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

timselectric said:
Unless you need AC coupling, why would you pay extra for features that you won't use?
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When off grid inverters are charging from generator they also have to pass through generator power to the loads correct? Or can they power loads from generator and battery at the same time?
 
1201 said:
When off grid inverters are charging from generator they also have to pass through generator power to the loads correct? Or can they power loads from generator and battery at the same time?
Click to expand...
There are versions of both that can blend grid and battery. But not very many off grid AIO's have the feature. I think that I read the 6kxp can. But not certain on that.
 
timselectric said:
It's the product type, not the use case.
All three types could be used in various use cases.
In fact I will have all three in my completed system.
My off grid use case.
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My mistake: I misread the title of this thread, it appears to be: Please add to my confusion… 😁

Of course this entire thread is an example of why there is no such thing as an easy answer once you get past some of the basic inverter types. Not everyone wants to do simple grid-tie, or is even able to. I hesitate to try to define what my system is going to be when I get it done, as it’s going to be (at least potentially) a mix-mastering of all of the above.

I’m not entirely certain how much energy it is worth trying to spend on defining the terminology, when everyone “knows” it should be used in different ways.
 
timselectric said:
There are versions of both that can blend grid and battery. But not very many off grid AIO's have the feature. I think that I read the 6kxp can. But not certain on that.
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Ok. I don't have an off grid inverter but the ones I know of couldn't blend battery and generator at the same time.

One thing I like about my hybrid inverter is that it can use battery and generator at the same time.
Many hybrids can supplement a weak generator from battery power.
 
wattmatters said:
That's understandable. Even the industry mixes terminology up.


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.
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Thanks for summarizing it.

I’m still new to solar with only one year into my solar production and I’m still learning.
Hopefully the OP has some basic understanding of options available to him.

I opted for a 4KW grid tied system for a number of reasons:
1- Grid is stable and almost always available.
2- Grid tied simple, and easier to build, design, understand, troubleshoot and re-do when needed.
3- When the goal is to save energy costs, spending more than what would be paid to power company defeats the purpose. Grid tied was the most economical option for me.
4- With California about to adopt NEM 3 at the time of my solar energy research, I had less than 2 months to self educate, decide, design snd submit my applications. So I opted for the simplest system that covers only 100% of my consumption ( I knowingly stayed away from over paneling, and did DIY). Any export is free electricity for the power company paid for by me! I made every effort to minimize that.


I pulled ~50kwh from the grid in Dec. Jan. and Feb., each. And exported ~100KWH to the grid the rest of the year! I will find a way for that extra power to not export it to the grid! Probably will be running my hot tub more often!

Bottom line, even a small sized system can cover most, if not 100%, of electricity cost all year round.

My system will pay off in less than three years now per my current consumption theme.
 
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jdufford said:
I've been watching a ton of videos on solar. 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. 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.

Is it an "off grid" inverter I need? I want "zero export" (another term I keep seeing). I understand grid-tied can feed back to the grid (not what I'm looking for). I do not want to get permits nor a net metering agreement. But I want to hook into my breaker box to offset my home's consumption. I'm seeing these cheap Chinese inverters that say "grid tie inverter with limiter." The limiter is keeping anything from back feeding. Is that the same as "off grid"? Is off grid the same as zero export? Or, is "off grid" with my loads on a breaker box only connected to my solar inverter with no grid availability. And I don't think that's it, but I'm having a hard time putting this all together.

And if an "off grid" inverter is indeed what I'm looking for.....if there are open spots in my breaker panel, is there a need for a sub panel? I see people making sub panels with loads they want their inverter to run. What's the rationale for that versus just hooking it into the main? Thanks a lot.
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Depends on budget, and the inverter type you choose. The absolute simplest and most cost effective is a generator with a manual transfer switch on the main panel.

For a small off grid solar inverter with a few panels, you can treat it like a generator, but I would just use a seperate "critical loads panel" to start off.

No matter what you do, If you dont know electric code, please do get an electrician to help you. Safety first!

Based on a lot of the expertise on this forum, it's probably best to just bite the bullet and get yourself a quality grid tie string inverter like an SMA or Schnieder or Victron.

You should also watch a lot of Will's Youtube channel(He created and funds this forum).
 
This is why terminology is important. If by off grid system, you mean a system that can pull power off the grid and can also push power back on the grid sometimes, then you can certainly see how you get here from there. However, this whole thread is proof yet again that terminology is not worth fighting about.
 
wpns said:
This is why terminology is important. If by off grid system, you mean a system that can pull power off the grid and can also push power back on the grid sometimes, then you can certainly see how you get here from there. However, this whole thread is proof yet again that terminology is not worth fighting about.
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In my case it was a typo.
 
wpns said:
What do you call the solar setup with no grid connection (ie. cabin in the woods)?
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Lonely

wpns said:
So now we add ‘pure off grid’. Clear as mud!
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I already included that:
4. Off-grid with no grid support
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Confusion on meaning of Off Grid vs Grid-tie vs Zero Export

LOL, I keep clicking on this bold text, nothing happens.
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1201 said:
When off grid inverters are charging from generator they also have to pass through generator power to the loads correct? Or can they power loads from generator and battery at the same time?
Click to expand...
Many off-grid AIOs won't be able to blend an AC input source (be it grid or generator) with a battery source to power loads. A few can, so understanding what is required and the specifications of the specific inverters under consideration matters.

I think this is a key difference between a hybrid and non-hybrid inverter (aside from being DC coupled to a battery). The ability to simultaneously blend any or all input sources (PV, battery and AC input) to supply loads = hybrid.

It's not helped when some features are not well documented.

For instance I did not know (as it was not documented) that when my off-grid inverter is in SBU mode it is capable of blending grid and PV inputs to supply loads once the battery is full. It was a nice surprise to see it do that on sunny afternoons. My previous AIO inverter did not do this even though the documentation on how it operated was the same.

However I did know that the battery and AC input (Grid) cannot be blended to supply loads. As such it is not a hybrid inverter.

When I go back through the user manual, it makes me want to experiment a little with operating modes I don't currently use to discover how they actually behave, in case there is a chance of other undocumented nice surprises I can use to further optimise system operation.

Sanwizard said:
Based on a lot of the expertise on this forum, it's probably best to just bite the bullet and get yourself a quality grid tie string inverter like an SMA or Schnieder or Victron.
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Victron are not certified for grid-tied operation in many places, so check local regulations/requirements before spending any money.
 
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