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schalk-1 asked

ESS with Grid meter function/control with backup power

We have been experiencing something interesting with the Grid meters, specifically the ET112 and ET340. At one of our sites we have a 5kVa Multiplus II, with the ET112 Meter connected on the input of the inverter (basically after the Main breaker from the Grid in the DB). Between the inverter and the meter is all the "non-essential loads".

On the output of the inverter is all the essential loads. We installed the meter to try and enable the Victron to back feed excess solar power to the "non-essential" loads, without back feeding to the grid. This worked great, but what happens in the evening intrigues me.

The battery power of the system gets "dumped" to the "non essentials" during the evening, leaving no power for the essentials to run on at night. The battery reached the discharge floor before 7 at night, but when we removed the Non essential loads from the meter, the battery discharged normally and last the whole night.

My Question is: how can we prevent the battery from being "dumped" back to the "non-essentials" and only allow the backup power to supply the essentials/inverter output. I have been scanning through the manuals but i do not see this mentioned anywhere. Can someone be so nice to assist? Please?

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2 Answers
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johannes-cronje answered ·

HI @schalk@solarengineering

I going on assumptions here.t at 100 You are mentioning backup thus I take it that the battery bank is used as a backup and is supposed to be kept at 100% SOC at all times . The energy should then not flow in the evenings to the non essential section that is in front of the inverter. But if you run ESS and you running a storage setup it is a different story. The Energy meter becomes the metering point and the inverter will supply the essential as well as non essential loads when the grid is connected . You then want to use your excess Solar the recharge your battery's during the day . You will not be able to separate the essential and non essential loads if you want to supplement your loads during day time with solar and use storage power at night. If the batteries are meant to be in backup and need to kept full at al times and use solar power during day time to supplement essential and non essential loads . If you have a power failure your non essentials will obviously not be part of the backup power. Thus if you have not got enough storage capacity to supplement your loads during night time , as well as enough capacity for a power outage , just run ESS "keep batteries charged " . You cannot choose which loads should use power during night time from the battery because your inverter will produce power the all loads up until your metering point (energy meter). If you do not want your system to produce power during night time while the grid is connected to the NON essential loads you would need to disable the energy meter so that the inverter becomes the metering point but then you will not be able to supplement your non essential loads during day time with your Solar power.

If your system is designed to be a backup system , then keep the batteries charged at all times and use the solar power during day time to supplement your essential and non essential loads. When Power fails you the have the batteries for backup to all your essential loads.

If your system is designed as a storage system , then make sure you have enough capacity in the batteries the cover some usage during night time and still have enough backup for power failures for essential loads. Ensure you have enough excess solar the recover the night time usage to have a full battery by sunset.

I hope I could have been of assistance

Regards

Johannes Cronje

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schalk-1 avatar image schalk-1 commented ·

Good Day Johannes

Thank you for taking the time to explain this to me in detail. I had a feeling this would be the outcome, I just needed to confirm my train of thought.

Have a great day

Regards

Schalk

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dayandnight answered ·

Hello @schalk@solarengineering,

As far as I have understood you want to use the energy in the batteries exclusively over night only for your essential loads? During day it should work as "normal" ESS? Backup? Or what ever? Correct?

My idea, based on hardware: Just use a "big" relay to switch off AC Input from the Multiplus units in the night controlled i.e. by a timer. It will run than in Backup/USV Mode only during night. Fine-tuning in combination timer with "sun is available" or other conditions will be possible, too. It needs only some engeering and ideas for controling the "night-relay".

Only my view cents!

DayAndNight

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