Please critique system diagram for new EG4 18k based, grid-tied system

[pjv]

Hi all,

New to solar and putting in a new system for our small, existing rural midwest USA residence.

We’re doing a (Sinclair, season-adjust rack) ground mount array with 32 bifacial 400W Canadian Solar panels (CS3W-400PB-AG) connected to a newly-built insulated shed (190 feet away) next to the existing utility meter. Inside the shed will initially be an EG4 18k hybrid inverter and a rack of 6 EG4LL batteries. The shed is sized to accommodate another rack of 6 batteries and another 18k, and we’ll be pulling double the necessary wire through our bored conduit between the array and shed in case we later decide to put up an additional array.

We have an electrician experienced with solar installs who will be doing the wiring and we contracted out the production of a system diagram which I am attaching here.

I am an experienced DIYer and software engineer comfortable with tech but I have no experience at all with solar power or high voltage systems like this. I’m hoping some experienced eyes in here could offer feedback on anything in the diagram that doesn’t make sense or leaves you scratching your head.

My simplistic description of what we want to accomplish is that we want to power the whole house from the following sources in order of priority:
1. solar generation
2. batteries
3. grid

We’re looking to sell excess solar back to the utility when available, but this is a low priority due to the shamefully low rate our utility pays.

Based on our pretty modest usage, I think the single 18k will cover our needs but we’ll be prepared to add another if needed. Our design includes a 200A manual transfer switch so we can effectively flip back and forth between straight grid and the inverter powering the house …just in case.

 

[DIYrich]

I don't understand what you are trying to do with the transfer switch. One output should go to the load panel. You should also have a disconnect switch between the load panel and inverter.

 

[Zapper77]

I don't understand what you are trying to do with the transfer switch.

Agree...

 

[pjv]

Thanks to both of you. I don’t really understand the diagram that well (why I am asking for feedback on it), but I know what we’re trying to do with that transfer switch.

The shed where the EG4 will live is outside the house, right next to the meter. We’re wiring the EG4 logically in between the meter and the house (load panel). So the output from the meter which currently goes to the house will instead be going into the grid input on the EG4 and then the load output on the EG4 will go to the house. The intention for the transfer switch is to be able to switch the inverter entirely out of the circuit so that I can flip that switch and the house is back on grid only, isolated from the inverter (and the solar and the batteries). I hope that makes sense.

If I understand what the box labeled “Main Electrical Panel” is meant to represent, it’s misleading that it is shown as being right next to the utility meter. What I think of as the main panel is in the house basement. The meter is outside, about 50 feet away from the house and right next to the shed where the EG4 will be.

I think there is a 200A disconnect shown on the diagram just above and to the left of the transfer switch. Physically, it will be located on the outside of the shed, right next to the utility meter.

 

[oglark]

I think the confusion is that the 18k is a hybrid invertor with grid tie capabilities so transfer switch (more for emergency panel with an off grid invertor) looks like overkill.

If I read the drawing correctly you are connecting the battery with #6AWG. I think that is undersized for a 12,000 W invertor. You should consider 2/0 since you might be able to pull 200 amps.

I also dp not see a t-class fuse and/or breaker between the battery and the 18k.

 

[pvgirl]

Your drawing has no indications what is connected to where at the transfer switch and the inverter. There should only be 3 connections to the transfer switch.

The new disconnect at the service/meter, should run right to the grid input on the 18kpv, The existing main breaker should run to one side of the manual transfer switch. The Load connection of the 18kpv would run to the other side of transfer switch. The existing main electrical panel, which doesn't seem to be shown, would be connected to the center of the transfer switch.

Wiring to and from them 18pkv line and load should be sized for the for load of the house.

How or where the new panel in the shed gets it's power isn't shown.

If more then 3 ft of the PV source wires from the array are inside the shed an outside disconnect will be required.

Please clarify what year version of the NEC is in effect

See Diagram 4.3 on page 33 of the 18kpv manual: https://eg4electronics.com/backend/wp-content/uploads/2023/04/EG4-18KPV-12LV-Manual-2.0.4.pdf for a diagram of how to wire your system.