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

[jdufford]

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.

 

[wpns]

Since you are on grid, you want a grid-tie inverter. Since you do not want to sell any power to the power company, you want a zero export function, which puts current transformers between your meter and your main panel.

 

[1201]

Off grid means in our world means there is no parallel connection to the grid. The inverter can pull from the grid, like any regular appliance but cannot sell to the grid. The inverter must be capable of powering all the loads attached to it. It cannot support any loads not connected to it.

Grid tie is an inverter that is connected in parallel with the grid and pushes all its production into the grid. You need an interconnection agreement with the utility. The inverter does not need to be able to power all the loads because the grid will handle the difference. It supports all house loads


Zero export comes into play when someone wants the benefits of grid tie: supporting all loads, no concern about sizing, but does not want to get permission from the power company. They want to be connected to the grid but not export to the grid so that the utility does not know they are connected.

Zero export will still export in some cases and the utility might still know.

If you want to do it right without an agreement the only option is an off grid inverter attached to a separate loads panel.may not be what you want to hear but it's the right answer

 

[Mattb4]

If you go the route of grid parallel (grid tie, hybrid grid tie and Zero export units are grid parallel) you will likely need an interconnect agreement with your utility. They are on the look for any amount of back feed and can spot it with the smart meters these days. Alternate power source, such as when using a gas generator or solar inverter, must use either a transfer switch before main panel or breaker interlock kit to prevent inadvertent parallel with grid. Some folks use a critical load panel as another route to accomplish this.

Off grid AIO's can be thought of like a UPS (Uninterruptible Power supply) that can be set to choose either grid or PV/battery as the preferred power with fallback to the other source upon loss or setpoints.

Nothing wrong with smarting small but very difficult/expensive if you go the grid tie route.

 

[1201]

.

Nothing wrong with smarting small but very difficult/expensive if you go the grid tie route.

Im sure the grid tie route is FAR cheaper than going off grid. Far cheaper.

 

[jdufford]

Off grid means in our world means there is no parallel connection to the grid. The inverter can pull from the grid, like any regular appliance but cannot sell to the grid. The inverter must be capable of powering all the loads attached to it. It cannot support any loads not connected to it.

Grid tie is an inverter that is connected in parallel with the grid and pushes all its production into the grid. You need an interconnection agreement with the utility. The inverter does not need to be able to power all the loads because the grid will handle the difference. It supports all house loads


Zero export comes into play when someone wants the benefits of grid tie: supporting all loads, no concern about sizing, but does not want to get permission from the power company. They want to be connected to the grid but not export to the grid so that the utility does not know they are connected.

Zero export will still export in some cases and the utility might still know.

If you want to do it right without an agreement the only option is an off grid inverter attached to a separate loads panel.may not be what you want to hear but it's the right answer

Thanks for your response. I don’t mind to hear it, ultimately I want to make the decision on what I end up doing with appropriate understanding of what I’m doing.

Do I understand this right- If I have a separate loads panel, I can still use the grid to power those loads when there’s no power from solar, in a batteryless situation?

 

[1201]

Thanks for your response. I don’t mind to hear it, ultimately I want to make the decision on what I end up doing with appropriate understanding of what I’m doing.

For sure

Do I understand this right- If I have a separate loads panel, I can still use the grid to power those loads when there’s no power from solar, in a batteryless situation?

It's possible with a limited number of inverters. Most off grid inverters are battery inverters first. They need a battery. But a battery, even a small one is always recommended for off grid inverters, even if they can run batteryless

 

[Mattb4]

Im sure the grid tie route is FAR cheaper than going off grid. Far cheaper.

Not in my neck of the woods.

 

[1201]

Not in my neck of the woods.

What makes grid tie more expensive, in your neck of the woods

 

[Mattb4]

What makes grid tie more expensive, in your neck of the woods

Getting all the permission to interconnect. Paying an Licensed electrician to install the upload meters and all the disconnect components (which must be UL listed) Paying for insurance required by utility to have the interconnect. Though I am lucky enough not to have to involve a local permit process.

Much cheaper to simply buy what I want and install it.

 

[1201]

Getting all the permission to interconnect. Paying an Licensed electrician to install the upload meters and all the disconnect components (which must be UL listed) Paying for insurance required by utility to have the interconnect. Though I am lucky enough not to have to involve a local permit process.

Much cheaper to simply buy what I want and install it.

Ok. I see that. In my case it was far cheaper to go grid tie so I guess it depends on the poco and where you are.

I sent my poco an sld, installed a disconnect by the meter and they came and turned it on. They even told me they didn't require rooftop rapid shutdown.

 

[Lt.Dan]

Ok. I see that. In my case it was far cheaper to go grid tie so I guess it depends on the poco and where you are.

I sent my poco an sld, installed a disconnect by the meter and they came and turned it on. They even told me they didn't require rooftop rapid shutdown.

I think it definitely depends on your PoCo, as well as where you are at, and cost of solar installs.

I even live in Cali, and $30-60k solar installs are the norm. Its absolutely bonkers.

Even $30k can get you a very nice off-grid setup with batteries.

 

[1201]

I think it definitely depends on your PoCo, as well as where you are at, and cost of solar installs.

I even live in Cali, and $30-60k solar installs are the norm. Its absolutely bonkers.

Even $30k can get you a very nice off-grid setup with batteries.

That's comparing professionally installed to diy.

 

[Lt.Dan]

That's comparing professionally installed to diy.

Yes, that is true. My comparison is a bit applies-to-oranges.

 

[jdufford]

For sure

It's possible with a limited number of inverters. Most off grid inverters are battery inverters first. They need a battery. But a battery, even a small one is always recommended for off grid inverters, even if they can run batteryless

Am I understanding correctly- when you say the inverter has to be capable of powering all the loads connected to it, simply we're talking about the wattage capability of the inverter, if everything that's connected were turned on and being used, it would not exceed the stated wattage capacity of the inverter?

It's recommended to have a battery, even if it's small, to be in the system. Even if I don't have enough solar panels to feed my loads completely and keep the battery charged. The grid can help keep my battery charged. It just should be there.

 

[1201]

Am I understanding correctly- when you say the inverter has to be capable of powering all the loads connected to it, simply we're talking about the wattage capability of the inverter, if everything that's connected were turned on and being used, it would not exceed the stated wattage capacity of the inverter?

It has to be able to not only handle everything being on at the same time, it also must be able to handle any surge loads.

It's recommended to have a battery, even if it's small, to be in the system. Even if I don't have enough solar panels to feed my loads completely and keep the battery charged. The grid can help keep my battery charged. It just should be there.

Inverters that can mix grid and solar at same time are expensive. With the affordable batteryless inverters if you don't have enough pv to power the loads they will switch completely to grid, or shut down.

 

[millsan1]

I think it definitely depends on your PoCo, as well as where you are at, and cost of solar installs.

I even live in Cali, and $30-60k solar installs are the norm. Its absolutely bonkers.

Even $30k can get you a very nice off-grid setup with batteries.

For what I did for around $60K, I had installed quoting well over $120K. I am happy to pay for experience and expertise, and ease, but not 100%

 

[OffGridInTheCity]

Just to add to the discussion....

I'm 100% off-grid with grid-assist via ATS(s) - e.g. PV (15kw) -> Charge Controllers -> Battery (121kwh) -> Inverters (24,000w). I wire the inverter outputs to ATS(s) where the ATS(s) have inverter input and grid input (with grid as the default) and the output goes to the home circuits.

Effectively, when the solar system has enough battery charge, the inverters turn on and power the 'solar' leg of the ATS(s). This causes the ATSs to switch to 'solar power' to energize the circuits around the home. When the battery runs down and the inverters shut off, the ATSs automatically switch back to grid to energize the circuits around the home

Couple of pros...
1) No chance of backfeeding the grid / no interaction with power company required.
2) My home continues to function whenever I shut off the solar system to work on it / expand it (happy wife = happy life )
3) The ATSs are UL listed and easy to replace the internals.

Couple of cons...
1) ATS switching requires a UPS on sensitive circuits like computers.
2) ATSs are mechanically linked relays and I've had 3 of 5 fail after 4-5 years (~3,000 cycles). I didn't orient them as instructed so that might be part of the issue.
3) Excess PV is lost. This started at 0 but has gradually gone up to maybe 15% in summer due to more PV for winter.

My system is individual components but.....
They make off-grid AIOs these days that include ATSs and UPSs as part of the internals and operate as I've described above. For example, I use an MPP Solar 3048LV in my trailer that is off-grid with ATS and UPS built-in.

Essentially, these units invert off the battery all the time and take PV and grid input to charge the battery as it's inverting which effectively takes care of the UPS issue. This is a little different than my system in that the MPP Solar unit must be operational all the time whereas it's only the ATSs that must be operational 'all the time' in my system.

 

[1201]

@jdufford the best advice I can give is

Don't rush into anything. Solar is rewarding and it's a major commitment, usually. Take the time to fully understand your needs and what solar exactly is, before you make a decision.

Spend a year learning if you have to. That's what I did.

 

[robbob2112]

My quote was $90k for rooftop install without batteries. The installer was rabid about using solar shingles since I needed a new roof as well. So I had him quote it both ways and imagine that they cam out pretty close to the same.

That quote is what brought me here.

I learned that what he was proposing was nearly double the power I needed to run the house. He was depending on the grid banking my power and giving it back at night. Using the grid as a battery here is good since the bank power and only true up once a year. But they started charge peak demand time of $2.50kW... off peak is $0.1039

At any rate I deducted the $30k for the roof and that left $60k. It was basically 20kw of panels plus gt inverter which I figured to be between $15k and $20k for all parts. No racking since it was shingles, all conduit outside the house including the inverter with just a single line to the breaker panel.

No power during outages, nothing at night from it..... glad I gagged at the price and started looking at DIY.