Question About Preventing Grid Backfeed

[dinosaursolar]

In SBU mode it will use solar and battery together. And switch to grid as a backup if needed.
In SUB mode it will use solar and grid together. And switch to battery as a backup.
Grid and battery together is never a possibility. (always either/or )

I am looking to get the Luxpower SNA 6000 WPV (https://luxpowertek.com/wp-content/uploads/2023/11/SNA-3-6k-user-manual.pdf).

System mainly function as battery back to take advantage of cheaper tariff, time of use. Charge the batteries from 12am to 8am and use battery power from 8am to 12am.

The Luxpower SNA has an option to feedback to grid but can be turned off via settings, however from the thread, it might still export a little, not ideal.

Setup:
Grid > to AC in (SNA 6000)
15kwh battery > (SNA 6000)
(SNA 6000) > Sub panel (all loads)

No PV panel installed.

Settings
PV&AC take load joinly (Disable)
Export to grid (Disable)
"
2. Working as a traditional off grid inverter. In this situation, inverter either use (solar+battery) to takeload or use AC take load. Related settings
" (From the manual)

AC First Start time 00:00 AC First End time 08:00


Does it mean the it will run (SUB - Solar Utility battery) from 12am to 8am and (SBU - Solar Battery Utility) from 8am to 12am?
And seeing that there is no PV installed time frame where SUB and SBU is used. is there a chance for backfeed into the grid to happen?

Thank you

 

[ChrisG]

I am looking to get the Luxpower SNA 6000 WPV (https://luxpowertek.com/wp-content/uploads/2023/11/SNA-3-6k-user-manual.pdf).

System mainly function as battery back to take advantage of cheaper tariff, time of use. Charge the batteries from 12am to 8am and use battery power from 8am to 12am.

The Luxpower SNA has an option to feedback to grid but can be turned off via settings, however from the thread, it might still export a little, not ideal.

Setup:
Grid > to AC in (SNA 6000)
15kwh battery > (SNA 6000)
(SNA 6000) > Sub panel (all loads)

No PV panel installed.

Settings
PV&AC take load joinly (Disable)
Export to grid (Disable)
"
2. Working as a traditional off grid inverter. In this situation, inverter either use (solar+battery) to takeload or use AC take load. Related settings
" (From the manual)

AC First Start time 00:00 AC First End time 08:00


Does it mean the it will run (SUB - Solar Utility battery) from 12am to 8am and (SBU - Solar Battery Utility) from 8am to 12am?
And seeing that there is no PV installed time frame where SUB and SBU is used. is there a chance for backfeed into the grid to happen?

Thank you

Looking at the manual from the inverter you linked, seems like there is a possibility for PV/Battery/Grid to run in parallel and possibly feedback grid.

 

[dinosaursolar]

An off grid AIO won't/ can't backfeed the grid.
With one exception, SUB mode.
SUB mode allows the AIO to operate in parallel with the grid. And act like a hybrid AIO in zero export mode. It has the same advantages and disadvantages for that setup.
This type of function wasn't a problem until the utility meters became super sensitive to micro bursts of export.

I am thinking since i have no PV my system will funtion in two states.

State 1 (12am to 8am)
Power from grid in bypass mode, to charge batteries and power load.

State 2 (8am to 12am)
Power loan from batteries.

Will the inverter run in parallel with the grid? and hence have a slight chance of back feed?

 

[timselectric]

I am looking to get the Luxpower SNA 6000 WPV (https://luxpowertek.com/wp-content/uploads/2023/11/SNA-3-6k-user-manual.pdf).

System mainly function as battery back to take advantage of cheaper tariff, time of use. Charge the batteries from 12am to 8am and use battery power from 8am to 12am.

The Luxpower SNA has an option to feedback to grid but can be turned off via settings, however from the thread, it might still export a little, not ideal.

Setup:
Grid > to AC in (SNA 6000)
15kwh battery > (SNA 6000)
(SNA 6000) > Sub panel (all loads)

No PV panel installed.

Settings
PV&AC take load joinly (Disable)
Export to grid (Disable)
"
2. Working as a traditional off grid inverter. In this situation, inverter either use (solar+battery) to takeload or use AC take load. Related settings
" (From the manual)

AC First Start time 00:00 AC First End time 08:00


Does it mean the it will run (SUB - Solar Utility battery) from 12am to 8am and (SBU - Solar Battery Utility) from 8am to 12am?
And seeing that there is no PV installed time frame where SUB and SBU is used. is there a chance for backfeed into the grid to happen?

Thank you

I'm not familiar with that unit. But since it runs in parallel with the grid , it can export. (Even when told not to)

 

[timselectric]

I am thinking since i have no PV my system will funtion in two states.

State 1 (12am to 8am)
Power from grid in bypass mode, to charge batteries and power load.

State 2 (8am to 12am)
Power loan from batteries.

Will the inverter run in parallel with the grid? and hence have a slight chance of back feed?

It is a possibility.

 

[bhbaker220]

May be a technicality, but it would appear to me that an off grid inverter can export electricity if the grid is down ... if it is wired through a sub panel that is connected to the main panel (or to the main panel directly) and the breaker is on and there is no interlock kit. This is what scares the crap out of the utilities and if I were a lineman, it would scare me as well.

 

[ChrisG]

May be a technicality, but it would appear to me that an off grid inverter can export electricity if the grid is down ... if it is wired through a sub panel that is connected to the main panel (or to the main panel directly) and the breaker is on and there is no interlock kit. This is what scares the crap out of the utilities and if I were a lineman, it would scare me as well.

That’s a different problem than the inverter allowing grid feedback after large loads stop and inverter doesn’t throttle down quick enough.

 

[timselectric]

May be a technicality, but it would appear to me that an off grid inverter can export electricity if the grid is down ... if it is wired through a sub panel that is connected to the main panel (or to the main panel directly) and the breaker is on and there is no interlock kit. This is what scares the crap out of the utilities and if I were a lineman, it would scare me as well.

Yes, if connected incorrectly it will be a problem.

 

[dinosaursolar]

Good to know thank you.

Is there anyway i can test this inverter to see if it back feed the grid?

Or to test if it runs in parallel with the grid?

How would i go about doing it?

 

[timselectric]

Good to know thank you.

Is there anyway i can test this inverter to see if it back feed the grid?

Or to test if it runs in parallel with the grid?

How would i go about doing it?

If it's in any mode, where it's using grid and either solar or battery together, it is running in parallel.

 

[bhbaker220]

You could buy a monitoring system like Emporia Vue with a couple of CT's around leg 1 and leg 2 wires coming into your main panel to see if you are exporting. My smart meter is able to read not only the kwh incoming into the house, but also reads and documents the amount of kwh exported. I'm on Entergy in Texas and don't know if most of the smart meters that have been installed have this capability.

 

[ChrisG]

You could buy a monitoring system like Emporia Vue with a couple of CT's around leg 1 and leg 2 wires coming into your main panel to see if you are exporting. My smart meter is able to read not only the kwh incoming into the house, but also reads and documents the amount of kwh exported. I'm on Entergy in Texas and don't know if most of the smart meters that have been installed have this capability.

@bhbaker220 how does backfeed show up in the emporia. I accidentally backfed before and didn’t see it in the monitor.

 

[bhbaker220]

@bhbaker220 how does backfeed show up in the emporia. I accidentally backfed before and didn’t see it in the monitor.

I have a grid tied inverter and see it all the time with a negative reading on one or both of the mains. It matches up fairly well with the utility company but the lowest frequency they report from their system is in 15 minute intervals. I have an off grid inverter on a manual transfer switch and have never tried to intentionally backfeed.

 

[bhbaker220]

I have a grid tied inverter and see it all the time with a negative reading on one or both of the mains. It matches up fairly well with the utility company but the lowest frequency they report from their system is in 15 minute intervals. I have an off grid inverter on a manual transfer switch and have never tried to intentionally backfeed.

In the EMporia Vue setup, you do need to tell it that you have solar installed. I don't recall all of the additional steps that I needed to go through but you can call them for help. I have CT's on the mains as well as on the breaker for the grid tied inverter.

 

[doc3g]

I've read through this thread at least a couple of times, but just to confirm my understanding, I wanted to draw it out.

1. The attached diagram reflects:
   1. "critical loads" panel that contains a single circuit, "Kitchen light"
      1. Power comes in on a single leg from an EG4 3K inverter
      2. A single breaker feeds the "Kitchen light" circuit
         1. When Inverter is set to SBU then:
            1. Inverter tries to power light w/ solar, if insufficient will also pull from battery
               1. When battery hits a predetermined low voltage, system switches to AC input from the grid

In this first setup, there would be a true ZERO export to the grid?

Scenario two would be SUB setup, and in that scenario, I am technically parallelling the grid and there is a chance to feed energy back to the grid?

 

[Mattb4]

Yes and yes.

 

[bhbaker220]

I originally had an EG4 3k and a Reliance manual transfer switch instead of a critical loads panel. I never experience any back feeding to the grid regardless of SBU or SUB. Since your critical loads panel is not connected to the main panel, the path to back feed to the grid would have to be through the AC in. I guess anything could happen but that seems like a very low likelihood. The likelihood of one leg (120 volt) from the inverter being in sync with on leg of the grid also seems very low. If it's out of phase, I'm not sure if a breaker would trip or if it would fry the inverter.

The OP had a different inverter and no diagrams, so the answer there could have been different.

 

[timselectric]

I originally had an EG4 3k and a Reliance manual transfer switch instead of a critical loads panel. I never experience any back feeding to the grid regardless of SBU or SUB. Since your critical loads panel is not connected to the main panel, the path to back feed to the grid would have to be through the AC in. I guess anything could happen but that seems like a very low likelihood. The likelihood of one leg (120 volt) from the inverter being in sync with on leg of the grid also seems very low. If it's out of phase, I'm not sure if a breaker would trip or if it would fry the inverter.

The OP had a different inverter and no diagrams, so the answer there could have been different.

In SUB mode, the inverter will be connected in parallel with the input (grid). And remain in sync with that input. While it's not designed for exporting. It can and will export small amounts of current, whenever large loads stop. Because the inverter can't stop producing fast enough to avoid it. This was never a problem, until the utility meters evolved to very sensitive detection.

 

[OffGridForGood]

I am thinking since i have no PV my system will funtion in two states.

No PV, energy sources are only Grid, and Battery - no other sources.

State 1 (12am to 8am)
Power from grid in bypass mode, to charge batteries and power load.

State 2 (8am to 12am)
Power loan from batteries.

That is one option, see below another option:

Will the inverter run in parallel with the grid? and hence have a slight chance of back feed?

Yes, it is possible - say you are running a big load like a dryer or a large motor from battery, and then it shuts off - there is a (good) chance that back feed to grid takes place while the inverter changes to match the new lower load.

Simpler option, guaranteed Not to backfeed grid ever:
Run the loads via the Inverter in "SBU" solar - battery- utility (yes I know you don't have any PV)
Install a chargeverter between grid and your battery, put the chargeverter on a timer controlled relay. ( a HWT timer would work) to run during the hours you have low cost power ToU rates.
Set the low battery cut off (edit: in the inverter settings) to some low value like 10-20% - if the battery gets this low, the inverter switches to Utility power.
Set the "return to normal" (edit: in the inverter settings) at some higher setting maybe 30-40% - when the inverter believes the battery is charged to this level it returns to inverting mode and stops using grid for loads.

(edit: during the next off-peak ToU, the chargeverter will again recharge you ESS at lowest cost power rates back to 100% SOC.)

 

[timselectric]

No PV, energy sources are only Grid, and Battery - no other sources.

That is one option, see below another option:

Yes, it is possible - say you are running a big load like a dryer or a large motor from battery, and then it shuts off - there is a (good) chance that back feed to grid takes place while the inverter changes to match the new lower load.

Simpler option, guaranteed Not to backfeed grid ever:
Run the loads via the Inverter in "SBU" solar - battery- utility (yes I know you don't have any PV)
Install a chargeverter between grid and your battery, put the chargeverter on a timer controlled relay. ( a HWT timer would work) to run during the hours you have low cost power ToU rates.
Set the low battery cut off to some low value like 10-20% - if the battery gets this low, the inverter switches to Utility.
Set the "return to normal" at some higher setting maybe 30-40% - when the inverter believes the battery is charged to this level it returns to inverting mode and stops using grid for loads.

I think that in the scenario described by the dinosaur. It's going to be better to get as much from the grid as possible, during the low price times. So, I would set the charger for a full charge. So that they can get the most inverter time, during the higher price.

 

[OffGridForGood]

I think that in the scenario described by the dinosaur. It's going to be better to get as much from the grid as possible, during the low price times. So, I would set the charger for a full charge. So that they can get the most inverter time, during the higher price.

With the chargeverter on timer set up, they will hit 100% SOC every night - unless the battery is too large for the CV to charge it in 8 hours.
They could put two CV's though, if needed.

My thought on the low SOC switch back to Utility was just to ensure they never have a power outage, from the battery being too small to supply 16-hours of loads during 8:00 AM to midnight. In this case the inverter switches using it's internal ATS to utility preventing a loss of power in the home, and I assume that this would most likely happen during expensive utility power time-of-day, since otherwise the CV is on charging batteries. Even if it is night, the CV and Utility-first can operate together without any issue.
However since this is likely the expensive power time of day, we limit the Utility-first to just bring the SOC up a to a suitable level say 30-40% such that we don't end up mini-cycling the batteries waiting for the low cost ToU period.

 

[timselectric]

With the chargeverter on timer set up, they will hit 100% SOC every night - unless the battery is too large for the CV to charge it in 8 hours.
They could put two CV's though, if needed.

My thought on the low SOC switch back to Utility was just to ensure they never have a power outage, from the battery being too small to supply 16-hours of loads during 8:00 AM to midnight. In this case the inverter switches using it's internal ATS to utility preventing a loss of power in the home, and I assume that this would most likely happen during expensive utility power time-of-day, since otherwise the CV is on charging batteries. Even if it is night, the CV and Utility-first can operate together without any issue.
However since this is likely the expensive power time of day, we limit the Utility-first to just bring the SOC up a to a suitable level say 30-40% such that we don't end up mini-cycling the batteries waiting for the low cost ToU period.

I may have misunderstood your other post. I thought that the charger was only being used between 20% and 40%. But if that's only the internal transfer switch settings, and the timer controled external charger is going full charge. Then yes, I completely agree.

 

[doc3g]

In SUB mode, the inverter will be connected in parallel with the input (grid). And remain in sync with that input. While it's not designed for exporting. It can and will export small amounts of current, whenever large loads stop. Because the inverter can't stop producing fast enough to avoid it. This was never a problem, until the utility meters evolved to very sensitive detection.

I'm guessing that this is device-dependent from what I've been reading. So, for example, clothes dryer, water heater, range, microwave, HVAC, etc. What I'm wondering is if there is a safe range where someone could parallel the grid and reasonably expect to not back feed. For example, if I shut off 300 watts worth of lights at the same time, would it still back feed?

 

[timselectric]

I'm guessing that this is device-dependent from what I've been reading. So, for example, clothes dryer, water heater, range, microwave, HVAC, etc. What I'm wondering is if there is a safe range where someone could parallel the grid and reasonably expect to not back feed. For example, if I shut off 300 watts worth of lights at the same time, would it still back feed?

Maybe
But the likelihood definitely increases with the size of the load turning off.

 

[cs1234]

I'm guessing that this is device-dependent from what I've been reading. So, for example, clothes dryer, water heater, range, microwave, HVAC, etc. What I'm wondering is if there is a safe range where someone could parallel the grid and reasonably expect to not back feed. For example, if I shut off 300 watts worth of lights at the same time, would it still back feed?

The problem is that the POCO meters have gotten so incredibly sensitive, and that they have gotten so incredibly butt hurt about solar. They are coming after people for even trace amounts of backfeed, let alone if a few hundred watts slips through accidentally.

Does your utility let you put in an old non smart meter for extra money? Here where I am in Texas, you can pay like $15-$25 or something extra per month to have an old style meter that somebody has to come out and read. Those ones aren't capable of registering tiny amounts of backfeed (to my knowledge). It would give them a monthly opportunity to gander at your property though.