question

You don't say what voltage your batteries are.

MPPT output in watts is charging voltage times current. As the MPPTs are over 90% efficient and panels rarely have enough light for full power, you can calculate roughly as follows:

Panel power/Charging voltage * 90% is output current.

You'll have to buy a second MPPT. Don't forget that the MPPT won't start charging until the panels give 5V more than the current battery voltage. So if you have a 48V battery pack, you'll need at least two panels in each string. Also do the low temp calcs, two panels with 46Voc is close to the limit for a 100V controller. There's an online Victron solar calculator that will size the MPPT for you.

Sorry. 12v system and lithium - so I'm not worried about the 5+vbat. I did the online calculator for both 1 panel and 2 panels in series. They are 100/35 and 150/35 respectively.

Here is what I'm trying to decide and could use some help on...put the 5th panel on the roof and buy an extra MPPT if its worth it, or just stick it in storage as a back up in case another gets broken.

So I guess I'll clarify based on your above formula and you can tell me if I'm correct.

390/14 volts = 27.85 * 90% efficiency = 25.07 amps would be the max I could get out of 1 panel? I used 14 volts as a ballpark since its a lithium battery bank.

My concern with both options is I won’t have enough pv to actually get the mppt’s to reach close to the max charge output

With not enough PV panels you won't use an MPPT to the maximum, but this also means that the MPPT will run cooler (and potentially last longer).

On the other hand, for an RV (with very limited mounting surface for PV panels), I would go for under-paneling rather than over-paneling, to make sure I get the most from the PV panels in perfect weather conditions.

For a house system with plenty of room to put PV panels, I would prefer the opposite (over-paneling), to make sure I get the most energy I can in bad conditions (low/not favourable Sun position, clouds) in a certain budget.

I can’t safely put all 5 of these into the 250/100 but wondering if it’s even worth it to get a second mppt (100/30 or 100/50) for a single panel. Other option would be run a string of 3 panels to the 250/100 and then 2 panels to a 150/35 or 150/45.

If the 4 panels connected to the 250/100 are all oriented the same (facing the same way - on the RV roof, I suppose), go for the first option (a second 100/30 MPPT for a single panel), because this smaller MPPT is cheaper than a 150/60 MPPT. Unless you plan for future expansions/repurposing (for instance if later you might switch to a 48V system), then get the 150/60 Smart Solar and connect 2 PV panels on it even for your current 12V battery.

Make sure you get a SmartSolar, not a BlueSolar.

Then, if you do not also have a GX device and if your existing MPPT is SmartSolar, use VE.Smart Networking.

@kevgermany and @Seb71, thanks for your responses! I think I’m in agreement with you @Seb71 about just doing the single panel on a 100/30. My other 4 panels are mounted north to south on the rv. This panel will have to mount east to west. Plus, I’m currently getting 95-100 amps from those 4 panels through the 250/100. I fear dropping it to 3 would make my investment in the 250/100 somewhat obsolete.

If I do this, I’ll get the 100/30 smart solar and connect them via V.E. Connect.

In your opinions, is my above math somewhat close to what I could actually expect out of a single panel into a 100/30 - about 20-25 amps?

One final question as I’m moving forward with the additional mppt. Any reason I cannot wire both mppts to a single appropriately sized fuse on a lynx distributor if space on the distributor is at a premium?