DIY Hybrid Inverter without permit?

[silverramp]

I'm wondering if anyone has experience using a split phase hybrid inverter (like the eg4 pv18k) + battery + grid tie + solar PV + dedicated breaker panel and setting the inverter to NOT back feed to the grid?

My thinking is that one could set the inverter settings such that you could prioritize solar and off peak grid power. But because you'd never be feeding the grid, you wouldn't need permission from your utility. Though I suppose that you'd probably still need building permits.

Anyone have experience with this style of system in their home?

 

[ricardocello]

The only way to ensure you never feed back to the grid is to never run in parallel with the grid, i.e. grid tied, grid-interactive.

The only way to do this is to feed grid power directly through to the loads as is, or at most use grid power to charge batteries.
If you want to run your loads off-grid using only the inverters for a portion of the day, that is ok. It is all or nothing.
If you want to use the grid only to charge batteries using a dedicated charger, and simultaneously run all of the loads from the inverters, that’s double conversion, and is fine as this cannot back feed.

Magical hybrid inverter settings and “zero-export” schemes using CTs are doomed to fail.

 

[SunSurge]

I'm wondering if anyone has experience using a split phase hybrid inverter (like the eg4 pv18k) + battery + grid tie + solar PV + dedicated breaker panel and setting the inverter to NOT back feed to the grid?

My thinking is that one could set the inverter settings such that you could prioritize solar and off peak grid power. But because you'd never be feeding the grid, you wouldn't need permission from your utility. Though I suppose that you'd probably still need building permits.

Anyone have experience with this style of system in their home?

I am looking at doing something similar except with the GridBoss, Flexboss21. I plan on installing most of it and then having an electrician inspect and make any final adjustments or connections etc. You may want to check with your local jurisdiction regarding permits etc.

 

[Smorris998]

I have a hybrid ghetto approach of running my mini splits directly off the solar with a Growatt inverter and batteries. I do use the utility charging feature but the only time people I’ve noticed having trouble with the Growatt back feeding is when they have all their loads completely running on the Growatt and it drops the draw low enough for a few watts of back feeding to be detected. If you’re doing a hybrid/ish approach it’s not really a worry. You can always do a seperate charger to have a truly grid air gapped system.

Or if you wanted the simplest option, get a generator transfer switch installed, use it to run your entire home off solar. But again, that’s how you get noticed by utilities.

 

[timselectric]

Short answer.
If you don't want to export, you don't need a hybrid system.
There's no reason to pay extra for features that you won't use.
An off-grid system with grid backup, would be the better option.

 

[robbob2112]

Do we know how much power is exported when heavy loads turn off? And for how long?

NOTE - not proposing to do anything without an interconnect agreement, just curious?

 

[silverramp]

I was looking through the EG4 18kpv manual and found the following. It appears that it IS possible to set it to not export back to the grid. I reached out to customer support for confirmation.

 

[silverramp]

Do we know how much power is exported when heavy loads turn off? And for how long?

NOTE - not proposing to do anything without an interconnect agreement, just curious?

Yes, the idea would be to skip the interconnect agreement. Keep the grid as backup, and regularly use off-peak grid power to maintain some minimal battery SOC.

 

[ricardocello]

I was looking through the EG4 18kpv manual and found the following. It appears that it IS possible to set it to not export back to the grid. I reached out to customer support for confirmation.

Someone should give it shot!
Let us know if the utility meter detects any backfed grid power.
Hopefully the PoCo won’t shut you down.

If they truly respond in 20 msec when a big load is powered down, that may be sufficient.
The real question is, will a modern utility meter detect the backfed power if it is less than 20 msec.

Post in thread 'Question About Preventing Grid Backfeed'

Nov 24, 2024

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...

• cs1234

• 

 

[silverramp]

Someone should give it shot!
Let us know if the utility meter detects any backfed grid power.

If they truly respond in 20 msec when a big load is powered down, that may be sufficient.
The real question is, will a modern utility meter detect the backfed power if it is less than 20 msec.

Seems like that is the big question! I wonder what the penalty would be if the utility sees an unpermitted backfeed, even if it is less than 20msec.

 

[ricardocello]

Seems like that is the big question! I wonder what the penalty would be if the utility sees an unpermitted backfeed, even if it is less than 20msec.

Search the forum, people here have gotten PoCo knocks on the door within hours of commissioning a system.
Depends on the PoCo and the jurisdiction. Worst case they can pull your meter until you comply.

 

[silverramp]

Search the forum, people here have gotten PoCo knocks on the door within hours of commissioning a system.
Depends on the PoCo and the jurisdiction. Worst case they can pull your meter until you comply.

PoCo?

 

[ricardocello]

PoCo?

PoCo = Power company
AHJ = Authority having jurisdiction

 

[mciholas]

The real question is, will a modern utility meter detect the backfed power if it is less than 20 msec.

It will definitely detect it. The question is if it will report it to the utility, or if the utility will care.

CT based zero export systems can't avoid small amounts of backfeed when the load drops suddenly, like a compressor shutting off. The inverter control system simply can't respond fast enough.

The only sure fire way to solve this is to double convert. The grid charges the battery, the inverter uses the battery to power the house. This costs you some efficiency on grid power, but if you make most of your power via solar and only use the grid for back up, the hit is fairly small.

Many hybrid inverters have a generator port, and that would be what you hook to the utility.

Mike C.

 

[ricardocello]

PoCo?

Try this thread, I’ve linked to the middle of it but it will get you up to speed.

Post in thread 'DIY Thoughts on Building a Grid Backfeed Prevention Device'
https://diysolarforum.com/threads/d...backfeed-prevention-device.89791/post-1190550

 

[silverramp]

It will definitely detect it. The question is if it will report it to the utility, or if the utility will care.

CT based zero export systems can't avoid small amounts of backfeed when the load drops suddenly, like a compressor shutting off. The inverter control system simply can't respond fast enough.

The only sure fire way to solve this is to double convert. The grid charges the battery, the inverter uses the battery to power the house. This costs you some efficiency on grid power, but if you make most of your power via solar and only use the grid for back up, the hit is fairly small.

Many hybrid inverters have a generator port, and that would be what you hook to the utility.

Mike C.

Thats a great point, why not connect the grid to the generator port? I'll ask EG4 if this works!

 

[1201]

Do we know how much power is exported when heavy loads turn off? And for how long?

NOTE - not proposing to do anything without an interconnect agreement, just curious?

Yes, the amount of power the load was using. For up to a few seconds.


So if you have an electric dryer that cycles 6kw on and off several times in the drying cycle, you'll be exporting 6kw back to the grid several times that cycle for up to several seconds at a time

 

[silverramp]

Yes, the amount of power the load was using. For up to a few seconds.


So if you have an electric dryer that cycles 6kw on and off several times in the drying cycle, you'll be exporting 6kw back to the grid several times that cycle for up to several seconds at a time

up to 20ms at a time?

 

[1201]

up to 20ms at a time?

20ms is wishful thinking.
Seconds

 

[ricardocello]

20ms is wishful thinking.
Seconds

Until I see something with at least a 100 Hz sample rate or better connected to an independent CT sensing backfeed current, these are just unverified claims. Using EG4 software to measure backfeed current is not a valid test.

But let’s say they actually do sample the current at 50 Hz (20 msec), and make control loop adjustments at that rate. I can believe that.
But a PID controller simply cannot respond that quickly to cut off the backfeed. There are time constants involved.
I would guess a second or so. But I would love to see a test report showing otherwise!

 

[1201]

Until I see something with at least a 100 Hz sample rate or better connected to an independent CT sensing backfeed current, these are just unverified claims. Using EG4 software to measure backfeed current is not a valid test.

But let’s say they actually do sample the current at 50 Hz (20 msec), and make control loop adjustments at that rate. I can believe that.
But a PID controller simply cannot respond that quickly to cut off the backfeed. There are time constants involved.
I would guess a second or so. But I would love to see a test report showing otherwise!

Ive seen some tests(not eg4) and it takes seconds.

I did some tests myself. Also took seconds. So until i see otherwise i don't believe any wild claims like 20ms

 

[Madcodger]

See @timselectric answer. He’s spot on. You can do what you want rather easily and with less expense if you simply avoid a unit that CAN export to the grid. The 6000XP is a great choice for that, even if you need more than one. Other mfrs also make quality units with similar capabilities. You can use the grid as a means of recharging batteries, and even switch to it as needed, without confusing things with the potential to feed back to the grid. That’s where you open up a very big can of worms with the electric company, and rightly so. Just avoid those headaches altogether.

 

[timselectric]

Ive seen some tests(not eg4) and it takes seconds.

I did some tests myself. Also took seconds. So until i see otherwise i don't believe any wild claims like 20ms

Same here.
It's always at least one or two seconds to correct the production.

 

[sunsurfer]

I don't know what a permit is (never use them) but I would call your power company and tell them you need an analog meter installed so their digital one stops messing with your communications with ancestors in the spirit world. Then you can go full pirate solar mode.

 

[1201]

I don't know what a permit is (never use them) but I would call your power company and tell them you need an analog meter installed so their digital one stops messing with your communications with ancestors in the spirit world. Then you can go full pirate solar mode.

My power company has a $25 monthly charge for a non ami meter since they have to come out and read it manually.

But don't get it wrong- it's still not an analog meter and they will still see the backfeed.