Fronius 3kw with Mp2 5kva

Because of the upcoming summer…(preparation) i am seeking to lessen the temp deration weakness of the Mp2 when i wish to run 4kw loads contionously for at least 2 hours. My plan is to get the Fronius 3kw inverter with matching panels to ac couple on the output side

Any thoughts? I have peak loads of 4kw in the morning that comprises of

  1. 1 x gyserswith 2kw element that runs for about an hour . The gyser takes preheated water from the EVAC gyser 55degs to 80degs during the day and also from the batteries every morning at 3am if the batterys are more than 50 percent. This gyser is connected in series with evac gyser
  2. Induction cooking during the day
  3. An aircon from 10am till 4pm

Existing equipment is
1 xMP2 5kva 14.4kw of lithium
250 100mppt
2kw of solar
Rasp venus

Will i be able to maximise the fronious capacity of 3kw by limiting the MP2 load to say 1kw before losses with the Fronius playing is part during the day?

Hi Skye
If you are right with 2kw of solar, that’s the first place to improve. The 250/100 can produce 5kw from panels, I have 6kWp peak of panels on mine.

Yes, the Fronius will help as you are planning. But I would consider the 3600w model, with 4-5kw of panels since the sun does not shine at full strength enough of the time.

If you are running ESS the rasp will control the Fronius’ output to throttle it back when there is not enough load and the batteries are full.

Thank you very much. This the kind of infomation i was looking for. The idea of overpanelling didnt come to my mind…i appreciate the reasoning behind it

Do then still need an energy meter …?

Are you in the northern hemisphere?
Depending our your local laws, you may or may not export energy back to the grid.

In our case in Johannesburg, we have a lot of red tape to be able to export energy to the grid. If this is the case, you have to install an energy meter that measures your total current drawn from the grid - and then install ESS in the Victron system to balance the inverters (Multiplus and Fronius) to get your energy use close to zero.

Eg. if you get more energy from the sun than you consume, and your batteries are full, the inverters will be throttled back.

Note: currently I pay my council the same rate for any energy I export, as the energy I consume. The meter does not take the direction of energy flow into account…


This is my system right now - the only heavy load is the dishwasher. My grid setpoint is 50W, so the ESS system tried to keep it is close as possible. Jumps around a bit due to many small loads switching in and out.

The battery (4 x Pylontech us3000) is being charged with excess solar. Mid winter I will get a max of 4200W out of 6000W panels, due to the sun’s low angle.

Thanks a lot. I am in the Southern Hemisphere, Zimbabwe. Our summers are very hot. I had to built a special shed facing south with no exposed walls to mount the inverter. I like that it is a bit far from the living rooms too because i noticed the MP2 likes to kick in its fans past 1.2kw load. The fans can be reallly annoying when gysers kick in and the load reaches 3kw even for 30mins

So the idea of the fronius came in…to pack as much heavy loads during the day whilst the MP2 stays cool handling deficits here and there

I also have the carlo still in the box waiting to play with it as soon as the Fronius arrives. Me and my wife are also planning to purchase a nissan leaf to make things more interesting!

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Not a “weakness”, a clever thought-through design to make the inverter last longer. :wink:

With AC-coupled PV, the PV is always used for the loads first (just because that’s the shortest path for the current/energy to take) and what remains is used to charge batteries or to feed into the grid. If there is not enough PV, the rest is take from the battery (ie the Multi and the PV-inverter work together).

But there is something I must warn against: In an off-grid situation, or where there is a power outage, do not expect to be able to carry 4kW of load with a 3kVA Multiplus just because you have a PV-inverter on the output. This may work for short amounts of time, but it is not a stable configuration. The PV-inverter still checks the quality of the “grid” it is connected to, and if it disconnects it will take a minute or more to reconnect and start making power again. During that time, the Multi must be able to carry the whole load. If you want to power a 4kW load during a power outage, you need a 5kVA Multiplus.

Thank you. Yes that good news to me as i have already a 5kva multiplus. It the 3kw fronius that i intend to pair it with. I have learnt something really crucial

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