AC/DC coupled, grid tie, hybrid etc?

[realpinochet]

I'm just starting off in the solar tech and have some questions; perhaps they are documented elsewhere here? I'd appreciate some guidance on this path of seeking context and clarity.

1. Grid tie.

I've seen articles that seem to suggest this means only if the inverter is tied into the grid to sell back...I believe this is called net metering. I see others suggesting it can mean if the inverters are connected to the grid so you can use the grid as a source of energy if the sun isn't shinning and the batteries are empty..maybe even charge the batteries. Then it seems you have inverters that can use grid power not only to use if no other power source is available but can also be used in conjunction with other sources...I guess this is called grid assist. I find that there's inverters that can use incoming solar from the panels before it hits the batteries first, then batteries ..then grid last as a priority. Is this called "SBU" mode? It seems like even then you have inverters that can't use incoming DC to power the loads directly as it has to store it in the battery then pull from the battery and convert while others seem to be able to use in coming DC straight to the inverter without storage first. This all leads to other terminology questions.

2. AC coupling and DC coupling:

This seems to indicate how power was stored originally.

AC coupling: Pull from the grid, convert to DC and store in the battery. DC coupling: Pull from the incoming PV and store DC to DC in the battery.

So, what is it called when you have a inverter that can take incoming PV power from the charge controller directly and use it to power loads as much as possible first? DC to AC coupling? I guess then blend it if needed if there's not enough with battery or grid power? These seem to be a special kind of inverter, are these called hybrid inverters? This is the other question.

3. What exactly is a hybrid inverter, just a inverter that can pull from multiple sources? Do they all have the same features to be labeled hybrid? For example can all hybrids us PV input to power loads ..DC to AC coupling if that's what it's called?

I'm asking because I want to know what to look for when looking for a system. Some vendors just say hybrid or grid tie or whatever. In my usage case I'm looking for something like this.

A: I want to have a system that's capable of using the grid to not only power loads if no other source of power is available as in no sun and batteries depleted but also charge the batteries if desired and needed. But, I like the grid to also be able to step in if needed for supplementation on demanding loads. I don't plan on selling power back..so is this grid tie or grid assist?

B: I want a system that still works is the grid is down, it seems like some grid tie systems do not. If the grid is down I'd want my battery and PV power to work.

C: I'd like to have a system that can prioritize: Pull from solar power first, battery and then grid if needed. I want it to use PV directly as I'm reading it's more efficient.

D: (Stacking) Support multiple systems for redundancy and extra power.

* I'm assuming SBU mode means it can use incoming DC from the PV "directly" without storing and then converting back to AC?

My assumptions are I'm looking for a "Stackable" hybrid inverter system that can AC and DC couple? I'm still unclear on what it's called when using the PV directly without the need to store it first. It seems like most of the inverters marked hybrid are the mpp/growatt and other AIO units but what about more tier 1 systems that use a modular system like conxt 6848 or outback radian? I was trying to read the outback radian manual last night and that spurred this research. I need to understand the terminology and technology and how they associate / describe each other before trying to find out what I want to buy. I like the 6848 but can it use PV directly? Can it prioritize "sbu" ...I'm not sure cause I need more clarity on what I'm reading. I know this is a long read, I apologize but I'd like to have a better understanding instead of just buying what I saw a youtuber doing.

These are two of the several articles I found from my research.

AC Vs. DC Solar Battery Coupling: What You Need to Know

There are two primary ways of connecting solar panels and batteries: AC coupling and DC coupling. We cover the key differences.

news.energysage.com

What is a Hybrid Inverter?

What a hybrid solar inverter does, the options a grid-tied hybrid inverter gives you for home solar, how hybrid inverters compare to other inverters, and more.

palmetto.com

 

[timselectric]

Grid tied means that it can export (sell) power to the grid.
Off grid means that it can run off battery.
An AIO (all in one) means that it has several components incorporated into one case.
Hybrid inverter can have features of any of the above.

 

[timselectric]

Coupling is two systems tied together. Whether it is tied together via DC or AC, determine which it is.

 

[realpinochet]

Coupling is two systems tied together. Whether it is tied together via DC or AC, determine which it is.

Right, I mean I know what coupled means but in context to solar inverters. Is coupling only for storing to battery? Or, like I was saying if a inverter can use the grid for grid assist is that called AC coupling even if it doesn't charge the battery? What you're suggesting is AC or DC coupling means if it's connected to either AC or DC systems regardless of it's function. Is this what you're stating? Legit question, it seems like there was more context and circumstances to define these terminologies. Thanks Tim, I've appreciated your help on several forums.

 

[timselectric]

Right, I mean I know what coupled means but in context to solar inverters. Is coupling only for storing to battery? Or, like I was saying if a inverter can use the grid for grid assist is that called AC coupling even if it doesn't charge the battery? What you're suggesting is AC or DC coupling means if it's connected to either AC or DC systems regardless of it's function. Is this what you're stating? Legit question, it seems like there was more context and circumstances to define these terminologies. Thanks Tim, I've appreciated your help on several forums.

Coupling, whether AC or DC. Is a connection between two systems. It can be between grid and batteries, inverter and batteries, inverter and generator, or between two inverters. Coupling is the synchronization of two power generating sources.

 

[timselectric]

Grid assist is not generally considered coupling.
Although, sometimes it is similarly connected. In the case where the grid and inverter can share the loads.

 

[400bird]

AC coupling:
Solar panels to AC inverter to DC charger to battery

DC coupling:
Solar panels to DC charger to battery

They both have benefits and draw backs, it just depends on your priorities.

 

[timselectric]

AC coupling:
Solar panels to AC inverter to DC charger to battery

DC coupling:
Solar panels to DC charger to battery

They both have benefits and draw backs, it just depends on your priorities.

I wouldn't consider either of those examples "coupling". They are just two ways to get solar power into batteries.
I say this because there's no synchronization between any of those components.
A good example of AC coupled batteries. Would be Enphase battery systems. Where they use micro inverters connected to the battery modules. To charge and discharge through an AC connection.

 

[400bird]

I'm just starting off in the solar tech and have some questions; perhaps they are documented elsewhere here? I'd appreciate some guidance on this path of seeking context and clarity.

1. Grid tie.

I've seen articles that seem to suggest this means only if the inverter is tied into the grid to sell back...I believe this is called net metering. I see others suggesting it can mean if the inverters are connected to the grid so you can use the grid as a source of energy if the sun isn't shinning and the batteries are empty..maybe even charge the batteries. Then it seems you have inverters that can use grid power not only to use if no other power source is available but can also be used in conjunction with other sources...I guess this is called grid assist. I find that there's inverters that can use incoming solar from the panels before it hits the batteries first, then batteries ..then grid last as a priority. Is this called "SBU" mode?

This SBU, SUB, etc naming is very specific to a line of lower cost inverters. You won't likely find it reference by tier one inverters that do the same thing, but don't advertise it as a "feature" it's just treated as standard operations.

It seems like even then you have inverters that can't use incoming DC to power the loads directly as it has to store it in the battery then pull from the battery and convert while others seem to be able to use in coming DC straight to the inverter without storage first. This all leads to other terminology questions.

I agree the lack of standard terminology is terrible.
Depending on what you are looking at, some inverters can charge the battery and invert at the same time

2. AC coupling and DC coupling:

This seems to indicate how power was stored originally.

It's where the PV is first converted. I think I explained this in a previous post above.

AC coupling: Pull from the grid, convert to DC and store in the battery. DC coupling: Pull from the incoming PV and store DC to DC in the battery.

It's not about the grid at all.

So, what is it called when you have a inverter that can take incoming PV power from the charge controller directly and use it to power loads as much as possible first? DC to AC coupling?

AC coupling as the PV gets converted directly to AC

I guess then blend it if needed if there's not enough with battery or grid power? These seem to be a special kind of inverter, are these called hybrid inverters? This is the other question.

Not exactly, most quality inverters do this without even calling it a feature. I don't know how to tell you what to look for, maybe others can chime in?
Or post some inverters you're looking at.

3. What exactly is a hybrid inverter, just a inverter that can pull from multiple sources? Do they all have the same features to be labeled hybrid? For example can all hybrids us PV input to power loads ..DC to AC coupling if that's what it's called?

Hybrid is another mess.
Hybrid should mean a combination of two components. In this case a charge controller and inverter.
However, some creative companies decided to give it a different definition.

I'm asking because I want to know what to look for when looking for a system. Some vendors just say hybrid or grid tie or whatever. In my usage case I'm looking for something like this.

A: I want to have a system that's capable of using the grid to not only power loads if no other source of power is available as in no sun and batteries depleted but also charge the batteries if desired and needed. But, I like the grid to also be able to step in if needed for supplementation on demanding loads. I don't plan on selling power back..so is this grid tie or grid assist?

B: I want a system that still works is the grid is down, it seems like some grid tie systems do not. If the grid is down I'd want my battery and PV power to work.

C: I'd like to have a system that can prioritize: Pull from solar power first, battery and then grid if needed. I want it to use PV directly as I'm reading it's more efficient.

D: (Stacking) Support multiple systems for redundancy and extra power.

* I'm assuming SBU mode means it can use incoming DC from the PV "directly" without storing and then converting back to AC?

My assumptions are I'm looking for a "Stackable" hybrid inverter system that can AC and DC couple? I'm still unclear on what it's called when using the PV directly without the need to store it first. It seems like most of the inverters marked hybrid are the mpp/growatt and other AIO units but what about more tier 1 systems that use a modular system like conxt 6848

Can do what you want DC coupled PV.
Or if you want to AC couple it would require you to make a PLC or some external controller.

or outback radian?

Will also work fine either AC or DC coupled.

I was trying to read the outback radian manual last night and that spurred this research. I need to understand the terminology and technology and how they associate / describe each other before trying to find out what I want to buy. I like the 6848 but can it use PV directly?

No, both the Radian and XW are battery inverter/chargers only. You need a separate charge controller (to DC couple) or grid tie inverters (to AC couple)

Can it prioritize "sbu" ...I'm not sure cause I need more clarity on what I'm reading. I know this is a long read, I apologize but I'd like to have a better understanding instead of just buying what I saw a youtuber doing.

These are two of the several articles I found from my research.

AC Vs. DC Solar Battery Coupling: What You Need to Know

There are two primary ways of connecting solar panels and batteries: AC coupling and DC coupling. We cover the key differences.

news.energysage.com

What is a Hybrid Inverter?

What a hybrid solar inverter does, the options a grid-tied hybrid inverter gives you for home solar, how hybrid inverters compare to other inverters, and more.

palmetto.com

 

[realpinochet]

This SBU, SUB, etc naming is very specific to a line of lower cost inverters. You won't likely find it reference by tier one inverters that do the same thing, but don't advertise it as a "feature" it's just treated as standard operations.

I agree the lack of standard terminology is terrible.
Depending on what you are looking at, some inverters can charge the battery and invert at the same time

It's where the PV is first converted. I think I explained this in a previous post above.


It's not about the grid at all.

AC coupling as the PV gets converted directly to AC

Not exactly, most quality inverters do this without even calling it a feature. I don't know how to tell you what to look for, maybe others can chime in?
Or post some inverters you're looking at.

Hybrid is another mess.
Hybrid should mean a combination of two components. In this case a charge controller and inverter.
However, some creative companies decided to give it a different definition.


Can do what you want DC coupled PV.
Or if you want to AC couple it would require you to make a PLC or some external controller.

Thanks 400, I believe I was reading another thread you're on. You have a 6848 system right? Didn't you have a issue with pulling power or charging from the grid if needed? So, you're saying DC coupling is taking pv input and pushing it to the battery? But are you not AC coupled to since you're taking grid power to charge on days of no sun or high demand? I thought the 6848 could AC couple out of the box to use grid power to charge the batteries as it says inverter/charger. Assuming you do have a 6848 can it use AC power to charge the batteries, run loads or assist. And use PV directly as it comes in without storing to battery first? Again, I think it was you that had a problem with charging with AC and had to do something manually. Did that get resolved? If the battery get low in the night from saying running the AC I'd want the unit to switch to grid to run the load and charge..then when PV gets going in the morning it would sense this and switch back to charging from the PV loads without manual intervention.

 

[400bird]

Thanks 400, I believe I was reading another thread you're on. You have a 6848 system right? Didn't you have a issue with pulling power or charging from the grid if needed?

I do have a Schneider XW 6848 pro
My issue with charging from the grid is not technical, it is possible and I have done it.
My "issue" is the agreement with PGE. I can't charge from the grid because I can't discharge that power and sell it back to them.

So, you're saying DC coupling is taking pv input and pushing it to the battery? But are you not AC coupled to since you're taking grid power to charge on days of no sun or high demand? I thought the 6848 could AC couple out of the box to use grid power to charge the batteries as it says inverter/charger.

Maybe this link will help explain AC vs DC coupling.

AC vs. DC Coupling Energy Storage Systems — Mayfield Renewables

At Mayfield Renewables, we routinely design and consult on complex solar+storage projects. In this post, we outline the relative advantages and disadvantages of two solar+storage system architectures: AC-coupled and DC-coupled energy storage systems (ESS).

www.mayfield.energy

You've got to ignore the grid when differentiating AC vs DC coupled systems. It's just about where the AC/DC split is.

AC coupled you have Solar DC converted to AC (to power your loads) That AC is converted back to DC to charge your storage battery. The battery is AC coupled.

DC coupled you have Solar DC transformed down to battery voltage (for example 48vdc) by a charge controller (or hybrid) that 48 vdc can either charge the battery or be converted to AC to power your loads.

I wouldn't consider either of those examples "coupling". They are just two ways to get solar power into batteries.
I say this because there's no synchronization between any of those components.

I don't think synchronization or communication between components is involved. Here's another link, different from the one above. https://news.energysage.com/ac-vs-dc-solar-battery-coupling-what-you-need-to-know/
This image is pretty good in my opinion. I wish they labeled the components and didn't use an image with two arrows for the solar inverter, it isn't going to push power to the panels ever.

A good example of AC coupled batteries. Would be Enphase battery systems. Where they use micro inverters connected to the battery modules. To charge and discharge through an AC connection.

But that still ends up in the same spot.
PV is converted to AC (by the micro inverters on the panels) which is then converted to DC for you battery (by the micro inverters in the batteries)

 

[400bird]

I do have a Schneider XW 6848 pro
My issue with charging from the grid is not technical, it is possible and I have done it.
My "issue" is the agreement with PGE. I can't charge from the grid because I can't discharge that power and sell it back to them.

Quoting myself, what a weird place I find myself.

I just wanted to clarify that PGE is the power company here.

Here is my build thread:

Adding Schneider XW Pro

I forgot, I was going to include some screen shots from the EVSE interface. Yes, those parameters related to charging are part of the EVSE set up. "home screen" with the "advanced" option checked to display more settings and information "Home screen" Basic "settings" "Services" the...

diysolarforum.com

Here is another thread with an XW pro:

Adding storage to my Enphase system

Any new wireless chargers? Is there anything new in the house that might be running from 1:00 to 2:30? (I like where he said... my neighbor had a wireless charger). Have I mentioned I like my SDR dongle? ; -)

diysolarforum.com

Both are AC coupled with the same issue, totally avoided if you are building from scratch and go DC coupled.
Or build some sort of external controller to control the AC charging.

There are details in there from PVdude about his DC coupled system and a few others.

 

[realpinochet]

Quoting myself, what a weird place I find myself.

I just wanted to clarify that PGE is the power company here.

Here is my build thread:

Adding Schneider XW Pro

I forgot, I was going to include some screen shots from the EVSE interface. Yes, those parameters related to charging are part of the EVSE set up. "home screen" with the "advanced" option checked to display more settings and information "Home screen" Basic "settings" "Services" the...

diysolarforum.com

Here is another thread with an XW pro:

Adding storage to my Enphase system

Any new wireless chargers? Is there anything new in the house that might be running from 1:00 to 2:30? (I like where he said... my neighbor had a wireless charger). Have I mentioned I like my SDR dongle? ; -)

diysolarforum.com

Both are AC coupled with the same issue, totally avoided if you are building from scratch and go DC coupled.
Or build some sort of external controller to control the AC charging.

There are details in there from PVdude about his DC coupled system and a few others.

Got you sir, I think the "AC" was tripping me up as I've always associated it with the grid. I understand what you're saying now.

For tier one products I'm looking at the same 6848 you have or the outback radian which has more power for not too much more but doesn't have the surge time the 6848 has. Also, I was looking for where it says it can use pv to power loads directly and couldn't find that so I started this thread.

Outback Radian GS8048A-01 8,000 Watt Advanced Inverter/Charger

Note: This item is being discounted because of a special Outback promotion, while supplies last. It currently has a six week lead time before shipping. Please email us or give us a call if you need assistance. NOTE: The OutBack Power Radian inverter is not designed for use in mobile applications...

www.solar-electric.com

I might have to get a cheap setup first and am looking at.

MPP Solar Inc » SPLIT PHASE LVX SERIES – LVX6048

www.mppsolar.com

MPP Solar Inc » SPLIT PHASE LV SERIES – LV6548V 500V

www.mppsolar.com

 

[realpinochet]

One thing I've noticed is that both mpp and growatt list this as I guess a hybird feature.

"battery less operation"

I'm taking this to mean you can run without grid or battery as it take it from pv and powers the loads. Does the 6848 or radian do this? I'll have batteries like the eg4 ones or similar but just curious.

 

[timselectric]

But that still ends up in the same spot.
PV is converted to AC (by the micro inverters on the panels) which is then converted to DC for you battery (by the micro inverters in the batteries)

I can see it both ways, I suppose.
But the micro inverters on both ends have to synchronize with the AC power. When I think of AC coupling, I think of micro inverters connected to an inverter, that can use and control the output of the micro inverters. And DC coupling would be an inverter/charger that puts power into or draws power out of the batteries.
But, that's just what is stuck in my head. (Power flowing in both directions)
Otherwise it's just one thing using the output of another. (Which means a vacuum cleaner is AC coupled to the house power? lol)

 

[timselectric]

One thing I've noticed is that both mpp and growatt list this as I guess a hybird feature.

"battery less operation"

I'm taking this to mean you can run without grid or battery as it take it from pv and powers the loads. Does the 6848 or radian do this? I'll have batteries like the eg4 ones or similar but just curious.

It can power loads straight from the solar. But, without grid or Batteries connected the power can fluctuate greatly from passing clouds. So battery less should be used in SUB mode with grid connected. If you a want reliable steady power.

 

[realpinochet]

It can power loads straight from the solar. But, without grid or Batteries connected the power can fluctuate greatly from passing clouds. So battery less should be used in SUB mode with grid connected. If you a want reliable steady power.

Just curious. Say you're off grid and your battery bank takes a dump. Can you still power the fridge from PV only on a sunny day in say...Arizona? Again, just curiosity?

 

[timselectric]

Just curious. Say you're off grid and your battery bank takes a dump. Can you still power the fridge from PV only on a sunny day in say...Arizona? Again, just curiosity?

Yes, I have used it this way. But if a cloud moves across the sky while the compressor is running, it could shut down from overload. But in a pinch, it is nice to still have an option for power.

 

[400bird]

Got you sir, I think the "AC" was tripping me up as I've always associated it with the grid. I understand what you're saying now.

For tier one products I'm looking at the same 6848 you have or the outback radian which has more power for not too much more but doesn't have the surge time the 6848 has. Also, I was looking for where it says it can use pv to power loads directly and couldn't find that so I started this thread.

I don't know what you're looking for with "PV powering loads directly"
It could be many things. Nothing should be powered directly off the panels. Those should go to a PV inverter (to power AC loads) or a charge controller (to charge battery, you could power DC loads at battery voltage too)

Outback Radian GS8048A-01 8,000 Watt Advanced Inverter/Charger

Note: This item is being discounted because of a special Outback promotion, while supplies last. It currently has a six week lead time before shipping. Please email us or give us a call if you need assistance. NOTE: The OutBack Power Radian inverter is not designed for use in mobile applications...

www.solar-electric.com

I might have to get a cheap setup first and am looking at.

MPP Solar Inc » SPLIT PHASE LVX SERIES – LVX6048

www.mppsolar.com

MPP Solar Inc » SPLIT PHASE LV SERIES – LV6548V 500V

www.mppsolar.com

I'm no help with the MPP stuff.
Some of those lower end ones make choices that I can't understand. Things like not matching grid frequency, so you're either all battery or all grid. For example, at a 8,000 watt load your 6,000 watt inverter shuts down and everything comes from the grid. The Schneider or Outback would max out their output and let the grid supply any more that is needed.

One thing I've noticed is that both mpp and growatt list this as I guess a hybird feature.

"battery less operation"

I'm taking this to mean you can run without grid or battery as it take it from pv and powers the loads. Does the 6848 or radian do this? I'll have batteries like the eg4 ones or similar but just curious.

No, both the Outback and XW are battery inverters. They connect to AC (two inputs and one output) and the battery. No way they could support a load without the battery, there is no source of energy. If you're battery went down but the solar charge controller stayed alive, that would probably allow some limited function. But seems problematic and probably shouldn't be relied on.



Maybe a picture would help.
Both the Outback Radian and Schneider XW are the red circled component.
You'd need to add a solar charge controller (bottom green circle) or AC solar inverter (top green circle)

 

[Ampster]

AC coupling:
Solar panels to AC inverter to DC charger to battery

Yes that is the original concept. It has evolved to also mean using a grid forming inverter (hybrid) to AC couple with a GT, grid dependent inverter, to allow the GT inverter to function when the grid is down. The above graphic illustrates it well.
I hope we have answered or clarified the original questions of @realpinochet ? If not, feel free to ask.