adding batteries to existing system

[brankulo]

currently have 4.4 kw sytem on flat garage roof in Denver area. 1 string, 12 panels, 6 microinverters, runing into combiner through disconnect into my house breker panel.
we have been talking lately about adding battery backup. i would like to keep battery backup related items in the garage.

now as i understand, once the grid is down, my solar system shuts off to prevent feeding power to the grid and electocuting potential workers.
now with batteries, if they keep feeding power to my breaker box even during blackout, what prevents that power going to the grid?

also, i am looking for suggestion on how to add batteries to my system. i have not have much luck online finding something that works with microinverters. any idea as how to retrofit batteries to my existing system? i am attaching one line and roof plan for my system for reference.

if adding to existing sytem proves difficult, i am open to adding 2nd string. i did pre-wire for 2nd string and i have wires for it running from garage roof to combiner panel, they are just not used right now. with new string, i assume it should be easier to add battery backup. i am not set on microinverters so there should be more options? i see a lot of different approaches, and prices for batteries and inverters vary quite a bit. what would be a good value package? i dont really need anythig fancy, we dont get blackouts much, i mostly need it for my computers and animals during winter months. if i was to do 2nd string i would probably go for same size as my 1st string, or smaller, 3-4kw maybe.

any help appreciated

 

[MisterSandals]

now with batteries, if they keep feeding power to my breaker box even during blackout, what prevents that power going to the grid?

The batteries themselves are not feeding power to your breaker box. You will have a grid tied hybrid inverter connected to your breaker box (something needs to convert the DC battery voltage to AC grid voltage. This device should prevent sending current to the grid when the grid is down. Almost all of them operate this way.

 

[brankulo]

hi, yes my bad, i understand there will be inverter to convert battery dc to ac, but even then, the inverter be wired to my breaker box to feed power to the house, right? so my question still is, how will the power from batteries and converted by inverter and feeding my house during blackout through my breaker panel not feed the grid at the same time?
thanks

 

[MisterSandals]

the inverter be wired to my breaker box to feed power to the house, right?

This inverter would need to be between the grid and your house. There would need to be an ATS somewhere, either built into the inverter or stand alone ATS.

 

[brankulo]

ok, so this would be no option since i want to keep the inverter in the garage. so is critical loads subpanel my only option in this case?

 

[MisterSandals]

ok, so this would be no option since i want to keep the inverter in the garage. so is critical loads subpanel my only option in this case?

It seems like it, other than running your main, after the meter, to your garage inverter and then back to your main panel. This sounds like a sub-optimal solution.

Your situation sounds like mine. I have a sub panel in my garage that powers the kitchen and garage (chest freezer). This will be my critical load panel when i get my inverter (waiting for the next generation of inverters, hopefully Schneider, Magnum, Outback...).

 

[brankulo]

i wish my garage sub panel powered kitchen as well but it only powers garage and office. so i would still need to install new critical load sub panel next to main house panel.
can you actually have 2 critical load panels? that way my garage sub panel could become critical load panel as well. i assume it should not be a problem. or is there another way to make use of garage sub panel to minimize wire pulls an keep it simple?

 

[MisterSandals]

I reread from the top. Stepping back a bit, what are YOUR goals for your battery backup?
Are you trying to power a reasonable portion of your house to live semi-normally? Or are you trying to keep the refrigerator and freezer going, and maybe a furnace too? Or??

Currently, my battery backup is an "extension cord ready" battery and inverter for the refrigerator and freezer. Its sounds like your definition is somewhere between powering the whole house and my temporary backup.

 

[brankulo]

i would like to have power to heat, fridge, electirc stove, kitchen outlets, office outlets and maybe living room outlets. plus garage would be nice as well. but i guess i could live with the minimum of heat, fridge, stove and kitchen outlets.
garage and office feed from sub panel located in the garage. rest feeds off of main house panel.

 

[MisterSandals]

i would like to have power to heat, fridge, electirc stove, kitchen outlets, office outlets and maybe living room outlets. plus garage would be nice as well. but i guess i could live with the minimum of heat, fridge, stove and kitchen outlets.

Have you done an energy audit to see how many watt hours each day these will use?
The electric stove is setting off alarms in my head already...

 

[brankulo]

i have not, i only know we roughly use 13kw a day total. i mean i could live without a stove, blackouts here last only few hours, but of course they happen in the worst time possible.
attached is my rough idea on how to do this. i am wandering if there are any smarter ways to do this, maybe using garage panel.

 

[brankulo]

ah, and when i sey stove, i mean its just electric cooktop is all i need. i hav separate owen that i dont really need to have battery backup. if that changes anything

 

[MisterSandals]

i have not, i only know we roughly use 13kw a day total.

Ok, so we're designing a system without knowing what it needs to do. Not the way to get it right the first time nor the cheapest, but its a way.

attached is my rough idea on how to do this.

Is there a reason this needs to be tied into the grid, the garage sub panel, the garage critical loads panel and the house critical loads panels? This seems overly complicated.

This had come a long way from what your original thread title is asking. This is clearly not adding batteries to an existing system. I'd consider a new thread regarding creating critical loads panel(s) with hybrid inverters.

Sorry, i've probably already overstepped my knowledge and experience in this area.

 

[brankulo]

yeah i guess i am juggling too many balls here at once. my initial idea was to add batteries to my existing microinverter system but couldnt find much info so i started looking into 2nd string with hybrid inverter. and i kept thinking grid tied for some reason but no, it does not have to be grid tied at all. how would that simplyfy the system. could you direct me to schematic or one line diagram?
i only find diagrams as the one attached but dont really understand what happens after inverter, where it shows light bulb and says consumer. i still need critical load panel i assume?

 

[ncsolarelectric]

ok, so this would be no option since i want to keep the inverter in the garage. so is critical loads subpanel my only option in this case?

Yes! Back feeding to the grid during an outage is a federal crime that can kill people. Your system must be Engineered to prevent that from happening. Also, the utility company will not allow you to back feed without a proper interconnection application, and a signed-off permit inspection. Thank you for asking before doing!

 

[Calsun]

I lose power frequently where I live and had the option of something like the Tesla lithium power bank or a standy generator that would run off natural gas. The cost was roughly the same with either approach and so I went with the generator. The battery bank would have provided power for two days whereas the generator can run for months (unlike Texas we do not lose our natural gas supply in the winter).

There is a significant fire hazard with lithium power banks which not only catch fire but can release toxic fumes in the process. The only safe place for a power bank is outside the house and isolated from the structure and where toxic fumes cannot get inside the house.

In September a Tesla mega bank caught fire about 6 miles from my house at Moss Landing. It was allowed to burn itself out but the buildings and the highway were shut down for hours.

https://www.msn.com/en-us/travel/news/highway-1-reopens-after-tesla-megapack-fire-in-moss-landing/ar-AA122MUNhttps://www.msn.com/en-us/travel/news/highway-1-reopens-after-tesla-megapack-fire-in-moss-landing/ar-AA122MUN

 

[BillDStrong]

Since your Garage is a subpanel anyway, your could either gets its power directly from the emergency panel, or have a manual switch that switches over to it during an outage? You presumably won't use it that often during an outage, so letting it not be powered most of the time and manually switching during the few times you would doesn't seem much of a hassle. This should give you more flexibility.

So you would just add some breakers that can only be switched on when the main breaker is switched off, assuming your garage has a main breaker.