Isolate solar from grid

[oldguynewsolar]

I posted this on reddit and didn't get any feedback yet, so I joined and am copy and pasting here. Before I paste it, I'll add some additional details. I learned a lot from lurking on here. I'm going to get an estimate for a grid tied solar system in NY. Most likely the maximum 25kw system allowed, and we have 1:1 net metering. If the estimate is too much, I want to make my own estimate to compare for a diy system. If I go this route, I do not want to be grid tied, I do not want to deal with the power company. However, I do want to be able to charge my batteries from the grid during the couple of months in the winter when production is low. I've read some threads on here, and from what I understand, the only way to do that is "double conversion." I'm trying to avoid this:

Thread 'Utility company visited me for exporting from my solar Off-grid growatt LVM-ES SPF 3000TL'

Jun 3, 2024

I received a visit from my utility company today asking me to disconnect my solar panels system. I told him it was impossible because my system was not designed to export back to grid, it just help charge battery and support for my loads, because my system is off-grid. He told me my smart meter was giving an error, he was courteous indicating that this is just a request that but because I don't have a contract agreement with them they will lock my meter until I disconnect. They don't want to get that way because right now is extremely hot here in Texas, but they will if I don't comply...

• vallesj
• Replies: 256
• Forum: DIY Solar General Discussion

• 

So here is my copy/paste from reddit:

Isolate solar from grid​

Some of you may have noticed that I made a few posts recently. I've been doing a lot of reading to prepare for getting an estimate for a solar system with 1:1 net metering. If the estimate is astronomical, I'd like to make my own estimate for a diy system that can live alongside the grid. Going completely off grid diy would most likely be more expensive than having something installed for me. I'm pretty comfortable with electric work (I used to work construction.) I'm kind of figuring out solar...

So the problem that I see people run into is their system back feeding small amounts to the grid. I have a new smart meter, so I can't have that if I don't want to actually be grid tied. To be clear, I would like to avoid actually being grid tied and dealing with the power company. I would like to have a 30kwh to 60kwh battery bank, with the capability to charge the bank from the grid in the couple of winter months when solar production is low.

So from doing a lot of reading, the solution seems to be... Install a second panel next to my main panel, and move everything over to it. The second panel would be fed by the inverters, which get their power ONLY from the battery bank. The main panel would only have one breaker on it, which would feed an eg4 chargeverter. The chargeverter would be able to charge the battery bank from the grid just enough to make it through the night until the solar array starts charging the batteries in the morning. I expect this to happen mostly in Dec and Jan (I'm in the north east.)

My questions are:

1. Will this work without having to deal with the power company, with zero actual export? I need to read more about the chargeverter and how it works, but this is my understanding so far.
2. Again, I need to read more about the chargverter but... Can it be setup to start charging the battery bank when it gets below a certain state of charge? And then stop charging once the solar panels start charging? I also read on a forum that it can be setup to charge at a similar rate that your house is pulling from the batteries, so that you don't top them off overnight before the solar panels can charge them. If anyone has a link to some reading about setting up a chargeverter like this with a zero export setup, that would be awesome.

Thanks for the help, this has been a lot for me to digest. I'd like to have a plan ready when spring arrives and the ground is thawed.

I am using an EG4 12000XP exactly as you describe. Currently 10.8kW solar and 48kWh batteries. The inverter has a 100A passthrough and is more than capable of handling "grid" charging although with the inefficiencies you have recognized already. I run the inverter full time using the various timer functions to control when and how charging takes place. "Make hay when the sun shines" is the motto to follow. Also found a Free Nights plan and this makes charging with grid painless now. I had an isolation switch / breaker setup in a panel next to my meter and this is where the grid passthrough is routed so that the inverter power can be shut off as it runs with a tap. 50amp breaker installed in the main panel to run my whole house including 5 ton a/c unit. When the power goes off, we never even notice. Have an EG4 Chgargeverter connected to my genny to charge batteries during prolonged power outages if the solar doesn't fully charge the batteries. No back feed issues whatsoever and still have grid power when and if needed.

 

[billvon]

No guarantee that it works. And why people are doing the double conversion.

If the grid is only connected when they need it (i.e. the battery is close to zero and they have set it to charge) and disconnect it before they get to 100% - it will never export. Accidental export happens when the load changes abruptly AND the remaining load is insufficient to pull any load from the grid. Then when the inverter cannot respond quickly enough, you get some small amount of export. If your loads are far higher than generation (i.e. full rate charging of the battery) that won't happen.

 

[timselectric]

If the grid is only connected when they need it (i.e. the battery is close to zero and they have set it to charge) and disconnect it before they get to 100% - it will never export. Accidental export happens when the load changes abruptly AND the remaining load is insufficient to pull any load from the grid. Then when the inverter cannot respond quickly enough, you get some small amount of export. If your loads are far higher than generation (i.e. full rate charging of the battery) that won't happen.

True, but why risk it? You have to remember to turn off the grid input , before you get to full.
I can't recommend a hybrid AIO without getting an agreement with the utility company. If they want to get an agreement, then that's fine.

 

[HarryN]

"Better isolation" - nope.

Inverter/chargers like the Samlex EVO series cannot feed anything back to the grid. Unless you have made an error in your wiring and have a "downstream" connection back. If you make such a mistake and the EVO sees AC on its output, it will refuse to start until you clear the problem.

We are talking about two completely different things and approaches, but whatever.

He is talking specifically the case of not wanting to feed the grid, which is perfect for a pure charger.

 

[teal95]

As was said before, aim for covering 90% or so of your consumption. You can't reasonably cover all your use in December and January. You'll need about 3x the panels and 5x the batteries needed to cover the rest of the year.

 

[MegaMike]

Well i just got my estimate and it was crazy. So thank you for helping me plan this out everyone. Since this method let's me seamlessly pull from the grid, I'm going to start with ~15kw of panels (because pallet), (1) eg4 12000xp, and (2) eg4 wall mount batteries. I'll move some circuits over to the new panel, and add more solar, batteries, and a second inverter as I go to keep this debt free. In the end, all circuits will be moved to the new panel except for 1 or 2 breakers for the inverters ac inputs, which means I have one last question:

I just realized I don't know how running power to the ac inputs with (2) 12000xp in parallel works. Either I missed it in the manual, or they skipped over it. I'm assuming you run one circuit to each inverter. I have a 150 amp service. What size circuit would people recommend I run to each one to have access to my full service capacity? I don't really need to, but why not? (2) 70 amp circuits, or just do (2) 100 amp circuits, which I beleive is technically legal?