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EG4 18kPV System Partial Vs. Whole Home backup

waileepai

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Dec 11, 2024
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HI - I'm in the beginning stages of spec'ing, purchasing, installing, commissioning, etc. a hybrid solar pv system for my 2-level house here in western North Carolina.

Current/Future Goals:
1. current - battery power backup for critical loads (240V well pump, 240V water heater, 240V central heat, 120V refrigerator, 'select' upstairs/downstairs 120V lighting/wall outlets
2. future - reduction in power bills (via multiple strings of solar panels, load shedding, power shedding, smart load, net metering agreement with utility)

To date I've invested in (1) 18kPV Hybrid Inverter, (1) conduit box, (1) EG4 wallmount indoor battery, and (10) 400W solar panels. I initially will install the inverter and battery for use as critical loads backup. The solar panels will install later.

Question:
I'm reviewing EG4 literature '18kPV 1Line Diagram - v1.3' and evaluating which design options best suits my current & future goals.
In above document under notes for 'Critical Loads Panel' there is a note to 'Refer to EG4 Design Guides for discussion of partial home and whole home backup'. I can't seem to locate any EG4 'Design Guides' about this, so if you know what they're talking about please let me know :-) I'd love to read it. (I sent EG4 an email requesting this same info, no reply back yet).

Thanks in advance for any feedback!
 
1 battery isn’t enough to hit 12kW-AC or absorb all the solar this can produce at peak. You also need an energy audit to see how far 14kWh gets you

You can tag some EG4 reps for pointers, otherwise you could also spam pictures of existing conditions and forum people can make suggestions. They are unlikely to draw diagrams from scratch for you unless they really like you.
 
Are you doing the Backfed Breaker or the Supply Side Tap diagram?
And when you say current does that mean you already have an existing Critical load panel?
 
Are you doing the Backfed Breaker or the Supply Side Tap diagram?
And when you say current does that mean you already have an existing Critical load panel?
Thanks for the quick reply!

I'm evaluating (4) of the scenarios in the 18kPV Line Diagrams:
1. 18kPV with Backfed Breaker and Partial Home Backup
2. 18kPV with Supply Side Tap and Partial Home Backup
3. 18kPV with Supply Side Tap and Whole Home Backup
4. 18kPV with Feeder Tap and Whole Home Backup

--> First, to answer your 2nd question , I don't have a critical loads panel, but I have a sub-panel that could potentially be repurposed as a critical loads panel.

Regarding my existing (current) load centers/panels - the 200A main panel is upstairs, and feeds the downstairs sub-panel via 60A breaker.

Plan is to mount the 18kPV and battery on the wall next to the sub-panel, with the battery directly underneath. There's space on the wall/floor for future battery & inverter additions.

Today the sub-panel has a few of the critical load 'candidates' already on it: well pump 240VAC 20A, water heater 240 VAC 30A, A/C 240VAC 30A.
The main panel has the remaining candidates, incl.: 120V refrigerator, 240V 60A furnace, kitchen outlets, kitchen lights, router/tv outlets.
So for the existing sub-panel to function as critical loads panel, I'll have to pick loads that work within panel/sub-panel total amperage constraints, and then move some from the main panel to the sub-panel and vice versa. In reality I think it will be well pump, hybrid water heater running on 'max efficiency' mode, refrigerator, and a useful string of lights and wall sockets upstairs.

--> Second, to answer your 1st question - and based on my overall goals and the EG4 literature, I would be steering towards 4. unless there is a show-stopper for going that route.

My rationale is that it appears to provide the best upgrade path for the future, with the ability to bolt-on additional batteries, solar strings, or even 18kPV units, without having to go back to the well to redesign the system, get design approval, permit, electrician re-wire. Additionally the EG4 literature indicates 'FEEDER TAPS ARE THE IDEAL AND SAFEST WAY TO TIE YOUR INVERTER TO THE UTILITY GRID...'.

But - and I don't know if this allowed/safe/gonna-pass-design/inspection approval, in a grid down situation I would need to manually flip off breakers so that only critical loads are powered.

In the 'backfed breaker' scenario, I don't think I would have this same issue.

As zanydroid pointed out I need to do an energy audit (it's in process). I'll also dig in on his other comment regarding single battery limitations.
 
Hey there!

Sounds like we may be neigbors? I'm near Waynesville.

I have similar goals as you: Have power for critical loads incase Helene ever happens again; Reduce/eliminate my electric bill; etc..

I've got two 18kpv's, 90kwh of battery, and currently 10.7kw of panels on the roof. My grid agreement is up to 25kw, and I'm going to get started adding panels here shortly to get up to my Max

DM me, I'm happy to discuss in depth
 
Interesting to know there are more 18Kpv's here in Waynesville.

I recently installed this system in Waynesville, NC using an 18Kpv and the EG4 recommended installation for "Whole Home Backup using a Feeder Tap." I omitted the Feeder Tap breaker from my design because I have both a main disconnect and a main breaker on the inside main panel. Feel free to reach out if you want more info...



EG4_wiring-diagram_edit3.png
 

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