Hi all, hoping someone is able to help. Have been chatting with the installer and can’t seem to work out what the issue is.
Our setup has a single phase inverter for our 6.6kw solar panel (even though we have 3 phase power). We’ve had our 3 phase foxess cq7 20kw battery installed with a 3 phase inverter installed for the battery. The solar panel inverter was not removed.
After the install I’ve been monitoring the usage and set time for forced charge and balance as Self Use mode. I’ve noticed on my electricity retailer app that during the night the battery will discharge and feeds back to the grid. It’s been happening since the install last week. I’ve currently had to set it to back up mode between 11pm-6am so that the system doesn’t discharge the battery completely back to the grid. I’ve been losing approximately 4-5kwh each day as I can read this from my electricity retailer app. Strangely the Foxess app is only showing less than 1kwh going back to grid.
Another strange thing that occurs is that during forced charge during the day, my home usage shows negative values occasionally which is weird.
Any help or anyone else experiencing this?
It sounds like the meter (or at least one of the CT's) have been fitted facing the wrong direction if the battery is dumping to the grid whilst set to Self Use, the negative load may be the same thing but it can also be if your installer has not fitted a 2nd CT clamp to monitor the output of your single phase solar inverter.
it would be helpful if you could post the home page of the app (with the image of the house) when solar is generating and also the app statistics graph, click on 'Daily Production' and screen shot the Statistics graph for a full 24 hour period.
it would be helpful if you could post the home page of the app (with the image of the house) when solar is generating and also the app statistics graph, click on 'Daily Production' and screen shot the Statistics graph for a full 24 hour period.
Thanks for the reply Dave. I’ve attached some images from the foxess app for the 23 July. The app doesn’t appear to show much discharge back to the grid, I’ve had the battery to force charge up until 4pm at which it starts to discharge for self use.
I’ve attached a graph from our electricity retailer which shows the feed back to the grid from 4pm onwards, up until the battery runs out. It almost appears that when we’re using the battery part of it goes back to the grid as well. I’ve tested on setting the battery on back up mode during the night to stop the battery from discharging to the grid, and checking the electricity retailer app, that seems to stop discharging back to grid as the electricity retailer graph doesn’t show any power going back to the grid as soon as my battery is on back up mode.
The solar going back to the grid is through one of the phases, could it be that it somehow reads the battery as solar as takes the power back to the grid?
There is the image that you asked for during that same day on the 23rd July while we have solar charging, this shows the house being negative
I’ve attached a graph from our electricity retailer which shows the feed back to the grid from 4pm onwards, up until the battery runs out. It almost appears that when we’re using the battery part of it goes back to the grid as well. I’ve tested on setting the battery on back up mode during the night to stop the battery from discharging to the grid, and checking the electricity retailer app, that seems to stop discharging back to grid as the electricity retailer graph doesn’t show any power going back to the grid as soon as my battery is on back up mode.
The solar going back to the grid is through one of the phases, could it be that it somehow reads the battery as solar as takes the power back to the grid?
There is the image that you asked for during that same day on the 23rd July while we have solar charging, this shows the house being negative
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It’s now during the day solar is charging the battery, I’ve swapped between the forced charge mode and self use mode and this is what I’m getting. See images
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Does the 3 phase inverter have a meter fitted or is it reading the phases with CT clamps ? - if it is CT clamps you should be able to see 3 clip on clamps in the supply cupboard, but this looks as I thought like a metering problem.
If you are in Self Use mode overnight your battery shouldn't discharge to the grid, the fact that it is suggests that either the inverters meter (or CT's if used) are not wired to the correct phase and so what happens is as you use power overnight the inverter 'sees' a load on a phase, it applies power to the phase to counter balance it and what shoudl happen is it reads zero and stop outputting, but if you have the phases mis-wired the inverter outputs on the wrong phase and so 1) doesn't balance the load, and 2) it exports to the grid up to it's max power on that phase.
I think what the installer needs to check is that the R/S & T phases are wired exactly point to point (R/L1 inverter=R/L1 supply) and that the inverters meter is correctly reading each phase when a load is applied to that phase i.e. if you apply a 1kw load to the R phase, the inverter should output 1kw on the R phase only (the inverter screen will allow you to see what each phase is doing) - ideally do that testing with the other solar inverter off as it will only confuse the readings.
When you put the inverter in backup mode the battery is held preserved which is why it stops discharging, but if you can find out which of the phases have been reversed it will operate correctly.
If you are in Self Use mode overnight your battery shouldn't discharge to the grid, the fact that it is suggests that either the inverters meter (or CT's if used) are not wired to the correct phase and so what happens is as you use power overnight the inverter 'sees' a load on a phase, it applies power to the phase to counter balance it and what shoudl happen is it reads zero and stop outputting, but if you have the phases mis-wired the inverter outputs on the wrong phase and so 1) doesn't balance the load, and 2) it exports to the grid up to it's max power on that phase.
I think what the installer needs to check is that the R/S & T phases are wired exactly point to point (R/L1 inverter=R/L1 supply) and that the inverters meter is correctly reading each phase when a load is applied to that phase i.e. if you apply a 1kw load to the R phase, the inverter should output 1kw on the R phase only (the inverter screen will allow you to see what each phase is doing) - ideally do that testing with the other solar inverter off as it will only confuse the readings.
When you put the inverter in backup mode the battery is held preserved which is why it stops discharging, but if you can find out which of the phases have been reversed it will operate correctly.
Thanks Dave. Yes we have a meter fitted. i'm not sure if the CT Clamps are on 3 clips in the supply cupboard. I'm trying to get the installer back to check (he believes everything is correct).
I've been checking and switching between self-mode to backup mode, or self-mode to forcedcharge mode, and I believe the 'Home' usage is a just net calculation. Further, I suspect the reading from the Grid supply is not reading from all 3 phases. The battery or solar readings appears to be correct. This might explain why during the day when the battery is charging, i get a negative value for the "home".
From my earlier images, during the day i had 3kw of solar coming in, 2.82kw to charge the battery, and it was showing 214w to the home (with 36w coming from the grid). I believe the grid readings are incorrect and understated, therefore the end value for home calculation is also lower than actual usage. When we switch to Forced Charge mode, the battery is now drawing power at 4.87kw, with solar contributing at 3kW, and the incoming grid at 1.46kw. Because the measure from the grid could be missing a phase reading, the end calculations for the home usage becomes a net negative.
What i don't get is how would this cause the battery to supply excess to the load that leads to power going back to the grid overnight...
I've just run another test at night now while the battery is discharge load, and swapped between Self-use and Backup mode. I get a jump in Home calculations:
Self-Use mode - batt discharge 2.48kw, grid import 16W, Home use 2.5kW
Back-up mode - batt discharge 16w, grid import 1.34kw, Home use 1.36kW
Do you think, while we're in self-use mode when the grid is reading only 16W (but the real grid import value is higher as it's understated), the system is applying a load at 2.48kW to the Home which could be the actual home load (but it doesn't realise there's also a feed from the grid as well). In backup mode, it's reading the grid import at 1.34kw, but that really should be 2.48kw as its understated. This would mean the grid is feeding in an excess of 1.14kw during self-use mode.
I've been checking and switching between self-mode to backup mode, or self-mode to forcedcharge mode, and I believe the 'Home' usage is a just net calculation. Further, I suspect the reading from the Grid supply is not reading from all 3 phases. The battery or solar readings appears to be correct. This might explain why during the day when the battery is charging, i get a negative value for the "home".
From my earlier images, during the day i had 3kw of solar coming in, 2.82kw to charge the battery, and it was showing 214w to the home (with 36w coming from the grid). I believe the grid readings are incorrect and understated, therefore the end value for home calculation is also lower than actual usage. When we switch to Forced Charge mode, the battery is now drawing power at 4.87kw, with solar contributing at 3kW, and the incoming grid at 1.46kw. Because the measure from the grid could be missing a phase reading, the end calculations for the home usage becomes a net negative.
What i don't get is how would this cause the battery to supply excess to the load that leads to power going back to the grid overnight...
I've just run another test at night now while the battery is discharge load, and swapped between Self-use and Backup mode. I get a jump in Home calculations:
Self-Use mode - batt discharge 2.48kw, grid import 16W, Home use 2.5kW
Back-up mode - batt discharge 16w, grid import 1.34kw, Home use 1.36kW
Do you think, while we're in self-use mode when the grid is reading only 16W (but the real grid import value is higher as it's understated), the system is applying a load at 2.48kW to the Home which could be the actual home load (but it doesn't realise there's also a feed from the grid as well). In backup mode, it's reading the grid import at 1.34kw, but that really should be 2.48kw as its understated. This would mean the grid is feeding in an excess of 1.14kw during self-use mode.
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You are correct in that the load and grid import are calculated by the inverter based on a calculation which takes into account the inverters output and what it measures on each phase at the CT clamp/meter - these have to be accurate.
But if either the meter is not reading one of the phases (or 2 phases have been crossed over) then the inverter won’t be able to calculate the load and those statistics will be meaningless. It’s also possible that the meter has not been setup correctly (or the wrong CT clamp ratio has been used) which means it will be reading the output but it will be at the wrong scale.
The battery power is internally measured by the inverter and will be correct.
This really needs your installer to methodically work through and find the problem, starting with a visual check that the L1/2/3 (or R/S/T as Fox label them) are connected accurately point to point from the inverter to the meter - secondly by applying fixed loads to a phase and monitoring the inverter output and measuring at the supply meter to establish that the meter is reporting the correct scale and each phase is being reported correctly.
Fox themselves are usually pretty good at helping the installer with these issues as they can easily see the 3 phases being output.
The latest Fox cloud website will let you see the R / S & T power graphs which should help you understand what the inverter thinks it is doing (and why), if you go to the Fox cloud website (latest V2), choose ‘Devices’, click on ‘Inverter’ then click on the inverter picture that will take you to the Real-Time Curve, click the ‘Filter’ icon and choose the items to add to the graph. The ones to look at are MeterR(S/T)Power to see what it is receiving from each meter phase, R(S/T)Power is what the inverter is outputting on each phase to balance the power, and LoadsR(S/T)Power is it’s ‘calculated’ load
But if either the meter is not reading one of the phases (or 2 phases have been crossed over) then the inverter won’t be able to calculate the load and those statistics will be meaningless. It’s also possible that the meter has not been setup correctly (or the wrong CT clamp ratio has been used) which means it will be reading the output but it will be at the wrong scale.
The battery power is internally measured by the inverter and will be correct.
This really needs your installer to methodically work through and find the problem, starting with a visual check that the L1/2/3 (or R/S/T as Fox label them) are connected accurately point to point from the inverter to the meter - secondly by applying fixed loads to a phase and monitoring the inverter output and measuring at the supply meter to establish that the meter is reporting the correct scale and each phase is being reported correctly.
Fox themselves are usually pretty good at helping the installer with these issues as they can easily see the 3 phases being output.
The latest Fox cloud website will let you see the R / S & T power graphs which should help you understand what the inverter thinks it is doing (and why), if you go to the Fox cloud website (latest V2), choose ‘Devices’, click on ‘Inverter’ then click on the inverter picture that will take you to the Real-Time Curve, click the ‘Filter’ icon and choose the items to add to the graph. The ones to look at are MeterR(S/T)Power to see what it is receiving from each meter phase, R(S/T)Power is what the inverter is outputting on each phase to balance the power, and LoadsR(S/T)Power is it’s ‘calculated’ load