question

bradhale avatar image

Prioritise PV from MPPT over Grid power

I have a Grid-Tied Quattro 48/15000 with 860 Ah of battery power with a usable 20 kWhr .

My maximum allowable grid usage is 5.5kW and I have a PV array of 36 panels with a peak output of 8KW.

There are two 18/250w MPPT’s attached that act as charge controllers and supply AC power when required.

It is setup as an ESS system with Self consumption (With Battery life) and DVCC disabled

The problem is that the system prioritises the Grid input over spare PV power. Therefore it is inefficient and I am paying for grid energy when spare energy is freely available from the PV/MPPT.

I am reducing grid power usage by modifying the 'Grid set point' in ESS depending on the weather and my energy requirements. Ie When I have a high demand, I set the grid to maximum and at night reduce this down to a much lower level.


Is there a way to instruct the system to use maximum PV output for AC and only use the grid to fill in any shortfalls?

The installers here in Spain do not have a lot of experience of these Victron systems and have not been that helpful in fixing these complex issues.



MPPT - Solar Charge Controller
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3 Answers
remigius avatar image
remigius answered ·

I have a MultiPlus, MPPT, BMV 712 smart and Cerbo GX in the RV. As stated in this thread I also noticed that grid 'always' takes priority over PV.

2021-04-17-1653grid-no-pv.jpg

Intitial status: connected to grid.

Although there is plenty of sunshine the MPPT seems shutdown.


2021-04-17-1700no-grid-pv.png

Grid disconnected, I pulled the plug.

PV takes over with 107W


Now the surprise on 2021_04_18

2021-04-18-grid-and-pv.png

Why do they work together now?

PV should always be leading, the grid supplementing. In this way cost is minimal and system operates in environmental friendly mode.

I did not change any of the settings, just disconnected and reconnected the grid because we moved the RV. I am not that familiar with the system to change settings on my own.

Did Victron update the MultiPlus or what did I miss?


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Hi @Remigius

This happens because one charger is seeing a slightly different target V than the other, and the higher will dominate. You may be afraid of changing settings, but it can be fixed..

If you're using Temp Compensation, make sure both chargers are using the same value.

Set the mppt Absorb and Float targets slightly above the Multi's. 0.1V should do.

With a system like that, you could also be using DVCC to share the V and T readings, so you know for sure they're seeing the same thing. Typically the V from the BMV and the T from the Multi.

Changing settings in the Multi can be a challenge, but the mppt is simple with VictronConnect.

You may also find occasions when the mppt drops to Float before the Multi, then the Multi will surely dominate.

This can all be tuned by someone with a little experience, or take the time to learn yourself.

bradhale avatar image
bradhale answered ·

My AC loads sometimes reach 12kw. The PV system will supply about 6KW and if I set the grid point to 4520W then I can fill the load gap from the batteries. However, when the system loads reduce down to about 4 kw, the system uses the grid power and not the available PV power. This is the problem I'm having. It is using Grid as priority when I need it to use PV. I do not have enough capacity to use only PV and battery as it will deplete the system too quickly. But I need the additional power to take up short term loads.

As the system is in Spain I cannot export excess power to the grid but I need to have the grid available for import.

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If exporting power to the grid is explicitly prohibited, you should NOT be using ESS. ESS has the potential to feed in to the grid if you drop large loads.

For your system, you should use the virtual switch option (assuming that is available on that model) and set it up to ignore AC input when battery is >(x)% SOC, do not ignore AC input when battery voltage is back above (y) VDC. You can then further add to not ignore AC when loads exceed (z) Watts and use power assist plus AC current input limit to basically split the loads between battery/solar and grid. This is rudimentary compared to ESS and depending on the transfer switch of your model could even result in dropping AC loads (a big flaw between Multiplus I and II was the MPII had transfer switches roughly half the size of the MPI). This causes a physical switch to connect or disconnect the incoming AC lines as opposed to just software programming to mix the AC power sources. Because of the way AC power works, paralleling power can always result in feeding AC power into a generator if not properly set up.

As stated by WKirby, the grid set point is what the system tries to keep on the grid. It should be renamed like Artificial Load or something to indicate that the system will try to maintain that large of a load on the grid to minimize the chance of feeding in. So basically it will try and power 4.5 kw of load from the grid before even considering using DC power. And depending on how ESS is programmed and the inverter/charger voltages are established could put more on the grid before using DC power.

Your best bet is to try and set up a virtual switch to ignore AC. This will cause more wear and tear on your equipment by actuating the transfer switch and will cycle your batteries more. So if you are using lead acid, it could run through your battery life span in a short period of time. If you are using LiFePO4, it wouldn't be as big of a deal.

ESS is great, but only if you are allowed to feed in to the grid since you will always have the potential of doing so even if you have it programmed otherwise.

wkirby avatar image
wkirby answered ·

So you have told the system to take 4520W from the grid. It is trying to do that but there are not enough loads to take that much power from the grid and the battery is also full.
Solar will not start to produce until your loads total more than 4520W.
Alternatively, you could reduce the grid set point. If the grid set point is 0W then the system will use solar, then battery if solar power is not enough and actively try not to take from or send to grid.

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