Can I backfeed to loads that are fed from my Main Meter Panel?

[solr2aguy]

Hi,

I have a panel at my meter with a 200A breaker that is the main disconnect for my house and also for a 100A feed to my barn. I'll be bringing DC from my array into my house basement. The 200A load panel for my house is also in the basement. The 200A load panel in the basement is fed by the 200A panel at the meter. See attached diagram.

I'm planning to use the SolarEdge Backup Interface which creates a microgrid when the grid is down, allowing the grid-tied inverters to function when the grid is down. The optimizers and inverters are also SolarEdge. The Backup Interface is supposed to be installed with the Grid and Inverters as inputs and the load panel wired to the output (see attached SolarEdge graphic). When there is an excess of solar power, the Backup Interface backfeeds to the grid.

My question is that when I am backfeeding to the grid, which would also be backfeeding my 100A feed to my barn, do I need to be concerned about the backfeed power quality to loads in my barn? For example, voltage or frequency variations? If this is a concern, is there anything I can do about it?

 

[DIYrich]

My question is that when I am backfeeding to the grid, which would also be backfeeding my 100A feed to my barn, do I need to be concerned about the backfeed power quality to loads in my barn? For example, voltage or frequency variations? If this is a concern, is there anything I can do about it?

solaredge follows the grid. So if you have clean grid power, you will have clean power at the barn. If you get dirty power from the grid, you will get dirty power at the barn.

 

[Zapper77]

If I understand your question right. Your inverter will not backfeed if the grid is down.

 

[Hedges]

There are many choices in PV inverters, battery inverters, hybrid inverters. If you aren't already locked in to a particular ecosystem, price the alternatives. If you have PV inverters already, there may still be options for battery inverters.

Proprietary battery solutions are often more expensive. But they may work more seamlessly.

Your second picture shows hybrid Solar Edge inverter with batteries, first picture doesn't show batteries.

The topology of the two drawings differs. Solar Edge drawing shows Backup Interface acting as a transfer switch, with grid going to it. Your drawing shows grid going to main panel.

I think you need to put Backup Interface between grid and main panel.

As for power quality during backup operation, some systems do vary frequency a few Hz (which shouldn't be a problem unless you rely on electromechanical timers), but vendor documentation should describe it.

 

[solr2aguy]

I already have the SolarEdge hardware. I was supplying the SolarEdge diagram in my posting as a reference to how they expect the Backup Interface (microgrid) to be connected. The first diagram was an attempt to clarify what my question was about and whether or not backfeeding from the SolarEdge inverters and Backup Interface will produce clean power to feed my barn which is fed from the panel at my meter.

Thanks for reading my post.

@DIYrich seems to have answered my question.

 

[solr2aguy]

If I understand your question right. Your inverter will not backfeed if the grid is down.

I am not concerned about backfeeding when the grid is down (although that is a good point to bring up). My question was whether or not I would get clean power to my barn when the SolarEdge inverters and Backup Interface are backfeeding with the grid connected. I am ok with not backfeeding when the grid is down. I won't have critical loads in my barn.

 

[solr2aguy]

As for power quality during backup operation, some systems do vary frequency a few Hz (which shouldn't be a problem unless you rely on electromechanical timers), but vendor documentation should describe it.

I do have a fence energizer powered from the barn which has a digital display and has configurable pulse frequency of sending a pulse every 1.5s or every 2.5s.

 

[Hedges]

That wouldn't be affected. Probably has an analog circuit for timer.
If you had a timer dependent on 60 Hz and backup operation deviated, times would get off.

With grid connected, your power quality will depend almost entirely on the grid. Your inverters will raise voltage a couple volts, but still in spec.

If you're putting in a backup interface, you must have something you want to back up.
If not inserted between grid and main panel, you could still feed it to an interlocked "generator" breaker if you want to manually power some loads there.

 

[solr2aguy]

If you're putting in a backup interface, you must have something you want to back up.
If not inserted between grid and main panel, you could still feed it to an interlocked "generator" breaker if you want to manually power some loads there.

I got the new-in-the-box Backup Interface in an auction from an installer that went under. So I am going to install it in case I ever want to add battery backup to the system. It's my understanding, however, at least with SolarEdge branded hardware, that the only way to be able to run off-grid with their inverters is to have the Backup Interface which creates the microgrid to keep the inverters "happy" when the grid is down.

 

[DIYrich]

I got the new-in-the-box Backup Interface in an auction from an installer that went under. So I am going to install it in case I ever want to add battery backup to the system. It's my understanding, however, at least with SolarEdge branded hardware, that the only way to be able to run off-grid with their inverters is to have the Backup Interface which creates the microgrid to keep the inverters "happy" when the grid is down.

Might want to consider exchanging the Solaredge for something else (EG4?)

 

[Hedges]

So long as SolarEdge GT PV inverter implements Rule-21, it should play nice with several brands of battery inverter that support AC coupling.
That would include SolArk, Radian, Schneider, Sunny Island, a number of others.

Since you've got Backup Interface, and presumably SolarEdge (or do you have StorEdge?), the idea is to make use of them.

Does Backup Interface contain a battery, or connect to a battery? What does that external battery cost? (could be more than a different inverter + battery!)

Or search eBay and save search so it notifies you. I've picked up so proprietary batteries for cheap that way. Those were the LG RESU-10H with firmware for Sunny Island; a different model works with Solar Edge. (This probably isn't a model you want, recalled for fires. Maybe "Prime" version is better, but a LiFePO4 chemistry would be safer and have longer life.) I haven't found yet what batteries work for your inverter.

Or, does Backup Interface allow batteryless backup, producing limited AC power in the microgrid direct from PV?

You will want to have some protected loads on output of Backup Interface. Could move those loads to a sub-panel, or use something like Reliance manual transfer switch, or put an interlocked "Generator" breaker in your main panel, to be backfed from Backup Interface.

I originally had my battery inverter fed by main panel, also backfed to "generator" breaker, in addition to feeding a protected loads panel. So I turned off breaker feeding inverter when turning on generator breaker. Now it is fed by a "load side tap" between meter and main panel so it can provide UPS operation to main panel if desired in addition to protected loads panel.

 

[solr2aguy]

Might want to consider exchanging the Solaredge for something else (EG4?)

I got a very good deal on the SolarEdge hardware, so I am running with it.

 

[solr2aguy]

Since you've got Backup Interface, and presumably SolarEdge (or do you have StorEdge?), the idea is to make use of them.

Yes, that is correct. I have newer inverters that are the "Home Hub" inverters. StorEdge are the older generation inverters.

Does Backup Interface contain a battery, or connect to a battery? What does that external battery cost? (could be more than a different inverter + battery!)

The Backup Interface does not have any internal batteries. The SolarEdge diagram I attached on my post shows that the batteries connect to the inverter(s). Batteries supported are SolarEdge, Tesla, and LG.

You will want to have some protected loads on output of Backup Interface. Could move those loads to a sub-panel, or use something like Reliance manual transfer switch, or put an interlocked "Generator" breaker in your main panel, to be backfed from Backup Interface.

Yes, I already have an Interlocked breaker for switching most of the critical loads in my house over to a gas powered Honda generator. I have not decided yet if I will leave that as it is or if I will run the generator through the Backup Interface, which is supported also (see again their diagram I attached).

 

[Hedges]

Backup interface seems to be a transfer switch.
Similar to ABU (which I don't have) for Sunny Boy Storage (which I do.)

If you have a generator inlet plug, you might use a cord to connect backup interface instead.
Generator into backup hub could be convenient. Do you know if it switches, or if it blends inverter power with generator? (the latter would depend on generator characteristics.)

Hardwired would be nicer, but power cord would be a good way to test it out.

Still need a battery, correct?

Tesla, so far as I know, is an AC coupled battery and can be used as grid forming.
LG is DC coupled, and then your Energy Hub would be grid forming.

Any of those batteries is going to be more expensive per kWh than alternatives people here use.
Santan has a Tesla Powerwall battery available, price not shown. You might want to see if it is discounted.
There may be some LG batteries getting closed out. But specific models require specific inverter firmware revisions and models, so be sure of compatibility.

Earlier LG batteries have had multiple recalls for fires (as have their batteries in the Bolt), so I think should be placed a distance from the house.