how many MPPT controllers is too many?

[Brann]

I have a 45ft sailboat with a hardtop bimini full of solar 4x250w)
I'm also considering adding some flexible panels on the deck

I don't expect all my panels to receive the same amount of sun at any given time (I have the boom and the mast to account for)


on one hand, if I have only one MMPT, the selected point in the power curve is not going to be optimal at all (unless there's no shade at all). And I will have no redundancy in case my MMPT fails



on the other hand, if I use one MMPT per solar panel, the charging will start later in the day (because the voltage wont be high enough) and it will stop earlier. Also this adds cost and complexity


I'm tempted to take the middle road and use 2 MMPT (one for port one for starboard), but before making the decision I would love to hear some real life feedback from fellow sailors !


Thanks in advance

[SailingHarmonie]

Originally Posted by Brann

I have a 45ft sailboat with a hardtop bimini full of solar 4x250w)
I'm also considering adding some flexible panels on the deck

I don't expect all my panels to receive the same amount of sun at any given time (I have the boom and the mast to account for)


on one hand, if I have only one MMPT, the selected point in the power curve is not going to be optimal at all (unless there's no shade at all). And I will have no redundancy in case my MMPT fails



on the other hand, if I use one MMPT per solar panel, the charging will start later in the day (because the voltage wont be high enough) and it will stop earlier. Also this adds cost and complexity


I'm tempted to take the middle road and use 2 MMPT (one for port one for starboard), but before making the decision I would love to hear some real life feedback from fellow sailors !


Thanks in advance

If you are worried about low panel voltage preventing charging, the answer is simple: use higher voltage panels!

The more MPPTs you have the more power you make in a partially shaded installation. You might not want to pay for it, but that’s true. There will come a point where the extra power will be cheaper by adding controllers than by adding panels. Especially if you are using expensive per watt flexible panels.

[HankOnthewater]

I have also 4 panels, all parallel, and I had one PWM controller. I then went with 2 MMPT controllers, and in each set, 2 panels parallel: a noticeable improvement. Sorry, did not document and logged output of the PMW controller, and now.... purchased a further 2 smaller controllers, so I can have one controller for each panel... just not fitted these last two yet. All 12 Volt.
Hmmm, not sure, as you said, that the charging starts later in the day. I assume you had previously panels in series? I doubt if that will be the case with a controller for each panel.

Yes, shading is a bummer in big way, I notice that even the shadow of the standing rigging reduces output, not the $$.
Of course with multiple controllers one has more redundancy, but cost is slightly higher. My biggest problem was adding additional wiring to the panels.

[barnakiel]

Imho as long as the panels are 24 and the batteries are 12 then there are few ways to wire it "wrong".


For on one hand you want to avoid too little V difference between the panels and the battery, while on the other hand you do not want twenty regulators onboard.


If the shade shifts from one side to the other in your situation (sailing or docked) then I would use one regulator per side (2 total in your boat). If the boat is permanently docked or else anchored in a fixed - shade situation (common in the tropics / trade wind anchorages) then I would be tempted to use just one regulator.


Having just one regulator has some disadvantages though :
- if it fails, you have no energy.
- it will be bigger = more expensive.


Mind you can have a switch board and use 2 regulators in some moments, but then switch all batteries onto just one regulator at other times.


A switch board also makes for fast switching if any of the regulators fails. But this is also very easily done as long as the regulators are the same size and style.


So. 2 makes perfect sense. To me.


b.

[Brann]

Originally Posted by barnakiel

If the shade shifts from one side to the other in your situation (sailing or docked) then I would use one regulator per side (2 total in your boat).

The problem is that I can envision situations where one of my panel on starboard is shaded by the boom whereas the other is entirely in the sun.
It seems to me any combination of shading is possible on my 4 panels (arranged in a square on my hardtop bimini)


What I'm trying to establish is the impact of individual regulators. Is this going to be a 5% improvement over 2 mmpts (starboard+ port). Or 20% ? I don't know and I would love to hear from people who did that little experiment in a real world situation

[barnakiel]

You likely will not know. You would need to simulate the situation and calculate the results for each case. Probably a job for a tech department of a small university.

Ultimately, the most common limitation is not your solar / regulator / battery kit, but much rather the acceptance rate of your batteries. Unless you are lithium.


Mind that you can get much more gain in tilting the panels, and yet, so few boaters do. So as long as your set up is sound, with good V margin on the panels, quality regulator and sound batteries, the remaining factors are interesting to consider but not huge game changers.


b.

[noelex 77]

Originally Posted by Brann

on the other hand, if I use one MMPT per solar panel, the charging will start later in the day (because the voltage wont be high enough) and it will stop earlier.

This is a very minor factor that makes little difference to overall solar harvest unless the solar panel voltage is unsuitable.

In low light conditions, all solar panels can still produce near normal voltage. The low current is the real reason why the output is low. Connecting multiple panels in series does not increase the current, so it is of limited value in extending the solar day.

You have not listed the specifications of your panels, but most 250W panels are high voltage models, which is already well above the battery voltage. This is electrically the same as multiple "12V” panels in series.

[barcoMeCasa]

Originally Posted by Brann

on the other hand, if I use one MMPT per solar panel, the charging will start later in the day (because the voltage wont be high enough)

For victron mppt which say > "for the solar charge controller to start charging, the PV voltage must exceed the battery voltage by at least 5V"..

....it's not an issue at all, with the regulator in off state the panels are open circuit & it takes only little light to get the voltage high enough to turn on.

Much less light than is needed to actually put anything more than mA into the batteries.

[Bellinghamster]

Most, if not all, MPPT charge controllers have the ability to "boost" the output voltage. Victron looks like it needs input >5V above bat voltage to start, then 1V above to keep going. What panels do you have? What's their max power voltage rating? As long as that's above battery voltage then you should be fine with one MPPT per panel, which will optimize system power output when various combinations of panels are shaded. Only downsides are more wiring and cost of purchasing multiple MPPT units. Upsides are better system performance, easier troubleshooting and performance monitoring, redundancy. I will run individual MPPTs when I add solar to my current boat next year - (2) ~100W panels hinged on each side lifeline rail aft of the gate. I have ketch so rigging and mizzen mast shading is pretty much guaranteed.

[noelex 77]

Originally Posted by Bellinghamster

Most, if not all, MPPT charge controllers have the ability to "boost" the output voltage.

This is a common misconception.

Only a very small percentage of specialist MPPT controllers possess the capability to increase the output voltage above the input voltage.

The overwhelming majority of these controllers function solely as buck converters.

Originally Posted by Bellinghamster

As long as that's above battery voltage then you should be fine with one MPPT per panel, which will optimize system power output when various combinations of panels are shaded. Only downsides are more wiring and cost of purchasing multiple MPPT units. Upsides are better system performance, easier troubleshooting and performance monitoring, redundancy. I will run individual MPPTs when I add solar to my current boat next year - (2) ~100W panels hinged on each side lifeline rail aft of the gate. I have ketch so rigging and mizzen mast shading is pretty much guaranteed.

[Bellinghamster]

I stand corrected!

[CaptainRivet]

Originally Posted by Brann

I have a 45ft sailboat with a hardtop bimini full of solar 4x250w)
I'm also considering adding some flexible panels on the deck

I don't expect all my panels to receive the same amount of sun at any given time (I have the boom and the mast to account for)


on one hand, if I have only one MMPT, the selected point in the power curve is not going to be optimal at all (unless there's no shade at all). And I will have no redundancy in case my MMPT fails



on the other hand, if I use one MMPT per solar panel, the charging will start later in the day (because the voltage wont be high enough) and it will stop earlier. Also this adds cost and complexity


I'm tempted to take the middle road and use 2 MMPT (one for port one for starboard), but before making the decision I would love to hear some real life feedback from fellow sailors !


Thanks in advance

You can have never too many MPPTs as one per panel is technical optimum. And it depends on location, way of install and many other parameters if you can get away with a slightly bigger that saves you one or two smaller and in the end money.

The key question or solution is here to wire every panel to the location where the MPPTs sit as this will cost you more money and time then the MPPTs itself. If you can do that there is no technical better way then one MPPT per panel on a boat.
And in 90% of cases it's actually that this is huge costs and effort compared to one or two cables for all panels and you just use then a bigger MPPT.
We are on boat here where ever square millimeter of solar space count and wanna squeeze max from the given surface. And when sailboat we have a mast and sails that will produce shading in one way or the other. One MPPT per one panel just delivers the best result it can.

[nfbr]

7 is too many. I have 7.
MPPT’s dont help shading. Let the hate begin.
They help angles, but not shading.

[CaptainRivet]

Originally Posted by nfbr

7 is too many. I have 7.
MPPT’s dont help shading. Let the hate begin.
They help angles, but not shading.

They help shading if you have 2 panels in series where only one is shaded as that significantly reduce the output of both.
If both are in full sun, there is no difference but we have a sailboat with mast and sails so there is always somewhere shading.
On bifacials you get approximately 10% more output if one panel per MPPT or 2 on a bigger MPPT. I had that and my data over 2 years proven that with 365W Longli bifacials and Victron MPPTs (same location, just 2 instead one). Must have to do with the rear side delivery and the powerpoint tracking.

[toddedger]

I just added two more arrays each made from four 100 watt simi- flexible bifacial pannels. The four 100 watt pannels are wired in parallel. I run the two 400 watt arrays into one 50 amp victron mppt. I find no difference in output when I switch each paralleled array off and on.

I think it's important to look for pannels with high amount of bus bars in rig shading locations. Very happy with these 100 watt Topunive bifacial pannels. Wire tied four together and made a very nice folding array that can be set up at anchor for added solar, yet stowed on passages.