Victron MPPT quantity for 4 panels

[yabert]

Hi
We plan to add 4 panels on a 40fts catamaran sailboat to have around 1600W of solar for a 12V system (5 kWh LFP battery).
I can use 1 or 2 or 4 MPPT for this project. It's just to choose between different Victron product (one 250/100 or two 100/50 or four 100/30).
Remark that all those MPPT are underrated compare to panel power (1300w-1560w mppt vs 1600w solar), but it's find for us since panels will rarely give their max power.
In my mind, a single MPPT is a huge no because of the potential shade on a sailboat and 2 MPPT is a good compromise for redundancy vs wires management vs shade.
But what about 4 MPPT? Is the extra wires management and price worth the extra 16% power and shade capability?
Is there other facts that I didn't think of?
Let me know.
Thanks

 

[chrisski]

I’m not sure how much price is on these pieces, but I like two SCCs the best.

But what about 4 MPPT? Is the extra wires management and price worth the extra 16% power and shade capability?

I like this if you have four different panels.

I imagine putting panels on a boat is the same jigsaw as an RV. I was on top of my roof with cardboard cutouts to the dimensions of three different panels to see what’s best. This could be the difference of a couple hundred watts of panels.

For me, I have three different types of panels. I got the first for 600 watts of flat roof production and in theory it was maxed out. The second I got for a different panel set for portable ground panels, and the third I got for more panels of a different type mounted to the roof.

one 250/100

I like this if the panels are the same.

All four panels can still be placed in parallel which means one panel shaded won’t affect the other. Also leaves opnen the option of upgrading to 48 VDC. Unfortunately, this one piece of gear is quite pricey.

two 100/50

I like this best overall because of the redundancy. One SCC down won’t kill the system. The panels can still be in parallel. It also allows two different sized panels on the two different SCCs. Should make a difference in overall wattage installed.

 

[sunshine_eggo]

A 150/100 would also work.

Consider two scenarios:

a) 4 individual panels on 4 separate MPPT
b) 4 panels in parallel on one MPPT

a and b will perform essentially identical to each other. Shading become more problematic as panels are installed in series, not parallel.

I would split the difference and go with 2X 100/50 with two panels in parallel on each. This is simply to have redundancy in the unlikely event that one fails. 2X 100/50 are also likely cheaper than either 100A option.

 

[Solar Guppy]

The shading in your application would be a real challenge, I would have a low cost mppt for each string, not a real need for top tier units if you have redundancy. If you are OK with spending the money, nothing wrong with Victron as well

 

[yabert]

A 150/100 would also work.

Good point. I miss this one and thought the 250/100 was the only one who can give 100A.
In our system, the 4 panels will be the same model.
Thanks for the comments all. I also think that 2 MPPT for this situation is the best compromise.

 

[rhino]

Also remember if you get "split cell" panels you can have the bottom half or top half of the panel in shade and you'd still produce 1/2 the power of the panel instead of almost none like most other non-split cell panels.

 

[sunshine_eggo]

Also remember if you get "split cell" panels you can have the bottom half or top half of the panel in shade and you'd still produce 1/2 the power of the panel instead of almost none like most other non-split cell panels.

Excellent point.

 

[Partimewages]

What is a split cell panel? Got any examples?

 

[sunshine_eggo]

New QCells 390W Half-Cell Mono Solar Panel | SanTan Solar

These New QCells 390W solar panels are the ideal option for residential, commercial and industrial rooftops. They come with manufacturer warranty.

www.santansolar.com

Cells are half size of typical and you end up with basically 2X 60 cell panels in parallel. Shade half, and the other side is completely unaffected.

These are also available as "144" cell panels (2X 72 cell in parallel).

Note how the junction box and panel leads are in the middle of the panel rather than one end.

 

[yabert]

One of my concern is about current when panel are in parallel.
Let start with 2 pair of panel in parallel vs 2 pairs of panel in serie. The input current it double, so around 26A at 31v instead of 13A at 62V.
Is there efficiency chart/graph for Victron 100/50 who indicate conversion efficiency at 26A instead of 13A? The output in both cases is the same at around 13V and 50A

I know that efficiency of the Victron is only one variable and panel in serie can supply lower overall energy over a day cause of the shade, but I'm curious to know.

 

[sunshine_eggo]

Around water, most seem concerned with limiting voltage.

MPPT are most efficient at about 50% above system voltage, i.e., 18V in your case. Higher voltage DC to DC conversion is less efficient.

Efficiency losses are usually offset by reduced wiring losses, but this is less significant with short wire runs.

Simply put, if shading is a concern, parallel is the only option.

 

[yabert]

Around water, most seem concerned with limiting voltage.

Fair point. In a salty water environment 31V will always be less dangerous than 62V. It's not my boat, so lower/safer voltage can be an advantage.

Simply put, if shading is a concern, parallel is the only option.

 

[wholybee]

On my boat, I have 7 panels, on 2 controllers. For the first 4, I have them paired, 2 on each side of the boat. Both panels on the same side are in series, and then both sides are paralleled together into one controller. This works out as a good compromise, with lower current than all panels being in parallel(less loss in the long wire runs), and the higher voltage gives me better output on cloudy days when parallel panels would not create enough voltage to turn on the MPPT. Likely both sides of the boat would not ever be shaded at the same time. And also likely, if one panel on one side is in the shade, both would be, so there isn't really a downside to series in that case.

The other 3 panels are more randomly distributed, and are connected in parallel to the second controller.

As a complete system, it works really well in a variety of shading conditions.

 

[wholybee]

One of my concern is about current when panel are in parallel.
Let start with 2 pair of panel in parallel vs 2 pairs of panel in serie. The input current it double, so around 26A at 31v instead of 13A at 62V.
Is there efficiency chart/graph for Victron 100/50 who indicate conversion efficiency at 26A instead of 13A? The output in both cases is the same at around 13V and 50A

I know that efficiency of the Victron is only one variable and panel in serie can supply lower overall energy over a day cause of the shade, but I'm curious to know.

I would be less concerned about the efficiency of the controller, and more concerned with losses in the wire, and gains when it is slightly overcast from higher voltage. Without issues of shading, the series panel works better. The challenge is how to balance resilience to shading with the better performance of series panels.

According to the ABYC charts, with 10AWG at 20A and the panels 25 feet from the controller (50ft total run) there is a 10% loss. That is really significant. At higher currents, it gets worse. Double the voltage and half the current, and that loss drops to 5%.

 

[scrubjaysnest]

I'm building my off grid system around 4 100/20 cc's. Flexibility and redundancy the main reasons.

 

[HarryN]

Take a look at Genasun for your sail boat application. Their mppt controllers are specifically designed for that application.

40 ft is a big boat for a 12 volt power system. Can you do 24 volt?

 

[yabert]

40 ft is a big boat for a 12 volt power system. Can you do 24 volt?

It was also my first thought. But every other systems are 12V, it actually have 12V LFP battery and the consumption is kind of low.
The owner is certainly not interested to change everything for 24V and simply need a good amount of solar (1.6 kW) in order to start the genset only in rare occasion.
So the only downside is higher current out of the MPPT/higher MPPT and cable price.

 

[yabert]

I drew this for the owner of the boat. He is happy.
What a terrible experiment to do this with Powerpoint
What are simple and free software to do this type of schematic?

 

[yabert]

What are simple and free software to do this type of schematic?

After a bit of search, it seem peoples use those softwares to draw schematics:
-Powerpoint
-Google slides
-Visio
-draw.io.
-Photoshop/Illustrator
-Canva

I think I will try draw.io as it seem interesting.