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kensea avatar image
kensea asked

75/15 or 100/20 MPPT Controller for 200W, 4 panel installation

I spent a lot of time last night on Victron's published tools for selecting MPPT charge controllers.

The Online MPPT Calculator recommendation was for a 75/15 controller. However, when using the MPPT Excel sheet, the results showed that I would be 'output current limited' (to 15A) at both MPP min temp and MPP max temp with a 15A controller.

By reselecting the 100/20 controller, Excel shows output current of 18.8A (min temp) and 15.2A (max temp).

Is this justification to spend the additional money on a 100/20 controller? Also, by limiting output current to 15A, might the 75/15 controller be subject to higher heat buildup?

(Note: in all scenarios, I entered custom V, I and Temp values for Renogy 50W panels, installed as a 2-in-series by 2-in-parallel array.)



MPPT Controllers
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kensea avatar image kensea commented ·

This is a 12V-battery system.

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seb71 avatar image
seb71 answered ·

I would recommend to select the charger(s) based on the solar chargers datasheets and only use the MPPT sizing tool to check.


Will all 4 PV panels be installed on the same surface (in the same plane)? If not, don't connect them to the same charger.

Will you have shade issues? If yes, then multiple chargers are worth considering.


SmartSolar 75/15 would be enough for 200W of PV in a 12V system. On a boat you probably will never get 200W from the panels anyway.


Two SmartSolar 75/10 are also worth considering (especially if you have shading issues).



The naming scheme of Victron solar chargers (such as SmartSolar 75/15) refers to the maximum PV array voltage the charger can handle (75V in this case) and the maximum current it can load the battery with (15A in this case). In cold weather, the panel voltage will be higher than nominal Voc, so you must account for that.


Also the PV array voltage must be at least 5V higher than the maximum battery voltage (and preferably more than 5V higher, so that the charger has a bigger "room for maneuver" in days with less sun).


By multiplying this maximum output current (into the battery/loads) with the battery voltage (use the maximum battery voltage/fully charged), you get the maximum power it can charge (or power loads) with.

If your PV array has less power than that, the charger will always run cooler (good for electronics).

If your PV array has more power than that, in sunny days your charger will run at full power (so hotter) and still won't be able to use all available power from the PV array (so you "waste" some potential solar power), but in cloudy days you will be glad you have a bigger PV array (but don't exaggerate with oversizing the PV array).


Another thing to check is if the battery can take the maximum current your charger(s) can output (but also consider any loads you migh have running all the time, since those will consume a part of the solar charger power/current and only the rest will go into the battery).

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spanner avatar image
spanner answered ·

Sorry to be blunt, but one key bit if information mussing from your question is the size of your solar panel/s? And ratings?

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kensea avatar image
kensea answered ·

It's four 50W, 12V panels (200W total)--2 parallels of 2 in series. Voc=21.8, Isc=3.1, Vmp=18.3, Imp=2.9, ∆VT=-.33%, ∆IT=.05%.

A 12V marine installation on a 10 meter sailboat.


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kensea avatar image
kensea answered ·

"Will all 4 PV panels be installed on the same surface (in the same plane)? If not, don't connect them to the same charger."

Actually, three different planes: one panel inclined eastward; one inclined westward (these will alternate as the boat swings from north to south along with the tides); two panels roughly horizontal.

"Will you have shade issues? If yes, then multiple chargers are worth considering."

One of the east/west panels will always be facing away from direct light while the other has direct light. The two horizontal panels will receive partial shading from the boom and sail cover.

Can I do two 75/10 chargers wired in parallel to a single battery bank (12V, 160A-hr)? In this case, each charger would connect to two 50W panels (one inclined E/W, one horizontal) in series. Is this better?

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seb71 avatar image seb71 commented ·

Is this boat permanently anchored? So for instance a panel facing East will ever face only East?


You can use two or more solar chargers in parallel on a single battery. They can be synchronized using VE.Smart Networking.


As I said, all panels connected to a certain charger should be on the same plane. So if you can place each panel pair on the same surface (and wire each pair of panels in series), that would be better. So two panels in series placed on that horizontal surface and the other two panels in series placed either on the W surface or on the E surface.


In fact, giving the shading issues on the horizontal surface, it might be better to put two panels on "East" side (in series) and two panels on "West" side (also in series), each with a SmartSolar 75/10. That is, if you can fit two panels on each side (E and W).

You say that these E and W surfaces only get indirect light. Are they really never in direct light?


Shade is a PV power killer. So if at least one of the panels on the horizontal surface would always be in shade, don't put panels there.

Even when a panel is only partially shaded, the power goes down (current drops) for that panel. And when having panels in series, the power of the entire string goes down even when just one panel is shaded.

If the panels are in parallel and one panel is shaded, the other one is not affected.


If you stick with one charger, at least make series from panels mounted on the same surface (same plane). Then put those in parallel.


For each of those E and W surfaces (if you can't fit two panels on one side) you could use one solar charger, but the single panel voltage is borderline (low), so not that good (but it should work).


Do you already have these 50W panels?

If not, do you have room for a 60-cell panel (one 60-cell panel is about 1.6m x 1 m)?

A single 60 cell panel has about 250-300W. And it has voltage high enough (about 30V) for a 12V system (12V battery).

But again, if there is always shade there, that is very bad.

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kensea avatar image kensea seb71 commented ·

They can be synchronized using VE.Smart Networking.

Ok, this is a new idea to me. So, two SmartSolar (say 75/10) controllers and a Smart Battery Sense Unit, would be able to network with each other right out of the box?

Yes, I already own two of the 50W panels, and I'm considering adding two more.

Thanks for clarification about panels being similarly oriented. With just 2 panels, it sounds like I would be better off building a 2-panel series on just the port side of the boat. Then when adding two more panels, building a mirror-image system on the starboard side.--the two sides being synched with VE.S.N.



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seb71 avatar image seb71 kensea commented ·

It should work with a Smart Battery Sense, but if you want to add more devices, you could also consider a SmartShunt instead (significantly more expensive than the Smart Battery Sense though).

And later a Cerbo GX (but this is not quite justifiable on a small system like yours).


the two sides being synched with VE.S.N

I don't quite understand what you mean by this orientation, but don't place any PV panel facing North (in the Northern hemisphere).


PS

Check my above reply, I edited it to add more considerations.

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kensea avatar image
kensea answered ·

If I may summarize: The boat is on a buoy so it can move freely in all directions. About 60% of the time, it faces south, so the starboard panel will face W. About 30% of the time, it faces north, so the port panel will face W. At any given time, only one of the two panels will get much direct sunlight. These panels are mounted to side-rails at the stern of the boat. My primary purpose of solar here is just to keep the battery bank topped-up, as currently it drains slowly from self-discharge and passive loads (I'm not trying to design an offshore system here).

1. So, with my two existing 50W stern-mounted panels, I assume:

- wiring these two in series is no good

- wiring these two in parallel is better, but the low voltage output during low sunlight may not meet the Vbatt + 5V threshold to activate the controller.

- wiring each of these panels to a separate controller is also acceptable, but still suffers from the Vbatt + 5V problem

2. Now, consider adding additional panels. I assume:

- that adding dissimilar panels (ie, 100W Panels, "24V"/60-cell), etc) is problematic, thus I should stick with adding similar 50W panels (I also prefer the (approx .6m x .6m size) 50W panels for use on a sailboat.

- that the best addition of two more 50 W panels would be to add one each to port and starboard, next to, in series with, and in the same orientation, as the existing port and starboard stern-mounted panels (this would be like having a single, "24V" panel on each side of the boat). As only one side or the other is in direct sunlight at any given time, each side should have its own controller, with the controllers synced via VE. Smart Networking.

- since the above is a tough physical installation, the next best option might be: adding two panels to the "horizontal surface" (the boat's canvas dodger/entryway cover). The starboard horizontal panel to be wired in series with the stern-mounted starboard panel and the port horizontal panel to be wired in series with the stern-mounted port panel. The port and starboard sides would each be wired to its own controller, with the controllers synced via VE. Smart Networking. I could make additional efforts to tilt the "horizontal" panels to match the orientation of the stern-mounted panels.

3. Regarding VE Smart Networking (VE.S.N):

I understand that both the Smart Battery Sense and the Smart Shunt are capable of facilitating the VE.S.N with SmartSolar MPPT controllers.

I prefer the Smart Battery Sense because I already have a Balmar SG200 battery monitor and Balmar shunt installed.

I understand that the Smart Battery Sense will provide Temp. and Voltage information to the MPPTs via VE.S.N., but that is will not provide Amperage information as the SmartShunt would. Apparently, this limits the MPPTs ability to utilize tail current settings.

Can you elaborate on the effects of losing tail-current settings?

I'd like to keep my system simple but effective. I probably won't get to the level of adding GX devices.

Thanks!

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seb71 avatar image seb71 commented ·

Maybe you could experiment with various placements and wiring (serial/parallel) of the panels to see which arrangement gives the best results in your actual conditions (with placement and shading restrictions you have), before bolting them down permanently.

You want direct sun and no shade for as long as possible.


- wiring these two in series is no good

Only because you have permanent shade there.


- wiring each of these panels to a separate controller is also acceptable, but still suffers from the Vbatt + 5V problem

And this option also suffers from the $$$ problem.

Too expensive to buy one solar charger for each 50W panel for that little energy production. I would only consider this (one charger per panel) for 250W-300W panels (and which can't be installed in optimal position).


- that adding dissimilar panels (ie, 100W Panels, "24V"/60-cell), etc) is problematic, thus I should stick with adding similar 50W panels

It's problematic only if the new and different panels would be connected together with the old panels at the same charger. With a separate charger(s) it is not problematic at all.


Regarding VE Smart Networking (VE.S.N):

Ah. I did not understood your abbreviation. I thought that by VESN you meant the cardinal points (West, East, South, North), so I could not figure the "orientation" you were talking about.


Can you elaborate on the effects of losing tail-current settings?

When charging batteries, as the battery gets close to full, the current the battery takes is gradually decreasing.

You can configure the charger(s) to stop the Absorption (and switch to Float) when the current into the battery reaches a certain low value (this is "Tail current"). Something like 0.05C or even slightly less (there is also a minimum battery voltage condition together with a minimum duration condition for this to be triggered). This helps to not overcharge the battery.

This works best in sunny days and especially when charging from the grid.

But when there are clouds, the current into the battery can drop because there is a cloud and the panels do no longer get enough energy so in turn they can no longer charge with the same current. Then the solar charger will change from Absorption to Float too soon, falsely "thinking" that the battery is fully charged.


The value of this Tail current setting is that you can configure the solar charger(s) for longer Absorption duration (necessary during cloudy days), but still stop the Absorption in time during sunny days.


If you only have a single solar charger, you can still use the Tail current and should work as designed even without a SmartShunt.

But if you have multiple solar chargers and no SmartShunt (or BMV) to measure the total current into the battery and report it to the solar chargers, each solar charger will only know the current it is charging with. So the Tail current setting from each charger won't work as good (but I think it should still be somewhat usable).

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kensea avatar image kensea seb71 commented ·

Great info-I really appreciate it!

Can I buy a BMV712 packaged with a SmartShunt, or do I have to purchase the SmartShunt separately?

Also, I like the Victron MPPT Control display (it looks like a BMV), versus having to access things through my phone. Would the Victron MPPT Control be functional with two MPPT controllers synched via Smarthunt or BatterySense?

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seb71 avatar image seb71 kensea commented ·

BMV 712 includes a shunt. So you either buy and use a BMV (with the included shunt) or a SmartShunt. Not both.


Victron MPPT control (without the dedicated case) is almost as expensive as a 75/10 charger. And you would need one (and a VE.Direct cable) for each charger.

I think it is better with a phone for all devices (including for the SmartShunt, if you get that).

If you really want a good monitoring solution, better go the Cerbo GX way.

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