What defines a grid-tied vs off-grid system?

[sowbug]

I'm designing a PV/ESS system for my home in California. I expect to hire Greenlancer for the plan sets I'll need for the county permit. But I'd like to avoid working with PG&E. On this forum I probably don't have to justify that desire, but my specific reason is that I already have a NEM 2.0 interconnect application for a separate PV system that is mired in red tape (details here), and I'd like to let that sleeping dog lie as long as possible. I especially don't want System #2's PTO to get stuck in PG&E's queue behind System #1. Thus I'd like to design a system that doesn't interconnect, in the PG&E sense of the term.

My cocktail-napkin sketch is this:

1. New subpanel.
2. PV on the roof (with Tigo optimizers/RSD etc. to comply with 2017 NEC 690.12).
3. EG4 batteries.
4. EG4 18kPV, configured for zero export.
5. Inverter charges the batteries from the PV and supplies the subpanel (assume I add or move home circuits to the sub and that it's properly grounded).

At this point I'm pretty sure even PG&E's strictest bureaucrats aren't interested in this system. It has no connection to the grid at all. But then I can go in one of two directions:

• Option A: add a male plug to the inverter's GEN input, stick the plug into the nearest dryer plug in my garage, and configure the inverter to draw a safe current when needed.
• Option B: connect the inverter's GRID input to a new breaker in my main panel.

If I understand them correctly, Option A differs from Option B in that Option A can't backfeed, but Option B could if it were misconfigured (mistakenly not zero export).

I want to do Option B, because Option A is hacky and underpowered, and I assume it's not to code. But on an SLD, Option B looks exactly like something I'd expect to require PG&E PTO.

Is a software configuration enough to distinguish a grid-tied system from an off-grid one for PG&E PTO purposes? What direction should I give Greenlancer to produce a plan set that my county will approve, but that doesn't describe a system needing PG&E approval? (Feel free to rephrase my questions if I'm asking the wrong ones.)

 

[DIYrich]

"Grid interactive" is better for your purposes than "Grid Tied". All AIO tend to have the ability to USE the Grid. "Grid Interactive" have the ability to Export to the Grid. At that point, the Utility cares. If you are just a "taker" of grid power, they don't have much rights.

The 18kPV can export to the grid, even in "grid zero" mode. So, the utility has a right to care the moment it is connected to the Grid.

If you want a setup that the utility cannot complain about, it would be an EG4 6000xp system you will want to look at. The EG4 6000xp can pass grid power when PV/Battery is insufficient. But, it can never export to the grid.

 

[sowbug]

Thanks, that's helpful. I think you've answered my question -- unfortunately, it's more the capability than the configuration of an inverter that influences whether PG&E would want a say. (It's fair to ask the more practical question how PG&E would find out, but I don't want to get into such a situation to begin with. DIY bureaucracy is not as much fun as DIY home improvement.)

I preferred the 18kPV over the 6000XP for the many reasons that Will highlighted in one of his videos (outdoor rating, slightly lower quiescent power consumption, line balancing, better build quality, longer warranty, etc.). And if the current CPUC regime is ever toppled, I'd obviously appreciate the ability for this second system to participate in NEM. But most important, my locale's quick-approve permit application system lists only EG4's hybrid inverters, not their off-grid ones (which I assume tracks the CEC equipment list). So if I went with a pair of 6000XPs, I'd get kicked into the slow queue, and possibly not get approved at all. But we're going a bit off track from my original question. Thanks again.

 

[k490]

California AHJ's are now requiring all battery inverters to carry the 9540A ESS UL cert even if you have a shack in the desert 100 miles from the nearest power line. That means can't use the 6000xp it's not as of yet CEC and 9540A certified even with the EG4 power pro. 18KPV is approved but have to convince them to allow charging likely they won't allow you to connect the grid input to the utility grid. You could use a chargeverter to assist with charging the battery. Might not even be worth all that just grid tie it and not bother with exporting.

Does the AJH require you to even talk to PG&E to get the inspection approved.

 

[Quattrohead]

Either of your options can feed back to the grid if mis-configured.
Just make it 100% off grid, a solar charger connected to your battery and sub panel.
Get it inspected and then sort out grid charging.
It is totally possible to set the 18k to NEVER feed back but still use the grid for battery charging and load assist.
Here are the settings I used for 8 months.

 

[sowbug]

Just make it 100% off grid, a solar charger connected to your battery and sub panel.
Get it inspected and then sort out grid charging.

That sounds like a pragmatic approach. If the county asks why the heck I'd want to do this, I hope something like EV charging from a NEMA 14-50 off the subpanel is enough to satisfy them (it's also true).

 

[sowbug]

Does the AJH require you to even talk to PG&E to get the inspection approved.

My understanding is PG&E holds PTO until AJH permit finaling. But not the other way around -- my county doesn't appear to invoke PG&E in their process.

 

[k490]

My understanding is PG&E holds PTO until AJH permit finaling. But not the other way around -- my county doesn't appear to invoke PG&E in their process.

If PG&E sees have solar on your roof without a interconnect agreement not much they can do your county approved it as long you don't backfeed.

 

[time2roll]

My understanding is PG&E holds PTO until AJH permit finaling. But not the other way around -- my county doesn't appear to invoke PG&E in their process.

Yes the PTO agreement is only applied for and processed after the installation is approved by your local jurisdiction.
The installer will leave the system off or set to no export until the PTO is approved.

 

[pgrovetom]

I'm designing a PV/ESS system for my home in California. I expect to hire Greenlancer for the plan sets I'll need for the county permit. But I'd like to avoid working with PG&E. On this forum I probably don't have to justify that desire, but my specific reason is that I already have a NEM 2.0 interconnect application for a separate PV system that is mired in red tape (details here), and I'd like to let that sleeping dog lie as long as possible. I especially don't want System #2's PTO to get stuck in PG&E's queue behind System #1. Thus I'd like to design a system that doesn't interconnect, in the PG&E sense of the term.

My cocktail-napkin sketch is this:

1. New subpanel.
2. PV on the roof (with Tigo optimizers/RSD etc. to comply with 2017 NEC 690.12).
3. EG4 batteries.
4. EG4 18kPV, configured for zero export.
5. Inverter charges the batteries from the PV and supplies the subpanel (assume I add or move home circuits to the sub and that it's properly grounded).

At this point I'm pretty sure even PG&E's strictest bureaucrats aren't interested in this system. It has no connection to the grid at all. But then I can go in one of two directions:

• Option A: add a male plug to the inverter's GEN input, stick the plug into the nearest dryer plug in my garage, and configure the inverter to draw a safe current when needed.
• Option B: connect the inverter's GRID input to a new breaker in my main panel.

If I understand them correctly, Option A differs from Option B in that Option A can't backfeed, but Option B could if it were misconfigured (mistakenly not zero export).

I want to do Option B, because Option A is hacky and underpowered, and I assume it's not to code. But on an SLD, Option B looks exactly like something I'd expect to require PG&E PTO.

Is a software configuration enough to distinguish a grid-tied system from an off-grid one for PG&E PTO purposes? What direction should I give Greenlancer to produce a plan set that my county will approve, but that doesn't describe a system needing PG&E approval? (Feel free to rephrase my questions if I'm asking the wrong ones.)

I have a 12+KW NEM 2.0 system I built back in 2008 and upgraded in 2013 but I spoke with PG&E and if I add more than 10% more capacity to my system, I will need a new interconnect agreement and at NEM3.0. I believe anything you do that would ever allow the new power to combine with your old system power, they would probably classify it such that you would lose your NEM2.0. I thought about taking my pool off grid and building a system just for that but it would not have any long weather or cloudy day backup so just wouldn't work well with lots of expensive batteries. If you simply ran a new system into a breaker, it would combine and be classified as grid-tie interactive and PG&E could force you to NEM3.0.

 

[zanydroid]

I have a 12+KW NEM 2.0 system I built back in 2008 and upgraded in 2013 but I spoke with PG&E and if I add more than 10% more capacity to my system, I will need a new interconnect agreement and at NEM3.0. I believe anything you do that would ever allow the new power to combine with your old system power, they would probably classify it such that you would lose your NEM2.0. I thought about taking my pool off grid and building a system just for that but it would not have any long weather or cloudy day backup so just wouldn't work well with lots of expensive batteries. If you simply ran a new system into a breaker, it would combine and be classified as grid-tie interactive and PG&E could force you to NEM3.0.

I'm not sure about that.

Zero-export is allegedly popular among turnkey residential installers in California for NEM2 expansions. I've posted a few times about how people wouldn't stop talking about it on r/solar couple months back. Ask about it there, and I'm sure you'll find someone to talk your ear off.

One popular way to do it, as I'm told, is to do battery-less zero export with GTIs to increase self-consumption during daytime hours. Obviously wasting production, but that waste costs less than using UL9540 batteries to capture more of the production.

 

[altenergy21]

Forgive me if I change the topic too much. You need to hire someone to design you a contactor solution - ABB and others.
Buy a cheap ATS from Amazon (Will covered this in one of his videos) and switch to grid when your batteries are low.
This contactor has an interlock and only grid or solar can feed the house load at one time. Switching is fast - in ms.
Diagram here https://solarsite22.bravesites.com/ (scroll down). Apologies for the poor quality.

A contactor is just a switch but it's a very beefy switch and it acts fast. There are all sort of logics one can design from the basic contactors.
ABB has a YT channel you can watch some of that. I found a bro on YT discussing it and I contacted him, luckily he responded and gave
me the sketch. I gave him $100 or something and then I had to implemented it myself. It worked!

I had to do a lot of reverse engineering and trying to understand the design. I even tried to guess the model of the ABB contactor.
This is the comment that got me going. https://www.amazon.com/gp/customer-...=cm_cr_getr_d_rvw_ttl?ie=UTF8&ASIN=B07F12RDZ2

 

[pgrovetom]

I'm not sure about that.

Zero-export is allegedly popular among turnkey residential installers in California for NEM2 expansions. I've posted a few times about how people wouldn't stop talking about it on r/solar couple months back. Ask about it there, and I'm sure you'll find someone to talk your ear off.

One popular way to do it, as I'm told, is to do battery-less zero export with GTIs to increase self-consumption during daytime hours. Obviously wasting production, but that waste costs less than using UL9540 batteries to capture more of the production.

If the PG&E meter is bidirectional and you add another inverter source anywhere on the AC line, how do you prevent ( in real time cases) pushing extra current out through the meter unless you measure it and throttle the new inverter? Is this actually done using CT transformers that measure the current and throttle the new additional inverter to not push power out across the network interface? I'm just speculating based on your comment but this could be done if PG&E trusted it? This is not something I'm familiar with but PG&E told me twice that if I increase my power by 1KW or 10% above my NEM agreement, I would be bumped to NEM3.0. They did not mention any workaround methods such as the one mentioned. But they were just thinking about the NEM agreement. These were not equipment nor experts but simply people who knew the basic rules. Certainly its theoretically possible to design a system that adds extra home/internal ( inside the meter) power that is throttled so it does not violate the NEM power through the meter.

 

[DIYrich]

I'm thinking if you have NEM1 or NEM2, then adding a grid interactive inverter and setting it to zero export should be ok. If it does export, it will be within the 1kW or 10% limit allowed by NEM1/NEM2.

 

[zanydroid]

If the PG&E meter is bidirectional and you add another inverter source anywhere on the AC line, how do you prevent ( in real time cases) pushing extra current out through the meter unless you measure it and throttle the new inverter? Is this actually done using CT transformers that measure the current and throttle the new additional inverter to not push power out across the network interface? I'm just speculating based on your comment but this could be done if PG&E trusted it?

The new system uses zero export CTs.

This is not something I'm familiar with but PG&E told me twice that if I increase my power by 1KW or 10% above my NEM agreement, I would be bumped to NEM3.0. They did not mention any workaround methods such as the one mentioned. But they were just thinking about the NEM agreement. These were not equipment nor experts but simply people who knew the basic rules.

Talking to the wrong people. You need to talk to the installers on r/solar, they are more useful than PG&E customer support. The CALSSA and some consultants literally have full time staff figuring out how to game the rules.