I have Trina 415w panels, on the back it states power voltage as 41.7v and open circuit voltage of 50.0v
Are Victron mppt voltages listed for open circuit of power voltage?
If I got a 100/50 for two series panels that's 100v open circuit and 83.4v power voltage, so which applies for a 100/50 mppt?
Open circuit. Connect in parallel.
It depends what system voltage you have...
1) In case of 12V, put em parallel but the 100/50 will not deliver the maximum power of the two 415Wp panels. If you WANT the maximum power, then go with the 150/60 and put the panels in series which will give you an enormous advantage from autumn to spring.
2) In case of 24V, parallel works, but you go better with a 150/35 and put the strings in series
The 4 panels in question will go on my shed roof. I was planning to connect two in series, and the two strings in parallel, which gives 100v open circuit and 20a short circuit, so what mppt should I use? Also with a view of adding a further 4 panels in a location next toy shed, which would give 100v open circuit and 40a short circuit. Would a 100/50 still be ok or should I go for a 150/60?
Are you aware of the MPPT Calculator? It will help you make some of these decisions. Link here: https://www.victronenergy.com/mppt-calculator
I have a system with 16x Trina 425w panels which also have a Voc around 50V. I have arranged these as four series strings of four panels each. The means each string is around 200V but that's at standard temperature and can go a bit higher when it's very cold. So I use 250/60 MPPTs and I have two of them. Each MPPT has two of the strings attached in parallel so eight panels per MPPT. The max Isc current per MPPT is around 21A and because I'm only combing two strings in parallel, I don't need string fuses. My panels are also completely unshaded and on the same roof so no need for optimisers or diodes or what not. My PV max power is 6.8kWp in total and my MPPT max power at a charging voltage of 52.4V (48V system) is around 6.3kWp so my array is slightly oversized for the MPPTs. Arguably I should have gone for the 250/70 MPPTs but in practice it makes little difference to my system.
So, if you have 4 panels just now and expect to add another 4 in future, I would seriously consider a 250/60 MPPT and start with the first 4 panels in series, then add the second 4 panels in parallel with that later. Essentially the same as my setup but only one MPPT instead of two. If you start with 2s-2p then when you add another 2s-2p array later, that will leave you with 2s-4p which will require string fuses.
HTH
