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simon-t asked

Controlling the maximum current output on the AC side of a Multiplus 2

a774ef79-2c22-4567-9328-891625a3aba6.jpegI hope to use a Multiplus 2 as a grid tied inverter. I live in rural Scotland. Although I have mains electricity, my DNO has put significant restrictions on the maximum size of a grid tied PV inverter I can have. Apparently the infrastructure around me is ‘fragile’ I am allowed a maximum of 7.36 KW with an ELS so that I never export more than 3.68KW.

I hope to get around this by having a large PV (circa 17kw) array to charge a suitably sized battery bank (in the style of attached picture but without the Genset).


My question is around controlling the output of the Multiplus. I plan to use the 8000VA model as specs say its continuous output power is 6400w, but its peak power is 15000w. I am worried the DNO might use the peak power as an excuse to say no. Can limits be set so that the output power of the Multiplus never goes above 7.36kw?

I know it seems a bit ridiculous, but the DNO have final say here, and ultimately a grid tied system will be so much easier to integrate into my house.


Thank you



Multiplus-II
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2 Answers
nickdb avatar image
nickdb answered ·

With the ESS assistant you can limit the inverter output power to anything you want.

This doesn't affect passthrough AC though.

The peak is transient anyway, it's not for sustained use.

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Jason - UK avatar image
Jason - UK answered ·

@Simon_T If you have a limit on your export, the DNO will look at the maximum output of the grid tied PV array regardless to your battery storage system as if the batteries are full, their concern is you will then export your surplus energy to the grid with no locked / certificated means of limited that.

You would be better with a grid tied PV inverter or PV array (what ever is the smallest) no greater than the limit you have which will give you your certificated export connection to the grid, the have what ever size PV array connected to your batteries via a MPPT. Then you limited your feed in the remote console to 3.68W, that way your system as a whole only exports a maximum of 3.68kW, either by the grid tied PV system or any surplus energy form your PV array via the MPPT & Multiplus.

The grid tied PV system will generate what ever it can based on the solar generation and unless you have a interlock to stop it generating, it will need to keep discharging, whereas the DC-DC PV system will stop when the batteries are full and the Multiplus doesnt allow it to export.

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Using the below layout, grid tied PV on AC out1 limited to the 3.68kW, Then have PV though the MPPT but off the top of my head, I am not sure if there is a limit other than limited by the MPPT for the DC-DC PV system.

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simon-t avatar image simon-t commented ·

Thank you for your thoughts. It is certainly great food for thought.a couple of questions:

‘@Simon_T If you have a limit on your export, the DNO will look at the maximum output of the grid tied PV array regardless to your battery storage system as if the batteries are full, their concern is you will then export your surplus energy to the grid with no locked / certificated means of limited that.’

The 8000Va Multiplus 2 seems to have a maximum output of 6400w which is less than the 7360w I am allowed to generate. I can then use an ELS to limit my grid feed to 3680w. No matter what size of PV array/battery bank I have this cannot be altered. As a result, surely the DNO won’t care what the size of my PV array or battery bank is? Tell me if my logic is not sound?


For me this is all about the ability to self generate and self consume electricity using a grid tied system. I am not trying to generate electricity to export and sell



Second point:

You would be better with a grid tied PV inverter or PV array (what ever is the smallest) no greater than the limit you have which will give you your certificated export connection to the grid, the have what ever size PV array connected to your batteries via a MPPT. Then you limited your feed in the remote console to 3.68W, that way your system as a whole only exports a maximum of 3.68kW, either by the grid tied PV system or any surplus energy form your PV array via the MPPT & Multiplus.

The grid tied PV system will generate what ever it can based on the solar generation and unless you have a interlock to stop it generating, it will need to keep discharging, whereas the DC-DC PV system will stop when the batteries are full and the Multiplus doesnt allow it to export.

There is a potential hole in this logic. My maximum generation capacity becomes the Multiplus 2 and the PV inverter. Even with an Export Limitation system, I cannot theoretically generate more than 7.63kw. But maybe the DNO might accept the ability of the Multiplus 2 to have feed in turned off. It’s all great food for thought!


Thank you so much for taking the time to answer





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