Hybrid inverters supporting Zero Export to External CT on AC input

[fafrd]

I don't think the multiplus ii 120x2 has ul listing though, too bad.

Ummm, pretty certain that’s exactly wrong:

https://www.solar-electric.com/lib/wind-sun/Multi-II-2x-120V-UL458-certificate.pdf

 

[cs1234]

Ummm, pretty certain that’s exactly wrong:

https://www.solar-electric.com/lib/wind-sun/Multi-II-2x-120V-UL458-certificate.pdf

My apologies, for multiplus' I look for UL1741 as I plan on using it on a building, not a car/boat.

 

[Cheap 4-life]

HYD 3000~6000-EP

SINGLE-PHASE ENERGY STORAGE INTEGRATED INVERTER

www.sofarsolar.com

Single phase, nothing a transformer wouldn’t fix for the offgrid side, it’s 48v though, has zero export control

 

[robot_zombie]

goodwe 5048d-es has adjustable export that can be set to zero (measured via CT in main panel), and supports loads on the grid side from battery (also quite cheap, I picked it up for $1800 AUD) I have one working at the moment with a 204ah pack, and aside from the charging settings being fairly clunky (working without a BMS that can talk to the inverter) it has been working pretty well.

 

[Cheap 4-life]

goodwe 5048d-es has adjustable export that can be set to zero (measured via CT in main panel), and supports loads on the grid side from battery (also quite cheap, I picked it up for $1800 AUD) I have one working at the moment with a 204ah pack, and aside from the charging settings being fairly clunky (working without a BMS that can talk to the inverter) it has been working pretty well.

I thought I read that the goodwe can’t use battery to supply loads in the main panel when operating as a grid tie inverter? I’m trying to remember where I read it

 

[fafrd]

goodwe 5048d-es has adjustable export that can be set to zero (measured via CT in main panel), and supports loads on the grid side from battery (also quite cheap, I picked it up for $1800 AUD) I have one working at the moment with a 204ah pack, and aside from the charging settings being fairly clunky (working without a BMS that can talk to the inverter) it has been working pretty well.

Clearly supports Zero Export to CT with an external meter, but seems to only be single phase 230/240VAC.

The price is certainly attractive but I’m going to limit this thread to Hybrid Inverters approved for use on the US 240/120 Split-phase grid…

 

[robot_zombie]

I thought I read that the goodwe can’t use battery to supply loads in the main panel when operating as a grid tie inverter? I’m trying to remember where I read it

no issues with that here, I have it running in the default mode (grid use minimisation) so PV first supplies the load, excess goes to the battery, further excess goes to export (which I have limited @ 3.6kw). When the sun goes down the battery supplies the loads (or during the day when load>PV generation), then once the battery runs out (or hits SOC discharge limit anyway), it goes back to the grid. I don't actually have anything connected to the back up supply on the inverter at this stage either!

 

[RCinFLA]

By specifying 'Zero Export to CT capability' I assume you are speaking about an external CT sensor that allows you to export to main input AC panel loads and still keep any inverter current export from leaking back into external grid.

This remote CT sensors adds another level of feature beyond just zero export.

There are more inverters that will prevent export from their AC input port, with internal AC input CT sensor, than ones that have the remote CT sensor to allow export to supplement local loads and still block export to external grid.

 

[fafrd]

no issues with that here, I have it running in the default mode (grid use minimisation) so PV first supplies the load, excess goes to the battery, further excess goes to export (which I have limited @ 3.6kw). When the sun goes down the battery supplies the loads (or during the day when load>PV generation), then once the battery runs out (or hits SOC discharge limit anyway), it goes back to the grid. I don't actually have anything connected to the back up supply on the inverter at this stage either!

Nice!

Exactly the sort of architecture I’m hoping to build (but supporting US grid standard).

 

[fafrd]

By specifying 'Zero Export to CT capability' I assume you are speaking about an external CT sensor that allows you to export to main input AC panel loads and still keep any inverter current export from leaking back into external grid.

Yes, correct.

This remote CT sensors adds another level of feature beyond just zero export.

There are more inverters that will prevent export from their AC input port,

Do you mean export to their AC input port???

with internal AC input CT sensor, than ones that have the remote CT sensor to allow export to supplement local loads and still block export to external grid.

Yes, I understand that hybrid inverters that use an internal CT sensor to prevent energy export out into their AC input port are a dime a dozen (most common architecture).

That more common architecture is unable to offset load consumption connected to the mains panel, which is precisely the functionality I am seeking.

If your point is that ALL hybrid inverters support ‘Zero Export to CT Sensor’ then perhaps I should modify the title if this thread again to read:

‘Zero Export to External CT Sensor’

 

[Mattb4]

I think ‘Zero Export to CT’ is pretty clear.

Yes, Zero Export to CT implies that you are grid-tied and outputting energy that is matching phase and frequency with grid (on both L1 and L2).

In addition, ‘Zero Export to CT’ implies you are exporting energy towards the grid but not enough export and power past the CT sensor that is limiting export.

The analogy I find more helpful is that if a DC-coupled array charging a battery through an SCC.

As the battery approaches full charge, the MPPT will throttle-back PV power to exactly match constant-voltage battery charge power.

If additional loads draw more DC energy from the battery, the MPPT will draw more power from the solar panels to supply that additional DC load.

Zero Export to CT is similar except that the approach of consumption where the CT is placed approaching Zero Amps plays the role of a battery approaching full charge state in the DC-coupled analogy and the inverters ability to throttle-back input to avoid Export past the CT sensor plays the role of the MPPT in the DC-coupled analogy.


No, the solar and the charging are not required. What is required is the ability of a DC-powered (battery and/or SCC) inverter to throttle-back grid-tied power generation to avoid export past an external CT sensor clamped to the same leg.

Not understanding how that is relevant, but if you want yo provide a link, I’m happy to have a look…

The Zero Export to CT capability I’m discussing is no different than what any Solark Hybrid inverter can deliver (as well as the Schneider Conext XW Pro).

Zero export to CT is poorly worded. You are not sending anything to the CT. You use a CT to measure current direction and strength. Zero export to grid can be achieved by not being in parallel. Grid tied with limiter is about the most accurate identification. You limit generated AC output from your system to that of your house loads. It is not in any way similar to battery charging.

The word coupled is tossed about too often when the word parallel should be used. A MPPT SCC is in parallel with the battery.

 

[newbostonconst]

How big are your loads....would you be open to powering your whole house from the hybrid inverter and just use the AC input to supply house when batteries are dead? My power company know the minute I back feed the grid when finalizing my system....I would hate someone you not involve the power company and then have the CT screw up and you are backfeeding and getting into trouble....

 

[fafrd]

Zero export to CT is poorly worded. You are not sending anything to the CT.

I beg to differ. You are exporting power towards the CT (but not enough to export past it).

You use a CT to measure current direction and strength.

Correct

Zero export to grid can be achieved by not being in parallel.

Agreed, but so what?

Grid tied with limiter is about the most accurate identification.

I’ve used GTIL (and still do) but no one understands it. Since Solark started using ‘Zero Export to CT’ I’ve decided that is a much better and easier-to-understand term for the capability (precisely because the exported power is being pushed out towards the CT but prevented from exporting past it).

You limit generated AC output from your system to that of your house loads. It is not in any way similar to battery charging.

My point was that from a control point of view the throttling of power generation is similar. In the case of DC-coupled battery charging, the SCC detecting that the battery is approaching full and switching to CV mode translates to higher string voltage to throttle-back PV power generation.

In the case of an ac-coupled GTIL / ZECT inverter, the inverter detecting that the import current at the external CT sensor is approaching zero and nearing export causes the inverter to throttle-back power generation to prevent export.

The word coupled is tossed about too often when the word parallel should be used. A MPPT SCC is in parallel with the battery.

Agree. But at this point the entire industry has adopted ‘coupled’ and it also suggests interface/connection and communication in ways that ‘parallel’ cannot.

 

[Mattb4]

..

I’ve used GTIL (and still do) but no one understands it. Since Solark started using ‘Zero Export to CT’ I’ve decided that is a much better and easier-to-understand term for the capability (precisely because the exported power is being pushed out towards the CT but prevented from exporting past it).

...

The problem is that you are not preventing power from being exported back to grid. You are just trying to match loads that your house has and not exceed them. Exceeding them means export. Sudden load drop on the grid side can also mean export.

From the grid side of things it is loads carried by generation. The supply does not discriminate with which loads it powers it just raises and lowers output based on total. When you parallel with it and pick up load you can pretend it is just your house loads you pick up but the grid does not know this because it is still connected but seeing less demand. Straight grid tie relies on the fact that the grid always has loads to pick up unless grid goes down. Limited grid tie is simply supplying enough to cover partially or entirely what otherwise would be your loading on the grid.

 

[cs1234]

I’ve used GTIL (and still do) but no one understands it. Since Solark started using ‘Zero Export to CT’ I’ve decided that is a much better and easier-to-understand term for the capability (precisely because the exported power is being pushed out towards the CT but prevented from exporting past it).

I think the term "Zero Export Past CT" would be a better expression, implying that the CT is like a gate beyond which it shall not pass. Ignore the fact that the CT can't actually block anything if it wanted to.

EDIT.. maybe "Zero Export Beyond CT".

 

[fafrd]

The problem is that you are not preventing power from being exported back to grid. You are just trying to match loads that your house has and not exceed them. Exceeding them means export. Sudden load drop on the grid side can also mean export.

Ahhh, you’re talking about the distinction between ‘True Zero Export’ and ‘Pseudo Zero Export’…

True Zero Export is pretty much impossible to deliver without a transfer switch (true off-grid). Not particularly relevant to this discussion.

Relevant to this discussion is Virtual Zero Export meaning that the response time of the system is fast enough to correct any transient Export faster than the utility meter could detect it.

So between settings parameters to consume an average level if import providing additional margin against unwanted export and having a Zero Export solution faster than the response time of the utility meter, there are a couple different avenues for a Pseudo Zero Export solution to deliver Virtual Zero Export.

From the grid side of things it is loads carried by generation. The supply does not discriminate with which loads it powers it just raises and lowers output based on total. When you parallel with it and pick up load you can pretend it is just your house loads you pick up but the grid does not know this because it is still connected but seeing less demand.

Agree.

Straight grid tie relies on the fact that the grid always has loads to pick up unless grid goes down. Limited grid tie is simply supplying enough to cover partially or entirely what otherwise would be your loading on the grid.

And I agree with all of this as well though you are kind of preaching to the choir since I was one of the first to start a number of threads on Grid Tie Inverter Limited which few were interested in or responded to.

Technically more accurate term but lousy from a marketing perspective.

Solark figured this out and marketed the feature as ‘Zero Export to CT’ which is much more descriptive and intuitive (though less technically accurate).

So I’ve kind of just decided to go with the flow and adopt the popular term rather than limit myself yo the most technically accurate term.

 

[fafrd]

I think the term "Zero Export Past CT" would be a better expression, implying that the CT is like a gate beyond which it shall not pass. Ignore the fact that the CT can't actually block anything if it wanted to.

‘Thou Shall Not Pass’ - I like it!

It’s a good suggestion and perhaps I’ll hope if we start promoting it here on the Forum that Solark will take note and refine their marketing .

 

[Mattb4]

...

And I agree with all of this as well though you are kind of preaching to the choir ...

Sorry about that.

 

[Cheap 4-life]

I think (if anything) the title should say bi-directional AC input.. most hybrid inverters have an AC input for battery charging or bypass. Most do not have the ability to send power out of the AC input in the other direction to act as a grid tie inverter and directly supply the main panels loads without going thru a critical loads/offgrid panel..

 

[TrueNorthSolar]

From what I’ve understood, the SW will not export AC power Into the AC input (offsets loads onAC output only).

The XW Pro apparently will (using an external energy meter that communicates with it) but it’s more complex to get set up than in on inverters such as Solark with inputs for exterbal CR sensors…

SW will not export but it does have a generator assist function that will effectively work as a peak load shaver if you’re running from a grid source vs. the generator. I’ll say that’s as close as you’ll ever come to getting the functionality you‘re looking for in 24V. Curious: why are you putting a 24VDC condition on the system? You’ll benefit from going to 48V in choice, performance and flexibility.