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bclaude avatar image
bclaude asked

Is it better to use multiple MPPT controllers as opposed to a large one when solar panels have different sun exposure

Hello;


I have 8 solar panels of 125W each installed on a boat

The system is using 4 separate BlueSolar MPPT 75 10

Each Controller drives a pair of Solar Panels connected in serie to the controller.

My battery bank is 600Ah in 24V


The yard installed 4 controllers instead of a larger one because they said that if some panels are in the shade and somme panels receive full sunlight, the over all output of the system will be higher with separate controllers. The panels are located under the boom/sail and therefore some will have more shade than others at different times of the day . What is best practice in terms of installation in situations like this? Is it true that I am better off with multiple controllers or would one big one produce the same amount of power in the end? If there is a difference, is it material?


Also I want to upgrade my system with a smart dongle for Bluetooth monitoring. Do I need to install 4 different dongles? All I am interested in is to monitor what my entire system is producing in terms of power. I don’t see much value in getting 4 different measurement for the different sections and having to add them together. If I do need 4 dongles, is there a way to aggregate the measurements into one display in the app?


The reason I am asking these questions is because there is not much difference between the price of 4 smart dongles and the price of a new SmartSolar MPPT 100 50 (with Bluetooth built in and enough capacity to drive my 8 Solar Panels) and at least with that I would have a combined read out of what my entire system is producing.


Many thanks for your assistance.

MPPT Controllers
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5 Answers
jbakuwel avatar image
jbakuwel answered ·

Hi @BClaude,

Yes, it is better to use 4 separate charge controllers for precisely the reasons the yard mentioned.

Central monitoring makes sense. I would not even consider connecting to each charge controller with your phone and add numbers manually. BlueSolar controllers can be wired to a Venus GX system. In your case a Raspberry Pi running VenusOS might be a cheaper option, but you'd also need 3 VE.Direct-USB cables. I am not sure if a VenusGX (or a Raspberry Pi running VenusOS) can work with Bluetooth. Having said that ... do you have a BMW battery monitor installed? That would be the first component I'd add to the system if you don't have that already. You can pick the BMW-712 with Bluetooth so you can check it with your phone. You won't get the details from the charge controllers but you may not need those (as much as you need the details about the battery charging and discharging). While you're at it: trust you've got a battery protect installed as well?

Hope this helps,
Jan

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bclaude avatar image
bclaude answered ·

Thanks for all the good feedback Jan.

At the risk of being unpopular, my boat is 90% Mastervolt... The only VictronEnergy products I have are the MPPT Controllers and an Engine Start Battery Charger. I am starting to get the benefits of one System vs. the other but I am not in a position to replaced my entire system. The VenusGX and Raspberry Pi probably have more functions/complications simply to monitor my solar panels. Since I have a main battery monitor, I assume that I could insert the BMW-712 in the negative cable between the solar panels and the battery bank. Can you confirm?

That would allow me to monitor the Amp/h my panels are producing. It's probably a bit overkill since all functions related to battery discharge and % state would not be used. Cost is about twice the cost of 4 Dongles but its definitely more convenient that having 4 separate read outs.


Thank you!

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jbakuwel avatar image
jbakuwel answered ·

Hi @blaude,

It does not make sense to use a battery monitor such as the BMV-702 (which does coulomb counting: energy in and energy out) to monitor your solar power generation as there is no energy going out of your batteries to your panels (note: this is possible but besides the point here; look up blocking diodes).

If you already have a Mastervolt battery monitor, what additional information are you trying to get? I suspect your Mastervolt battery monitor will tell you how much energy is going into the batteries when they are being charged?

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bclaude avatar image
bclaude answered ·

The main Mastervolt battery monitor doesn't make the difference between what the solar panels are contributing vs. all the other sources of power. Understanding how much Amp/h I can expect from my solar panels vs their rated specs and over say a season or a sailing passage is helpful info to determine wether they are of sufficient size and where they are in their life cycle. Thats why I would like to collect that data with a simple and reliable device. Raising the complication level of equipment on board is something that I have lived to regret in the middle of an ocean.

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Joka GIMENEZ avatar image
Joka GIMENEZ answered ·

Hi,

One thing that surprises me here (and sorry to revive the subject but I'm interested in your answers) is that the OP mentions he has BLUEsolar MPPTs, not smartsolar.

As far as I know, the bluesolar can't communicate with each other (even when connected wih the VE direct cable) to synchronise the charge cycle between the mppts (bulk, absortion and float), so when one controller will decide by its input that it's time to go to absorbtion mode, the sudden change in voltage will push all mppts to go to absorbtion, way before their ideal time, resulting in a big impact on efficiency...

It seems to be notorious that the mppt will work better with their cycles synchronized, which is not available on the bluesolar. Or did I miss something?

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seb71 avatar image seb71 commented ·

As explained, technically the best way in this case is to add a GX device (on which you then enable DVCC) and a SmartShunt or BMV battery monitor. But the cost of these is not worth it for small systems.

the bluesolar can't communicate with each other (even when connected wih the VE direct cable)

You should not directly connect solar chargers with a VE.Direct cable between them. It's not intended for that.

so when one controller will decide by its input that it's time to go to absorbtion mode, the sudden change in voltage will push all mppts to go to absorbtion, way before their ideal time, resulting in a big impact on efficiency...

The switch from Bulk mode to Absorption mode is not based on PV input. It is based on battery voltage during charging (the solar charger switches to Absorption from Bulk when the battery voltage reaches the value configured in the solar charger settings - so all solar chargers should be set the same in this regard). So it's the "ideal time" for all chargers connected to the same battery.

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adrianp105 avatar image adrianp105 seb71 commented ·
@Seb71 I have a question about this. I have a system I'm building with three arrays and plan to use 3 SmartSolars plugged into a Cerbo GX with VE.Direct cables. I understand this is preferred. But with what you said about the battery dictating the charge algorithm, what exactly is the Cerbo GX doing that is better than simply connecting the charge controllers by themselves (master/slave)?
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seb71 avatar image seb71 adrianp105 commented ·
Besides the GX device, the idea is to also have a Battery Monitor (like a SmartShunt, a BMV or the monitoring from the battery BMS in some cases) which can measure the actual battery voltage and the current entering into the battery (charging) or coming from the battery (discharging).


This way all the components work together and you have better control, useful for instance for limiting the battery charging current to its maximum allowed without also limiting the MPPTs to that value (so the system will know how much current from the MPPTs output goes to the Victron inverter and how much it goes into the battery).

There are also other functions which can only be used if you have a GX device (such as ESS for systems connected to the grid).

VRM is also extremely useful for monitoring how your components work and (based on that monitoring) for fine-tuning various settings (and VRM also requires a GX device).

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adrianp105 avatar image adrianp105 seb71 commented ·
Perfect. I will get a SmartShunt as well. I had planned on using all 3 VE.Direct inputs to the Cerbo for my controllers, but with the SmartShunt I'll have to revise that plan. Thanks @Seb71 !
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seb71 avatar image seb71 adrianp105 commented ·
Check the Cerbo GX manual for connection options.


If you do not already bought the MPPTs, you might look into models with a VE.CAN port (but those are only bigger MPPTs).

What battery do you have or plan to get?


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