Backfeeding the grid

[L-P-G]

If you back feed and do not have a net meter, you will be paying for what you are supplying to the grid!
The meter only knows the current is flowing, it doesn't know you are sending it or receiving it.

So don't back feed. The best you can hope for is slowing down your grid meter to at or near zero.

That's only on some cases. Some new meters detect power flow direction, if you're not signed up for net metering you just won't get paid for your export, it won't charge you for your export as if it was usage.

as always YMMV depending on your meter.

 

[jasonhc73]

That's only on some cases. Some new meters detect power flow direction, if you're not signed up for net metering you just won't get paid for your export, it won't charge you for your export as if it was usage.

as always YMMV depending on your meter.

There is no "flow", the solar panels just have a higher voltage. So, to find out if it is "illegal" or not then it's a state regulatory mater, and pretty much every state is different.

 

[L-P-G]

There is no "flow", the solar panels just have a higher voltage. So, to find out if it is "illegal" or not then it's a state regulatory mater, and pretty much every state is different.

What are you talking about? Meters measure power in kWh which does flow forward (increases your consumption) or backwards (decreases your consumption). When you say "the solar panels just have a higher voltage" are you referring to the 350-600VDC they produce?

 

[jasonhc73]

What are you talking about? Meters measure power in kWh which does flow forward (increases your consumption) or backwards (decreases your consumption). When you say "the solar panels just have a higher voltage" are you referring to the 350-600VDC they produce?

A/C is back and forth. It's amplitude is its Voltage. The voltage from the grid(transformer) is 240V/60Hz(split phase)

When you "backfeed", the solar panel inverter is getting its frequency from the grid, 60Hz, and syncing to it. The solar inverter is sending out 246v, a higher amplitude A/C. The net meter measures there A/C 246, records that as distributed production and "turns in reverse".

246 is just an example, it is a variable amplitude. As long as the amplitude of the "grid tied" solar inverter is taller ("higher voltage") the meter turns backward.

When/if the grid goes offline. The 60Hz is gone, then the grid-tied inverter has nothing to sync with, the grid-tied inverter shuts down. The grid can turn of the solar panels by sending out a different frequency also. For example 62.5 Hz will turn off your "grid-tied" production, usually for at least 5 minutes.

In A/C electricity current (amps) is actually a measure of the maximum amplitude of the voltage., a cheap Harbor Frieght type a/c electric monitor will show all the numbers of the electrical sine wave. An RMS monitor will just show the "RMS" on a/c and the number will basically be unchanging.

 

[L-P-G]

When you "backfeed", the solar panel inverter is getting its frequency from the grid, 60Hz, and syncing to it. The solar inverter is sending out 246v, a higher amplitude A/C. The net meter measures there A/C 246, records that as distributed production and "turns in reverse".

Yea... that's not how meters work. The meter doesn't "record in reverse" when the voltage rises above the grid supply voltage. You're charged for the kW which is the voltage*amps used. Voltage is just the speed, amps is the volume.

I think you're getting hung up on the fact that AC alternates back and forth, what you need to remember is that even though it alternates it is still consumed and flows from production to consumption, in other words it still has a directional flow. So when you're producing more than you're consuming those electrons are backfeeding through your meter (creating a reverse EM field) to be consumed by your neighbors.

A/C is back and forth. It's amplitude is its Voltage. The voltage from the grid(transformer) is 240V/60Hz(split phase)

This is also wrong. frequency and voltage are related to each other and changing frequency does affect the perceived voltage but that's only because you're getting more or less 0v points in the wave. if you were to change the frequency to 0hz you'd end up with 170v, in other words the supply voltage is always the same, the changes between crest and trough cut up that 170v to give you 120v in one of the legs.

 

[jasonhc73]

OK.

If you want to go take physics and study the difference between DC and AC nothing is stopping you from doing so.

It's OK to have opinions on this.

 

[L-P-G]

OK.

If you want to go take physics and study the difference between DC and AC nothing is stopping you from doing so.

It's OK to have opinions on this.

Yes, Opinions are totally fine. However, in a forum where the main goal is to have discussions on how different mechanisms work, opinions passed as fact can be dangerous. I wasn't trying to be an ass, I was simply pointing out that not all meters will detect backfed power as consumption.

 

[Supervstech]

Yes, Opinions are totally fine. However, in a forum where the main goal is to have discussions on how different mechanisms work options passed as fact can be dangerous. I wasn't trying to be an ass, I was simply pointing out that not all meters will detect backfed power as consumption.

True.
There are a huge variety of utility meters and they do not all operate the same.

 

[SolarRat]

True.
There are a huge variety of utility meters and they do not all operate the same.

Yes, mine is digital and remotely monitored by FPL. I'm pretty sure they will immediately know if I start backfeeding without their permission.

 

[Sojourner]

Now if you connect Utility Power, you can choose from the standard options what you would like to happen when:
A) The Inverter is overloaded - it will automatically switch the load over to grid/utility power
...

The grid feedback system works it will slow your meter down even if you don't have net metering.
UL listing is on schedule for early 2020 for this particular model (It has approvals for European countries in its current 120V and 240V option).
We ask customers to NOT use this function in a formal setting, but we do have many customers who use it, and have the approval and buy in from their local utility companies too.

Questions:
1) "If the inverter is overloaded - it will automatically switch the load over to grid/utility power" <<does this include situations, for example, a large spike load from a water pump or miter saw starting up? Often, this causes high frequency inverters to fail. What would happen in the case of the MPP unit discussed in this thread that's grid connected? Would the inverter instantly switch to grid power and avoid failure, or would it cut off?

2) Since we're well into 2020, did this unit get UL listing status?

Thanks!

 

[doctorcupcakes]

Questions:
1) "If the inverter is overloaded - it will automatically switch the load over to grid/utility power" <<does this include situations, for example, a large spike load from a water pump or miter saw starting up? Often, this causes high frequency inverters to fail. What would happen in the case of the MPP unit discussed in this thread that's grid connected? Would the inverter instantly switch to grid power and avoid failure, or would it cut off?

2) Since we're well into 2020, did this unit get UL listing status?

Thanks!

I'm wondering the same thing. I wouldn't be surprised if it was delayed because of the coronavirus. The lack of UL certification is they only thing keeping me from buying one of these units, as my POCO won't allow me to use an inverter without UL certification to backfeed.

 

[Hedges]

"Flow" etc. ...
The meter doesn't detect difference in voltage between what you produce and what's on the grid.
If it is a true watt-hour meter, it measures the vector product of current and voltage, which are both nominally sine waves. That's the "cross" product, not the "dot" product.
Pure resistive loads have current in phase with voltage.
Reactive loads like motors tend to have a phase shift between current and voltage. Each cycle they suck power from the grid part of the time and shove power back in part of the time. This causes higher than necessary current, and warms the birds feet. Reactive compensation like capacitors is sometimes used to reduce reactive power. Industrial users are charged for their reactive loads, not just for net power consumed.

Grid-tie inverters shove current into the grid 180 degrees out of phase with voltage, so the power flows out not in. It's like if you fall overboard, and someone extends an oar to pull you back. You can hold or pull so they do "work" on you, or you could push so you do "work" on them.

Meters could compute power delivered, or they could just multiply voltage and current without considering phase and charge you for power delivered. I think these days they tend to take multiple digitized voltage and current readings considering polarity during a single cycle and compute power. The old mechanical meters measured power continuously with analog/magnetic mechanisms, and would spin backwards.

 

[iceledoar]

To be clear are you saying you can turn off the back feed into the grid?
One of the drawbacks of these is in a power outage they are a dangerous device for backfeeding and killing a linemen.

Having the ability to sense grid power and subsequent shutoff would be a mandatory requirement for these things.
If they don't they would be illegal in most areas.
Your liability would be huge

Can someone clearly answer this.
Is there a setting so they shut off in a power outage?

For safety's sake, during a grid power outage, if your grid tied, please save lives and turn off the MAIN!!!.

 

[soleilaumesa]

This device has Anti Islanding as a industry standard , so in the case of a power failure - it would not feed back.

The model I have is a Growatt Off Grid Solar Inverter SPF 3000TL LVM. Does this have Anti Islanding? And If not what can I do?

 

[Hedges]

The model I have is a Growatt Off Grid Solar Inverter SPF 3000TL LVM. Does this have Anti Islanding? And If not what can I do?

It appears that inverter serves as a UPS, fed from the grid and disconnecting during grid failures, but doesn't backfeed the grid. So it doesn't perform UL1741 anti-islanding. In fact, it's description is "off grid"

You can hook its input to the grid (it has a 1500W or 2000W battery charger), connect batteries and PV panels, connect protected loads like computer and refrigerator to the output. That will keep them operating during power failures.

What it can't do is feed solar power back into the grid, "net metering". Other models or brands would do that.
Don't hook the output of your inverter to the grid, will destroy it.

Growatt