This site is now in read-only archive mode. Please move all discussion, and create a new account at the new Victron Community site.
Hi everyone,
Newby here so please be nice.
I need to upgrade my current temporary system and have a question about mppt selection. A have 12 panels and want to know if I should run them in parallel or 6 strings of 2 panels in series and which mppt should I select. The panels I have are as follows 
I would like to run a 3000w inverter and approx 300-500a/h 24v battery bank. I can give more details if needed just ask please.
Any help and advise would be much appreciated.
Regards Dan.
Antiques! CSG 180. Nothing wrong with old as long as they are in good condition.
Depending on how cold your panels get, will depend on whether you can go 2 or 3 panels in series.
Lithium or lead batteries?
Those are effectively 24v panels - so you need to be aware of when having them in Series you will have an Open Circuit voltage (Voc) of about 88.4v So making sure any MPPT you get can support that for a start, so nothing with the first value below 100 , i.e. don't go 75/15
If you have a Higher VoC than what the MPPT can handle, it will fry them. Current on the other hand will be limited, so you CAN go over the Current limit, it just means the MPPT will not deliver more than it's rating.
So if we did the Maths for that...
You could have:
6P x 2S for 88.4VoC and 32.1Amps (short circuit current - Isc) - so 88.2/32 = MPPT of 100/50 would be OK.
Or
4P x 3S for 132.6VoC and 21.4Isc = MPPT of 150/35
Or
3P x 4S for 176.8VoC and 16Isc = MPPT of 250/100
The advantage of Series is More solar energy over a longer period of the day, vs higher amperage for a shorter period. But if you are going to a 24v Bank, even just the 2S of those particular panels will definitely get a significant amount of energy from Sunrise to Sunset.
Thanks for the reply mate, I was originally leaning towards the 100/50. I’m I correct in my thinking that if I was to go with a higher voltage mppt like a 150/60 and 4 strings of 3 panels that the mppt would convert the extra voltage to more current as 3 panels in series would be approx 122v but only about 5amps? So essentially does the mppt use the extra voltage to increase amps out?
No, the voltage limit is a hard limit on the PV side. The current limit is a soft limit on the battery side (the MPPT can handle an array larger than its output capacity).
The current limit for a given battery voltage fixes the max power you can get out of the MPPT. The only way to increase the power out of a given MPPT (if one starts with a 12V system) is to increase the battery voltage.
Increasing voltage on the PV side does not increase the amount of amps out.
Dan.H, I would go with 3 strings of 4 panels each and use either the SmartSolar 250/70 or 250/85, which can deliver 2000W and 2400W @24Vdc respectively.
The 100/50 can only handle 1400W @24Vdc = wasted PV power.
The 150/35 can only handle 1000W @24Vdc = wasted PV power
The 250/100 is overkill.
Hi @Dan.H
you can use Victron calculator
https://www.victronenergy.com/upload/software/VE-MPPT-Calc-3_6.xlsm
