Will this work in an emergency power outage?

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nicobie   1.21 GW

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Will this work in an emergency power outage?

Post by nicobie » Apr 05 2021 3:24pm

Would it be possible in a power outage to manually disconnect from the grid then use a small battery and 220v inverter to power up my solar system's inverters so I can then get emergency power for my house? Would the small inverter hold up to the solar backfeeding it?

My simple mind says it will work, but something is telling me it's too simple of a solution to this common problem.

I'm using Enphase micro inverters with my panels.
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Re: Will this work in an emergency power outage?

Post by spinningmagnets » Apr 06 2021 7:35am

I do believe it's possible. I have purchased two inverters as a backup for my retirement, but I havent tried to hook them up yet. They are both a nominal 48V DC to 120V AC, and the specs say they can take an input up to 60V, so my 14S "52V" ebike packs are 58V when fully charged, and should work fine...in theory.

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Re: Will this work in an emergency power outage?

Post by nicobie » Apr 06 2021 2:45pm

spinningmagnets wrote:
Apr 06 2021 7:35am
I do believe it's possible. I have purchased two inverters as a backup for my retirement, but I havent tried to hook them up yet. They are both a nominal 48V DC to 120V AC, and the specs say they can take an input up to 60V, so my 14S "52V" ebike packs are 58V when fully charged, and should work fine...in theory.
That's what I'm thinking too. I have what's needed to try it out but am too chicken to risk my system. Don't wish to piss off the power company either as I am on a sweet grid tie agreement with them. (city owned power)
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Re: Will this work in an emergency power outage?

Post by Hwy89 » Apr 06 2021 3:25pm

I also think it should work. The grid tied inverter only needs to see the voltage and frequency of the signal power in order to have something to sync to. Just be sure the utility power is disconnected and they will never know what you are up to.
I asked this same question to the Instructor of a solar installation class I was taking ten years ago. I wasn’t able to get him to grasp the concept and his answer was a flat no. I remained unconvinced.

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Re: Will this work in an emergency power outage?

Post by spinningmagnets » Apr 06 2021 3:44pm

Here's my take on power backups. A decade ago, many people were arguing that buying solar panels, an inverter, and a big battery had a poor Return On Investment /ROI. it might save you $50/month, but the system costs $5000, so it would take 100 months to "break even". (8 years?)

For me, it was never about ROI. If the power is out, nobody cares if getting power is expensive. A 2 hour power bump is nothing, but if power is out for 2 weeks, I want a solar panel and inverter (in my closet). so I have that, plus three large ebike batteries of 52V.

I will cut the breaker to the city power, I wont connect my system to the utility.

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Re: Will this work in an emergency power outage?

Post by rowbiker » Apr 04 2022 7:25am

I'm in *exactly* the same position as all of you in this thread, and have the same philosophical approach to solar backup as spinningmagnets. I acquired both an Enphase IQ7+ and an IQ8A (just recently available) for experimenting, but have not had useful results. The IQ8 series of microinverters is *supposed* to be "grid-agnostic", meaning it is designed for use with grid, or without it. When I connected it to a correctly matched solar panel, it went through a sequence of flashing lights of various colors but ended up flashing red at about 1 Hz frequency. There was never a measurable voltage on the 240AC output, to which I had connected a 28W 240VAC light bulb. I have a question about this submitted to Enphase about a week ago but have not heard anything back yet.

There is a youtube video by ES's doctorbass that proves this can be accomplished with earlier (grid-tied) Enphase microinverters, but his solution is NOT simple or straightforward.

I'm at the point where I'm willing to 'smoke' things just to find out what the easiest/simplest/cheapest method is of using microinverters off-grid (or when the grid is down). I'm pretty sure it can be done with the new IQ8 family from Enphase, but I'm not ready to drop $$$$'s into their proprietary switches/controllers/batteries to make it work. My ultimate goal is to charge up my ebike batteries and dump the output of ten 370 watt solar panels into a Tesla Model Y.

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Re: Will this work in an emergency power outage?

Post by fechter » Apr 04 2022 8:26am

If your system has micro inverters, it may be possible to connect the panels together on the DC side and have a separate DC feed going to a separate off-grid inverter. What I don't know is if the micro inverters are isolated. This should be fairly easy to test with an ohmmeter. As long as they are isolated, you can wire the panels in series or series/parallel to get a useful DC feed. The off-grid inverter may need a battery to work well. I have a 3kwh battery made from old Fisker batteries that can run my refrigerator for about 24 hours. If I had solar panels and some sun, the battery would only need to work at night.
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Re: Will this work in an emergency power outage?

Post by rowbiker » Apr 04 2022 3:44pm

fechter wrote:
Apr 04 2022 8:26am
If your system has micro inverters, it may be possible to connect the panels together on the DC side and have a separate DC feed going to a separate off-grid inverter. What I don't know is if the micro inverters are isolated.
So far I've only gotten the two microinverters for testing purposes, so my planned ten panel array is not yet mounted or wired together. Also, I just heard back from Enphase (the company that makes these microinverters) saying that to use the IQ8 series of microinverters in "off-grid" mode (something they call "sunshine backup"), you need to spend multiple thousands of additional dollars acquiring their proprietary equipment to be able to do that. This might make sense for a full-house size installation, but I'm only doing ten panels for a 'side' project. There aren't really any circumstances in which you'd use both microinverters and an alternate direct DC feed to a centralized (string) inverter, so the question of isolation wouldn't really ever come up.

What I'm now likely to do is simply get an 'all-in-one', off-grid capable MPPT controller/charger/inverter of sufficient current capability to handle my panels, and do a direct DC connection in whichever S/P combination that makes sense. Like you, I'll likely add a battery into the system, preferably a 48V type to have some compatibility with my bike batteries. Maybe I should start looking for a crashed Fisker!

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Re: Will this work in an emergency power outage?

Post by liveforphysics » Apr 04 2022 10:11pm

It can work perhaps if you have a good sized inductive load always running, like a big table saw motor or something. You would need to first get that table saw running from a battery powered inverter, like a 12Vdc unit from your car's battery or whatever. Once the inverter is running the saw, try connecting the solar inverters into the active AC circuit. They will only run when they can see an existing stable AC circuit to sink and source current from, and hopefully the big motor running will offer that to spoof them into running as though they are pumping the grid. Its going to rise in AC voltage really quickly if you're not matching the AC loads to the solar output power, and this will cause the inverters to trip if they go above a given threshold. I would call it iffy to work well depending on how loose they set the 'grid tied' operating conditions in the solar inverters firmware. If you do get it to run, load it as much as possible and monitor voltage though the day not to over-voltage your local mini-grid.
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Re: Will this work in an emergency power outage?

Post by rowbiker » Apr 05 2022 7:54am

Wow -- I've read some really well-considered responses, but this one might top them all -- thanks!!

As nicobie (OP) stated at the beginning of t(his) thread, I think this needs to be done in the US 240VAC single "split-phase" world, although I'm not positive about this. The Enphase microinverters are spec'ed to have their AC output on two wires, both 'hot' with 120V sine waves on each, 180 degrees out of phase, to get to the RMS 240VAC. In the event of multiple microinverters, they are simply paralled until they reach a certain theoretical maximum current flow (~ 10-16 microinverters) per array.

As it happens, my wife recently upgraded us to a new table saw, so I have available an older 10" saw motor I have wired for 240VAC. I don't yet have a 240VAC inverter, but would be perfectly happy to add that for educational purposes. I guess I'll have to do the math about current draw of the motor at no-load and match that to the inverter's rating, plus deciding what battery to use it with. This would form the proposed off-grid 'microgrid', to *fool* the microinverters, correct?

If I understand this setup correctly, the major concern would be to not overload the 'starter' inverter via back-feeding it, once the solar panels start pushing electrons through the microinverter -- which will turn on once they detect that the microgrid is up and running. Managing this power flow without blowing up the inverter is where I'm still fuzzy, I guess. My first step probably should be to find a bi-directional wattmeter for 240VAC circuits. BTW, I'm perfectly happy to 'blow shit up' (other than my shop or body) for the purpose of our collective educational advancement!

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nicobie   1.21 GW

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Re: Will this work in an emergency power outage?

Post by nicobie » Apr 05 2022 3:17pm

rowbiker wrote:
Apr 05 2022 7:54am
BTW, I'm perfectly happy to 'blow shit up' (other than my shop or body) for the purpose of our collective educational advancement!
Thanks!

Be sure to let us know how this turns out. :bolt:
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Re: Will this work in an emergency power outage?

Post by rowbiker » Apr 07 2022 9:53am

nicobie wrote:
Apr 05 2022 3:17pm
Be sure to let us know how this turns out. :bolt:
I'm starting to order the actual parts now.

I've also updated my Will so that my surviving heirs will post photos of what's left after I plug everything together. :flame: :D

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Re: Will this work in an emergency power outage?

Post by ynot » May 04 2022 7:23pm

nicobie wrote:
Apr 05 2021 3:24pm
Would it be possible in a power outage to manually disconnect from the grid then use a small battery and 220v inverter to power up my solar system's inverters so I can then get emergency power for my house? Would the small inverter hold up to the solar backfeeding it?

My simple mind says it will work, but something is telling me it's too simple of a solution to this common problem.

I'm using Enphase micro inverters with my panels.
Since you must be using grid tied inverters, would it not be simpler just to cut them out of the house circuit and pass the solar current through them directly to what ever load you want to use?
Just flip the switch when you flip the circuit breaker.

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Re: Will this work in an emergency power outage?

Post by nicobie » May 04 2022 7:32pm

The only switch I control is the main disconnect
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Re: Will this work in an emergency power outage?

Post by ynot » May 06 2022 7:36pm

Since you are not automating the mains disconnect, and have to flip one switch, it seems some folks want complicated rather than simple. You could automate the switch to off grid inverters.
Have to be careful not to back feed the grid, although any competent lineman will ground the wires when working on downed lines.

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Re: Will this work in an emergency power outage?

Post by scrambler » May 06 2022 8:19pm

Grid tied inverters and micro inverters are built to disconnect when the grid is down.
In order for Solar to stay on in an outage, you need a hybrid inverter with a transfer switch and a battery.

The transfer switch will disconnect the grid, and the battery will work with the hybrid inverter to keep solar going.

As for powering the home, you usually have a critical load panel connected to the Hybrid inverter so that when the transfer switch disconnects the grid, the inverter can power the critical load panel using the battery.

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Re: Will this work in an emergency power outage?

Post by nicobie » May 07 2022 1:05pm

I'm curious, by chance do you have a link to a hybrid inverter like you are talking about?
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Re: Will this work in an emergency power outage?

Post by scrambler » May 07 2022 1:24pm

These are solar inverters with Battery management and are normally installed with the Solar system

Most providers of solar equipment have Hybrid models that can work with solar and battery, like Solar Edge, Outback, Goodwe, Fronius, sol ark and many more...

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Re: Will this work in an emergency power outage?

Post by ynot » May 07 2022 3:07pm

scrambler wrote:
May 06 2022 8:19pm
Grid tied inverters and micro inverters are built to disconnect when the grid is down.
In order for Solar to stay on in an outage, you need a hybrid inverter with a transfer switch and a battery.

The transfer switch will disconnect the grid, and the battery will work with the hybrid inverter to keep solar going.

As for powering the home, you usually have a critical load panel connected to the Hybrid inverter so that when the transfer switch disconnects the grid, the inverter can power the critical load panel using the battery.
More elegant description than mine, was not familiar with hybrid inverters. Was kinda sorta hoping that it was a grid tied that would convert to off grid, on disconnect, that would be cool. The Renogy one that I looked at is very pricy you could split out the solar controller from the inverter and save a bit of money.

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Re: Will this work in an emergency power outage?

Post by scrambler » May 08 2022 3:31pm

Just to be clear what I meant by Hybrid inverter are Grid tied Hybrid inverters.
They work with the grid when its up, then isolate themselves from the grid when it goes down, so they can keep working with solar and battery to deliver power.

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Re: Will this work in an emergency power outage?

Post by ynot » May 10 2022 7:20pm

scrambler wrote:
May 08 2022 3:31pm
Just to be clear what I meant by Hybrid inverter are Grid tied Hybrid inverters.
They work with the grid when its up, then isolate themselves from the grid when it goes down, so they can keep working with solar and battery to deliver power.
Perfect and the obvious intelligent way to go.
Do they disconnect from the grid before they switch functions, or do they wait until they are physically switched,
My concern is for the linemen working on downed lines who are trained to ground lines before working on them, but in the heat of the moment..............

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Re: Will this work in an emergency power outage?

Post by scrambler » May 10 2022 7:25pm

It is automatic, as soon as the grid goes downs the built-in transfer switch disconnects the inverter from the grid so no power can be sent to it and endanger anyone.

The critical loads panel connected to the inverter continue to work uninterrupted, fed by the inverter sourcing power from the battery and solar instead of the grid.

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Re: Will this work in an emergency power outage?

Post by ynot » May 12 2022 9:13am

scrambler wrote:
May 10 2022 7:25pm
It is automatic, as soon as the grid goes downs the built-in transfer switch disconnects the inverter from the grid so no power can be sent to it and endanger anyone.

The critical loads panel connected to the inverter continue to work uninterrupted, fed by the inverter sourcing power from the battery and solar instead of the grid.
This is really good information, thank you.
Do you know of any hybrid inverters that will not backfeed the grid.
Our utility charges equally, no matter which way the meter runs.

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Re: Will this work in an emergency power outage?

Post by scrambler » May 12 2022 11:33am

Not familiar with Off Grid Inverter except smaller configuration like the Victron for van and such, but I am sure they exist.

Many modern grid tied inverters have a "No export" operating mode available so you can configure them not to back feed the grid.

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