diy solar

diy solar

First Home DIY install. Would love some advice.

gocfella

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Feb 22, 2023
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8
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Ireland
Hi.

I am collecting 5 panels tomorrow (Canadian Solar cs6w 545w)

I can fit 2 in one orientation (S facing, almost horizontal, maybe 5° at best) and 3 in another (E facing, 25° inclination) so 2 separate strings. Panels have vmp of 41.5v and current of 13.14a.

I intend to use a 48v battery.

My query is concerning the best way to set them up. Separate mppt controller for each string? Dual mppt hybrid inverter?

It seems that most of the dual mppt hybrid inverters have quite high minimal voltage so intended for minimum 4 x 48v panels on each string? My 2 panel string in series will be 80v and the 3 panel 120v.

If I were to get 2 separate victron controllers I would need 100/15 for the 2 panel string and 150/35 for the 3 panel string AFAIK. That would be a very expensive solution. Does anyone have any suggestions or feedback? Thanks very much.
 
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Nope. You're indicating Vmp, which means their Voc is likely close to 50V, and Voc is what you use when connecting to a MPPT. You can only go 1S on 100V and 2S on 150V. 3S will require a 250V unit. Ask me how I know...
 
Nope. You're indicating Vmp, which means their Voc is likely close to 50V, and Voc is what you use when connecting to a MPPT. You can only go 1S on 100V and 2S on 150V. 3S will require a 250V unit. Ask me how I know...
Ok How do you know? ?

The voc is 49.4v yeah. I presumed maybe incorrectly that as long as the voc of the string was technically below the max of the controller it would be fine as it would almost never be presenting that voltage in actual use? Am I to assume now that victron are not a good way to go with small numbers of 48v panels? Any ideas what to do as an alternative? Cheers
 
Welcome. Hard limit on voltage. And you need to understand low temps can increase voltage. I’ve been informed Voc times 1.2 should not exceed mppt limit.
 
Welcome. Hard limit on voltage. And you need to understand low temps can increase voltage. I’ve been informed Voc times 1.2 should not exceed mppt limit.
Thanks.

Ok fair enough I get you and mine will see low temps down to - 4C/25F in Winter. So going down the victron route for charge controllers would be super expensive in my case. My problem is that my smaller 2 panel string will only have 80-100 volts which wouldn't be enough to activate the 120v minimum 2nd mppt input on, say, a growatt 3k hybrid. Not sure what to do now at all... A 6th panel would solve my problem but no room for it unfortunately...
 
Thanks.

Ok fair enough I get you and mine will see low temps down to - 4C/25F in Winter. So going down the victron route for charge controllers would be super expensive in my case. My problem is that my smaller 2 panel string will only have 80-100 volts which wouldn't be enough to activate the 120v minimum 2nd mppt input on, say, a growatt 3k hybrid. Not sure what to do now at all... A 6th panel would solve my problem but no room for it unfortunately...

Sometimes limitations have consequences. This isn't a Victron thing, this is all MPPT.

Due to two different voltage strings facing different directions, you must have two different charge controllers. You need one capable of 150V for the 2S and one capable for at least 200V for the 3S. Their listed voltage is "never exceed" and you must factor in elevated voltage due to cold temps. Midnite Solar unit have a "hyperVoc" mode where they can tolerate higher voltages, but they won't operate until the panels are heated enough to drive the voltage low enough, but if you think Victron is expensive...

Have you investigated if any other panels would fit. 60 cell panels might give more flexibility. Furthermore, you might find a cheaper PWM controller for 2S 60 cell panels on a 48V battery will work very well in all but extreme heat (guessing that's not an issue in Ireland).
 
Sometimes limitations have consequences. This isn't a Victron thing, this is all MPPT.

Due to two different voltage strings facing different directions, you must have two different charge controllers. You need one capable of 150V for the 2S and one capable for at least 200V for the 3S. Their listed voltage is "never exceed" and you must factor in elevated voltage due to cold temps. Midnite Solar unit have a "hyperVoc" mode where they can tolerate higher voltages, but they won't operate until the panels are heated enough to drive the voltage low enough, but if you think Victron is expensive...

Have you investigated if any other panels would fit. 60 cell panels might give more flexibility. Furthermore, you might find a cheaper PWM controller for 2S 60 cell panels on a 48V battery will work very well in all but extreme heat (guessing that's not an issue in Ireland).
Sorry I never replied at the time. I changed to 6 450w panels. Going to parallel 2 x 3s with 250/100 victron. Be some loss I'm sure with different orientation on one tracker but hey! I shall find out how much soon. Thanks for help.
 
Sorry I never replied at the time. I changed to 6 450w panels. Going to parallel 2 x 3s with 250/100 victron. Be some loss I'm sure with different orientation on one tracker but hey! I shall find out how much soon. Thanks for help.

Since the strings are the same voltage (3S), as long as the 3 panels in string 1 are all facing the same direction and the 3 panels in string 2 are all facing the same direction (strings 1 and 2 can have different facing), there will be no penalty.
 
Since the strings are the same voltage (3S), as long as the 3 panels in string 1 are all facing the same direction and the 3 panels in string 2 are all facing the same direction (strings 1 and 2 can have different facing), there will be no penalty.
I didn't think that was the case but if I am wrong then that is great. I was under the impression that the MPPT would be tracking max power for an average figure half way between both string voltages. This would mean it is not working optimally for either string but optimally for the combination. I thought that the most loss would be when the strings light levels contrast the most. Maybe not a huge loss but some loss.

If this is incorrect then that is good news 👍
 
I didn't think that was the case but if I am wrong then that is great. I was under the impression that the MPPT would be tracking max power for an average figure half way between both string voltages.

Okay, I think I lost track of the conversation. Looking back at your OP...

I'm concluding:

String 1: 3S with 2 panels facing South with the third panel facing elsewhere.
String 2: 3S facing East.


String 1 will only perform as well as the least favorably oriented panel.
String 2 will experience no penalties.

The two in parallel will not significantly influence each other because they will be at the same voltage.
 
Nah the extra panel will be on the same plane in String 1.

Maybe I am overestimating the voltage delta between the strings when their light intensity levels diverge the most in morning and evening. I know the current is the main change but the voltage also changes a bit right? Maybe not enough to have a significant effect?
 
Nah the extra panel will be on the same plane in String 1.

Ah Good!
Maybe I am overestimating the voltage delta between the strings when their light intensity levels diverge the most in morning and evening. I know the current is the main change but the voltage also changes a bit right?

Barely.

See the figure here:


Maybe not enough to have a significant effect?

Correct. So, we're back to this:

Since the strings are the same voltage (3S), as long as the 3 panels in string 1 are all facing the same direction and the 3 panels in string 2 are all facing the same direction (strings 1 and 2 can have different facing), there will be no penalty.

:)
 
Well that sounds promising. That will teach me to look at the curve for my own panels on their datasheet instead of guessing pessimistically 😁 Cheers mate
 
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