mppt sizing

[michaelemerson]

hi all I would really appreciate help on this

I have a victron 100/20 MPPT I also have 2 off 230w mono panels which I plan to wire in series 10m max run in likely 6mm cable

each panel is identical spec and im in England so im gonna get plenty of cloudy days but some decent sun as well hopefully

max current imp 10.8A
max voltage vps 21.2v
short circuit current isc 11.5A
open circuit voltage voc 25.6v

so I am checking the mppt is correct and I have been advised to use a 100/30 100/50 75/15 by different people , I basically want the most efficient option I understand that the units will limit the current and all will actually do the job , I dont plan on installing any more solar as its on a van roof with limited space , im leaning towards swapping it for a 100/30 , is there any real benefit in doing this and pls explain what this would be in real terms

please help any techys

br Michael

 

[justinm001]

12volt? 460w at 12v is 38.3 amps. Even a 30amp will leave a bit on the table. Id go with 100/50 and you have room. As far as efficiency I'm not sure if the size matters, but larger ones will have larger heatsinks so less chance of it derating.

 

[RV8R]

I like what @justinm001 wrote

First, your need to identify your Battery Voltage ? 12v 24v or higher ?

If you are 12v then best to go 100 | 50. IMO well worth the money to go “Smart” versions on the Victron with the Bluetooth as it makes it so easy to setup on your device & look at things on your phone or tablet.

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-100-30-&-100-50-EN.pdf

Here is the sheet on the 30 & 50;




Here is the 20;



If 12v the 20 is max “usable” 290W.

So, as you can NOT go over the 100v on any of the ones you are looking at it comes down to “the charge amperage”. The 20 & 30 as Justin pointed out ( if on 12 v battery ), don’t make the grade.

Let us know if you have other questions.

BTW; Typically those chargers need battery voltage + 5volts on the panels to start charging. So if a battery is say 12.5v the panels need to be generating 17.5v to start the charging process.

I have a 100 | 50 @ my Cabin using a 60v @ 10a Array ( 600 W ). Here is a screenshot in April;




I like the 100 | 50 so much I bought a 2nd one for my Portable Solar Charger project;

Portable Solar Charger

So recently I cobbled together a box to basically utilize a Victron 100 | 50 MPPT Solar Charger. Why 🤷‍♂️? ,,, Well the first 100|50 worked very well until one day when about to hook up the alligator clamps, I stood “red 2 red” & “black 2 black” & while pondering the tiny spark I was...

diysolarforum.com

 

[fratermus]

im leaning towards swapping it for a 100/30 , is there any real benefit in doing this and pls explain what this would be in real terms

This is going to sound heretical but I think the 20A will be sufficient. I downloaded the PVwatts hourly insolation data for Derbyshire and found that, on average and assuming 14.2v Absorption, 460w of flatmounted panel will exceed 20A output in only 2.17% of daylight hours.[1] Please do check my math on this.

If the above is correct, how badly do you want >20A output during that 2.17%?

I have been advised to use a 100/30 100/50 75/15 by different people

FWIW, when I ran your system and location through the Victron MPPT calculator and checked "Allow oversizing above 130%"[2] it gave the 100/20 as the first choice.


-----
[1] ie, hours with estimated harvest >0w. Of 4,518 daylight hours in the set 4,420 had harvest <248w. Maximal harvest was 329.211w at noon on June 14th. To capture 100% of the power would require a 23.19A controller.
[2] I think Victron's nomenclature is goofy here. IMO it would either be "sizing 130%" or "oversizing 30%" but not "oversizing 130%" which would suggest sizing to 230%.

 

[Boomerweps]

My initial thought was the same as Fratermus, for similar reasons but had not thought to check the local sun exposure.
The currently owned 100/20 would be as effective as possible given the sun exposure there with the panels in series. In parallel, there could be a slight loss of produced power limited by the SCC.

 

[Skari]

I have 2 180w panels with a 20A MPPT living in south of Norway I still have not seen 20A on a good day it will get op to 17A Im shore Ill see 20A at some point but to be honest during those type of days I simply don't need all that power. and people need to remember that we newer have a optimal angle to get the max out of solar panels when they are installed flatt on the roof of a camper. So I say just use what you have and if you see it constantly banging 20A during long periods and you feel you have use for it then upgrade

 

[sunshine_eggo]

I'm reporting this whole thread as spam. PV in the UK? Gotta be a troll.