Pontoon Solar Roof

[Steven Braun]

The setup is two LiNMC 14s batteries rated at 57.6VDC at 150A with a BMS each connected in series to produce 115VDC powering an 18KW electric outboard. Shoreside charging consists of breaking the series link and each battery charged with its own 8A LiNMC battery charger. System works pretty good.

I am contemplating adding somewhere between 1500 and 220W of solar panels to the roof.

Question:
What is the best way to charge the two batteries connected together in series while underway with the single solar array?

I don't really want to charge at 96+V because this somewhat defeats the purpose of the BMS if the batteries ever get mismatched voltages.

 

[sunshine_eggo]

The setup is two LiNMC 14s batteries rated at 57.6VDC at 150A with a BMS each connected in series to produce 115VDC powering an 18KW electric outboard. Shoreside charging consists of breaking the series link and each battery charged with its own 8A LiNMC battery charger. System works pretty good.

I am contemplating adding somewhere between 1500 and 220W of solar panels to the roof.

Question:
What is the best way to charge the two batteries connected together in series while underway with the single solar array?

I don't really want to charge at 96+V because this somewhat defeats the purpose of the BMS if the batteries ever get mismatched voltages.

split the array in half and feed each half to a MPPT attached to each of the two batteries.

 

[Steven Braun]

Thought briefly of that solution. Pretty elegant. The array at 1500W is three solar cells which is a problem. However, with four cells the power is 2200W which is no problem except it covers almost half of the boat.

 

[sunshine_eggo]

Thought briefly of that solution. Pretty elegant. The array at 1500W is three solar cells which is a problem. However, with four cells the power is 2200W which is no problem except it covers almost half of the boat.

Two different sized panels?

1500W/3 = 500W
2200W/4 = 550W

There are a huge variety of options besides 500-550W panels. 4X 400W panels would cover nearly the same as the 3X panels and be easily split into two groups.

 

[Steven Braun]

Yes. Loads of different panels.
My initial calculations figured a 580W panel that produced 1740 or 2320 total watts. It was selected because it spanned nearly the entire 8' width of the boat thereby simplifying the installation.

The main thing really centers around using two MPPT's. I'm still a little concerned about being underway with two batteries connected in 115 VDC series with two MPPT 57 VDC controllers each connected live to a corresponding battery. At the dock, the main contactor connecting the batteries in series is powered down.

 

[0xkruzr]

huh. we are doing almost exactly the same thing. https://diysolarforum.com/threads/s...astructure-for-all-electric-boat-build.65899/ except mine has two 2.2KW 48V "super trolling motors" and is powered by two different pairs of 24V 100Ah batteries. I haven't bought any solar equipment yet, just motors and batteries, so I'm free to do whatever makes the most sense there.