What solar panels ???

BDW

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Oct 31, 2021
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I am confused ... I want to do a simple (all in one) 24V system . Looking at the Growatt 24V 3000LVM, using a Rack Battery 200ah, 5Kwh. LiFePos. I need help to understand the Solar panels I need. 12v or 24v panels. Series or parallel? I am terrified of purchasing the wrong panels and over loading the system. Any guideance would be a blessing and a huge help.
 

Hedges

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Mar 28, 2020
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Check specs of the inverter, in particular maximum voltage for PV input, and maximum current.
Check data sheet of PV panels you consider, especially Voc, Isc. Maybe also temperature coefficient of Voc.

Your panels could be 12V, 24V, 36V (nominal), but with several in series, Voc adds up. In cold weather Voc increases.
For a conservative estimate, just assume Voc could increase by 20%
If you want to sharpen your pencil (and squeeze in more panels in series), you have to use record cold temperature of your location and temperature coefficient of the panels.

Design the PV array on paper, considering voltage and current limits, before buying anything.
 
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BDW

New Member
Joined
Oct 31, 2021
Messages
3
Check specs of the inverter, in particular maximum voltage for PV input, and maximum current.
Check data sheet of PV panels you consider, especially Voc, Isc. Maybe also temperature coefficient of Voc.

Your panels could be 12V, 24V, 36V (nominal), but with several in series, Voc adds up. In cold weather Voc increases.
For a conservative estimate, just assume Voc could increase by 20%
If you want to sharpen your pencil (and squeeze in more panels in series), you have to use record cold temperature of your location and temperature coefficient of the panels.

Design the PV array on paper, considering voltage and current limits, before buying anything.
Thanks, Very helpful.
Went back and looked, the Solar Charge Controller spec's show Max PV array power to be 2000W, the MPPT operating voltage 30vdc - 115vdc and the Max PV array operation current to be 145 VOC.
So if I understand your point, I would calulate like this......
1) Assuming three 335W 24V soler panels; that would be 1005 Watts (well under the 2000W spec)
2) Three 24v panels wired in series would be make nominal voltage 72v (3x24v) which falls in the spec of 30vdc - 115vdc
3) The panel spec shows Voc of 41.6v so I times that by 3 panels and get 124.8 Voc. Now this falls under the 145Voc limit of the solar charger. However, if I multiple it by another 20% as you suggested it moves to 149.76 Voc. Now it is slightly over the 145Voc. Is this too close?

Am I doing these calulations correctly?
 

Hedges

I See Electromagnetic Fields!
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Mar 28, 2020
Messages
9,145
Close enough to sharpen your pencil and do the math. It will probably turn out to be OK.
Look at PV panel data sheet for "temperature coefficient of Voc"
Look up record coldest temperature for your location. However many degrees below 0 C, add 25 to get degrees below nominal 25 C.
Multiply that by temperature coefficient to get a more accurate adjustment; use that instead of 20%.

You can generally put in more watts of panels than charge controller spec.
You can also parallel strings of different orientation. Their peaks come at different times, reducing peak wattage but extending hours.
Number in series (voltage) should be the same for strings in parallel.
 
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