Combining solar panels onto a single controller

[IStream]

Sorry - I didn’t really word things well. Typing on a phone on the fly.

What I’m wondering is, if I paralleled the two 100w panels and put them on their own controller together, and then put the proposed/possible future 50w one on its own controller, would the total output be any different than if I did not parallel the two 100w panels and instead left them each one their own controller (with the 50w on also on its own controller). Is there an appreciable output difference between the two wiring/panel set up scenarios?

The general answer to your question depends heavily on whether you wire the 100W panels in series or in parallel. Separate controllers will get you higher overall output compared to series-wired panels if one panel is shaded. However, parallel wiring the panels inherently prevents the shading of one panel from drastically affecting the output of the other, so I doubt you'd gain much overall output in a shading scenario with separate controllers versus parallel-wired panels.

Since you'd plan to wire them in parallel, I don't think a fourth controller will get you much more than redundancy. If you value that, I'd suggest getting four controllers and size all your controllers such that they can handle 200W (with appropriate voltage limits). With that, any one of them can shit the bed and you'll still be able to go to a 200W + 2x100W (2P1S) + 50W config. If two of them shit the bed, you'd still have 400W available in a 200W + 2x100W (2P1S) config with the 50W panel disconnected.

 

[Hale Moana]

I have not read this entire thread. This is my experience with the panels on my boat.

First off. When wiring in series the voltage increases and the amps remain constant. When wiring in parallel the voltage remains constant and the amps increases. No different from wiring batteries in series or parallel.

I have four 65 watt panels on my boat. Three of the panels are the same manufacture and the other is different. I don't remember the brands of the panels. The panels are wired in parallel. Don't remember the make of the controller. All of my panels run through the same controller. I bought the controller and one of the panels from Downwind Marine in San Diego. I have not noticed any problems from shading voltage wise. 14.6 volts is always going to the batteries even if one or more panels is shaded. The amp out does decrease due to shading. How much depends on how the cells in the panel are wired. The early panels were wired in such a way that even a thin line of shade across the panel caused to panel to produce little or no power. Modern panels are wired in such a way that even if some of the cells are shaded the rest of the cells still produce power. My panels have modern wiring and and consistently produce close to maximum power. My system has been in use for around 15 years.

I read that if the panels have different wattages the entire array will be down graded to the lowest panel. Read this when I was researching putting solar on my house in a grid tied system with an inverter that was converting the DC voltage from the panels to AC house current. Don't know if this is true for a strictly DC system charging batteries.

 

[mckenzie.keith]

parallel wiring the panels inherently prevents the shading of one panel from drastically affecting the output of the other, so I doubt you'd gain much overall output in a shading scenario with separate controllers versus parallel-wired panels.

Yeah. While I have not personally done this (all my panels are in series), this is true from the theory etc. The shaded panel may not add many amps, but it will not prevent the panel in the sun from putting out its max power. I consider parallel wiring to be a bit more difficult, but it is not really a big deal, I guess. Just use a parallel kit. Or, if you want, you could run all the panels to the controller and parallel them there (where the connections are protected from the elements). Mor wiring and more copper, but it is an option.

Solar panels are inherently current limited so there is typically not a fuse between the panel and the controller. But if you parallel more than two panels, then each panel needs its own fuse (the fuse rating should be listed on the panel). The reason is that if current flows from two panels into one that is faulty, the wires going to the faulty panel may be over-loaded by the 2-on-1 pile-up. You can parallel 2 panels without individually fusing each panel.

 

[Hale Moana]

I think that there is confusion on the difference between series and parallel wiring.

In series wiring the current flows through the panels. You connect the + lead on one panel to the - lead on the next panel. Then the + lead on this panel is connected to the - lead on the next panel and so on for each panel. Just like when batteries are connected in series the voltage increases whereas the amps stays the same.

In parallel wiring all of the + leads are connected together as are all of the - leads are connected together. The current from one panel does not flow through the other panels. Back to the battery analogy the voltage stays the same whereas the amps increases.

Solar arrays connected in series are limited by the lowest wattage panel because the current flows through the panels. This does not happen in arrays connected in parallel because the current does not flow through the panels.

 

[mckenzie.keith]

I think that there is confusion on the difference between series and parallel wiring.

In series wiring the current flows through the panels. You connect the + lead on one panel to the - lead on the next panel. Then the + lead on this panel is connected to the - lead on the next panel and so on for each panel. Just like when batteries are connected in series the voltage increases whereas the amps stays the same.

In parallel wiring all of the + leads are connected together as are all of the - leads are connected together. The current from one panel does not flow through the other panels. Back to the battery analogy the voltage stays the same whereas the amps increases.

Solar arrays connected in series are limited by the lowest wattage panel because the current flows through the panels. This does not happen in arrays connected in parallel because the current does not flow through the panels.

I can't speak for anyone else. I am definitely not confused though. I think the issue is that EVERYONE besides me is taking for granted that the panels are nominal 12 V panels with 36 solar cells on the panel. This may be pretty reasonable in the narrow confines of the boating world. I don't know. I don't have any gripe with anything you are saying either. It is all accurate and helpful I am sure.

But I think that at least some cruisers are putting larger 60-cell and even 72-cell panels on boats. You would not want to parallel a 60-cell panel with a 72-cell panel because they will have different voltages. Likewise, you don't want to parallel either one with a 36-cell panel. If you do, then you will not be able to get maximum power from them all at the same time. Putting them in parallel forces them to have the same voltage.

Even though the latest and greatest silicon solar cells are 150 mm (6"), there are also a lot of 125 mm (5") silicon cells out there. So you can still encounter both sizes on new panels. The easiest thing is to just look at the Vmpp and Impp on the panels. Same Vmpp = parallel OK. Same Impp = series OK. Old panels will not be as good as new panels, regardless of silicon wafer size (which might even be smaller than 125 mm on old panels). Also some new panels cut the silicon wafers in half to help with shading so that is another variable.

 

[IStream]

I agree that you can't just wire together unmatched panels willy-nilly, whether serial or parallel.

I've confined my discussion of paralleling panels strictly to Jud's matched 100W units. I wouldn't do it with any of the others and that's why I recommended that if he's down to only two controllers, he not use the 50W panel, just the 200 and 100+100 panels.