Solar panels in parallel - shading and voltage issues.

[Privilege]

I have two sets of identical solar panels mounted on different parts of the boat. They are all connected in parallel to my MPPT controller. When one of them is better orientated to sunlight and is therefore putting out a higher voltage, does my MPPT controller assume that the two sets are mismatched voltage panels?

The reason I ask is this; I have three sets of solar panels on my Catamaran. One set (set A) consists of four 100 W panels on the stern davits. The second set (Set B) consists of four identical panels on the starboard side of the hard top and the third set (Set C) consists of two 180w panels on the port side of the hard top. The 100w panels are rated at 21v open circuit, the 180's are rated at 24v open. I have two MPPT controllers, both able to cope with any combination of the three sets. Now I just need to decide how to pair the sets of panels to the controllers. I'm lucky enough to have so much wattage so I want to get it right. The Google suggests that all of the panels rated at 21v should go to the same controller, however these two sets of 100w panels are at different orientation to the sun and will therefore be putting out different voltages causing the controller problems? In fact, all three sets will be putting out different voltages at any given time. Does this matter seeing as everything is in parallel to the controllers?

I'd appreciate any advice.

[smac999]

Get a 3rd controller. Put a,b, c. On own controller. In parellel.

Im not sure what you asking. How to put 3 sets into 2 controllers? The anwser is you don't

For best results you'd have one controller per panel.

For 2nd best results you'd have 3 controllers. Each for set of same panels

Don't mix panel types on same controller

[billknny]

As has been said, don't mix panel types with an MPPT controller. It defeats the purpose of the MPPT controller because the max power point for the different panels will be... wait for it... different so the controller can not track the optimum voltage.

If your controllers can handle the voltage and are designed for it, you gain some benefit by rigging the panels in series. The higher panel side voltage means that you have lower loss in wire resistance, and you gain shade tolerance because the voltage stays high even if some cells are not working.

We have two 37V panels in series feeding a Victron MPPT controller that can pull power from the panels at any voltage between about 35 and 75 to charge our 24 volt batteries.

[sailorboy1]

I asked the mmpt controller once and they said the controller would just adjust for output

[billknny]

Originally Posted by sailorboy1

I asked the mmpt controller once and they said the controller would just adjust for output

There are two questions here: First, Will it work? Yes, it will work. It will charge your batteries.

Second question: Will it work well? That is more complicated. To understand you have to really understand what an MPPT controller is doing.

The voltage at which a solar panel will produce maximum power varies with conditions. Primarily the temperature of the panel and the degree of shading. A Maximum Power Point Tracking (MPPT) Controller adjusts the voltage at which it draws power out of the panel to find the optimum voltage for the current conditions. Different types of panels will have different optimum voltages under the same conditions, even if their nominal voltage is the same. So it is impossible for the MPPT controller to track the maximum power point because it is different for the different panels, so whatever it does is necessarily a compromise. The more divergent the panels are the less good the extra money you spent for the MPPT controller is doing you.

If you want the all benefit that an MPPT controller can give, you need to have the same type of panel connected.

If you must have a variety of panels connected to the same controller, it might be economically more efficient to just stick with a good PWM controller.

[sailorboy1]

I just posted what the manufacturers told me. There’s no point in quoting me to go on a prove me wrong campaign

[SV THIRD DAY]

In an ideal world you would have a separate MPPT controller for each solar panel.

Now since cruising boat systems are often a mix of budget and "good enough compromises" you do the best you can and move on, leaving the fretting for chat rooms.

[Privleoplag]

Everything I've read about solar shows better shade tolerance in parallel rather than series.

[SV THIRD DAY]

Originally Posted by Privleoplag

Everything I've read about solar shows better shade tolerance in parallel rather than series.

and as important is putting a individual MPPT controller on each panel.
It costs more...but will give you more Amps over the lifetime of the panels.

[Scott Berg]

Actually individual MPPT controllers need not cost more. Controllers are pretty much priced by the Watt; sticking with top shelf gear: 4 150 Watt Victron 75/15's cost about $400; a single Outback Flex 60 costs more... and there is a huge advantage of having each panel putting out it's max output.

[Privilege]

My thread had been unanswered for a while so I reached out to Tri Star; my MPPT manufacturer. (What a novel idea!) They said the same as you guys insomuch as the ideal setup is a different controller for each bank, even if different banks have the exact same panels. If you guys tell me, 'that's the right way' and the MPPT manufacturers tell me 'that's the right way', then he'll, that's good enough for me.
Thanks to all for your guidance. David.