Hi all,
I'm quite new to PV and still have no clear idea of what I don't know yet.
So the answer to my question might be very obvious ;)
However I'd appreciate any insight you are willing to offer :)
I installed three 120W modules in series on the roof of my RV and the online calculator recommended the MPPT 100/20 for them.
So I went ahead and bought it, not understanding at that time that "20" is the max A to the battery (I belive at 14,4V? - so max output to the battery would be about 290W?).
The MPPT 100/20 charges a LiFePo4 battery, most of the bulk charge happens at 13 to 14V, so 260-280W..
The highest peak power I got out of the panels during the last couple of days was about 270W according to the Victron App. Battery SOC between 20% and 90%.
Conditions: Clear Sky, Germany, about 51° latitude and 7° longitude (I've calculated an airmass of about 1.2, but I could be wrong), module temp about 50-55°C, panels flat. Cables about 6m 4mm² (single length) from the modules to the controller and 1m 4mm² to the LiFePo4.
I'm wondering if the panels are just not delivering their rated power (within this conditions I'd expect to see above 300W) or if the MPPT 100/20 is a bit undersized. Or if the values in the app are simply not accurate ;)
Today I played with the Excel calculator "VE-MPPT-Calc-3_7" and after slightly altering it to show the calculated max current instead of limiting it to the max output current of the charger the diagrams look like this:
To me it looks as if the available power of the panels is limited by the MPPT 100/20 even at high temps.
So now (finally) my question: why is the online calculator recommending the MPPT 100/20?
Is it (for example) normal that panels are far from their rated power so it makes sense to undersize the controller in relation to the specs of the panels?
What am I missing?
Thanks for helping me understand :)
