Feedback and suggestions on 13 kw off grid system with sma sunny island

sashko559

New Member
Joined
Oct 11, 2021
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4
Updated:
Feedback on off grid solar with transfer switch to power house loads

Hi, I am building an off grid system to charge a tesla and also an a second panel where I can switch off some load from the house (mainly AC or well pump or the whole house since there is outage often) to my system sometimes. I have 2 x sunny islands (5048) that will give me split fase 240V around 10 KW connected to 12 x 100 Ah Lead acid batteries 12v each in series 4 each to make a 48v power bank. I have used 40 panels that are 250W each that I bought as well as 16 panels that are 195W each. I can connect them through AC. Coupling.
I have 2 x 7.7 Sunny Boy's PV Inverters and theoretically I connect them on Load Panel with the Sunny Island which will allow me to use the solar power and the excess to charge the batteries. It will also give me freedom to add more panels, Sunny boys and or Sunny Islands later to expand if I need to as well as the ability to add a backup generator.
I am confused how to connect on the sub electric panel the sunny islands and sunny boys with other loads. Which breakers and which panel should I use? Also can you recommend any transfer switch panels I can put in the house and wire a load from this sub panel to switch some loads independently off and on from grid and solar system
Please Provide feedback and suggestions:
  • Type of wires to connect within the system the Inverters, panels, and the batteries.
  • Overall Design of the System and any improvements and changes.
  • What kind of panel and switches I would need to put that would allow me to transfer switch every load depending whether I want it on the grid or on the solar system?
Thank you very much for all the help so far!
Love this community and the videos!
 
Last edited:

Pyrofx

Flux capacitor builder
Joined
Jul 27, 2020
Messages
522
Location
Oatman Az
I use 2 of the sboy 7.7, and 2 s island 6048.
The islands will control the charging of the batteries, then the boys will ramp down the islands charge rate when full. The boys will also increase you ac load available.

The boys have 3 mppt inputs , and you can parallel the inputs.

Stand by , Hedge will chime in soon . He is an SMA slut . He is who talked me into my 5 sma units.
 

sashko559

New Member
Joined
Oct 11, 2021
Messages
4
I use 2 of the sboy 7.7, and 2 s island 6048.
The islands will control the charging of the batteries, then the boys will ramp down the islands charge rate when full. The boys will also increase you ac load available.

The boys have 3 mppt inputs , and you can parallel the inputs.

Stand by , Hedge will chime in soon . He is an SMA slut . He is who talked me into my 5 sma units.
Because I have different solar panels listed above, do you think the 3 strings on the sunny boy input have to have same voltage and panels each? Or can I do different amount on each string? Specifically I want to do 10 panels 250w in series on string 1. String 2 is identical. String 3 would be 8 panels 195w each. Also which 5 SMa units are you talking about?
 

sashko559

New Member
Joined
Oct 11, 2021
Messages
4
What kind of panel would you recommend to use as AC combiner box and where I can add few loads
 

sashko559

New Member
Joined
Oct 11, 2021
Messages
4
I use 2 of the sboy 7.7, and 2 s island 6048.
The islands will control the charging of the batteries, then the boys will ramp down the islands charge rate when full. The boys will also increase you ac load available.

The boys have 3 mppt inputs , and you can parallel the inputs.

Stand by , Hedge will chime in soon . He is an SMA slut . He is who talked me into my 5 sma units.
Can you share please a picture of your sub panel or critical loads panel? I a bit confused on which breakers to use for each inverter sunny boy and sunnn island on that sun panel if my sunny boys are 240v and 2 sunny islands are split phase 240
 

ghostwriter66

"Here - Hold my Beer"
Joined
Nov 13, 2019
Messages
1,643
Location
From LA -work in South Texas/New Mexico region
Can you share please a picture of your sub panel or critical loads panel? I a bit confused on which breakers to use for each inverter sunny boy and sunny island on that sun panel if my sunny boys are 240v and 2 sunny islands are split phase 240

For your sub-panel you really need to decide which circuits you want to drive and then get the panel size accordingly ....
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,338
If all PV is AC coupled,
You'll want a load-shed relay. This is the SMA branded one, which I bought.
Shipping from Europe was a good fraction of purchase price. I bought two, wish I got three.


The second relay in master Sunny Island defaults to load-shed at 70% DoD. If that happens, it reconnects at 50% DoD. The relay is SPDT dry contacts, good for DC or AC. PTC fuses connect to battery positive and negative, can be used through the signaling relays to control power relays such as this one.

This power relay has particularly good economizer. The 10 ohm coil at 50V would draw 5A (250W!) for milliseconds, and when relay slams shut it opens an extra contact, putting a much higher impedance "hold" relay in series.

I think AC relays inherently have an economizer function, because core pulled into coil increases its inductance.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,338
As for sub panels, they're supposed to have a busbar heavy enough that the breaker feeding it (from Sunny Island) and the breaker back feeding it (from Sunny Boy) don't exceed 125% of busbar rating.

I use a bunch of Square D QO panels. Some are 225A busbar, some are 125A, some smaller. The larger have copper busses, the smaller are aluminum. Some have "plug on neutral" which supports GFCI/AFCI without an extra pigtail wire. Some accept half-width breakers. Might have a slot for "circuit limiting" models. Have longer ground busbars (since you might install 24 circuits in a 12 slot panel.)

Of course some panels are indoor (either flush or surface mount.) Some are 3R outdoor.

I let Sunny Island be a UPS with automatic transfer for primary loads (house). That is separated by load-shed relay from panel with Sunny Boys (which could have critical loads.)

I use interlocked breakers to backfeed from Sunny Island into a panel for shop tools and the like. Also another one to bypass Sunny Islands, put house direct to grid in case of failure.

Surge arrestors for AC input. The ones Midnight offers look good.
 

MurphyGuy

Solar Addict
Joined
May 20, 2020
Messages
609
If all PV is AC coupled,
You'll want a load-shed relay. This is the SMA branded one, which I bought.
Shipping from Europe was a good fraction of purchase price. I bought two, wish I got three.


The second relay in master Sunny Island defaults to load-shed at 70% DoD. If that happens, it reconnects at 50% DoD. The relay is SPDT dry contacts, good for DC or AC. PTC fuses connect to battery positive and negative, can be used through the signaling relays to control power relays such as this one.

This power relay has particularly good economizer. The 10 ohm coil at 50V would draw 5A (250W!) for milliseconds, and when relay slams shut it opens an extra contact, putting a much higher impedance "hold" relay in series.

I think AC relays inherently have an economizer function, because core pulled into coil increases its inductance.

I use an Allen Bradley AE95. 48 volt DC coil, 125 amps, draws 4 watts to hold the coil.

Got it on Ebay for $40
 
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