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General Ideas and Electrical Planning

Banjoman

New Member
Joined
Jul 5, 2023
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124
Location
Middle TN
Alright guys I wanted to start a thread to make sure I am not missing anything or there is a better way to go about what I am trying to do. In short I currently have a single 14.3kwh EG4 indoor wall mount battery with a Midnite 12KW AIO and 9 of my 400w Hyperion panels mounted on a south facing array. I am looking to finish the AC side of my system and the main goal is to maintain being off-grid but utilizing the grid as a grid assist function as well as keeping my generator port open for future installation of a full size backup generator to charge my batteries.

Initial schematic of what I am planning to do is attached. System would be expanded further with a 36 panel 400w Hyperion bifacial carport setup as my covered porch next to the garage (where the inverter, batteries, 200amp grid service is located) as well as future additional capacity of more batteries (probably additional EG4 power pros mounted on the garage sill plate) as well as one additional Midnite AIO. Idea is to have a minimum of 60KWH of battery capacity and enough inverting capability to run everything in the house. Thoughts are to gradually expand but have everything wired to where I can simply add capacity as required. Entire system is able to be put back to grid only if there were any solar side failures by a 200amp double throw Siemens MTS that I have already procured. I also have already purchased a Siemens Catalog Number SN4060B1200 Plug on Neutral Main Breaker Load Center and a Siemens Catalog # SN2040L1200 SN Series Main Lug Load center for both combined inverter outputs to feed to then go to the main breaker load center.

*Initial thoughts were to use a chargeverter to directly top off batteries from Grid but I am rethinking that and directly tying in AC in from Grid on inverters*

Photos of said area where all of this will be installed is included. Thoughts are to surface mount the load panels and run a trough between the main grid load center and the additional items. Not sure what I want to do yet with the Tesla Charger. (Excuse the mess in the garage it's been nuts with projects lately). Another idea I am stealing from Adam De Lay is to use Mersen Power Distribution blocks so I can easily combine AC in from Grid and AC out from Inverters when paralleling. Let me know your thoughts and what you may change or feel would be a better solution.
 

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utilizing the grid as a grid assist function as well as keeping my generator port open for future installation of a full size backup generator to charge my batteries.

The thing that I have run into with a similar train of thought is that true grid assist (paralleling the grid) will likely require an interconnect agreement with the power company unless you have an old, dumb meter (as opposed to the new smart meters). It has been explained to me that if you are paralleling the grid and a heavy load shuts down (e.g., AC or oven kicks off), you will back-feed the grid. Smart meters can detect even minute amounts of back feed. If you don't have an interconnect agreement, you'll get a visit from the power company threatening to shut your service off.
 
The thing that I have run into with a similar train of thought is that true grid assist (paralleling the grid) will likely require an interconnect agreement with the power company unless you have an old, dumb meter (as opposed to the new smart meters). It has been explained to me that if you are paralleling the grid and a heavy load shuts down (e.g., AC or oven kicks off), you will back-feed the grid. Smart meters can detect even minute amounts of back feed. If you don't have an interconnect agreement, you'll get a visit from the power company threatening to shut your service
Idea is to program the inverter as off grid with grid assist as it has that functionality
 
Idea is to program the inverter as off grid with grid assist as it has that functionality

Yeah, I've tried to wrap my brain around it because the cost of getting an interconnect agreement is a real pain (my AHJ required both electrical and structural stamps in addition to a plan set + inspection fees, etc). However, I can theorize a scenario where you still would backfeed even if you have a constant load.

I'm not familiar with your inverter but the only technology I've seen for any inverters to try and prevent backfeed are with CT sensors, and even with the CT sensors, there is a delay in reading + reacting.

I would imagine that on a humid but overcast day your system is drawing 3Kw from AC and 2Kw from other loads and your inverter is pushing 3Kw and you are drawing 2Kw from grid, that when the AC kicks off there will be a brief period where the inverter is still pushing 3K but your load is only 2K. During that brief moment it seems that extra 1Kw has to go somewhere and I think that somewhere is back to the grid. The only way that I can see a 100% certainty that it would never backfeed is if your inverter never pushes more than your constant load.
 
Understood. The inverter has CTs and you can actually configure a grid input constant feed value to offset any back feed potential
 

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