Multiple choice array?

[robknotts]

Newbie here,
We've built a 36 panel 250W each array with a 10K inverter and 700W DC optimizers. The original plan was to tie 3-panel series (110v) into a parallel string. This, alas, resulted in too gig of amperage.

Is there a perfect combination of parallel and series to reach 10Kw while keeping amps below 15?

Thanks, Rob

 

[J.P.]

More information needed.

What is the Open-Circuit Voltage (VOC) and Short-Circuit Current (ISC) of your panels.

Also, I do not see how you can get more than 15A from a 3S 250W panel. I would expect the ISC on a 250W panel to be somewhere b/t 8.5 and 9 Amps. Remember when you put panels in Series the voltages add but the Amps stay the same. When you put panels in Parallel, the voltage stays the same and the Amps add.

To answer your question, we also need to know how many Charge Controllers you will be using (Or how many inputs your AIO has) and what the maximum input volts and Watts they can handle.

 

[robknotts]

My panels are 36v 9 amp...so if I do 2 strings of 15 panels in series that would 540v each. The Growatt 10k inverter has ports for 4 strings. Can each string be 540v? Or is 540v the combined total of all 4?

More information needed.

What is the Open-Circuit Voltage (VOC) and Short-Circuit Current (ISC) of your panels.

Also, I do not see how you can get more than 15A from a 3S 250W panel. I would expect the ISC on a 250W panel to be somewhere b/t 8.5 and 9 Amps. Remember when you put panels in Series the voltages add but the Amps stay the same. When you put panels in Parallel, the voltage stays the same and the Amps add.

To answer your question, we also need to know how many Charge Controllers you will be using (Or how many inputs your AIO has) and what the maximum input volts and Watts they can handle.

 

[robknotts]

And I'm not sure what a charge controller is?

 

[J.P.]

I would feel more comfortable knowing exactly what model of panels you have or seeing a picture of the electrical specs sticker on the back of one of the panels but if your VOC = 36.0V and your ISC = 9.0V and if you have the Growatt 10kW Grid-Tie Inverter | MIN10000TL-XH-US then you have 4 PV Inputs with (550V and 16.9 ISC) max.

You also have to take into account, (especially since you live in an area that gets really cold) the effect that temperature will have on your voltage output. Although simple math would yield a maximum of 540V on your 15S string, taking into account that temps can easily get as low as -40F in Montana, that could cause your panels to produce 675V and that would almost certainly cause you problems and probably burn out your charge controller(s).

Honestly I do not know enough about your particular Growatt to confidently tell you what is BEST but if it were me, I would run (3) 12S strings and leave one of your inputs open for future expansion. There are other options but that seems the safest to me with the information provided.

If I am wrong, hopefully someone else will chime in and detail it.

CAUTION: That kind of DC voltage can kill you so be careful!

 

[J.P.]

And I'm not sure what a charge controller is?

Charge Controller or Solar Charge Controller (SCC) - Is a component (or part of your All In One unit) that takes the input from your solar panels and controls and regulates the voltage and current to charge your batteries.

 

[robknotts]

Here's the MFG label for panels and inverter

 

[J.P.]

Here's the MFG label for panels and inverter

Assuming the temperatures will not get colder than -40F at your location.
For (36) panels, I would use (3) strings of (12) panels in series.
This will use (3) of your (4) PV inputs.
If you wanted to max out your Growatt, you could add another (12) Panels in series to the (4th) PV Input.

 

[MisterSandals]

Its interesting that the PV input range is 50V-600V yet the DC operating voltage range is 350V-600V.
Usually there is an MPPT range which is the PV voltage range where the unit is optimized.

Without knowing more, my gut feel and what i might try first, would be to balance the 4 PV inputs evenly with 9S strings.

9 x 30.2Vmp = 271.8V

If that did not produce enough voltage to run satisfactorily, 3x 12S as J.P. suggests would be a good option to try. It mostly depends on how the Growatt is designed to work using only 3 of the 4 inputs (maybe its not an issue, i dunno).

 

[robknotts]

So...? Is the lower end of the voltage range (270-360v, 9-12 panels) better/more efficient than the upper (18 panel) 550v?

 

[J.P.]

So...? Is the lower end of the voltage range (270-360v, 9-12 panels) better/more efficient than the upper (18 panel) 550v?

First of all, when calculating voltage, you have to use the VOC (Voltage Open-Circuit) number.
Second, you have to compensate for temperature. The VOC shown on your solar panel is at the Standard Test Condition of 25C. As solar panels get colder, they will produce higher Voltages. Here is an article where you can read about it. https://gold-coast-solar-power-solutions.com.au/solar-power/solar-panel-maximum-voltage-calculator/

To answer your question about whether high voltage is more efficient. I believe that to be the case but read this thread to learn more. https://diysolarforum.com/threads/s...pv-input-with-an-mppt-charge-controller.7648/

 

[robknotts]

Thanks! I'd never considered negative temperatures would effect the panels that way. Looks like series of 12 it is.