diy solar

diy solar

voc / vmp

polygon

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Dec 3, 2021
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Hello i am tring to find out what would be the best option for my growatt charger

MPPT Range @ Operating Voltage 60VDC ~ 115VDC

Maximum PV Array Open Circuit Voltage 145VDC

i want to use 540W panel JAM72S30 540

AT STC
voc 49.45v
vmp 41.64v

AT NOCT
voc 46.43v
vmp 38.99v

My question is can i use these panel in a 3x series?

I live in an area where the temp almost never is under 25c/77f

thank you
 
I live in an area where the temp almost never is under 25c/77f
The tricky word in that statement is "Almost".

If it gets below 25c... the risk begins and the further below 25c... the higher the risk.

It may work just fine for you, but in the words of Dirty Harry "Are you feeling lucky?"
 
The tricky word in that statement is "Almost".

If it gets below 25c... the risk begins and the further below 25c... the higher the risk.

It may work just fine for you, but in the words of Dirty Harry "Are you feeling lucky?"
I should have been clearer during day time and sunny day the temp on the solar panel never gona be under 25c.

i do not 100% understand how voc/vmp work and if i put the solar panel in 2S will it be sufficient all the time to have 60 vdc to feed the charger

do voc/cmp varie depending on solar irradiation/cloud or it is a fixed value that get affected only by temperature?


thanks
 
i do not 100% understand how voc/vmp work and if i put the solar panel in 2S will it be sufficient all the time to have 60 vdc to feed the charger
Yes. 2 x 38.9 = 77.8V
do voc/cmp varie depending on solar irradiation/cloud or it is a fixed value that get affected only by temperature?
Yes, the voltage does get affected by the solar conditions, but it does not take a lot of sun to achieve Voc. Keep in mind that when the battery is full, the charge controller turns off and this appears as an Open Circuit to the panels. Consequently, you should assume Voc is a common occurrence.
 
Yes. 2 x 38.9 = 77.8V

Yes, the voltage does get affected by the solar conditions, but it does not take a lot of sun to achieve Voc. Keep in mind that when the battery is full, the charge controller turns off and this appears as an Open Circuit to the panels. Consequently, you should assume Voc is a common occurrence.
thank you this help a lot!! I have a last question is there any advantage to go close to the limit of the mpp range?
 
I have a last question is there any advantage to go close to the limit of the mpp range?

Not really..... unless by going with the higher voltage you can avoid extra parallel strings in the array. If you can reduce the number of parallel strings, the current will be lower and there fore the wires can be smaller and the line loss will likely be smaller.


In your case you are dealing with 3 possibilities:

1) One panel in series. This will not work well because the voltage is too low.
2) Two panels in series. This will work well because your voltage is in the middle of the MPPT range.
3) Three panels in series. This has the over-voltage potential we discussed before. It also puts the Vmp slightly above the MPPT range.
When I asked Growatt what happens between the top of the MPPT range and the max voltage they said it would work but would be less efficient....... I have no idea how to quantify that so I don't know if being slightly high is very bad or not.
 
Not really..... unless by going with the higher voltage you can avoid extra parallel strings in the array. If you can reduce the number of parallel strings, the current will be lower and there fore the wires can be smaller and the line loss will likely be smaller.


In your case you are dealing with 3 possibilities:

1) One panel in series. This will not work well because the voltage is too low.
2) Two panels in series. This will work well because your voltage is in the middle of the MPPT range.
3) Three panels in series. This has the over-voltage potential we discussed before. It also puts the Vmp slightly above the MPPT range.
When I asked Growatt what happens between the top of the MPPT range and the max voltage they said it would work but would be less efficient....... I have no idea how to quantify that so I don't know if being slightly high is very bad or not.
Thank you I appreciate you take the time to help me. I will go for 2 panel in series.
 
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