Confusion on meaning of Off Grid vs Grid-tie vs Zero Export

[timselectric]

I don’t disagree with your statement, but the issue is that the various combinations and variations that fit the definition make the term useless in describing anything specific. Telling someone an inverter is a hybrid tells them nothing about the inverter.

It tells them that it's both. A grid-tied inverter with battery backup.

 

[wattmatters]

I'm paralyzed to get anything really going because I'm not sure I 100% fully understand the difference on the types of systems. The semantics are getting to me.

That's understandable. Even the industry mixes terminology up.

I'm basically wanting to start small and expand over time. I have three 370Watt panels. I'm wanting to set them up to ease the burden of my electric bill and slowly start offsetting my use of the grid. I do not have a battery currently but would like to add one sometime in the future. I'd like to start collecting wattage from the panels during sun to help out my system and get a battery soon and go from there.

I think there are two paths for you:

i. keep researching, think long and hard about what it is you are actually wanting to achieve, and then design and implement a solution to deliver on those goals, or

ii. just get started with something, anything, and learn by doing.

They are equally valid approaches.

i. makes sense if the big picture matters most, and is probably lower cost over the long haul. But it can also mean a much larger financial commitment up front and that is daunting, especially if you have doubts or perhaps unsure if the time frame for it to make sense is longer than you are comfortable with.

ii. is good in that you can just make something happen, gain some benefits and start with something lower cost. However starting small/low cost and expanding later inevitably means abandoning what you have built for something more suitable for the end goal / big picture.

ii. is also partly about enjoying the process of learning new stuff. That may or may not appeal.

As has been mentioned, one of the key factors to understand are the local regulations concerning connecting any generation source to the grid. Utilities will typically have pretty strict requirements for that and the costs of complying will vary enormously depending on where you are.

There are four basic options (but there are nuances and frankly it's almost a spectrum of options):

1. Grid-tied PV

The inverter is connected to the grid. Its AC power output is synchronised with and operates in parallel with the grid. This type of inverter will (typically) draw every last watt it can from the solar PV and that production is added to the grid's power supply.

How your home is deemed to consume energy from your PV system and the grid is then a function of the utility's metering, and that's a whole 'nother level of operational variance across regions/the world. With modern meters and an approved installation, the normal metering set up is your home first consumes your own production, and the grid manages the balance, be that importing any deficit or exporting any excess. Because the energy sources operate in parallel and one of them is the grid, you have little concern with being able to cover load demand.

But there are variations from this typical set up. One of those are where export limitations are applied by the utility. In these cases the inverter may be required to restrict or prevent export to the grid and the inverter must be capable of complying with these restrictions. Usually the inverter will have a means of monitoring the power flow to/from the grid and adjust output accordingly so as to remain within the regulatory limit.

Grid-tied inverters will need to be approved for use in your region/country and have all the necessary safety systems to ensure it can never energise the grid should the grid's supply go down. Most standard grid-tied PV inverters require a grid signal to operate, and without it they simply shut down. No grid, no PV and this is how they comply.

But understand they provide zero backup power in a grid outage. There are some exceptions to this but they are not common, examples are Enphase's promised battery-less backup and Fronius PV backup point (which is not available in the US) - but these operate with very limited capacity/capability.

2. Grid-tied Hybrid PV + battery

As per #1 above excepting these are hybrid systems operating with batteries. Such systems usually (but not always) have the capability to continue to operate when grid power is lost, so they need an approved method of completely isolating from the grid should there be a grid outage. Under no circumstances can they be allowed to energise grid power lines if the grid power is out.

There are multiple solutions like this. It is the most flexible option for a home since under normal operation they operate in parallel with the grid so no concern with supply capacity to meet load demands while they can continue to operate should the grid power supply be cut (but keep in mind the power supply is then limited to what the inverter/battery/PV can supply). Downside is they can be very costly and of course the local regulatory environment can make life hard/expensive.

The can work with or without solar PV, the idea being to charge the battery when power is cheap (be it from solar PV or during off-peak grid tariff periods) and discharge it to power the home when grid power is expensive. How financially sensible this is will depend on the tariffs in your region and the costs of installing the system.

Here in Australia grid-tied PV is a no brainer because install costs are low (and is why 1/3rd of all homes already have such a system) and they will easily cover their cost within a handful of years. But a hybrid system with battery (or even an AC coupled battery add on like a Tesla Powerwall) is generally a dud deal because batteries approved for grid connection are so damned expensive here. There is no DIY option for grid-tied anything here. The equations for each however vary greatly depending on where you are located.

3. Off-grid with grid support:

This is an off-grid inverter which can accept power input from the grid but it does not synchronise with nor operate in parallel with the grid. It has no capacity to export to the grid.

Most will require a battery to operate, and even the ones which can operate without one, really should still have some battery.

Most of these inverter types will offer the feature to pass grid power straight through to loads and some can blend the grid and PV so as to reduce the amount of energy required from the grid. If grid power is lost they will auto cut over to run from the battery and PV (if available). Like a big UPS as mentioned already.

They can also be set up to run primarily off-grid from PV and battery and treat the grid like a backup, e.g. when battery state of charge gets low and/or there is insufficient PV output to power the home and charge the battery.

The primary limitation is the loads you can support at any one time are limited to the output capacity of the inverter. In some cases only selected loads are connected to the inverter's output, while heavy loads may be left to be supplied by the grid only.

Another limitation is if the inverter fails, then you have no power for loads. In this case it is recommended to have a means by which the off-grid inverter can be bypassed and the grid (or an alternative power source) is able to power loads directly.

They are flexible in how they can be used and with their various functional capabilities are a pretty neat option. As a rule of thumb the regulatory requirements are less onerous since you are not connecting a generation source to the grid but of course all the normal electrical regulations/standards apply.

4. Off-grid with no grid support:

Pretty much same as #3 but without any grid power supply at all. PV and battery connected to an inverter supplying loads. Both the loads and the inverter are entirely independent of the grid and can only support loads up to the rated capacity of the inverter and battery. It is often desirable to have an alternative source of power should it be needed (e.g. a generator), typically used to keep batteries charged if solar PV cannot.

Where I am there is zero chance of grid-tied DIY unless I am working alongside a licensed electrician who also has their solar installation certification. It's a closed shop. So while that kinda sucks, at least professionally installed grid-tied PV installation here are cheap. However grid-tied battery systems are not cheap, they stupid expensive.

5. A Combination
Naturally you can have a combination of more than one of the above. Pick and choose which is suitable for your needs, capabilities, budget and local conditions.

I have both #1, a grid-tied PV system as well as #3, an off grid PV + battery system with grid support. The latter runs most of the general power supply to our two homes and shed, while heavy loads are supplied by the grid only. On weekends my utility provides a 2-hour free electricity period (noon to 2PM), so I will be ramping up the supplemental grid charging of my off-grid system battery, as well as charging up the EV. I was going to also switch the water heater onto full power but it has already finished heating from PV.

Note: Some small edits made for clarity.

 

[timselectric]

That didn’t occur to me. I don’t recall how I found his build thread last year, but it probably was on one of the rare times I was on a computer……

Or possibly happened upon it in "show and tell".

 

[MajicDiver]

It tells them that it's both. A grid-tied inverter with battery backup.

So, Is the backup output separate from grid tied output? Does it pass the grid thru it to loads or does it sync in parrell with the grid? It goes on and on and on….

 

[Ampster]

the various combinations and variations that fit the definition make the term useless in describing anything specific. Telling someone an inverter is a hybrid tells them nothing about the inverter.

I do not think the term hybrid is intended to describe anything specific. All it tells us is that, as @timselectric said, it is a combination of off-grid and grid tie. One needs to read the specs to to understand the functionality and probably the manual to understand to programming options. I went from and Outback Skybox to a SolArk based on what I read here and what I learned from downloading and reading the manual. The biggest differences among inverters is their functionality. In addition the functionality continues to evolve. My first Radian did not even have AC coupling functionality.

 

[timselectric]

So, Is the backup output separate from grid tied output? Does it pass the grid thru it to loads or does it sync in parrell with the grid? It goes on and on and on….

Usually the answer is always yes.
Because it does it all.

 

[Ampster]

So, Is the backup output separate from grid tied output?

It depends on which output you are talking about. The output of a hybrid is typically to a critical loads panel. When it is exporting in grid tied mode, that output is to the main service panel. A grid tied inverter typically sends its output to the main service panel but could be wired to a sub panel.

Does it pass the grid thru it to loads or does it sync in parrell with the grid?

To me that is the same thing. It has to sync to the grid because you cannot have two different AC frequencies in a home. Depending on whether it is importing then the grid passes through and mixes with the inverter output. When exporting the loads are covered first and then the excess is exported.

 

[MajicDiver]

To me that is the same thing. It has to sync to the grid because you cannot have two different AC frequencies in a home.

Nope, it very different. One difference, if it passes thru, the inverter must be capable of passing the entire house load. If it fails, house loses power.

If it’s what I’m calling parallel, house remains powered regardless of what happens to inverter.

Of course there are virtually endless variations on this little piece of functionality.

 

[timselectric]

One difference, if it passes thru, the inverter must be capable of passing the entire house load. If it fails, house loses power.

Not necessarily. It just has to be capable of passing the loads connected.
If it's large enough, this could be the entire house. But that's just a difference of size, not functionality.

But it doesn't change what category it falls into.

In the simplest form.
Grid-tied can export.
Off grid can stand alone.
Hybrid can do both.

 

[MajicDiver]

It just has to be capable of passing the loads connected.

Of course

 

[MajicDiver]

Hybrid can do both.

I think we are agreeing that if someone tell you they have a hybrid you still no nothing of use about what they have

 

[Ampster]

Nope, it very different. One difference, if it passes thru, the inverter must be capable of passing the entire house load. If it fails, house loses power.

I disagree. The size of the inverter main breaker determines whether the entire house load can be serviced by the grid. I do not know all the variations of main breaker sizes versus inverter capacity but you have to dive into the specs to see what they are. I know for a fact that some hybrids can pass more power than the inverter can produce. We are splitting hairs here. Loads do not pass through an inverter. Power passes through and inverter to service loads.

What is your use case? What inverter are you using and does it fit your needs?

 

[timselectric]

I think we are agreeing that if someone tell you they have a hybrid you still no nothing of use about what they have

Not at all.
If someone has a hybrid. They can export to the grid and/or run on battery without the grid.

 

[MajicDiver]

I know for a fact that some hybrids can pass more power than the inverter can produce.

Yes, but it still must be able to pass the load thru it.

 

[MajicDiver]

What is your use case? What inverter are you using and does it fit your needs?

Was grid tied without permission from mid December, 2021 to 21-July-2023. First with one inverter in parallel with grid and zero export, then two, then when enough battery, cut the cord.

 

[Ampster]

Yes, but it still must be able to pass the load thru it.

That is where things are getting lost in translation. I see power passing through the inverter to service the loads. Essentially the loads pull the current and in that situation it only goes one way. That capacity may be higher than the capacity of the inverter to export or service loads. If the inverter cannot service the loads the grid covers the difference and some hybrids allow you to set parameters of grid versus inverter support for loads.

 

[MajicDiver]

f the inverter cannot service the loads the grid covers the difference and some hybrids allow you to set parameters of grid versus inverter support for loads.

I’m assuming if your inverter fails, your loads lose power?

With mine, when grid tied it didn’t matter if inverter was alive or not, house stayed up. And I didn’t have to worry about limiting the connected loads to whatever the inverter could power or pass thru.

 

[MajicDiver]

And, one reason to carry on the back and forth is to illustrate how many different ways it can be done if anyone else is learning from this

 

[Ampster]

I’m assuming if your inverter fails, your loads lose power?

No, the grid passes through to the loads unless the grid input breaker opens because the loads were greater than the breaker size. My Outback Skybox functioned differently and I had to wire a manual bypass just to take the inverter portion offline. To be clear, the hybrid box is more than just an inverter, it is a transfer switch, a charge controller, a battery charger and an inverter.

 

[MajicDiver]

If someone has a hybrid. They can export to the grid and/or run on battery without the grid.

And everyone that sells the inverters I’m using calls them gridtied, but of course they are hybrid by that definition. Edit: Well, not everybody- it appears there are exceptions.

 

[Ampster]

And I didn’t have to worry about limiting the connected loads to whatever the inverter could power or pass thru.

I believe there was some limit unless you were using an external transfer switch. Even a transfer switch has a current limit.

 

[Ampster]

And everyone that sells the inverters I’m using calls them gridtied, but of course they are hybrid by that definition.

Marketing talk is just that. As mentioned a hybrid is both grid tied and off grid capable. All hybrids by definition are capable of being grid tied, but not all grid tied inverters are hybrids. If this conversation continues any longer I will be having dreams about splitting hairs. Good night.

 

[timselectric]

And everyone that sells the inverters I’m using calls them gridtied, but of course they are hybrid by that definition.

Marketing can be confusing.
You could complain to them. But I don't think they care. They will say whatever they think will produce the most sales.

 

[dougbert]

I have the XW Pro hybrid inverter, but I run my system in off grid operation, with the grid breaker in OFF position. I have the grid but want to live without it and am growing my system to be able to do that in the winter.
April to Oct I am 100% running on solar photons, including the electric range
Winter months I need backup power, automatically from the grid when the battery gets low with a chargeverter or manually if needed by generator

I do not want nor need or desire Netmetering
I do not like to do grid pass through, rather I live on the battery
To charge the battery I use Chargeverters powered by the grid or by a generator
I use my inverter strictly as an inverter and not as a charger. I have it wired to do so, but my policy is not to do that

My build in linked in my signature as MY BUILD THREAD as well
In post #1 is my 1 line schematic of the system plus fairly current photos

 

[jdufford]

LOL, I keep clicking on this bold text, nothing happens.

I was able to click on it from a desktop computer