Using DC Solar Trailer as Rooftop Battery Backup

abilityonline

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The generator in the diagram is the same generator setup that came with the trailer. Currently the generator feeds the two SI through a 6awg 50 amp twist lock cable into the back of the utility box. The SI then charge the battery from the generator. So it appears if I want to use the generator as a last resort backup I would want a 400 amp transfer switch between SI and Grid/Generator. I guess the other option would be to unplug the generator cable when using a grid tied/net metering setup and plug the rv plug from the main panel. In case of grid failure and wanting generator backup, I would plug the generator back in. I suppose that would essentially be the same a manual breakers.

My gridtied inverters are Solaredges HD wave but I'm banking on them being able to frequency shift loads between them and the SI. Nevertheless I need a transfer switch with a 5 second shutoff between transfers.
 
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Hedges

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Sunny Island can pass through 56A, so about a 70A breaker on main panel feeding SI is suitable.
Generator output is similar.
A 70A transfer switch could connect SI to either grid or generator.

A plug-in cable could be used instead of generator. But make sure in all cases Neutral gets bonded to Ground in exactly one place. Also, that SI is informed whether generator or grid.

Unless you want the portability, you might unmount the equipment from the trailer and hard-wire it.
 

abilityonline

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Thank you again Hedges. I already wired a 50 amp plug outlet with 6awg wire (3 foot run to bottom of the panel) if I went 70 amp, would 6awg be beefy enough? Additionally my cables and plugs are 6 gauge cables. If passing 56amps I feel 6 gauge would be fine.

I do want to keep the trailer portable. I was wondering, is it possible to pre program different SD cards based on settings and simply reboot the SI and they take on those settings upon booting up?

Also, I have neutral and ground securely attached to the same bus bar in the panel. When you say "in the exact same place". Is the same bus bar sufficient or do you mean they share the same bus bar hole and screw?
 
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Hedges

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A 50A plug is supposed to have 50A breaker.
6 awg, if rated 90 degrees C, can have 70A breaker. 75C can have 65A, 60C can have 55A.


I think SI can read configuration from SD card. Not sure, but might read (stale) battery SoC and cycle data from it too.


SI doesn't bond N and G internally. In my system, it inherits that from main breaker panel. See what yours had - may be bonded in the panel on the trailer - if so, I think that should be isolated (might need separate ground bar), and would inherit bonding from your grid system. When cord moved to generator, a bond you put in generator would take care of it. Always plug into one or the other when operating, so it is bonded.

If generator would feed SI when SI feeds Sunny Boys, make sure control input informs SI about generator. Could be an ear on the power cord pushing a switch next to the plug.
 

WYtreasure

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... I was wondering, is it possible to pre program different SD cards based on settings and simply reboot the SI and they take on those settings upon booting up? ...
Someone may have said this before, but I have not seen it.

Awesome time saving idea. I'm thinking you should get a point for that one. (y)(y)
 

abilityonline

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Hedges, in your vast helping of others, thank you again by the way. I have a 2 part question.

Part 1, have you seen if simply activating California rule 21 on the solaredge inverters is enough to activate frequently watt shifting between SE and SI? I found this video,
at the end it talks about updating per your grid specs. I know the standard is 60hz and that I need SE to throttle down as Hz goes up due to battery being topped off while the grid is down not allowing back feeding. As to not overcharge the battery bank.

Part 2

Also can I set my SI's to Grid/Gen mode?

Hopefully this makes sense as I describe my process. I currently have my SI's in grid backfeed mode so my DC trailer is backfeeding the grid for net metering credits (in addition to the credits I get from my normal rooftop PV). Currently when the grid goes down, I would go to my critical loads panel, manually shut off grid power in breaker (interlocking kit) turn on inverter power breaker for power into panel. I then transfer off the power from my main panel and connect my Solaredge GT inverters to the critical loads panel (via manual transfer switch) so that my critical loads panel is now powering my SE inverters and the Se inverters are backfeeding my critical loads panel. It's at this point, I unplug my SI that feeds the grid in normal good grid operations, I unplug the backfeeding and would plug my generator back into the SI power in. I then currently have to change SI settings from Grid mode (backfeeding) to Gen mode. Long question but... Is there a setting where I can unplug the backfeeding cable and plug in the generator cable without having to change SI settings? Currently it makes me shut down the inverters to go from Gen to Grid mode.
 

Hedges

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I think I heard video say Q(U) is volt-watt. See if you can select frequency-watt.
It probably has that. Possibly some inverter firmware has rule-21 without frequency-watt but an update might provide.

You can configure SI to automatically accept both grid and generator. Normally that would be a transfer switch (ensure 5 seconds off time before connecting different AC source). A signal input must be used to tell SI generator is connected, so no backfeed.

You could hardwire neutral and ground so N/G bond always happens at your main panel (assuming generator doesn't also have N/G bond) and use a pin of the plug to communicate signal generator vs. grid. Of course, not many plugs suitable for 56A.
 

abilityonline

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N/G is on the trailer and generator. By switching plugs, it's essential a poor man's transfer switch. Would I just set the SI to Gen/Grid setting?
 

Hedges

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"GenGrid Battery-backup grid with generator"

Page 139 of manual:

"An auxiliary contact is used because the Sunny Island must "know" whether it is connected to the utility
grid or whether it must manage a diesel generator.
To enable such an operation, you must set parameter "231.06 ExtSrc" to "GenGrid" (see Section 8.2
"Starting the Quick Configuration Guide (QCG)", page 69)."

Figure page 138 shows signal to Digin.
 

abilityonline

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Hedges, I wanted to thank you and give you an update. I ran my first full-scale test by disconnecting from the Grid. Everything worked perfectly. My house was being run by my critical loads panel. My PV was charging my battery. My Sunny Islands were providing the Grid to the Grid Tied inverters. My SolarEdge began to throttle down when the battery was at 90%. I was using the settings on the California 21 rule. I'm not sure if the way they lowered production was perfect. Not only did GT inverters slow production but they would bump offline and then count down to reinitialize. I'm not sure if that is a strain on the inverters or if I shouldn't worry about it? Nevertheless, you can see the voltage from the PV did what I was hoping. I didn't have the time today to see the batteries go to 100%. It would have taken all day because they were just creeping up by the end of the day. But I feel like this solution will work perfectly. I'm just not sure if I should worry about the GT inverters being knocked offline. You can see their output in graph 2. The rolling hills is the output being pushed on and off line. It gets the job done, just not sure if it's the most elegant way. But come to think of it, I'm not all that elegant to begin with...

1653188066329.png
1653188272152.png
 

Hedges

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GT PV Inverters may drop offline when grid goes down, but they're supposed to remain on line after that when Sunny Island providing the grid.

Mine also dropped offline when they shouldn't have. I figured out a work-around:


What error was shown then your Sunny Boys Solar Edge went off line? There may be yet another bug, in your model.
In a video from SMA, I heard the suggestion to run the -40 and -41 models in "offgrid" mode when behind Sunny Island; that disagrees with SMA's written instructions. But maybe there is a reason they're saying that. I think the Rule-21 limits should work fine with Sunny Island, but maybe there is an issue. I would have thought off-grid parameters were only needed for a small generator that wasn't real stable.

Are there various options for Solar Edge? Any values you can change?
Sunny Island probably drops frequency to 59 Hz (at some of the times 100% power is desired.) If that is a problem it can be disabled.
 
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