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jm0278 avatar image
jm0278 asked

Does ESS Violate Anti-Islanding?

New residential install of a Multiplus-II with 600 watts of solar from SmartSolar MPPT. I'm in the U.S. and must NOT feed back into the grid during a power failure. Despite having DC feed-in disabled, the system still shows several instances during the day when AC in was negative and Grid Feed-In was positive. Batteries were not fully charged and the amount of solar at the time was only about 100 watts.

I've set the Grid Set Point to zero and that seemed to reduce the feed-in from a couple hundred watts to just a couple dozen. But I need to know: will this system attempt to feed power back into the grid during a power failure, thereby creating a hazard for utility workers or will this behavior only ever be seen when grid power is available? The whole concept of ESS is one of the primary reasons for buying this system and I don't want to give up on it needlessly.


Multiplus-IIESSgrid
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2 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @jm0278,

The MultiPlus-II in ESS mode tests the incoming AC input to make sure there is an independent AC grid supply, and if an incoming AC input cannot be detected, it will disconnect the AC-input relay with a double acting internal transfer switch. These anti-islanding protection rules (how quickly and under what conditions the grid is considered missing (low voltage/frequency etc)) vary country by country, so you need to make sure that the correct grid profile is selected for your country when the MultiPlus is initially programmed. This setting is password protected.

You can test this anti-islanding yourself by disconnecting the AC input with an external isolation switch from your main switchboard, you will be able to hear the internal relays of the Multi click to isolate. Then you can reconnect it, and wait a minute and hear the click again when it reconnects internally.

It is possible to see some power flow back into the grid (as you are observing) when the AC input is working normally. This is a function of fluctuating power demands and supplies, a large load turning off suddenly, or a large surge in solar with a full battery might lead to some back feed for a second or two. This is very rarely an issue, but the 'grid set point' is a way to minimise this if you are experiencing issues with your meter.

In some places in the world the grid meter will physically lock itself and disconnect if backfeed is detected, even in those rare cases, it's not common for the MultiPlus to trigger that mechanism unless there is some other issues.

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bonie-wanda avatar image
bonie-wanda answered ·

I also have grid-feed-in disabled. I also do get those rare overshoots of grid-feed-in that last a few seconds when the grid is live, especially when the Multiplus is using AC-IN for power assist to grid-direct appliances like water heaters. This usually happens when the grid-direct appliance stops consuming.

So through time lag/delay ESS will feed-in but for a short time.

I haven’t seen any grid-feed-in during outages and load-shedding (we have a lot of those here) though so I assume it’s pretty safe.

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