Adding an "off-grid" inverter to my "on-grid" house system?

[Little-Acorn]

5 years or so ago we got a Solar City system (Later Tesla bought Solar City, so now we're Tesla) for our house. Unfortunately when city power goes off, our solar system also shuts down. I understand the reasons why, don't want a line repairman to get shocked by a house somewhere in the system etc.

But I would like to have our house capable of operating off-grid when city power goes down, during daylight hours at least, obviously. Most straightforward way seems to be to buy a second inverter capable of running off-grid, and a big switch. Purpose of the switch is to (a) disconnect the house from the grid, and (b) then connect the house's solar cells to the new off-grid inverter, which then powers only this house. No power placed on the grid, no danger to technicians working on the city lines etc. Switch set up so that you CAN'T activate the new off-grid inverter unless the house is first disconnected from the grid.

I've heard it can be done with batteries (Tesla Powerwall etc.), but I want to explore the simplest partial-solution first. So that next time city power goes out, we can at least keep the refrigerator running in daylight, the computers and radio, etc.

Anybody else done this?

 

[jasonhc73]

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[Steve_S]

There is a high likelihood that an Inverter with a Battery subsystem could be installed, it all depends on what equipment you have already as to how it can be best accomplished.

If you list what equipment you have and any more info, it would be easier for people to offer up suggestions or ideas. Many have converted their ON-Grid system to include batteries while still pushing to grid. Others have gone off-grid as well with Battery & Genset backup while others have gone Hybrid with using the grid ONLY as backup once they've fully covered themselves with battery storage.

 

[Little-Acorn]

We have nineteen of the Kyocera KU260-6XPA panels on the roof, with a single Delta inverter, # SOLiViA 5.2TL. Apparently a 5200W unit, though the highest I've seen out of it is around 3200W to 3500W. Panels are 31V each under load, 8.4A. Angled 18 degrees off vertical, to the south (lucky us!)

Thanks for the help!

 

[Little-Acorn]

Can anyone suggest an add-on inverter that doesn't need a grid connection, that I can bring in to operate after city power goes down?

 

[Matz]

I don't think an inverter without a battery would work. What if you have a cloud come through? Do you want your devices to go off?
The battery in a solar system balances the power between solar and the requirements of the consumers. It is required to my knowledge.
Maybe checkout solar generators as an alternative. I built one myself after being inspired by Will Prowse on YouTube.

 

[Little-Acorn]

Do you want your devices to go off?

My devices are already off. City power just went down. And my solar system promptly shut down, even though the cells are still on the roof and the sun is still shining. I'm hoping to find a way to run at least some of "my devices", such as the refrigerator before the food spoils, the phone to call for help, a radio or TV to find out what's going on etc. At least while the sun is shining and no clouds are in the way (a common condition in San Diego).

 

[jasonhc73]

Can anyone suggest an add-on inverter that doesn't need a grid connection, that I can bring in to operate after city power goes down?

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[schmism]

You can check out my build. dual 3kw Growatt (6kw 120v) critical loads panel install. When I have enough solar and/or battery everything runs off it. When i run out of either it transitions to grid passthrough without me ever knowing. If the grid goes down and I have battey, it transitions to battery and I never know. Runs my furnace, fridge, lights, etc

 

[newbostonconst]

I would suggest a hybrid inverter. They are more complex to install but will run itself once installed and likely be able to power up your solar panels to charge a battery and supply your house. Your inverter is ( HECO grid selectable) to make your solar be shutdown by the hybrid inverter if you are producing to much solar then you are using and your batteries are charged.

Here is a nice list of hybrid inverters with most of them listed.

Hybrid Inverter | Hybrid Solar Inverter | altE

Hybrid inverters, mostly used in grid-tie solar systems, can provide backup power when the electric grid fails. Call 877-878-4060 to size your system today.

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Just hooking an inverter into your panel and shutting off the main could be done but you would have to be careful on what breakers you switch and in what order....an invertor may also power up your panels but without a place for the power to go you my fry something, so turning off your solar inverter would be the smartest...

 

[Burke]

I am doing this now, hybrid inverter, 14KW LiFePo4 Battery built from Lishen cells. I have a thread going, and numerous other threads of people doing similar things. It has been a really fun project so far.

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[12VoltInstalls]

My devices are already off. City power just went down. And my solar system promptly shut down, even though the cells are still on the roof and the sun is still shining. I'm hoping to find a way to run at least some of "my devices", such as the refrigerator before the food spoils, the phone to call for help, a radio or TV to find out what's going on etc. At least while the sun is shining and no clouds are in the way (a common condition in San Diego).

So basically others have done what you’re trying to do.
While it’s not groundbreaking, you can use your grid-panels to power a battery bank (powerwall if you’re too sexy for your shirt) and auto-switch grid to batteries. The trick is capturing the solar for backup or battery maintenance /before/ it hits the control snd meter circuitry. Then you merely wire it with a transfer switch that isolates your transfer sun-panel from the grid. With NEC compliance.

The other way is similar in use but different in execution: buy your own panels and batteries and run a “solar transfer switch” to operate an independent panel that views the /grid/ as the backup. Sorta like spending money twice though.

So yes it can be done either method. Yes i think you need some batteries. But I think (since you have framed the question like you did) you probably need a licensed electrician to both be safe and effective. BTW the phone is usually not going to be down as the phone lines aren’t powered locally by the grid, they have their own native low-voltage AC (60V?).

 

[soleilaumesa]

Yes, it can be done. I have a partial system consisting of 960 watts of PV on my garage roof. These feed into a Growatt SPF 3000TL LVM mounted on a west wall in the garage. This charges a 3kWh BigBattery which then powers 2 outlets in the garage with only one used for a 24" refrigerator/freezer. This wire then runs trough the wall into the Living room powering a TV, cable box, Roku, modem and WiFi. Everything worked since last November until just now when my PV panels stopped - to be fixed. The Growatt is connected to Utilities and is only used by the Growatt if solar fails.
My only regret is going for the largest panels that would fit and I ended up with 3 panels in parallel, now I think it would be better to do 2S2P for more volts and less Amps.

 

[Hedges]

Simple way to connect either an inverter or generator to your electric panel is buy a $50 interlock (piece of sheetmetal) meant for your exact breaker panel. Put a 30A (or appropriate) breaker in a slot next to the main breaker, and install interlock so only one can be closed at a time. Add a 30A plug feeding that breaker.

That will work with an off-grid inverter, or a grid-backup inverter (with grid input to charge.) If input and output both go to same panel you just have to remember to turn off input when you turn on the output (backfeed breaker) so it doesn't try to power itself.

Fancier way is various inverters wired as UPS, so they pick up protected loads the moment grid goes down.
Nicest setup interacts with your existing GT PV inverters. See what that vendor offers.
Or, install a hybrid and rewire some existing PV panels to it.
Otherwise, I've figured out ways to disconnect and rewire PV panels from a grid-tied inverter to a charge controller for a separate inverter.

BTW the phone is usually not going to be down as the phone lines aren’t powered locally by the grid, they have their own native low-voltage AC (60V?).

What world are you living in? POTS is so last century!

(If you don't have battery backup for your internet box with Voip, when the lights go out the phone does too. ATT offers a UPS with battery for just that purpose.)