AC coupled wiring example

[erniehart]

I recently had a solar only system installed and am looking into adding a battery backup to it.

the current system is 39 400w panels using iq8+ micros giving me 11310w going into the normal combiner then going to my main electric panel. the main panel had a 200 amp main breaker but that was derated to 175 to support adding a 60 amp breaker for the panels.

I don't want to break the bank installing batteries, thinking a budget of around 5k usd, and would like to be able to DIY this. also thinking whole home backup would be easiest to to a diy install. FWIW I don't plan on getting permits but would like it do be installed as close to code as possible. aiming for a battery size of around 20kwh, not really worried about grid being down long term, 20kwh should get me about half a day battery only usage. The enphase battery options are way more then I am willing to pay.

What are my options? How would I wire this up?

I think since I have 11kw in AC solar watts I need an inverter that is about the same size. Assuming that is true and I find an inverter that is about that can I just add in another 60 amp breaker for the inverter and hook up the batteries and call it a day or is there anything else I need to add. Will I need something between my meter and main panel to prevent power going out to the grid in the event the grid is down? what could I use there if so. I am in Virginia on Dominion energy if that matters

I have been looking at the growatt inverters such as the MIN 5000TL-XH-US but don't really like that, from what I understand in the data sheet they can only put out 5Kw from the battery, don't think that is enough for whole home backup so would need two but then I think that breaks code cuz I would need two 40 amp breakers.

 

[zanydroid]

I think you neglected to look up battery prices before setting the $5000 budget. An inverter will be about $1000-1500 and batteries are more like 14kWh for $4000.

You would need to get a 12kW inverter/charging capacity for AC coupling in the sense of being able to activate and charge from grid tie inverters when the grid is down. Otherwise there is no way to turn them on. And note IQ8 have terrible track record of AC coupling to non Enphase hardware anyway

It sounds like you do not need this feature which is at present expensive (you said 0.5 day endurance is the target). In that case you can use almost any off grid AIO to charge from grid and operate in UPS mode. These also do not backfeed grid so you don’t need to redo the backfeed bus at calculation on your main.

I would recommend waiting a year for AC coupled batteries and inverter market to stabilize. More features for less price

To prevent backfeeding grid you need either (1) a Microgrid Interconnection Device (MID) between your inverter and the grid (Dcbel, Growatt, Tesla, Enphase all have this, it achieves the disconnect and optionally neutral forming). (2) a hybrid with built in 200A bypass capability, that can then sit between the grid and your house loads, (3) backup loads only on critical loads panel rather than whole house. Basically you need the disconnect and grid/up down sensing magic somewhere.

 

[solar8484]

Budget is way off especially if you are considering the MIN TL-XH-US inverters as they require high voltage batteries.

 

[ncsolarelectric]

I recently had a solar only system installed and am looking into adding a battery backup to it.

the current system is 39 400w panels using iq8+ micros giving me 11310w going into the normal combiner then going to my main electric panel. the main panel had a 200 amp main breaker but that was derated to 175 to support adding a 60 amp breaker for the panels.

I don't want to break the bank installing batteries, thinking a budget of around 5k usd, and would like to be able to DIY this. also thinking whole home backup would be easiest to to a diy install. FWIW I don't plan on getting permits but would like it do be installed as close to code as possible. aiming for a battery size of around 20kwh, not really worried about grid being down long term, 20kwh should get me about half a day battery only usage. The enphase battery options are way more then I am willing to pay.

What are my options? How would I wire this up?

I think since I have 11kw in AC solar watts I need an inverter that is about the same size. Assuming that is true and I find an inverter that is about that can I just add in another 60 amp breaker for the inverter and hook up the batteries and call it a day or is there anything else I need to add. Will I need something between my meter and main panel to prevent power going out to the grid in the event the grid is down? what could I use there if so. I am in Virginia on Dominion energy if that matters

I have been looking at the growatt inverters such as the MIN 5000TL-XH-US but don't really like that, from what I understand in the data sheet they can only put out 5Kw from the battery, don't think that is enough for whole home backup so would need two but then I think that breaks code cuz I would need two 40 amp breakers.

There is quite a bit more to it than that. Here is a diagram to assist you, when doing AC coupling to a microinverter system.

 

[k490]

The only way I could see this working without a fully permitted system like the diagram above is an off-grid inverter connected to batteries then use a generator transfer switch on the circuits you want to use the battery + inverter. The off grid all-in-one inverter would charge the batteries from its AC input from a breaker coming off your main panel which is being powered from the micro-inverters and the grid. This way you would not need to worry about back feeding from the inverter connected to the batteries.

 

[erniehart]

From what I am seeing I don't feel like I am as off on budget as you all are saying, I have seen signature solar has 5kwh batteries for 1k and I have seen some Growatt inverters for around 1.5k that's about 5500 total

anyway I couldn't just do something like what I have in the attached images? Would a transfer switch for a generator system work or is there something better out there.

 

[Hedges]

the current system is 39 400w panels using iq8+ micros giving me 11310w going into the normal combiner then going to my main electric panel. the main panel had a 200 amp main breaker but that was derated to 175 to support adding a 60 amp breaker for the panels.

I've read here people have major problems trying to AC couple to IQ8.
I think Enphase battery is the only option likely to work.

With some other GT PV inverter that is well behaved for AC coupling, you can either rewire to put battery inverter in-line, or use interlocked breakers and have it charge from main panel and backfeed main panel (manual switching to backup.)

 

[k490]

I've read here people have major problems trying to AC couple to IQ8.
I think Enphase battery is the only option likely to work.

With some other GT PV inverter that is well behaved for AC coupling, you can either rewire to put battery inverter in-line, or use interlocked breakers and have it charge from main panel and backfeed main panel (manual switching to backup.)

If he installs another inverter and battery just connects to a 2nd solar breaker back feeds with his inverter/battery he could charge all day, and then back-feed into his main panel using the CT clamps to prevent selling power to the grid. The problem is his battery inverter plus the micro-inverters plus grid power will likely exceed the busbar limits in his service panel can't go more then 120%. Potentially your house pulls everything at once you exceed the 200 or 225 busbar limits melt the thing.

I think if it was me I would just install a pure off-grid inverter and battery use the input from your grid/micro inverters. Connect your loads you want to use this battery / inverter. Buy a decent inverter like a Sol-Ark. I'm going to use a Reliance control transfer switch. Technically could just not use a transfer switch the off-grid inverter will be your transfer switch. This way not having to worry about trying to AC couple or overloading your main panel with too much back feeding power. The downside is have to splice in lot of wires to do this instead of just back feeding to the main panel where everything is already wired

 

[solar8484]

From what I am seeing I don't feel like I am as off on budget as you all are saying, I have seen signature solar has 5kwh batteries for 1k and I have seen some Growatt inverters for around 1.5k that's about 5500 total

If you want accurate feedback then provide the specs and links for the inverter and batteries.

 

[Siamac]

There is quite a bit more to it than that. Here is a diagram to assist you, when doing AC coupling to a microinverter system.

View attachment 183513

Just curious, why didn't you derate the main panel breaker here? What are the requirements for derating?

 

[ncsolarelectric]

Just curious, why didn't you derate the main panel breaker here? What are the requirements for derating?

It can be done either way.