Off-Grid Home Backup - California

[Hedges]

Anti-islanding prevents export when grid goes down.

Zero-export is good enough for places like Hawaii where they can't handle more distributed PV.
But with load-dump, it can't respond fast enough to prevent a second or so of export, and smart-meters tattle on you. A problem only without a net metering agreement.

Since you have a small net-metering agreement, limited-export setting of an inverter can avoid going over your allowed amount, and likely utility won't notice your additional production. Especially if it only supplies 100% of household consumption, looking like you have GT PV and zero loads. If you export 3.7kW for 8 to 10 hours per day, that obviously exceeds what your originally permitted system was capable of. If you export after the sun goes down, obviously you have a battery which they weren't told about.

I'm not sure, but I think up to 100% of production from your original PV system is allowed to export. I think you are allowed to add a system which supplies loads but doesn't export. Don't know the details but I think it involves "PCS", Power Control System, which is one of the columns in California's CEC listing of equipment.

Adding a battery is allowed for existing NEM 2.0, but must be configured so you only backfeed electrons that came from PV, not electrons you drew from the grid. This can let you save mid-day production to backfeed during peak hours when it is worth about 50% more credit.

 

[Recovering EE]

I'm almost done doing something very similar to what you want.

I'm in So. CA, and have and existing 5kW system with two PowerWalls that were installed in 2016 (PV) and 2018 (PW). It's NEM 2.0. The whole house is backed up by this system. I did this during a major renovation. I've put in a mini-split in since then, so my true-up has gone up to about $900.

Here's one major difference...at that time, I purposefully put about 40% of the house on a 100A sub-panel.

I've installed a 2-pole 100A transfer switch from the Main e-panel to the sub. Off of the transfer switch is a 6000XP with one PowerPro battery (14.3kWh). I'm putting 6.4kW of PV on the roof (3.2kW facing east and 3.2kW west). This system is grid-interactive, i.e. it can charge from the grid, but doesn't export. I'm doing this entirely DIY.

 

[Hedges]

Do you use your powerwalls to time-shift exports?

That is at cross purposes with backup, since it means draining battery between 4:00 and 9:00 PM.
But it earns credits about 150% of what daytime export would, could eliminate the charge at true-up.

 

[mjsfbay]

I'm almost done doing something very similar to what you want.

I'm in So. CA, and have and existing 5kW system with two PowerWalls that were installed in 2016 (PV) and 2018 (PW). It's NEM 2.0. The whole house is backed up by this system. I did this during a major renovation. I've put in a mini-split in since then, so my true-up has gone up to about $900.

Here's one major difference...at that time, I purposefully put about 40% of the house on a 100A sub-panel.

I've installed a 2-pole 100A transfer switch from the Main e-panel to the sub. Off of the transfer switch is a 6000XP with one PowerPro battery (14.3kWh). I'm putting 6.4kW of PV on the roof (3.2kW facing east and 3.2kW west). This system is grid-interactive, i.e. it can charge from the grid, but doesn't export. I'm doing this entirely DIY.

This sounds like quite a project! Congrats on nearly being finished.

Be careful with diy PV jobs that involve mounting on the roof and/or adding panels - my understanding is it can void original installer warranty and technically can knock you out of NEM 2.0.

On another note, I also have a subpanel feeding an ADU with no transfer switch between. I’m curious… what’s the advantage of installing your 6000xp there? Maybe it’s something I should look into.

 

[billvon]

With your recommended configuration- it seems the critical load panel would essentially be reliant on off-grid power. How would you configure the panel to be backed up by grid if batteries are depleted and the sun isn’t out?

By connecting the GRID terminals on the AIO inverter to a breaker output from the main panel. From there you can program the AIO's behavior - i.e. it will fall back to grid power if the batteries get too low.

 

[mjsfbay]

Anti-islanding prevents export when grid goes down.

Zero-export is good enough for places like Hawaii where they can't handle more distributed PV.
But with load-dump, it can't respond fast enough to prevent a second or so of export, and smart-meters tattle on you. A problem only without a net metering agreement.

Since you have a small net-metering agreement, limited-export setting of an inverter can avoid going over your allowed amount, and likely utility won't notice your additional production. Especially if it only supplies 100% of household consumption, looking like you have GT PV and zero loads. If you export 3.7kW for 8 to 10 hours per day, that obviously exceeds what your originally permitted system was capable of. If you export after the sun goes down, obviously you have a battery which they weren't told about.

I'm not sure, but I think up to 100% of production from your original PV system is allowed to export. I think you are allowed to add a system which supplies loads but doesn't export. Don't know the details but I think it involves "PCS", Power Control System, which is one of the columns in California's CEC listing of equipment.

Adding a battery is allowed for existing NEM 2.0, but must be configured so you only backfeed electrons that came from PV, not electrons you drew from the grid. This can let you save mid-day production to backfeed during peak hours when it is worth about 50% more credit.

Thank you for this detail. I suppose, in theory, if I ran all loads through a separate off grid system, the original interconnection would export close to 100% of all PV generated energy. This would at least guarantee a $0 True-Up.

The other big issue I haven’t figured a solution to is building and connecting a solar array from my backyard, through a concrete slab, and into the house.

 

[mjsfbay]

By connecting the GRID terminals on the AIO inverter to a breaker output from the main panel. From there you can program the AIO's behavior - i.e. it will fall back to grid power if the batteries get too low.

Awesome. Thank you!

 

[Hedges]

The other big issue I haven’t figured a solution to is building and connecting a solar array from my backyard, through a concrete slab, and into the house.

There is directional drilling, already mentioned.
Saw through. What gauge? A bit wider than an expansion joint, lay a rigid pipe through, fill over the top.
Route around, like along a fence and cross at the side?
Overhead wire.

 

[DIYrich]

Just for my clarification: moving all circuits to another panel would be a subpanel - but I’d be using it as a main panel, right? Are there any limitations to using a panel downstream from the main panel?

No limitations, other than the size of the wire from the Service Panel (current Main Panel) to the Sub-Panel (new Main Panel).
Could be a benefit. If you have a 100 amp Service Panel, nothing prevents you from putting a 100 amp line between the Service Panel and new Main Panel, and making the new Main Panel a 200 amp panel (served by both Grid and Inverter).

Will it attempt to export energy to the grid in this scenario? Or would it just be utilized for real-time power and/or export to battery storage?

Any power not used would be exported up to the "Export Limit" set on the inverter.

Also, let’s say the input cables from SolarEdge are not long enough to reach the Gen port of new inverter - how would you go about extending them to reach?

Same way you extend any other wire. Add an extension.

This option is enticing…the 6000xp is a lot cheaper and we’ve had very few outages here. Even in this case, the battery storage should kick in.

The problem with the 6000xp is that it has a 50 amp passthrough limit. You would need 2 for a 100 amp panel. At that point, I would go with the original list and get the ability to use solar during an outage.

They wouldn’t be interested in the sharp increase of exported engergy?

You have NEM2. You are going to be exporting more anyway since you will be using less. I know the 15k has the ability to limit exporting to certain amounts during a certain period of time.

 

[SolarFlares]

You have NEM2. You are going to be exporting more anyway since you will be using less. I know the 15k has the ability to limit exporting to certain amounts during a certain period of time.

It also has a global sell limit so you could set the max watts its exporting at a time. If your original agreement was for a solar array of 3.4kw, you could hopefully export 3.4kw as often as possible. Will this potentially get noticed if you are exporting way more kwh per month? That we don't know.

But all these issues with your interconnect agreement makes me lean towards going completely off grid. But its much easier for me to spend your money

 

[hwy17]

There is no legal way to install solar without a permit. Only ways to get away with it.

 

[SolarFlares]

There is no legal way to install solar without a permit. Only ways to get away with it.

It's already installed. Is making modifications to your own equipment but still abiding by the original interconnection agreement run afoul of the SS in california?

 

[hwy17]

It's already installed. Is making modifications to your own equipment but still abiding by the original interconnection agreement run afoul of the SS in california?

Yes. Any modification or addition to the electrical system requires a permit. Not that I agree with it and I don't pull permits, but that's the ground rules.

There are some exceptions for like replacing an outlet but definitely not for anything to do with a solar system.

 

[mjsfbay]

There is directional drilling, already mentioned.
Saw through. What gauge? A bit wider than an expansion joint, lay a rigid pipe through, fill over the top.
Route around, like along a fence and cross at the side?
Overhead wire.

I’ve got to look more into directional boring. But trenching seems to the only other option.

 

[hwy17]

Concrete saw to cut the trench through the patio, then go up the exterior wall and in from there, however you can to the destination.

 

[mjsfbay]

No limitations, other than the size of the wire from the Service Panel (current Main Panel) to the Sub-Panel (new Main Panel).
Could be a benefit. If you have a 100 amp Service Panel, nothing prevents you from putting a 100 amp line between the Service Panel and new Main Panel, and making the new Main Panel a 200 amp panel (served by both Grid and Inverter).




Any power not used would be exported up to the "Export Limit" set on the inverter.





Same way you extend any other wire. Add an extension.




The problem with the 6000xp is that it has a 50 amp passthrough limit. You would need 2 for a 100 amp panel. At that point, I would go with the original list and get the ability to use solar during an outage.


You have NEM2. You are going to be exporting more anyway since you will be using less. I know the 15k has the ability to limit exporting to certain amounts during a certain period of time.

All understood! Thanks again.

 

[mjsfbay]

Concrete saw to cut the trench through the patio, then go up the exterior wall and in from there, however you can to the destination.

Really have been trying to avoid this inevitability.

Just as I was with the critical load panel…

Now look at me… gonna have to do both. Or, nothing at all.

 

[mjsfbay]

It also has a global sell limit so you could set the max watts its exporting at a time. If your original agreement was for a solar array of 3.4kw, you could hopefully export 3.4kw as often as possible. Will this potentially get noticed if you are exporting way more kwh per month? That we don't know.

But all these issues with your interconnect agreement makes me lean towards going completely off grid. But its much easier for me to spend your money

The steady voice of reason. I hear you!

I don’t think my backyard would be compatible with such a large array, though. My 3.7 kWp covers only 40% of my energy usage. Meaning I’d need something 2-3x the size. I want to be able to use my backyard for living.

However, as DIYrich brought up, I can plug my existing inverter into the Gen port of AIO and use that in conjunction with a new ground mounted array. Still technically all off grid with a single point of interconnection.

That might do the trick, no?

 

[hwy17]

Really have been trying to avoid this inevitability.

Just as I was with the critical load panel…

Now look at me… gonna have to do both. Or, nothing at all.

Me too until I finally did it. Now I bought an extremepower saw on Amazon and I'm ready to swiss cheese the patio for whatever lol. That saw trips 20 amp breakers though so the gas ones from the tool rental are easier if you're just gonna use it once.

 

[Ampster]

I didn't read the entire thread. There is an exception with PG&E for a backup system but it will require a break before make manual transfer switch. As pointed out earlier you will need a building permit or take the risk that you will get red tagged by your Authority Having Jurisdiction.

 

[AlpineJoe]

Also didn't read the whole thread, but the opening post was "I use 175 KWh per month" and "I have a 3.7 KW system" and a "$500 true up"

You should have a zero bill with your system if it's working correctly for as little energy you are using (<6KWh/day)

 

[mjsfbay]

Also didn't read the whole thread, but the opening post was "I use 175 KWh per month" and "I have a 3.7 KW system" and a "$500 true up"

You should have a zero bill with your system if it's working correctly for as little energy you are using (<6KWh/day)

Perhaps, but only about 40% of my energy usage is powered via PV generation according to all the data the utility is sending me.

Peak time of use falls between 1600 and 2100 every day… that might be where they’re getting me.

Also, I gave an average, with outliers removed. My highest month was 477 kWh and lowest -33kWh. But 175kWh on average.

 

[Recovering EE]

Do you use your powerwalls to time-shift exports?

That is at cross purposes with backup, since it means draining battery between 4:00 and 9:00 PM.
But it earns credits about 150% of what daytime export would, could eliminate the charge at true-up.

I'm not on a TOU. Based on SCE tariffs, their fixed costs on TOU were higher than any savings. I remain grandfathered on Residential Tiered, at $.32/kWh.

 

[Recovering EE]

This sounds like quite a project! Congrats on nearly being finished.

Be careful with diy PV jobs that involve mounting on the roof and/or adding panels - my understanding is it can void original installer warranty and technically can knock you out of NEM 2.0.

On another note, I also have a subpanel feeding an ADU with no transfer switch between. I’m curious… what’s the advantage of installing your 6000xp there? Maybe it’s something I should look into.

I have no connection to the existing system. The additional panels are on a separate roof plane from the existing PV array. The inverter is on the same wall in the garage, but it doesn't share any connections or conduits, etc. The roof penetration is separate, too. (BTW, my work is superior to what Solar City/Tesla did, eight years ago.) I'll be forced into NEM 3.0 before the end-of-life of both systems anyway, so the prospect isn't all that daunting. Besides, at 68 years old, I suspect my heirs will be dealing with it.

I used the sub as a convenient place to separate from the main house system. Similar idea to having a critical loads panel. Sounds like the ADU sub would be a good break point, too. I don't know that you could legally meter it and charge according to usage, though. You could perhaps have the rent include electrical power, completely separate from your utility...up to a certain number of kWh per month, then add a tiered surcharge? The legalities could get dicey. If you didn't have some kind of limit on usage, a tenant could set up a grow house.

 

[mjsfbay]

Also didn't read the whole thread, but the opening post was "I use 175 KWh per month" and "I have a 3.7 KW system" and a "$500 true up"

You should have a zero bill with your system if it's working correctly for as little energy you are using (<6KWh/day)

Gotta admit. If I wasn’t doing business with such a reputable energy utility, in the great state of California, … I’d think I was being scammed.

I tapped in to review my SolarEdge energy production and it looks like you’re right on point. It seems there should be no way I’d owe so much on True-up. (See attachments)

They must be getting me on the TOU surcharge…. Which means, theoretically, I should be able to get my bill to $0 with just an AIO inverter and battery… wouldn’t even need more panels. I could just run off battery storage during peak times and be good to go.

***Edited for follow-up question:

Would configuration just entail (in order):
1) move all circuits from main panel to a subpanel

2) couple with AIO inverter
* (This would be considered AC coupling, right?)
** (This will prevent power outage when battery bank is depleted, right)

3) move solar output from main panel (from original PV array > SolarEdge inverter) to GEN port of AIO
** (This done so solar panels can be utilized during grid outages and also to store excess energy in battery bank.)
Thanks to @DIYrich for this idea.

4) install batteries
*(Havent decided which product or size to go with. Cost is a factor. Any suggestions?)

What am I missing?