Converting main panel to off grid mode?

SunnyDBoy

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Jul 17, 2020
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Hey everyone!

I'm in the process of putting up a DIY 10kw solar array with an 8kw Sol-ark inverter and 20kwh of battery storage. The batteries are primarily for use of peak shaving, and our grid is reliable (99.95%). However, I would love to keep power going in the house during grid downtime and I don't want to have to rewire a lot to get a sub panel operational for critical loads.

Our whole house uses only ~500W and <4.5kw when the AC is on (AC is only on for ~5min at a time, 1-3x/hr on hot days). We have all gas appliances with exception of the dryer (which we wouldn't run during an outage anyway). Our batteries can output 120A @ 48V (5.76kw).

So the question is, if there's an outage is there any way for me to manually convert my main panel to off grid temporarily without having to reroute everything to a sub panel?

My thought is that if I turn off the main breaker to the service, I'm incapable of backfeeding to the grid. I then have a "critical feed" breaker set to go to the main panel, and manually flip that to the on position and my grid tie breaker to the off position. In theory, wouldn't that be telling the inverter that it's time for critical loads mode and the critical loads panel just happens to be my main panel?

If there's a better/more logical/automated way of doing this I'm all ears, thanks!
 
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MichaelK

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My thought is that if I turn off the main breaker to the service, I'm incapable of backfeeding to the grid. I then have a "critical feed" breaker set to go to the main panel, and manually flip that to the on position and my grid tie breaker to the off position. In theory, wouldn't that be telling the inverter that it's time for critical loads mode and the critical loads panel just happens to be my main panel?

If there's a better/more logical/automated way of doing this I'm all ears, thanks!
Flipping off the main breaker and backfeeding power is a really, really bad idea, and may actually be illegal. You don't want to do that. Invariably something will go wrong, and you will electrify a supposedly dead circuit and put someone's life in danger.

The PROPER way to accomplish what you are talking about is to install a transfer switch, which is typically an electromagnetic controller that automatically switches between grid and solar. With a transfer switch in place, your unit can NOT energize a supposidly dead grid circuit, so repair crews working on the line are protected.
 

Woody

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I have this SD-200A Square D Generator Interlock Kit installed on my house panel and assuming you’ve followed the direction, this is a manual transfer switch that physically locks out the main power and allows a back feed of power through a double pull breaker into the house. With the mechanical safety plate enabled, the shore power is selected and the alternative power source locked out. With the mechanical safety plate disabled the alternative power source is select and the shore power physically disconnected/locked out. An operator must physically move the breakers to the on or off position, along with physically moving the metal lock out plate in order transfer the power input sources. I find this manual transfer superior to the automatic transfer if you do not need continuous power. I control the power source selection and when it energizes. As for safety factors, automatic transfer switches have their own issues. As for code compliance, well that all depends upon where you are in the world.
 

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Hedges

I See Electromagnetic Fields!
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Flipping off the main breaker and backfeeding power is a really, really bad idea, and may actually be illegal. You don't want to do that. Invariably something will go wrong, and you will electrify a supposedly dead circuit and put someone's life in danger.

The PROPER way to accomplish what you are talking about is to install a transfer switch, which is typically an electromagnetic controller that automatically switches between grid and solar. With a transfer switch in place, your unit can NOT energize a supposidly dead grid circuit, so repair crews working on the line are protected.

Which is why you do what Schmism and Woody said.
Besides possibly electrocuting the lineman, likely to kill the inverter when power returns.

Pay fifty bucks for a piece of sheetmetal that mount on cover of breaker panel. So long as the cover is in place, it serves as an interlock so either main breaker to grid or backfeed breaker from inverter feeds it, never both.
Find the interlock which fits your exact breaker panel; every brand/model is different.

Do NOT operate those breakers with cover and interlock removed.

"... and my grid tie breaker to the off position"
Yes, that's a good idea so it doesn't mistake itself for the grid.

This is part of my setup, how I power the garage (main breaker) with grid down.
I also have a separate panels for loads always battery-backed. You may want to add that later.
 

SunnyDBoy

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Jul 17, 2020
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Excellent info and advice everyone, I love it!! Those metal plates sound exactly like what I was thinking of doing with the breakers, just in a foolproof safe way so nothing can go wrong. Plus it's a really cheap upgrade 😉

So to clarify (I apologize for the bad doodling), I would have the GTI connection on my Sol-ark going to the bottom of the panel for the day-to-day output. Then when grid goes down I turn the GTI and 200A circuits both off, then turn on the GEN output circuit that's going from the inverter to the top of the panel? Or do I even need 2 circuits, only one is needed?

NOTE: I accidentally labeled the LOAD connection as GEN on the drawing.
 

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Hedges

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As you have shown.

Yes, need two circuits.

One connects input of SolArk to main panel under normal conditions, so PV production backfeeds the grid through "GTI" input.
If grid goes down, the UL1741 with anti-islanding feature of SolArk will automatically stop backfeeding the grid, like any grid-tie inverter.

Output of SolArk remains on like a UPS, tries to drive any load. That goes to the interlocked "GEN" input.
You have to manually manage any excessive loads. You may be able to power a reasonable size A/C during the day but shut it off in the evening.

If you would like to add a protected loads panel, one option is the Reliance transfer switch shown below. For each circuit in main panel that you want to protect, a switch in Reliance lets you select between feeding it from its original breaker in main panel, or from a breaker in Reliance which is fed by SolArk. It is installed by connecting its flexible conduit to main panel and splicing wires, no need to re-route existing wires. But GFCI or AFCI breakers in your main panel aren't compatible.

 

Cheap 4-life

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As you have shown.

Yes, need two circuits.

One connects input of SolArk to main panel under normal conditions, so PV production backfeeds the grid through "GTI" input.
If grid goes down, the UL1741 with anti-islanding feature of SolArk will automatically stop backfeeding the grid, like any grid-tie inverter.

Output of SolArk remains on like a UPS, tries to drive any load. That goes to the interlocked "GEN" input.
You have to manually manage any excessive loads. You may be able to power a reasonable size A/C during the day but shut it off in the evening.

If you would like to add a protected loads panel, one option is the Reliance transfer switch shown below. For each circuit in main panel that you want to protect, a switch in Reliance lets you select between feeding it from its original breaker in main panel, or from a breaker in Reliance which is fed by SolArk. It is installed by connecting its flexible conduit to main panel and splicing wires, no need to re-route existing wires. But GFCI or AFCI breakers in your main panel aren't compatible.


So to confirm does the SolArk backfeed into the main panel by supplying power through its grid input directly to the main panel? If so they should relabel the grid input to grid bidirectional or just grid. Then I wouldn’t be asking this question
 

Hedges

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"Grid Sell Back – UL1741-2010/2018, IEEE1547a-2003/2014, FCC 15 class B, UL1741SA, CA Rule 21, HECO Rule 14H"

All that stuff means it is bidirectional to the grid. Probably an option that can be disabled if you want it to supply local loads only.
If backfeeding, then breaker sizing and location in main panel is subject to certain rules.
 

740GLE

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Is your inverter split phase 240v? if not worth a breaker interlock, you can rig up a 120vac inverter to just feed one leg of the panel, pick which leg you want and bam you’ll have 120 for half of your house.
 

Bossrox

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I have an automated system like what you're trying to do but in reverse. I have a high current relay between my grid breaker box & solar. If my solar was to go down, it would switch over to grid. The relay I have is good up to 50 amps so well within your highest demand which I might add is quite modest. I don't need to flip any breakers to keep power from back feeding into the grid. I have my inverter & grid neutral tied together & the relay just switches the hot sides however you'd need an inverter with a remote on/off connection to do an auto switch or turn on the inverter manually
 

Hedges

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I have a high current relay between my grid breaker box & solar. If my solar was to go down, it would switch over to grid. The relay I have is good up to 50 amps so well within your highest demand which I might add is quite modest. I don't need to flip any breakers to keep power from back feeding into the grid. I have my inverter & grid neutral tied together & the relay just switches the hot sides however you'd need an inverter with a remote on/off connection to do an auto switch or turn on the inverter manually

Got good fuses or breakers? Assuming you're switching two poles ...

I had set up a 30A relay to switch a couple 240V resistance heating elements series/parallel. Worked fine for a while, but I think had a contact stick and twisted. Didn't trip 50A breaker at the load but tripped a 70A that was 150' away.

When I put in my grid-tie inverters years ago, PG&E wanted a visible-blade disconnect.
If connecting a free-running inverter, I would want a transfer switch with positive "off" before "on".

Another forum member wired a Sunny Island with both input and output connected together. That confuse it, of course, but also put output across the grid, which was some wire length away. Fortunately the breakers tripped and no damage was done.
 
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