question

Hi @Dc1138

If you're going to stay at 12V, first look to your mppt capacity. I'll use a 'typical average' charge level of 14V to calculate. Your existing /15A unit is then good for just 210W, so for 600W ~43A, and 1200W ~86A.

You could parallel in more strings of identical batts, but the more strings, the more chance of imbalance. Each string might max out at ~30A charge capability.

This of course begs the question of whether you're getting the most from your existing panels anyway, and maybe you don't need 1200W?

And now the bubble-breaker. There's no way those panels are 300W. At most 250W ea from the specs, and maybe even worse than that..

Whatever they are, wire them in seriesed pairs for best results.

Have a play with this: https://mppt.victronenergy.com/

Come back as you need..

Hi John. Thanks for the info. I made a mistakein the first post. Its a victron smart solar 100/50 mppt solar charger.

I would lile to stay at 12v. Might need extra watts. I want it to use if the power goes out and need to power a 250 watt fridge and computer. Fridge eats through 2 baterys very fast so may need to go from 2 batterys to 6

Doesnt more panels/watts help charge batterys faster and could be helpful on cloudy days?

@Dc1138

Yeh, that's better, ha.

For sure it's ok to 'overclock' your panels, of course within the Voc and Isc limits of the mppt(s).

So yes, you really need to expand in all directions to satisfy your needs.

And then, sometimes it's worthwhile stepping back and reassessing the needs and the means. 1200W is at the upper limit of usefulness of a 12V system, 250W is a large fridge draw, and expanding to multiple batt strings has pitfalls too.

I expanded a 12V system in my early days, and soon learned to hate it, especially the multiple batt strings. A failed inverter (not a Victron) prompted me to replace the whole shebang with 48V. My bad fridges had already gone by then.

But it all comes at a cost, and only you can decide where to head. Good luck choosing..

Thanks again. I might ditch the fridge and go for a lower watt more efficient fridge soon. Do i need another charger or i should be able to just add 2 more of the same panels and batterys? 1200 wats should be fine if iam running low watt equiment.

These are the only specs for the panels i know of are

Max Wattage:300W
Max Power Current:16.6A
Max Power Voltage:18V
Maximum Power Tolerance:±3%
Max Power Voltage:18V
Max System Voltage:1000V
Operating Temperature Min:-40°C
Operating Temperature Max:85°C
Cell Tech:Mono-Si
Module Application Class:A
TUV Certification:Yes
Folded Size:675*910*70mm