Shed Solar - See any mistakes?

uzernaam

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Nov 6, 2021
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So this is my first solar install. I'm no expert, just a DIYer.

I have 10 Heilene 320w panels on top of my shed.

Cables run down to a combiner box, then DC runs out from that through an underground conduit to the house.

I'm using a Solar Edge midpoint transformer and a Growatt 5000 ES inverter to get split-phase 120.

One circuit from the service panel runs back to the shed, one to the garage, and one to garage lights.

I bought AGM batteries just to get started for now, but I'm looking at some lithiums in the near future.

You people who are smarter and have more experience than I do - can you see anything to nitpick here? What can I do to improve things? Anything I should address to get things more "up to code?"

Thanks!
 

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Johnson

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Looks great, tidy workmanship, can't fault it.

I ran my cables from outside in through the floor, makes mowing and painting easier. And since I put insulation and drywall inside, I kept the tails on my wires longer, in case I want to change things in the future.
 

Johan

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In the diagram, the 30A breaker does not disconnect the autotransformer from the Growatt. Was that the initial plan?
 

uzernaam

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In the diagram, the 30A breaker does not disconnect the autotransformer from the Growatt. Was that the initial plan?

The transformer is wired directly to the buses, no breaker in between.

I figure that since the transformer is a simple, large electronic component it has a low failure rate, and if anything does happen to it the output breaker (not pictured) inside the inverter or the input breaker on the panel will take care of it.

If I were to put a breaker between the panel and the transformer, if the breaker trips I've suddenly got a broken neutral and my AC phases become two 120V loads in series on 240V. That's bad.

I'll take the risks that the transformer will self-destruct over everything plugged into it downstream.
 

acdoctor

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Ok I’ll bite, 60amp battery fuse x 50 volts is 3000 watts. Is that all the 5000 growatt is? Or do we need a upgrade there?
 

uzernaam

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Johan, you found a mistake in my diagram! Yes, that's exactly how it is. I'm going to have to redo my schematic.

acdoctor - I only had 60A fuses on hand (more coming in the mail soon hopefully), so I set max charging on the growatt inverter lower than that.
 

smoothJoey

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fuse should be between the battery disconnect and the battery

5000 ac watts / .85 conversion factor / 48 volts low cutoff = 122.549019608 service amps
122.549019608 service amps / .8 fuse headroom = 153.18627451 fault amps.

You should be using a 150 amp class-t fuse and 4 awg wire minimum
better is 200 amp class-t fuse and 2 awg wire.
 

uzernaam

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smoothJoey - I have new fuses coming in the mail. My loads are nowhere near 5kw anyway and I've lowered the charging rate limit on the inverter. The battery cables are a pair of 4 AWG on each terminal, equivalent to 1 AWG.

Updated Diagram:
 

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smoothJoey

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smoothJoey - I have new fuses coming in the mail. My loads are nowhere near 5kw anyway and I've lowered the charging rate limit on the inverter. The battery cables are a pair of 4 AWG on each terminal, equivalent to 1 AWG.

Updated Diagram:
Its my policy to wire and fuse for the full inverter capacity.
Also the fuse should be as close to the battery main positive terminal as possible to minimize the chance of an upstream short.
Definitely the fuse should be upstream of the disconnect switch.
 

Johan

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Here is an example of out-of-the-box SolarEdge autotransformer short to ground:


In you case, such a short could trip the 30A double pole AC breaker, in turn also shutting off all 120V loads, reducing (removing?) the risk of a "floating neutral", so your 120V loads are probably better protected compared to the case where the ATF is on dedicated circuit breakers like shown here (Signature Solar):
and here (David Poz):

From the comments of user "Coty Condry" on the Signature Solar video:
"I set mine up with a 240v-only breaker panel (no neutral) and a second breaker panel for 120v loads that has a neutral. The 2nd panel and my autotransformer are fed from the first breaker panel using a single double-pole breaker. So if that breaker is tripped, all power to the 120v panel is disconnected and no floating neutral."

The advantage of Coty's setup is that is the ATF fails, then your (optionally critical?) 240V loads could keep running, unless the short is too violent. But if, in your case, you don't need that, then the simplicity of your design (regarding the connection of the ATF) wins, I would say.
 
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Johan

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@smoothJoey @uzernaam: How about a breaker instead of a (class T) fuse? A breaker can be easily reset. A breaker can also trip faster in the range of 125 to ~300% of the rated load as shown in the figure below (yet still allowing some inrush currents), and breakers can trip slower above ~300%, allowing higher optional inverter inrush currents without unnecessarily tripping like an "expensive" fuse may do.

EDIT: @smoothJoey - yes the Interrupt rating is important, I forgot about that here!

fuse VS breaker.png
 
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smoothJoey

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@smoothJoey @uzernaam: How about a breaker instead of a (class T) fuse? A breaker can be easily reset. A breaker can also trip faster in the range of 125 to ~300% of the rated load as shown in the figure below (yet still allowing some inrush currents), and breakers can trip slower above ~300V, allowing higher optional inverter inrush currents without unnecessarily tripping like an "expensive" fuse may do.
A breaker is fine as long as it has an AIC=arc interrupt capacity rating of ~20,000 amps.
 

uzernaam

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I had the fuses and fuseholders left over from my car stereo days, and decided that rather than take up space in a toolbox, I should put them to use.

I'm looking at DC breakers, but so many of them are made with iffy quality these days but I know 100% a fuse will blow on a short. Can you tell me the reasoning behind swapping the fuse and switch?

Johan - That's an interesting idea, but it would take another area of real estate on my wall and it's getting crowded.

Right now I'm only powering an occasional 120V load in the garage and shed, and some LED lights. This project has been a proof-of-concept effort to me so far, but I'll take all ideas here and file them away for future upgrades.

And as far as that transformer short - yikes. Almost makes me want to open mine up for inspection. So far so good, though...
 

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smoothJoey

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I had the fuses and fuseholders left over from my car stereo days, and decided that rather than take up space in a toolbox, I should put them to use.

I'm looking at DC breakers, but so many of them are made with iffy quality these days but I know 100% a fuse will blow on a short. Can you tell me the reasoning behind swapping the fuse and switch?
Since you indicated that you will have a 48 volt LFP battery over-current protection with an AIC rating of ~20,000 amps or better is indicated.
The fuse goes before the disconnect switch and as close as possible to the positive terminal to minimize the risk of an upstream short.
If you used a breaker the switch would become redundant.
Do you understand what I mean by an upstream short?
 
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Struc

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Good read on ANL vs Class T fuses:
 

Johan

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In his most recent use with the ATF, David Poz, like you, also correctly left out the dedicated breakers for the ATF. It's difficult to see in the video, but the ATF is directly (i.e. no breaker) connected into the wire nuts (instead of bus bars) as shown in this still:

InkedCapture_LI.jpg

I think this makes more sense than his previous videos that I linked to earlier above.

(Full video:
)
 

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