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Question About Preventing Grid Backfeed

ChrisG said:
I’ve got an always on load of 1.4kw from a pool pump. When my EV stops charging at 11kw or Dryer stops, sure something would be picked up by POCO with hybrid.
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The 1.4kw is safe to cover. You only have 1.4kw of "buffer" that is safe to export. How you use that buffer is up to you. If you run a 11kw worth of load.. and cover it with your grid-tied power.. once that load drops you will be briefly sending (11kw - 1.4k) back to the grid. They will measure something on these newer faster meters. What they will do about it, who knows.

The covered load must be permanent, 100% of the time, no downward deviations in wattage beyond what you are exporting / covering with your inverter.
 
zanydroid said:
Can you just chop off a subpanel for your 120V loads and do 6000XP SBU with a 5kWh battery? That is enough power for it. I doubt you can get cheaper/simpler than this
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And to sort of reinforce this. With all possible options you have to create a subpanel and move circuits over. So to follow what I believe to be the smart first move, you would move over only the 120Vs. You can move the 240 over later. So you can follow my proposal with almost zero additional implementation cost
 
cs1234 said:
The 1.4kw is safe to cover. You only have 1.4kw of "buffer" that is safe to export. How you use that buffer is up to you. If you run a 11kw worth of load.. and cover it with your grid-tied power.. once that load drops you will be briefly sending (11kw - 1.4k) back to the grid. They will measure something on these newer faster meters. What they will do about it, who knows.

The covered load must be permanent, 100% of the time, no downward deviations in wattage beyond what you are exporting / covering with your inverter.
Click to expand...
Just not worth it. Don’t want to have to think about it. 6000xp seems safe to use, at least so far it has been.
 
ChrisG said:
Just not worth it. Don’t want to have to think about it. 6000xp seems safe to use, at least so far it has been.
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I certainly don't blame you. Trying to do GTIL style export limiting without a feedback agreement is more trouble than most people want to deal with it.
 
zanydroid said:
And to sort of reinforce this. With all possible options you have to create a subpanel and move circuits over. So to follow what I believe to be the smart first move, you would move over only the 120Vs. You can move the 240 over later. So you can follow my proposal with almost zero additional implementation cost
Click to expand...
I'm not going to relocate loads. All of my loads are already in a sub panel which is what I will feed power to. I want to be able to put everything back when I move out so moving a couple of feeder wires is one thing, moving a bunch of loads is a whole other issue.
 
Just so my understanding is crystal clear, would I be good with an off-grid inverter (sized to my needs) set in SUB mode and a second charger?
This would give me:
1. Solar and battery as main supply and grid providing anything left over.
2. No export (not even micro amounts)
3. Grid assist, rather than a switch of sorts between self-gen and grid
 
jeff88 said:
Just so my understanding is crystal clear, would I be good with an off-grid inverter (sized to my needs) set in SUB mode and a second charger?
This would give me:
1. Solar and battery as main supply and grid providing anything left over.
2. No export (not even micro amounts)
3. Grid assist, rather than a switch of sorts between self-gen and grid
Click to expand...
Yes with the following pedantic adjustments on what are marked as sized to your needs (peak and sustained kW), which you only attached to one line item:

- battery
- charger

And with my reluctance to commit without the definition of grid assist redeclared crisply in this final conclusion roundup.
 
jeff88 said:
I'm not going to relocate loads. All of my loads are already in a sub panel which is what I will feed power to. I want to be able to put everything back when I move out so moving a couple of feeder wires is one thing, moving a bunch of loads is a whole other issue.
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Fair enough. You have explicitly declared that you prefer to buy more batteries and inverter capacity over adding a subpanel to do the split, and reverting it later. Which is certainly going to cost less in equipment, likely even if you factor in the fact that it is throwaway.

EDIT: and note in my previous messages I was assuming it was possible to add a subpanel within 24” nipple conduit distance to the original location, which allows for pigtailing of loads from the original to new location with what to me is barely an inconvenience if the presumed existing conditions are satisfied.
 
zanydroid said:
peak and sustained kW
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You also may have trouble passing the load calculation with a 9kW inverter/10kwh battery combo (giving the batteries a 10% derate). 9000/240=37.5A which is less than what your stove nameplate demands. So this is probably already out of compliance since a power source is required by code to be able to supply the nameplate of the single biggest appliance. Before you go into the additional validation of the load calculation.

EDIT: So this means you need 15kWh class of battery, and may need to parallel stack three 6kW inverters to meet the letter of code (since one 12kW / two 6kW may not be enough for peak).

Also, this capacity in chargeverter is very noisy, since those use data center grade flat form factor power supplies with super noisy fans.
 
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jeff88 said:
Just so my understanding is crystal clear, would I be good with an off-grid inverter (sized to my needs) set in SUB mode and a second charger?
This would give me:
1. Solar and battery as main supply and grid providing anything left over.
2. No export (not even micro amounts)
3. Grid assist, rather than a switch of sorts between self-gen and grid
Click to expand...
No.
1. Grid is in parallel
2. Possible export anytime grid and inverter are in parallel
3. Grid assist is grid in parallel with inverter.

If you run in SBU mode grid export is very unlikely if not impossible.
 
timselectric said:
Without AC input?
It won't run in SUB mode without AC input.
Click to expand...
zanydroid said:
Well then that forces OP to configure in SBU 🤷. Doesn’t really matter then
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It knows the difference between the AC just happening to be out at the time and there not being AC input at all? Or do they change their operating modes dynamically as conditions change? I figured you could set them to whatever mode you want, regardless. I guess maybe it has to have AC active at the time you are programming the settings to let you select SUB?
 
Working through this still. Building my SLD and researching which components I want.
Two questions at this point. First is which inverter! I see Sungold, MPP, Growatt all have off-grid inverters that are comparable, price wise. Are there any other options, or does anybody recommend one of these three?

Second question is related to the chargeverter we talked about before. It seems based on these specs that I don't need a separate component as grid charging should be more than enough for my needs. Am I missing something? If I have 100A load center, shouldn't the 120A max grid charging be enough for a no-solar-production day?

1000000070.png
 
jeff88 said:
Second question is related to the chargeverter we talked about before. It seems based on these specs that I don't need a separate component as grid charging should be more than enough for my needs. Am I missing something? If I have 100A load center, shouldn't the 120A max grid charging be enough for a no-solar-production day?
Click to expand...

The charger in the inverter is fine, if you are ok with doing an either or arrangement. Either you are using entirely solar/battery to power a load, or it switches entirely over to grid power if solar/battery aren't enough.

If you want a combination of grid power and solar/battery at the same time, without a feedback agreement with your POCO, you need to do the Chargeverter method.. that way your inverter isn't coupled to the grid directly.. then whatever it's inverter rating, you can use the chargeverter/solar/battery at the same time.. up to that inverter limit.
 
cs1234 said:
The charger in the inverter is fine, if you are ok with doing an either or arrangement. Either you are using entirely solar/battery to power a load, or it switches entirely over to grid power if solar/battery aren't enough.

If you want a combination of grid power and solar/battery at the same time, without a feedback agreement with your POCO, you need to do the Chargeverter method.. that way your inverter isn't coupled to the grid directly.. then whatever it's inverter rating, you can use the chargeverter/solar/battery at the same time.. up to that inverter limit.
Click to expand...
OK that makes sense, I didn't think about the backfeed part. So two more questions. If I put the 10kw inverter in SBU mode to not backfeed, do I need to connect it to the AC side at all?
Second, if my chargeverter is only "using" power from the utility's point of view, then does that mean I can connect it to any breaker in my system (meaning my main panel, sub panel, anywhere - doesn't matter)?
 
jeff88 said:
OK that makes sense, I didn't think about the backfeed part. So two more questions. If I put the 10kw inverter in SBU mode to not backfeed, do I need to connect it to the AC side at all?
Second, if my chargeverter is only "using" power from the utility's point of view, then does that mean I can connect it to any breaker in my system (meaning my main panel, sub panel, anywhere - doesn't matter)?
Click to expand...
I would not connect it to the AC output of your AIO. Perpetual motion machines have been outlawed.
 
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