Series or parallel?

[Lykos]

Sitting in my garage is two 100 watt panels and mppt controller. They'll be charging a 68Ah house battery. It's not the ideal setup but it's literally all I can fit in and on my suburban in it's current configuration.

Installation is imminent. My understanding is that by wiring the panels in series I'll get to optimal charging voltage sooner and maintain it longer in low light such as overcast and rainy days as well as morning and evening hours. I understand that the mppt controller is smart enough to push max amps with whatever voltage is being produced.

Solar overwhelms me just a bit. Please tell me if I'm wrong and that I should instead wire the panels in parallel. If so please explain why.

Thanks in advance for the help.

 

[dreadlocks]

Series, you'll get to charge voltage quicker and you'll experience less losses with cabling.. as long as your MPPT controller can handle the combined voltage its the way to go.

 

[luthj]

Yep, series. We are assuming you have 12v nominal panels, which produce ~18v open circuit. Make sure that no part of the panel is shaded by any surrounding objects. Such as racks.

 

[john61ct]

Get a controller with good data logging and the flexibility to go either way.

Then before permanently wiring, A/B test for your circumstances, including perhaps inevitable partial shading.

Victron SmartSolar 75/15 is my reco

 

[Lykos]

Get a controller with good data logging and the flexibility to go either way.

Then before permanently wiring, A/B test for your circumstances, including perhaps inevitable partial shading.

Victron SmartSolar 75/15 is my reco

I picked up a Renogy and added the Bluetooth dongle. The app logs data so I will try both as you suggest. Thanks!

 

[Lykos]

Yep, series. We are assuming you have 12v nominal panels, which produce ~18v open circuit. Make sure that no part of the panel is shaded by any surrounding objects. Such as racks.

The z71 roof rack is pretty robust for a factory rack. My brother is an auto body tech and suggested using 1x1 aluminum box tubing attached to the roof with panel adhesive to eliminate the need for holes in the roof. That also brings the panel flush with the side rails. The crossbars are for and aft to hold the awning... I'll make sure nothing is in the way. Good advice, thanks.

 

[67cj5]

The only down side to wiring them in series is if one panel gets a bit of shade on it then you get a drop in power where as if they are in parallel then if one gets shaded you still get the full power of the unshaded panel.

 

[dreadlocks]

The only down side to wiring them in series is if one panel gets a bit of shade on it then you get a drop in power where as if they are in parallel then if one gets shaded you still get the full power of the unshaded panel.

This can be addressed with a cheap bypass diode:

 

[luthj]

Many panels already have bypass diode(s). Best to check how they are wired though.

 

[dreadlocks]

Those just bypass series of cells within a module. They wont bypass anything if an entire module within a series of modules is shaded.

yeah they will, they just chain together..


Say this panel is in the shade and the other panel is in the sun.. the cell output will be lower than the left leg input so it will bypass and flow across all those diodes and back out the right leg like this panel was not even in the string.

 

[67cj5]

Sounds like too much messing about, Considering these vehicles travel all over the place I would not modify any thing and leave it as intended because that way you can buy off the shelf replacement parts at the nearest town and you up and running in no time KISS.

 

[dwh]

https://www.expeditionportal.com/forum/threads/roof-solar-panels-go-2-50w-or-100w.176160/

 

[Lykos]

https://www.expeditionportal.com/forum/threads/roof-solar-panels-go-2-50w-or-100w.176160/

NICE! Thank you!

 

[hour]

yeah they will, they just chain together..
View attachment 507866

Say this panel is in the shade and the other panel is in the sun.. the cell output will be lower than the left leg input so it will bypass and flow across all those diodes and back out the right leg like this panel was not even in the string.

Are you familiar with any off the shelf option for this? I have two 100w panels in series and occasionally carry a generator on what little space I have available on the rack. Depending on direction of travel and where the sun is, this nukes my output. I had no idea there was a solution for this.

 

[dreadlocks]

yeah just wire in your own schottky diodes, https://www.amazon.com/gp/product/B01CXOQMJ8/r

either see if you can pry open the wiring box on the back of the panel and put em in there, if its sealed off and you cant get in you can wire em up externally.. they allow current to flow from the black end to the silver capped end, but not the other way.