used my work drive as the baseline. Anything look weird?


We’ll see if I reach this estimate for the summer months. Skeptical..