Help please. Are these panels compatible for my 24 volt system?

dsj

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Please excuse my ignorance as im new to this... I want build a 24 volt solar system for my school bus conversion.

I bought 4 SunPower panels on market place for cheap. They are new too! Totalling 1340 watts. Did I make a booboo in buying these? Here are the specs.
20210423_094220.jpg

And also bought 8 batteries ( lithium - 3.2 volts 280 ah ) on aliexpress wired in series to make 24 volt.

Looking for advice to proceed in the purchase of the rest of the components,
Mppt charge controller 80 amp ??

Thanks in advance.




I
 

rmaddy

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For a 24V system, using an MPPT charge controller, those four panels setup in 4S would be about 230V at 62A at cold temps. In a 2S2P setup they would be about 115V at 62A. And setup as 4P they would be about 57V at 62A.

Seems like a 2S2P setup with a 150/60 or 150/70 MPPT SCC would be a good setup with those panels.
 

MisterSandals

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those four panels setup in 4S would be about 230V at 62A at cold temps.
No!
Wired in series, the panels would produce the panels' Imp which is 7.91a

An MPPT SCC could produce 1340w / (12.8v x 2) = 52a charging current

Perhaps instead of putting 4 panels in series because the Voc is so high would be to
run 2S2P for your panels (2 panels in series then those strings in parallel). This would give
you just over 100v Voc and really good for a 150v SCC.

An MPPT like this would be really nice (its not cheap but an SCC is the heart and brains so the place to invest $$):

https://www.amazon.com/Victron-SmartSolar-Charge-Controller-150V/dp/B07B4KF7LY/
 

rmaddy

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Sorry if I wasn't clear but I was referring to the output from the charge controller. The numbers I posted are from using Victron's MPPT calculator spreadsheet at -25ºC.
 

BlueFox

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Sorry if I wasn't clear but I was referring to the output from the charge controller. The numbers I posted are from using Victron's MPPT calculator spreadsheet at -25ºC.
In that case the relevant voltage would be the output of the MPPT controller, not the panel voltage. You've got panel voltage mixed with charge controller output current.
 

dsj

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No!
Wired in series, the panels would produce the panels' Imp which is 7.91a

An MPPT SCC could produce 1340w / (12.8v x 2) = 52a charging current

Perhaps instead of putting 4 panels in series because the Voc is so high would be to
run 2S2P for your panels (2 panels in series then those strings in parallel). This would give
you just over 100v Voc and really good for a 150v SCC.

An MPPT like this would be really nice (its not cheap but an SCC is the heart and brains so the place to invest $$):

https://www.amazon.com/Victron-SmartSolar-Charge-Controller-150V/dp/B07B4KF7LY/
Thanks a ton! didn't think to wire in 2S2P.
 

dsj

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For a 24V system, using an MPPT charge controller, those four panels setup in 4S would be about 230V at 62A at cold temps. In a 2S2P setup they would be about 115V at 62A. And setup as 4P they would be about 57V at 62A.

Seems like a 2S2P setup with a 150/60 or 150/70 MPPT SCC would be a good setup with those panels.
Thanks the help!
 

Hedges

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SunPower P17 series panels, a different sort of animal.

Rather than one series string of wafer cells with some bypass diodes, these have many small pieces wired series/parallel. No bypass diodes.
The anticipated use case for them is no shading, or all panels in a series string experiences similar shading due to multiple rows of panels mounted landscape orientation in a commercial installation shading each other.

Can you mount them where you won't have any shadows moving across them?

I don't think they have any bypass diodes, not even one to bypass the entire panel. It is probably important to not have a pole cast a narrow shadow across the entire width of a panel, because the rest of the 2s string it is in would reverse bias the shaded cells and try to force current through.
 

dsj

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SunPower P17 series panels, a different sort of animal.

Rather than one series string of wafer cells with some bypass diodes, these have many small pieces wired series/parallel. No bypass diodes.
The anticipated use case for them is no shading, or all panels in a series string experiences similar shading due to multiple rows of panels mounted landscape orientation in a commercial installation shading each other.

Can you mount them where you won't have any shadows moving across them?

I don't think they have any bypass diodes, not even one to bypass the entire panel. It is probably important to not have a pole cast a narrow shadow across the entire width of a panel, because the rest of the 2s string it is in would reverse bias the shaded cells and try to force current through.
Sorry John I didn't see your post. Well if what you say is fact about the P17 series then I'm most likely screwed. Because I already mounted them to my bus. Thanks for your help.
 

Hedges

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I've read literature from SunPower which said their panels perform decently or protect themselves OK even without diodes due to lower voltage drop through their cells.
Take a look at the cell layout (many series strings) of the panels and see where shadows fall. If flat on roof of bus, probably doesn't get much shadowing when sun is overhead. A tilted orientation on house roof or ground mounts would be more likely to have problems.
You probably also connect the panels in parallel, not series, so no problem of one panel pushing current through the next.
 

dsj

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I've read literature from SunPower which said their panels perform decently or protect themselves OK even without diodes due to lower voltage drop through their cells.
Take a look at the cell layout (many series strings) of the panels and see where shadows fall. If flat on roof of bus, probably doesn't get much shadowing when sun is overhead. A tilted orientation on house roof or ground mounts would be more likely to have problems.
You probably also connect the panels in parallel, not series, so no problem of one panel pushing current through the next.
Ok that gives me some peace of mind. However I planned on wiring 2S2P to keep amps down. As I bought 10 gauge wire rated for 30 amps and wiring in parallel now puts me at 32 amps. But the potential for one panel pushing current into another sounds disastrous. I guess 8 gauge would be safer option. Thanks again.
 

Hedges

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But the potential for one panel pushing current into another sounds disastrous.

Just add bypass diodes.
I think MC4 blocking diodes will work as bypass diodes, using "Y" cables to parallel one with each panel.
Don't know if junction boxes are easy to open in order to install there.

I don't know much about the P17, just read up on them and selected E20 instead.
It was SunPower literature on reliability where I read that even if their bypass diode fails, the lower reverse breakdown voltage of their cells reduces the power dissipated. But I don't have numbers for that.
 

dsj

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Just add bypass diodes.
I think MC4 blocking diodes will work as bypass diodes, using "Y" cables to parallel one with each panel.
Don't know if junction boxes are easy to open in order to install there.

I don't know much about the P17, just read up on them and selected E20 instead.
It was SunPower literature on reliability where I read that even if their bypass diode fails, the lower reverse breakdown voltage of their cells reduces the power dissipated. But I don't have numbers for that.
Ahh great fix! Just looked them up and apparently they do act as blocking diodes and cheap (y)
 

Hedges

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Ahh great fix! Just looked them up and apparently they do act as blocking diodes and cheap (y)

They come as blocking diodes, which isn't the function you need. Could be connected differently as bypass diodes:

 

dsj

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They come as blocking diodes, which isn't the function you need. Could be connected differently as bypass diodes:

Ok that clarifies it for me thank john
 
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