Export to grid battery settings - should it be set to 0?

[markosabanovic]

HI all, following on from the new FOX ESS 7.5 kWh battery system installed last month, I noticed that the batteries would export back into the grid once there was no load on the house and providing there was some juice in the batteries. As my PV system is already exporting I thought that having the batteries do the same would create problem for me as my FiT contract might be made invalid as it is based on the existing MCS certificate for PV capacity which is 3360 kW. I am one of those who was lucky enough to have the PV system installed before end of February 2012 after which the FiT prices were slashed. I still get 60 pence per kWh. Last calendar year the solar panels generated 4.1 MWh which was brilliant. My question is: was it correct to disable the export to the grid on the AC inverter (I've set it to 0)?

[sandeeppatel]

Did you ever get this reolved as I am too looking to reduce export to grid but not sure how to as Feed in is not so important for me.

[Dave Foster]

Did you ever get this reolved as I am too looking to reduce export to grid but not sure how to as Feed in is not so important for me.

You can reduce your export by changing the Export Control Limit in the inverter settings (from the inverter panel, or if you have an agent account)

The only thing to say is that it's rather self defeating and you may as well accept the feed in - When you are in the Self Use mode your house load is always covered first, then it charges your batteries, and only after that will any surplus be exported to the grid - if you reduce the grid export setting the inverter will then derate the MPPT as it cannot produce power without having a consumer for it.

[Suresh]

Hi, I am also interested in this setting. I have a separate inverter for generation. What I found was it was feeding in power into the grid even when there is no generation. Also, the feed in was more than the peak generation. I tried to get the tweaks done by requesting the installer (Solar UPS) but they are saying the feed in that I am noticing is necessary to balance the voltages, if so then the values should be fairly constant I would have thought. Today I managed to do some tweaks on the inverter myself, namely, I changed the export power and current to 0, now I will monitor the feed in to see if that made any changes. If you have any suggestions, please feel free

[Suresh]

So, this adjustment did not work

[Dave Foster]

When you say it is feeding in power to the grid even when no generation, is it a significant amount of power or a low power (~11 watts) - as this is a grid tied hybrid inverter there will always be a small amount of power flow on the output for it to remain in sync with the grid.
The export limit setting won't affect this small drain as it is a necessary requirement of a grid tied inverter.

When you are in self-use mode the inverter is biased from the grid, in feed-in mode it is the other way and you can reduce it a little by leaving it in feed-in overnight but not unusual for one of these inverters to use 0.5-0.7kw's a day particularly when the sun isn't shining.

If it's more significant than that (several hundred watts) then it's time to investigate further.

[Suresh]

Thanks for the update. Previously, it was feeding in 1.3 kW and 1.5 kW for intervals of 10 minutes, and I’m wondering if the installer adjusted something in response to my queries. Yesterday, it was sending 0.79 kW, even when the generation was only 0.35 kW. The feed-in bursts still last for 10 minutes each time.

FoxESS feed-in power.pdf

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[Dave Foster]

I think that is just a switching transient, whilst the graph shows a peak of power that lasts for 10 minutes, it was only a small transient but happened to occur just when the data sample is sent to the cloud. As the cloud data is based on 5 minute samples a well timed transient would appear to last for 10 minutes when in fact it probably only lasted for a few seconds.

So on to the subject of why you get data transients - a hybrid inverter senses the load with a CT clamp (or meter) just in front of the smart meter - the inverter attempts to balance the load that it measures from a mixture of solar and battery, if there is no solar it all comes from the battery.
The reason you get transients is the inverter cannot respond instantly to changes particularly with larger loads such as cookers and kettles - it is very quick maybe a second or 2 but for that second or 2, the load will be met by the grid. Likewise when the load or appliance turns off there is a moment where the batteries are providing the power but the load is no longer there and in this case you get an export transient which lasts for a very brief period of time.

This happens a lot when larger loads switch on or off, and some devices (particularly induction hobs) play havoc with it as they switch on and off very quickly so you get lots of small spikes of power in one direction or the other. When you look at the energy statistics they don't show because they are so small in duration , but occasionally it happens just as a cloud data sample is sent and then it looks like you have a spike of power lasting 10 minutes which is not the case.

The way to be sure is to look at the energy statistics for day by hour, I suspect it won't show much, if anything at all for that time period.

[Suresh]

Thank you, David, for your post. I checked the battery charge and discharge current settings, which were both set to 40A. I've now reduced them to 12A. My hope is that with this adjustment, during periods of high load, the battery will discharge at a lower rate and rely more on the grid. This way, when a large load like the oven is turned off, there won't be excess power feeding back into the grid. I'll test how this works and update you here. Cheers,
Suresh