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donnib avatar image
donnib asked

What settings to use for a Multi when grid export is strictly forbidden?

Hi,

I have two Questions created already where i have discussed various issues regarding my solution. See here :

https://community.victronenergy.com/questions/41291/multiplus-ii-disable-feed-back-entirely-possible.html and https://community.victronenergy.com/questions/42279/lom-detection-when-feed-in-disabled-why.html?childToView=42916#comment-42916

I am sorry that i now create another issue but i am not confident that what i want can indeed be done with the chosen HW/solution.

Background:

I am located in Denmark and wish to buy Victron products to make a hybrid/off-grid system where "All" i want is that i can pull/mix power from grid when i don't have battery/solar but NEVER feedback to the grid, just one little bit will get me into trouble. I assume feed-back and feed-in are the same things right ? The most important thing for me is to not feedback to grid and be able to pull and use the produced energy myself. I think this is called self consumption.

I read on https://www.victronenergy.com/live/ve.bus:grid-codes-and-loss-of-mains-detection :

Q4: I use ESS, but have disabled feed-back, is a grid-code still required?A: Yes, also in this case LOM is required to make for a safe and also local regulations compliant system. Running ESS with disabled-feed-back is still not the same as using a Multi in its default configuration without ESS.

I don't understand why do i need LOM for this ? Can somebody explain ?

Regarding my usage :
We (our family) have roughly 16-20kw consumption per day and in total 6000-7000kW yearly. I will also have a powerwall build myself using LiFePo4 batteries (48v) roughly a 10-15kwh.


System i have in mind :

1 x Multiplus II 5000/48
2 x SmartSolar 250/60
1 x Venus GX

I have 21pcs of 310W panels (https://bit.ly/2P1GL9O) so i was thinking to place 10 on each side of the roof meaning i would do 2 x 5 panels in series so i would have 200V for 5 panels then parallel the 2 strings and one string is 10A so 200V 20A for one charge controller. I think that is ok but that means I need to use the 250/60 solar charger model which is more expensive and i need two of those. Please correct if i am wrong.

I have 100% stable grid connection and since the Multiplus II can handle a big load in by pass i can practically run the whole house on the AC out from the inverter. Please correct if i am wrong.

Questions:

  1. I want to know if the above system is feasible ? Are there any other Victron HW that i also need which is not on my list above ?
  2. Can I use the system in such a way that i NEVER feed-in/feeback to grid in no circumstance but at the same time i can consume from the grid when no solar or battery is available ?
  3. If 2 is possible can the system be programmed in such a way that when the load is too big for solar alone or solar/battery combined to also mix in grid power BUT still without feed-in/feedback to the grid ?
  4. If 2 and 3 is feasible what do i need ? Do i need ESS or ignore AC input or both if that's possible ? How would one configure ?
MPPT ControllersESSPhoenix Inverter
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6 Answers
Alexandra avatar image
Alexandra answered ·

To answer your LOM question please see https://www.victronenergy.com/live/ve.bus:grid-codes-and-loss-of-mains-detection. The answer is mainly to do with safety.

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donnib avatar image donnib commented ·

Yes that is the link i did ready but this sentence is not clear, why is it not the same ? What is the difference ?

Running ESS with disabled-feed-back is still not the same as using a Multi in its default configuration without ESS
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Alexandra avatar image
Alexandra answered ·

We also live in a country with zero feedback requirements. There are several ways this can be achieved. One is by using an energy meter that can prevent this. We program ESS in and have a grid set point of about 150W, this can be set on a GX device after ESS is programmed (you may have to experiment with how low you can go). I think ESS will best suit your needs as it does allow a mix of Grid power when PV is not enough. You need an MK3 device to program the inverter with the ESS assistant.

You cannot use AC input ignore on Virtual Switch if you are using ESS and other assistants.

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donnib avatar image donnib commented ·

Ok so few questions :

  1. How does the energy meter prevent the feed in ?
  2. Is a energy meter required when running ESS if i still want to mix AND not feed in to the grid ?
  3. As mentioned in my first post i do have the intention of getting a GX device, at the moment i was looking at the Venus.
  4. Can you explain a bit what this grid set point is ? Is it the point when the inverter will start to mix grid with solar/battery or what is it ?
  5. Why is a MK3 device required when one has a GX device ? Can you not configure the Multiplus through the Venus GX ?


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Alexandra avatar image
Alexandra answered ·

To check your PV setup and MPPT choice there is an online calculator, https://mppt.victronenergy.com/

or a downloadable spreadsheet https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwi6morKp_LnAhUD1xoKHQOtB3UQFjAAegQIBBAB&url=https%3A%2F%2Fwww.victronenergy.com%2Fupload%2Fsoftware%2FVE-MPPT-Calc-2_4.xlsx&usg=AOvVaw1vFkExXqtI6Yb4juZxq9ZP

They will both allow you to experiment with different configurations and choose an MPPT to fit.

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donnib avatar image donnib commented ·

Cool. i will have a look, didn't know about this one.

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Alexandra avatar image
Alexandra answered ·

Since you are putting a lot of thought and research into your project I just wanted to add that even though the multi allows a large passthrough current you may want to consider what may happen if the grid fails and it has to suddenly switch to inverter mode. It will need to be able to handle the surge and can cause a system overload, you would need to be sure both the batteries can give the current draw and the inverter can take the surge. I do not know what loads are in your home I am just making an observation based on what I have seen in the field. Hope these answers help.

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donnib avatar image donnib commented ·

As far as i understand. If no solar/battery it will do a bypass to grid and in this case i can pull 50A which is more than enough and more than what i can pull on one phase which is 32A. I have a normal family house with normal consumers, oven, 2x fridge, dishwasher, vacuum, hairdryer. We have 100% stable grid here so incase of grid failure it depends when it happens. If it happens when the inverter was on bypass then yes the inverter will go to inverter mode but if there is no battery/solar it will stop or if there is and the load is to big it will shut down and then pretty much nothing else i could have done. If i did not have this system the house would be without electricity anyway so not much loss i would say.

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Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @donnib,

In a situation where grid feedback is strictly forbidden, and even a few watts will cause issues with your utility meter, or power company you should not use ESS which keeps the AC input grid connected at all times. Even with all feed in / feed back options disabled there is still a chance with ESS that there is some non-zero amount of power flowing back to the grid. For example when the inverter is assisting the grid to run a very large load with solar on a full battery and the load stops, it could allow some small amount of power back into the grid.

Instead you will need to investigate further the options for the ignore AC assistant. It will not be as smooth or elegant system as the ESS. The Multi (and battery system) is more likely to have to take greater load and more surges, and the internal AC relay will be doing more switching. Though correctly configured, it should allow for zero export, and your system to run loads larger than the capacity of the Multi alone.

There is more information about the Ignore AC function here - https://community.victronenergy.com/storage/attachments/3299-virtual-switch-ignore-ac-lesson.pdf

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donnib avatar image donnib commented ·

@Guy Stewart (Victron Community Manager) Thank you very much for your explanation and the link. This explains the issue i was having and trying to understand so it's clear to me now that i should not use ESS which means i loose the functionality of mixing grid with solar/battery. The Inverter will bypass when battery is to low or the load is to high. I also understand that i need to figure out how much load do i have during night so that i don't drain the battery to much so the whole house looses power because the Multi will run of batteries and not grid ? Is there no way to set this so that when the battery goes low (specific threshold) then it should switch to grid and stay on grid until battery is at a level where it can start to pull from it ?

Assuming i use the AC ignore do i need a GX box at all and would i gain anything for having one ? I am hoping your answer is you don't need it so i can buy this later....cut the upfront investment :)

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ donnib commented ·

The Multi will still mix grid with solar and battery, but only under certain limited conditions, that reduce the possibility of accidental feed-in, such as when the battery isn't full (as momentary surplus can then go into the battery).

The inverter will not be bypassed when the grid is connected. The difference is the AC input relay will be allowed to close (on) during times when possible feed in is minimal, instead of all the time.

Correctly configured, the system will not run out of battery. When the battery is low, the grid is allowed in to run the loads and maintain the battery voltage. Normally in ESS the grid is ALWAYS allowed in, and the system does it's best to balance the grid supply and battery/solar to keep the grid level to the set value (ie 0).

What you describe as how you want it to work, with the grid coming in when the battery is low, is exactly how it does work with the Ignore AC. As long as you configure it that way.

Now might be good time for you to open up the demo mode of VictronConnect, select the Multi, and look at the AC input control options.

The GX is no longer a necessity in this kind of system, but I personally believe it is the best value for money product that Victron makes, and you will get your money's worth, and make your system a lot more enjoyable and understandable.

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nigelfxs answered ·

Hi Donnib

"... but NEVER feedback to the grid, just one little bit will get me into trouble".

I am not familiar with the requirements in Denmark, however I recommend that you investigate this requirement in more detail - just to make sure there is no misunderstanding.

While feedback to the grid is never allowed during a power outage, in many cases it is okay to have a short-duration/low-power feedback to the grid. The reason for this is that many appliances, which have a motor, can feed back a small amount of power back to the grid when the load changes suddenly.

If you enable ESS, then you can minimise the total grid feedback by increasing the Grid Set point - see the picture below.

If you increase the Grid Set-point to 50W or 100W, then the probability of feeding back power to the grid (and total energy) gets smaller and smaller. Also keep in mind that the Multiplus-II will never feedback to the grid during a power outage.


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