question

michael-franzin avatar image
michael-franzin asked

MPPT Output Oversize by 104% OK ? VEcalc 4.0 ACCEPTED

Hi all,

I have according to the VEcalc - 4.0 an allowed system with 5 x 395 Wp in a row and 6 Parallel. Total of 30 PV Moduls ( Trina TSM-395 DE 9.08 ) - makes 11850 Wp.

I want to oversize as much as possible, as I got the PV Moduls quite cheap and I want to increase PV farming in Wintertime in north Germany.

The VEcalc says "Accepted" .

I set the worst conditions - highest minus temp.... highest possible plus temperature.....

What could happen?

I could turn off one string/line ( 5 (row) x 2 (parallel) = 10 in total) in summertime... if needed.

My setup :


Inverters:

3 x Multiplus II 5000 50-70 ( 3 phase setup) - Grid connected , excess harvest will be feed in, and optional Backup connect with manual switch when blackout occurs.

System max output MUST stay the same. Just want to be more independent in Wintertime.


Batteries 48V :

12 x Pylontech US3000C ( 4 x 3 connected ) : 42KW


MPPT´s:

2 x MPPT 250/100 with currently 16 x Trina TSM-395 DE 9.08 = 6320 Wp

( Intention to go to 30 x PV Modul = 11850 Wp - Max V = 228.1V in worst conditions ) (10 degree EAST-WEST )

- Oversized by 104% approx. ( Max output 250/100 = 5800 W )


1 x MPPT 150/85 with currently ( 2 row x 6 par) 12 x Trina TSM-395 DE 9.08 = 4740 Wp

( Intention to go to 18 x PV Modul ( 3 row x 6 par) = 7110 Wp - Max V = 138.4V in worst conditions )

- Oversized by 45% approx. ( Max output 150/85 = 4900 W )

1 x MPPT 150/60 with currently 8 x Trina TSM-395 DE 9.08 = 3160 Wp (10 degree EAST-WEST )

( Intention to go to 12 x PV Modul ( 3 row x 4 par) = 4740 Wp - Max V = 138.4V in worst conditions ) - CHANGE to FACADE direction 90 degree ( housewall - for max Winter

harvest when sun is VERY low - North of Hamburg - Germany)

- Oversized by 38% approx. ( Max output 150/60 = 3440 W )


The VEcalc is giving me all above calc as "ACCEPTED" .

In total :

NOW = 20.54KW/p

INTENTION = 35.55 KW/p

I do know that Oversizing that much would be a waste in summer, but I do want to get max possible output in Wintertinme, where we do have between 21KW/h per KWp per month and 27KW/h per KW/p per month - Nov, Dec and Jan. I could improve harvest :

1. in the above months extremely, because in these mth. the harvest will NEVER go on max.

2. the neighburing month where we do not have full on sun ( Sep, Oct, Feb, Mar), where the harvest will go VERY RARELY on max.

3. in the mornings and in the evenings in the main harvest mths. ( where the max is regularly reached - Apr. to Aug .

Obviously I do not want to damage my MPPT`s ......

Is my thinking correct?

Do I miss anything?30-x-trina-395-908-on-mppt-250-100-accepted.jpg


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1 comment
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Alexandra avatar image Alexandra ♦ commented ·
@Michael Franzin

As long as you don't exceed the input voltage at low temps and the short circuit input of the mppt model. ....

You will be golden.

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3 Answers
michael-franzin avatar image
michael-franzin answered ·

Hey Guys, I know I received an answer .. any more experiences? Any feedback from Victron Team ? possiblity of Overheating when in summer very long on max capacvity? Maybe installaling an PC Fan DIY ? Please guys, give me some peace of mind... even if it is soooo obviously, that it sooo ok !!

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jetlag avatar image
jetlag answered ·

As Alexandra already said, most critical is only the DC input voltage. When you not exceed the max. allowable voltage (open circuit voltage!) of your PV modules in cold temperature, then you are fine. Some % of over-panelling will be no problem, as the MPPT can reduce the current.

Nevertheless, the MPPT will get hot in summer when the power is incoming for hours. Although it is designed for that and can handle that, it is always better to help with some active cooling.

I'm planning to add some temperature regulated DC fan blowing toward the MPPT charger just to have a better feeling. ;-)

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Alexandra avatar image
Alexandra answered ·

@Michael Franzin

You can go up to 30% over on most mppts with no issues.

As long as you do not exceed the inout voc at min temps and the short circuit rating.

On the 450 series you can even put twice as much.

All that will happen is it will be peak shaved (capped at the max amp out of the charger) maybe run hotter so if your ambients are high mount them in the correct orientation, not on a flammable surface.

I have some 250/100s 30% over panelled, ambients quite high about 35°C, the MPPTs running about 79°C on the front with the flir, only seen a small derating, no extra cooling has been installed.

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