How to guarantee no backfeeding to the grid?

[Rational]

Hi guys,

Is there a way to connect my new inverter to the grid but guarantee the power company will not see any back feeding so they won't know it exists?

Is there a device I can connect in between the grid and feed that would take small loads that the inverter might put back towards the grid even when set for 'zero export'?

I have a Solis S6 11.4k inbound now. About to arrive in two weeks.

I want to power it up via the grid but ensure no visits or penalties by the local power company.

 

[Rational]

Also, reposting this question from another thread I'd asked this question in but didn't want to hijack the other member's thread so am posting here for input. Thank you guys.

"Hey @Zwy . Interesting post you have here. First I've heard of this 'sync phasing' topic. Is this what is set when you choose your grid-tie region code in the settings of an inverter to make sure it 'matches' correctly?

I ask, because I was perhaps mistakenly thinking I could connect any grid-tie hybrid inverter to the grid and just set it for zero export and it would still power up fine. I guess not? It has to have the correct grid code applied in the settings first or it can let the smoke out?

Or will it power up fine with any incoming AC power and the sync phase matching is only for export compatability?

I further ask because I'm about to receive a Solis S6 11.4k-US split phase model here in Japan. It does not have certification here in Japan. So I was going to use it off grid, but still connect it to the grid to power it up (as I don't have solar panels yet) and also to charge a battery pack I will be connecting to it. Not possible without the correct grid code applied?

Since I know there is no 'Japan' grid code in it as it's not certified for Japan by Solis, I wonder if there is a way to determine my power company's 'sync phasing' interval details with perhaps an oscilloscope and with that info find another code within my inverter that would work fine?

Here we have an incoming 208 volt (2 hots + 1 Neutral) from the pole. So each outlet has 104v coming out of it. 60hz.

 

[altenergy21]

Yeah use a contactor (ABB) with interlock - only one input at a time, either grid, or PV system, never both at the same time.

Home

solarsite22.bravesites.com

 

[Rational]

Yeah use a contactor (ABB) with interlock - only one input at a time, either grid, or PV system, never both at the same time.

Home

solarsite22.bravesites.com

Thanks for that input.

Based on that input, I have a couple more questions and some more clarification details if it helps:

So I am having an electrician come out in the next week or two to install a manual transfer switch (between the meter/grid and main breaker panel) as well as upgrade the building's incoming power from the pole from the current single 100v feed to a 200v feed. He will also be installing a new breaker panel inside to handle this as well as a generator connection from the new manual transfer switch. (And lastly a 200v EV power outlet so I can plug in our new Nissan Leaf EVSE cable to charge it. )This way I can manually switch between grid and "generator".

But actually my plan is to install my own off grid solar system and not a generator actually. That's why I am having the manual transfer switch installed. So I can manually switch between grid on one side and my own "generator" (my own solar system actually) on the other.

But... I'd still like to connect the inverter to the grid to power it up and charge the battery.

What's the best way to wire this up then? Seems I can't have both complete separation and still power the inverter from the grid with a manual transfer switch or your contactor with interlock, or can I?

 

[underdog5004]

I put all my house circuits in a sub panel. Subpanel is fed from a transfer switch. Either solar OR grid feeds that subpanel, never both. Grid connection to inverter could allow momentary backfeed, so I don't have grid connected to inverter. If needed, I can flip a grid side breaker and feed power into my batteries using a chargeverter (no backfeed possible).

 

[dougbert]

what I have done and what others do is use a second external battery charger called a Chargeverter

I ONLY use the inverter as an inverter, not as charger. In that way I steer clear of issues

Post in thread 'Solar house generator I started DIY back in 2000 - My path from Trace to Xantrex (on FLA battery) to XW Pro inverters on Tesla Model S batteries'

Dec 23, 2023

here is a pic of the 1 ChargeVerter (CV) that I currently have installed as mentioned above:



I have a 2nd CV that I currently have loaned to my son. Eventually, I will get that back and will place it in parallel with the above unit. I am providing 2 NEMA L14-30 receptacles coming from my 50 amp generator input circuit. This wil allow for a generator (like my 8000 watt Winco - which can support 6300 watts at this altitude of 5500 feet, running on propane) to power the 2 CVs with some 3000 watts each, if and when needed. Also, 2 is one......

future larger generators will...

• dougbert

• 

 

[Crowz]

Use chargeverters to power the battery side and don't connect the inverter to the grid at all.

 

[Rational]

I put all my house circuits in a sub panel. Subpanel is fed from a transfer switch. Either solar OR grid feeds that subpanel, never both. Grid connection to inverter could allow momentary backfeed, so I don't have grid connected to inverter. If needed, I can flip a grid side breaker and feed power into my batteries using a chargeverter (no backfeed possible).

Thanks. So you only power up your inverter from solar and/or battery?

 

[Rational]

Use chargeverters to power the battery side and don't connect the inverter to the grid at all.

what I have done and what others do is use a second external battery charger called a Chargeverter

Okay guys. I've heard of these and liked them when I first saw them 6 months ago. Wanted one ever since.

But I need a minute and perhaps a bit more info to grasp how I need to wire this up based on the above work my electrician is about to do.

Doesn't look like I can easily move my current breakers to a subpanel either nor am I sure there is a need? Because the manual transfer switch he is about to install is between the meter/grid and the current breaker panel. I asked him to do it this way so that I could switch between the grid and my 'generator' for when we have long power outages. I'm just not telling him I'm not actually going to buy a generator but instead will install solar on the generator side.

Trying to grasp where to wire in the chargeverter and still power up the inverter without solar for now. Also without battery for now as that's 'experimental'. It's a Leaf 24kwh pack that I need to get talking to the inverter via Dala's battery-emulator software on a lilygo.

So I need to power up the inverter for awhile somehow in the meantime.

 

[dougbert]

UPDATE: I have a 48v based system, not High Voltage (450v)


I "can" connect the grid to my inverter as the grid, so the mechanism is there, but my policy is that breaker ia OFF all the time in normal operation


okay, here is my schematic and then a pic of the physical layout

 

[dougbert]

I updated with schematic, refresh the page

 

[Rational]

I updated with schematic, refresh the page

Wow! This is great info!

Okay. Looking it over carefully now to grasp it. Thank you.

 

[dougbert]

here is link to post 1 of my build thread

Thread 'Solar house generator I started DIY back in 2000 - My path from Trace to Xantrex (on FLA battery) to XW Pro inverters on Tesla Model S batteries'

Sep 20, 2019

2025-04-11 Version Update When I started this thread back in 2019, I did not realize it would turn into a build thread of my system. It documents What and Why I did things as well has How they were accomplished. It also shows designs that didn't work out, and also designs that did work out great. I hope it is useful for others as it has been for me - I use it as a Reference document thanks Will for the "library" for my self and the GREAT stuff others have posted Schematic: See below...

• dougbert

• 
• 

it is my table of contents and overview of my build

 

[dougbert]

it has taken me years of various implementations to arrive at this design. might not fit others, but it fits mine and the limited space i have in the basement

have fun. any feedback is appreciated

 

[Rational]

it has taken me years of various implementations to arrive at this design. might not fit others, but it fits mine and the limited space i have in the basement

have fun. any feedback is appreciated

Will do! I'm reading your build thread from page 1 now. We're a lot alike I see. Love the detailed documentation and evolution over time also well documented. Very helpful. I will learn a lot here I can tell.

Also, I was originally going to go with those XW Pros as well as I saw this one guy who did a great demonstration of them starting up heavy inductive loads with them without a sweat as compared with some sol arks that couldn't start up the same loads. But the price has given me pause since. But I know they're quality. Maybe someday. Need to start where I can for now.

One quick question, what fuse breaker amp rating do you have in your transfer switch now? I asked for 60Amp be installed for us for now as our loads aren't that high and my S6 inverter is limited to 50A max anyway.

 

[dougbert]

Will do! I'm reading your build thread from page 1 now. We're a lot alike I see. Love the detailed documentation and evolution over time also well documented. Very helpful. I will learn a lot here I can tell.

Also, I was originally going to go with those XW Pros as well as I saw this one guy who did a great demonstration of them starting up heavy inductive loads with them without a sweat as compared with some sol arks that couldn't start up the same loads. But the price has given me pause since. But I know they're quality. Maybe someday. Need to start where I can for now.

yes, I love the XW Pro, but if I was doing this from start today, I would NOT do the same - cost way too much. I am thinking of NOT doing a 2nd XW Pro. Rather add a 2nd inverter to the battery like

• EG4 6000XP or 12000XP
• NHX-10kw
• Midnite Solar "The ONE"

then create another panel feed by the selected one above


the tech has gotten so much better in just the past 5 years, it is amazing
looking forward to reading more of the GRIDBoss and FleBoss

One quick question, what fuse breaker amp rating do you have in your transfer switch now? I asked for 60Amp be installed for us for now as our loads aren't that high and my S6 inverter is limited to 50A max anyway.

are you referring to the breaker FEEDING the transfer switch from 1) Grid or 2) from inverter? both are 100 amp. With 2 XW Pros in the system, they can support 100 amps (24,000 watts) for 1 minute

the transfer switch (ABB/GE) is 100 amp, as are some the panels, so I just went with the max

 

[Rational]

from 1) Grid

From the grid. I ask because our new house (duplex) has a single incoming main 75A breaker feeding both houses. We have gas so don't use a lot of power I guess compared to others. We use about 600kWh per month per house on average.

Just trying to grasp typical sizes required so was curious.

My Solis S6 install is actually at our old building and will use even less power. But it is a good test lab environment for me to set up things and learn.

I see in your diagram you have the two chargeverters connected directly to your battery bus bars. This typical? How do you do this now with a Tesla battery pack setup? It's more complex now and requires logic in between right? So what controls your charging rate and limits?

I'm still on like page 1 or two of your build thread though, so it will be a bit before I get to the most recent info.

 

[dougbert]

From the grid. I ask because our new house (duplex) has a single incoming main 75A breaker feeding both houses. We have gas so don't use a lot of power I guess compared to others. We use about 600kWh per month per house on average.

I first used #6 THHN wire and 60 amp breaker. Later I had to replace that wire with #2 wire. I learned to put in the wire you want to end up with, not just current needs. Breakers protect their wire. It is NO problem to use a 100 amp breaker with #2 CU wire downstream of a 75 or 60 amp main breaker. Some day you may up grade

Even now I am planning on an upgrade of my grid service panel from 125 amp to 200 amp and planning on 3/0 CU wire in a future panel

Just trying to grasp typical sizes required so was curious.

I understand, it takes repetition and practice to learn amplicity of the conductors

My Solis S6 install is actually at our old building and will use even less power. But it is a good test lab environment for me to set up

I see in your diagram you have the two chargeverters connected directly to your battery bus bars. This typical?

yes, some connect to battery proper

How do you do this now with a Tesla battery pack setup?

the same

It's more complex now and requires logic in between right?

nope

So what controls your charging rate and limits?

each chargeverter has a menu control panel where you set target voltage and amperage
my CV that keeps the battery floating when it gets low, I set to 43 volts (lowest setting) just to run the house at O-dark-thirty, until the sun comes up and the main solar chargers kick in

I'm still on like page 1 or two of your build thread though, so it will be a bit before I get to the most recent info.

wow, er, yeah

I suggest you create your own SHOW AND TELL build thread

I use mine for reference, documentation AND to show and tell. I also learned people like LOTs of pictures and minimal text, just the facts

 

[Rational]

• EG4 6000XP or 12000XP
• NHX-10kw
• Midnite Solar "The ONE"

I looked into the EG4 6000XP and liked it. But It's off grid only I believe, right? Also I've heard reports they are a tad loud.
Midnight solar the one is basically an EG4 18k but a bit better. I really like this one. But it's expensive as hell. And I read midnight solar was sold off?

No idea about NHX. I'll read up on them.

You might want to check into the Solis S6 11.4k I'm getting. @Solar Guppy as well has two in a failover setup. These are absolutely silent from what I hear. They seem to be the best value on the market currently at $2400 shipped. They also are on the approved list from Dala's battery-emulator for use with Tesla battery packs like you already have. Which is why I chose this one to work with my Nissan Leaf 24kWh pack.

But I'll share more once I have experience with it.

 

[dougbert]

I looked into the EG4 6000XP and liked it. But It's off grid only I believe, right?

yes, and only 5 year warranty - won't last as long as a 18kpv

Also I've heard reports they are a tad loud.

the XPs are quiet the EXs were terrible

Midnight solar the one is basically an EG4 18k but a bit better. I really like this one. But it's expensive as hell. And I read midnight solar was sold off?

No idea about NHX. I'll read up on them.

$2200 full hybrid grid inverter, there is a large thread on the forum discussing this one

You might want to check into the Solis S6 11.4k I'm getting. @Solar Guppy as well has two in a failover setup. These are absolutely silent from what I hear. They seem to be the best value on the market currently at $2400 shipped. T

hey also are on the approved list from Dala's battery-emulator for use with Tesla battery packs like you already have.

got a info link on this?

But I'll share more once I have experience with it.

 

[Rational]

got a info link on this?

I've posted the spec sheet and some other details in the first post of my thread on HV inverters here:

R

Thread 'Inverters that support high voltage (500v) storage batteries'

Jun 17, 2024

Hi guys,

Second post. I'm in Japan (100v 60hz) and am researching the best inverter brand and model to buy for a DIY solar build.

I intend to connect a Leaf 24kWh battery to it for home storage. I'm a member of Dala's EV discord group but have additional questions.

So far I've been able to determine that I need a single phase inverter (Edit: split phase) as that is what's used here in Japan. But very few brands support higher than 48v storage batteries as far as I can tell. Especially in single phase inverters.

Not sure if I will do grid tie right away but may want to later for net...

• Rational
• Replies: 221
• Forum: DIY Solar General Discussion

 

[stromy]

Hi guys,

Is there a way to connect my new inverter to the grid but guarantee the power company will not see any back feeding so they won't know it exists?

Is there a device I can connect in between the grid and feed that would take small loads that the inverter might put back towards the grid even when set for 'zero export'?

I have a Solis S6 11.4k inbound now. About to arrive in two weeks.

I want to power it up via the grid but ensure no visits or penalties by the local power company.

The "zero export" in a grid-tied inverter will normally not have a fast enough control loop to actually have zero export. Some small amount of export will remain. How much depends on the control loop parameters of the inverter and the salding/netting interval of your utility meter.
To really go to zero, you have to either use a transfer switch or send all your loads through the inverter, that is put everything on the "critical loads" port of a hybrid inverter.

 

[underdog5004]

Thanks. So you only power up your inverter from solar and/or battery?

Yup, grid is a honey trap

 

[stromy]

I ask, because I was perhaps mistakenly thinking I could connect any grid-tie hybrid inverter to the grid and just set it for zero export and it would still power up fine. I guess not? It has to have the correct grid code applied in the settings first or it can let the smoke out?

Or will it power up fine with any incoming AC power and the sync phase matching is only for export compatability?

These inverters normally need solar DC input to power up.
The "wrong" grid code will normally work, as long as the "basics" are the same, e.g. nominal voltage and frequency.
The rest of the grid code settings is things like safety limits, So just using a wrong grid code for a test should work. Permanently using the wrong code might result in sporadic false positive errors or unsafe situations that lead to fuse trips.
Please note: your stuff will release the magic smoke, if you mix up grid-tie and grid-building ports!

 

[Rational]

Yup, grid is a honey trap

Yep. For most regions nowadays that's true. In Japan at least for now they allow unlimited sell back at 16 yen /kWh. Locked in for 10 years from the time of sigh up, then 8 yen/kWh for the following 10 years.

So some people who are personally into solar set up a ton of panels and make money each month here still. Which is going away all over the world it seems elsewhere nowadays.

So for us we can get a 8500 kw grid-tied system installed for about $10,500 and sell back enough to cover the total price per month. But it comes without a battery.

I wanted to do our new house DIY, but family doesn't want to with my inexperience as yet with solar. So we will pay for this basic system install to get it runnning and certified. Then I will learn in my lab location and swap out the inverter next year and add my own batteries then most likely.