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jwr asked

MultiPlus and source prioritization

I'm planning an installation for a small workshop in a location where grid power is limited (230V/10A). There will be a constant load (heat pump) plus peak loads for a short period of time (say up to 6kW nominal power for a minute or so, when power tools are being used). I would like to supplement the available grid power with batteries for those peak loads.

I found the MultiPlus (48/5000/70-100) and it seems that its PowerAssist feature is exactly what I need. So far so good.

But — I could also add a small amount of solar to the mix. And that's where I don't understand things anymore.

Ideally, I'd like this ordering of power sources:


1. Use as much solar as is available at the moment.

2. Use the AC grid connection to pull up to 10A.

3. Use the batteries for anything on top of that.


But it seems that the MultiPlus does not have a separate DC connection for a solar power source. I found a system example (https://www.victronenergy.com/upload/documents/MultiPlus-system-example-5KW-24V-230V-AC.pdf) which is fairly close to what I want, but it seems that the output of the MPPT controller is connected directly to the batteries. It seems to me that in this system, if I configure the PowerAssist feature, the solar source can only supplement battery charging and supplement the power peaks over the 10A I can pull from the grid, but it can't participate in small loads if the batteries are fully charged?

I would like to avoid discharging the batteries as much as possible, to extend their lifetime. They should be used only for supplementing peak power above what grid+solar can supply at the moment.

Additionally, I do not understand this example: I thought batteries need to be charged according to a charging profile, and it seems like there are two chargers connected to the same batteries. How does one ensure proper charging?

I think what I was expecting was an inverter/charger with separate connections for battery and for DC in (from solar/wind), with source prioritization.

Can this kind of prioritization be done with the MultiPlus?


MultiPlus Quattro Inverter Chargersolarpowerassist
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klim8skeptic avatar image klim8skeptic ♦ commented ·

I would switch your priorities around,

1. Use the AC grid connection to pull up to 10A.

2. Use the batteries for anything on top of that.

3. Use as much solar as is available at the moment.


A word of caution. KISS. If you cant design/build/maintain/monitor it, avoid it.


Kiss would be,

1. Set multi up for power assist above 10a.

2. Set multi up for invert only (no batt charge).

3. Set mppt to charge batteries. (no export to grid for excess power)

NB: manually monitor KISS system and accept solar losses (no export/local regulations).


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jwr avatar image jwr klim8skeptic ♦ commented ·

With these priorities, the solar part makes no economic sense and the whole system is much worse because of increased battery wear. The whole point of adding solar here is to supplement the base constant power requirements (such as a heat pump).

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jwr avatar image jwr commented ·

Well, it would appear that what I'd like to do is not possible with the MultiPlus. I guess no solar for me, then.

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alan avatar image alan jwr commented ·

Install a multi, venus device, mppt and panels.

Then setting dvcc up, will do exactly what you want.


I suggest you do a lot more reading.

Start here https://www.victronenergy.com/upload/documents/Book-Energy-Unlimited-EN.pdf


Then here, https://www.victronenergy.com/upload/documents/Brochure-Energy-Storage-EN_web.pdf

(yours would be option 3)


Then https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf


And finally

https://www.victronenergy.com/live/ess:start

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alan avatar image
alan answered ·

Power will flow into the path of least resistance,

so it will flow from the MPPT to the battery terminals, then directly to the load (while its operating) without actually going into the battery as the path into the battery will have a higher resistance due to the chemical reaction taking place inside.


Charging is controlled by setting the same voltages in both devices or by adding a venus device into the mix and enabling DVCC to control both.

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