How ESS feed-in works

DIY
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1

Sorry if it is a “dumb” question, but…

If I have:

  • A PV generating 10kW;
  • The AC load, in this case a house, consuming 1kW;
  • Multiplus II with its batteries at 100% SOC;
  • On “Grid feed-in” ESS tab on Cerbo GX you select “Limit system feed-in” and set the limit to 1000W.

With the above scenario, I got in mind:

  • There is a power surplus of 9kW that will be fed;
  • If the grid is on, there is no way to have Multiplus II adjusting the frequency to lower the PV production;

Please notice that this is the core of my doubt, so my statements above may be wrong.

Question: How will Multiplus II limit the feed-in? Will it limit in someway I don’t know or it will just disconnect from the grid?

Thanks!

2

Simply put, enough power is only ever produced as required by a load. Even if the solar panel array has a 1000W potential, a 100W load will only result in a 100W (plus some possible losses) of power being produced and consumed by the load. To answer your question, no the system does not disconnect. PS - Best to think of it as 9kW of potential not realised as opposed to wrongly 9kW of power lost.

1 Like
3

Your response addresses the disconnection question as per your statement it will not disconnect.

However, how will Multiplus II limit the feed-in?

4

If the PV inverter is connected via the GX and supports it, then the system can tell the pv inverter to ramp down or run throttled.
For example Fronius suports control via modbus.

Not all PV inverters are fully integrated for control like that though. (Some only have basic monitoring)

Correct. They cannot.

5

Well… I am in Europe. Here you are not allowed to shift frequency when on grid and would need a lot of power to surpass the grid power capacity to shift it. So, it is not a problem on the inverter being used, Multiplus should not shift frequency while on grid.

6

While not mentioned in the documentation, I think this feed-in limit applies only when off-grid. That is why I am asking.

7

As LX mentioned: if your PV inverter is linked to and supported by your GX device (Fronius PV inverters work very well), the GX can tell the PV inverter to produce less power, so the FeedIn limit can be achieved without frequency shifting.
Because indeed: when you are connected to the grid you can 't shift frequency.

Another remark: your PV inverter should be correctly configured to properly integrate with a GX.
From the top of my head are these the settings that need to be configured on a Fronius inverter:

  • Modbus config needs to be set to the “int + SF” Sunspec mode
  • Inverter control via Modbus needs to be enabled
  • Control via Modbus should have priority

Please check the ESS manual on the relevant topics.

8

Thank all of you!

The problem is that this is an integration of Multiplus II on a site with SolarEdge inverters that also includes a battery. It gets quite confusing when it comes to decide who does what.

I guess that the best approach is to keep the SolarEdge power meter measuring the import/export (before the Multiplus AC input) and having SolarEdge, if necessary, limiting the export. But as a side effect, the SolarEdge battery will only get charged when the Multiplus’ batteries are fully charged as it will be seen, from the SolarEdge perspective, as load.

But… Life is what it is.

9

I just took a look on the ESS configuration and saw:

image
image2868×902 146 KB

So, it should be possible to limit the feed-in of the MPPT (DC-coupled) unless I am missing something.

10

Yes you can stop feed in from dc connected to mp.

If ac paralleled inverter is capable ( controlable from mp) this can also be limited.

I have mp2 that doesn’t feed in to grid and a sma ac coupled inverter that feeds into grid, sma inverter is seen by mp2 but isn’t controllable.

11

Correct, this is also documented as needed with some models. They use sunspea as does Fronius on some models. So the possibility for some models is there.

12

To make it a little bit more complicated, one of the two SolarEdge has a 10kW battery. The Cerbo GX Sunspec SolarEdge data collection will only work if you set the SolarEdge modbus number to 126 but, if you do this, then the SolarEdge looses control on its own battery (LG bug?). I have posted a question if it would be possible to change the Cerbo requirement of setting up the SolarEdge to modbus address 126, but got no answer from the community (too complicated?).

By other hand, I can have the SolarEdge always set to be on what they call Alternative Power Source mode (APS) were its production can be controlled via AC frequency so, by Multuplus II. Still, it only applies when the system is off-grid as you can not modulate frequency when on grid.

13

Does it need to control the solar edge though?
What would you need the control for?

14

When in off-grid (e.g.: the grid went down), if you do not control the production, and the batteries are full, there is no place were the power can go. As you loose the SolarEdge power meter (the grid line is “open”) then it will produce at its maximum. In this case, you need Multiplus to increase the frequency so it will reduce/stop the SolarEdge production and the SolarEdge must be in a state that adjust its production based on frequency.

15

Which it will be able to do when there is not grid. So then it is your option the APS mode.

Unless it has some relays or aux switches for power reduction signals.

16

I could use Multiplus II K1. However, K1 now is not a physical relay but a open collector transistor. So you need one external relay or an optocoupler. As Multiplus will always be driving the house, I think it is easier just to keep SolarEdge in APS mode.

17

So it’s not supporting the solar edge in ac coupling or needing to provice a grid reference (since the solar edge has a battery?)

18

No… SolarEdge does not provide off-grid without installing what they call “backup interface”. The backup interface is very expensive. Also, if grid goes down it takes few seconds to bring the power on back again. That is why I choose Victron Multiplus II.

In this case, Multiplus is always the AC reference. While on grid, it follows the grid; while off-grid, it generates the AC reference so the SolarEdge can keep producing. From SolarEdge I charge all the batteries. However, next week I will move one PV string out of one SolarEdge and connect it, via a Victron MPPT, to the Multiplus. This will provide starting capacity even if all batteries get totally discharged.

For those reading my posts, I guess now it will be more clear that much questions I am posting.

By the way, thank you all for helping. I hope I will soon be able to, in turn, help others too.