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Old 12-12-2019, 10:56   #1
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3 panels and 3 MPPT controllers?

Maybe this has come up before and I just couldn't find it. But here's the question:

I am planning to install three 320W solar panels. I think it best to install one Victron 75/15A MPPT controller per panel ie. three controllers.

Furthermore, I plan to put in a circuit breaker before each controller. All three controllers will be connected to the 'Charging' busbar (as will be the wind charger) so the battery monitor will just show amps in/out as the case may be.

So here's the question: Is my idea good or will I get more efficiency connecting the panels in series and putting in one, say, 150/75 MPPT controller?

What say you?
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Old 12-12-2019, 11:46   #2
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Re: 3 panels and 3 MPPT controllers?

1:1 ratio is ideal for shade handling, but takes a bit more space and wiring.

Those controllers only output 15A, so too small for those panels, unless you have a 24V House system.

What is the panel Voc rating?
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Old 12-12-2019, 11:55   #3
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Re: 3 panels and 3 MPPT controllers?

The Voc is 40.8V and the Imp (Max power current) is 9.56A. This is for a 12V system. I'm not too worried about the size of the controller - the dudes at the shop assured me the size of the controllers would be fine.

I'm more interested in whether putting all three panels in series and using one bigger MPPT controller would be more efficient.

I remember reading somewhere separating as I am planning makes for more efficiency (up to 25% - but darned if I can find where I read that - there is so much information out there its hard to work out what's best) by minimising shading effects and panel angles due to positioning.
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Old 12-12-2019, 12:13   #4
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Re: 3 panels and 3 MPPT controllers?

Quote:
Originally Posted by Pole View Post
The Voc is 40.8V and the Imp (Max power current) is 9.56A. This is for a 12V system. I'm not too worried about the size of the controller - the dudes at the shop assured me the size of the controllers would be fine.
If you have a 12v house battery system the “dudes at the shop” are wrong. 75/15 controllers are too small for you panels and will limit the output significantly. You need to look at the output current which will be well above 15A in better conditions.

I would buy 3x the Victron 100/30 models for the maximium output, redundancy and reliability.

Quote:
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I'm more interested in whether putting all three panels in series and using one bigger MPPT controller would be more efficient.
There are pros and cons of the two approaches but a single controller per panel will generally deliver more power on a sailboat although the difference is small.
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Old 12-12-2019, 12:25   #5
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Re: 3 panels and 3 MPPT controllers?

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If you have a 12v house battery system the “dudes” at the store are wrong. 75/15 controllers are too small for you panels and will limit the output significantly.

Why would that be? if Voc is 40.8V and the controller can handle 75V, and the Imp is 9.56A and the controller can do 15A, isn't that enough leeway to allow all the available power (I'm aware that it will be a rare day that the panel returns these numbers) to make its way to the batteries?

There are pros and cons of the two approaches but a single controller per panel will generally deliver more power on a sailboat although the difference is small.
Thanks for that. Won't complain if you want to more specific about the pros and cons. That's why I posted here. But if its too long, or too complicated, then not to worry. Its all a learning curve for me.

I'm hoping someone out there who's done something pretty similar will say so, and make a comment like "It'll work" or "Don't do that, go for the left-thread defirbricator, in conjunction with 9mm wiring from the G-box". And then I can work it out from there...

But thanks anyway. All advice is appreciated.
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Old 12-12-2019, 12:38   #6
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Re: 3 panels and 3 MPPT controllers?

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Thanks for that. Won't complain if you want to more specific about the pros and cons. That's why I posted here. But if its too long, or too complicated, then not to worry. Its all a learning curve for me.

I'm hoping someone out there who's done something pretty similar will say so, and make a comment like "It'll work" or "Don't do that, go for the left-thread defirbricator, in conjunction with 9mm wiring from the G-box". And then I can work it out from there...

But thanks anyway. All advice is appreciated.
Yes I have done almost exactly the same (3x335w panels with three controllers) my prevous boats had multiple panels connected to single controller.

The advantages of one controller per panel are better shade tolerance, a slightly higher overall output due to supperior tracking of each panel, together with redundancy if a controller fails. The drawbacks are more complicated wiring and software set up to ensure good performance together with slightly higher self consumption. The option of a larger more expensive single controller sometimes delivers a more sophisticated and capable single controller for a similar cost to three smaller and more basic controllers.

Costs are usually higher for one controller per panel, but the difference is typically small. Sometimes multiple smaller controllers are cheaper than a single larger controller so the costs depend on the specific case.
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Old 12-12-2019, 12:39   #7
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Re: 3 panels and 3 MPPT controllers?

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The Voc is 40.8V and the Imp (Max power current) is 9.56A. This is for a 12V system. I'm not too worried about the size of the controller - the dudes at the shop assured me the size of the controllers would be fine.
Just to be a bit more clear about the why... The controllers are rated on the basis of the maximum OUTPUT current, not input.

Your panels will potentially produce 40.8 * 9.56 = 390 watts

When we drop that to 14.0 volts (typical charge voltage):

390 /14 = 27.9 Amps.

The controllers the "dudes at the shop" are recommending to you will throw away almost half the charging current your panels will output. You need a 30AMP rated controller for each panel.

I would suggest you find another source of advice. Your "dudes" shouldn't be making recommendations to anybody..
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Old 12-12-2019, 13:33   #8
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Re: 3 panels and 3 MPPT controllers?

Maybe the "dude at the shop" had some excess Victron MPPT 75/15's he needed to get rid of.

I have a Victron 75/15 for my system which has a max of 155 watts worth of panels hooked up in parallel.
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Old 12-12-2019, 13:43   #9
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Re: 3 panels and 3 MPPT controllers?

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Originally Posted by Pole View Post
I'm more interested in whether putting all three panels in series and using one bigger MPPT controller would be more efficient.
IRL absolutely not.

Reducing the impact of transient partial shading is a lot more critical than other factors.
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Old 12-12-2019, 13:49   #10
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Re: 3 panels and 3 MPPT controllers?

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The Voc is 40.8V and the Imp (Max power current) is 9.56A. This is for a 12V system.
In order to get 320W in peak conditions, charging at say 14.5V, you need a controller that will output over 22A.

The 75/15, by definition, cannot output over 15A.

One limited to 20A would be fine, since only very rarely will that panel put out more, and max efficiency is really best targeted for below-average conditions, not peak insolation.

But if a 25-30A controller does not cost too much more, go for that.

But 15A is way too small.
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I'm not too worried about the size of the controller - the dudes at the shop assured me the size of the controllers would be fine.
Use a different shop, dude.
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Old 12-12-2019, 13:50   #11
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Re: 3 panels and 3 MPPT controllers?

dupe dupe
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Old 13-12-2019, 04:05   #12
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Re: 3 panels and 3 MPPT controllers?

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dupe dupe
Thanks for your enlightening comment. I hope we're not taking you away from your busy day...
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Old 13-12-2019, 04:15   #13
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Re: 3 panels and 3 MPPT controllers?

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Originally Posted by john61ct View Post
In order to get 320W in peak conditions, charging at say 14.5V, you need a controller that will output over 22A.

The 75/15, by definition, cannot output over 15A.

One limited to 20A would be fine, since only very rarely will that panel put out more, and max efficiency is really best targeted for below-average conditions, not peak insolation.

But if a 25-30A controller does not cost too much more, go for that.
Thanks. I really didn't get that part - so the 75 part of a 75/15 controller refers to the INPUT voltage, and the 15 refers to the OUTPUT amperage? Right?

But you, Bill and Noel seem agreed. Love it. Exactly what I wanted to hear when I posted. I am enlightened.

I'll certainly look at the 100/30 controllers.
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Old 13-12-2019, 05:19   #14
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Re: 3 panels and 3 MPPT controllers?

If in doubt, you can compare with the Victron MPPT Sizing Calculator for your custom setup. Plus there's tons of other information on their site.

Afterward, you can lookup the formula for amps and recheck

https://mppt.victronenergy.com/
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Old 13-12-2019, 05:39   #15
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Re: 3 panels and 3 MPPT controllers?

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Thanks for your enlightening comment. I hope we're not taking you away from your busy day...
That's all John61CT you're responding to. The one giving you good advice here. He had a duplicate comments by mistake probably and marked it as such with "dupe dupe".

Misunderstanding on your part.
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