olly12383 avatar image
olly12383 asked

Multiplus - modbus - grid tie solar 3ph - use spare energy

Hi, I have a house with a 4kW GT system on FIT on phase A

I have added a 12kW array which I am planning to split over phase B and C.

I want to use a multiplus II as a smart inverter/charger from a lithium battery to store excess energy from any phase.

My supplier meter is net metering (non smart). So what I (think I) need is my own net metering meter which talks to the Multiplus and tells it to charge or discharge the battery to keep the import/export at zero. However this will only be pulling off one phase. This is why I need the external meter. If I am exporting 1kW on phase B and C (for example), with no import, but the Multiplus is on phase A, it can still import 2kW on phase A with no supplier charges.

I have researched Modbus meters but I just wondered if anyone had done anything similar - presumably I need an interface between the Modbus and the Multiplus to convert Net Export Power into Victron charge now Power.

I will have a zappi car charger and a DHW store system to soak up the excess energy. Ideally this would be priority order

1. Car (if present)

2. House batt

3. DHW cylinder

4. Export.

Although I would be willing to always do House first if that is less complicated (the zappi and DHW system will communicate internally but I don't know if they would communicate with the Victron).

I believe delays can be programmed such that the Victron could have a shorter delay on start up than the Zappi which would ensure the house batt gets priority over the car.

Of course as the car isn't always there I thought that would be best if the car got first dibs as hopefully if its a sunny day the house would get a chance later after the car leaves.

I should be good for producing approaching 16000kWh per year with this system (the 1year old original 4kW array made close to 4000 in a year and the 12kW array is less shaded)

My background is Marine - off grid so use a lot of Victron products. I have used R pi a bit so I guess this or Arduino could maybe be a useful interface if there isn't a premade solution available.

Thanks in advance


ESSEnergy MeterModbus TCPgridsolar
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2 Answers
dayandnight avatar image
dayandnight answered ·

Hi @olly12383,

I am wondering about your question why nobody did answer it. I think what are you asking about is a typical Victron ESS system. When I am right it is rather simply to full fill your wishes. You need a Gavazzi energy meter, three Multiplus-II and of course batteries. Such an installation should be done by professional Victron reseller who has experience to do such a system. It is complex but not as doing a journey to the moon. ;-)

Read the above linked documents and when you need more details or you do have question, come back and ask.


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catraz avatar image
catraz answered ·

I’m also interested in this question. Can excess energy from a parallel PV inverter (on AC in) be used by the ESS to charge the batteries? Is this possible using the AC out connection?


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dayandnight avatar image dayandnight commented ·

Hello @Catraz,

"parallel PV inverter (on AC in)" Do you mean a PV system which is connected to the grid? In case yes and based on this little information the answer is YES - just have a look into the Victrons ESS system.


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catraz avatar image catraz dayandnight commented ·

Thanks for the reply. I have read the ESS manual several times. Loads of information but I’m struggling to see this question directly answered.

Its an interesting application when adding an ESS to an older PV inverter. In my situation the PV inverter is in a shed. The ESS / battery etc is separate with a separate solar array in a garage adjoining my house, Being able to charge via AC in an a meter to will help me best manage self consumption.

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dayandnight avatar image dayandnight catraz commented ·

Hello @Catraz,

I don't see any technical problem to work with any grid based PV inverter. It is more a question if it necessary to control or avoid with the ESS system feed-in to the grid. I guess grid feed-in is nothing you have to think about.

You need an energy meter, one Multiplus-II GX and a battery to start and of course your existing PV system.

The energy meters measure the flow of the energy to and from the grid. Based on this the ESS system controls charging and discharging of the battery. When sun shines and your PV produces more energy as you self consume, the battery is loaded. When there is an higher consumption of energy as the PV is able to deliver the energy will be delivered from the battery back to your "local" grid. There is no connection or interaction neccessary between your PV inverter and the ESS system. It is all done by measure with the energy meter the amount and the direction of energy flow to or from the grid. As long as there is energy from your PV or still in the battery your bill for electricity is 0, thanks to the ESS system!

It is really as simple as it sounds. Of course there are limitations based on the technical infrastructure on your site and the size of your PV. It has to be decided based on this what kind of Multiplus you need, how big the battery should be.

Beside the above three components you need wiring, network cables, fuses, a MK3 USB interface to start updating and programming the Multiplus and your technical know-how and understanding to install this equipment. And yes, there are many facts to think about and to understand. But all necessary information is in the Victron universe available and the community is very helpful, too.

In case working with grid components and setup complex systems is not yours, it is highly recommended to speak to a specialized Victron dealer and let him help you.

Kind regards


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catraz avatar image catraz dayandnight commented ·

Thanks @DayAndNight. I believe the knowledge here is higher than that with my Victron dealer (an online seller)

I have an Easysolar II GX with DC PV array connected in an ESS configuration. I also have a 2nd large PV array, AC grid connected with a SMA inverter. The two systems are physically separated. At the moment both systems work well, but in the near future the electricity retailer rolls but to a lower buy price for solar exported, hence I’d love to use the excess for battery charging.

Being a remote setup, adding a grid meter to allow the Easysolar to use excess power (that would be otherwise exported) would be a great outcome.


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