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Noob Questions -- Planning 18kw solar+30kwh battery across 3 building and 3 subpanels -- need help with design

Maksidaa

New Member
Joined
Oct 26, 2024
Messages
1
Location
Austin Texas
Hi all, I've been lurking for a while and need help with my grid tied design. I have a master electrician willing to help me on an hourly basis, but he is not very experienced with solar installs and grid tied battery systems.

I have 3 buildings (main house, garage, guest house) that will all have about 18kw of solar panels total installed by me. I plan on using a hybrid inverter like the EG4 18Kpv + EG4 wall mounted batteries. I have a 200 amp main panel connected to the meter on a pole in my yard, and then the 3 buildings all have subpanels that are directly connected to the main panel. The house is about 30 feet from the pole, the garage and guest house are about 100 feet away from the pole.

Right now, my plan is to install the solar panels, and then tie them all back to one inverter at the exterior wall of the house. Then, if possible, have the inverter and batteries feed all three buildings.

Due to the size of the solar design, I will need to either upgrade the main panel or do a supply side connection.

My current questions are:
1) Is it possible to tie all 3 sub panels to the inverter+battery with this layout, or do I need inverters and batteries for each building?
2) When it comes to supply side connection vs panel upgrade, what is the general consensus?
3) I am 99% sure if I use the 18kpv I do not need any microinverters, and all I need are the DC disconnects at each building for the solar panels. Is this correct?
4) I've seen the demo videos for the EG4 Gridboss and Flexboss. Would these be better in my case than the 18kpv?
5) If I use the Gridboss, would I replace the main panel with the Gridboss and then connect my subpanels to it?
6) Or, would I connect the Gridboss between the main panel and the sub panels?

I'm a little bit confused how to make this all work, I'm hoping you all can help. Thanks!
 
I have 3 buildings (main house, garage, guest house) that will all have about 18kw of solar panels total installed by me. I plan on using a hybrid inverter like the EG4 18Kpv + EG4 wall mounted batteries. I have a 200 amp main panel connected to the meter on a pole in my yard, and then the 3 buildings all have subpanels that are directly connected to the main panel. The house is about 30 feet from the pole, the garage and guest house are about 100 feet away from the pole.

Right now, my plan is to install the solar panels, and then tie them all back to one inverter at the exterior wall of the house. Then, if possible, have the inverter and batteries feed all three buildings.

Due to the size of the solar design, I will need to either upgrade the main panel or do a supply side connection.

My current questions are:
1) Is it possible to tie all 3 sub panels to the inverter+battery with this layout, or do I need inverters and batteries for each building?
There are other similar, recent threads regarding pole mounted meter and small main load center, feeding sub-panels for house and other buildings. *if* the wiring from meter/main service entrance breaker panel goes direct to each building... that is a problem. For which there are various options. Considering cost of hybrid inverts and batteries, it is typically much easier and cheaper to trench (if applicable, vs aerial wire) /re-wire, than set up 'stand-alone' inverters/batteries environments for each building... but it depends

side thoughts - Do you have Internet (ideally via Ethernet) in the out buildings? that is a consideration if you wanted separate inverters, as you will want management/monitoring for system

3) I am 99% sure if I use the 18kpv I do not need any microinverters, and all I need are the DC disconnects at each building for the solar panels. Is this correct?
correct... however, beware considerations of shading (ex from chimney, and/or tress with roof mount) and panel orientation per DC MPPT circuit. There are times when micro-inverters actually do make sense and it is not ideal but you can mix AC-coupled micro-inverter panels and DC-coupled strings ... some will howl at the suggestion... but depends on your specific panel mounting placement options, shade impact on those spaces, etc. Personally, I prefer to avoid the 'religious/fanboy' approach, and look at the details of your specific scenario, and weigh your options, recognizing Pro's and Con's of each approach, looking at ROI for your specific design, and your priorities/preferences.
For example, if you are going to ground mount the panels, and shade is a non (or negligible issue) then absolutely a DC-coupled setup probably makes most sense. But if you require using roof-mounting, on all 3 buildings due to overall energy generation need (and close to 50 panels, right), and if those roof angles are far from optimal ... then.. it depends.

Also, unrelated, but beware thinking Qty panels * panel rating (defined by lab condition testing) = real-world (and typical PoCo permission to interoperate permit amount for) system output capacity. For example, I have 19 x 425W panels for a marketing # of just under 8.1kW (solar energy), however, permit and PoCo list system as just under 7.3kW (which matches the panels max continuous output rating). And then there is max expected output based on panel location and orientation when installed. I mention this in case you need 18kW, and weren't aware of the need to adjust the panel class number to something 'real'
4) I've seen the demo videos for the EG4 Gridboss and Flexboss. Would these be better in my case than the 18kpv?
Newer, more modular, with some benefits... but depends on your specifics (especially max sustainable and surge electrical loads) and timing (as products not shipping yet). A big consideration is your expected electrical load, and what of that load you want covered (all/partial) during a grid outage.
5) If I use the Gridboss, would I replace the main panel with the Gridboss and then connect my subpanels to it?
6) Or, would I connect the Gridboss between the main panel and the sub panels?
Basically... numerous possibilities, each with own Pro's & Con's, and largely dependent on cost and practicality of re-wiring the buildings (common recommendation is to re-wire outbuildings (garage and guest house) sub-panels to be fed direct from main house... but it depends), amount of energy flows (ie how much power draw/service feed Amps to garage and guest house)
For example, you could wire/trench from main house to meter/pole/service entrance panel, and basically extend garage and guest house to main house, if that is easier than new wire/trench from each building to main house (new hybrid inverter). There are numerous different wiring possibilities.. and whether you plan a Critical Loads Panel or not, and whether Critical loads circuits exist outside the main house... all impact wiring update considerations

Just an example, if you existing 200A service is adequate, and no change in sub-panel feeds, you could put inverter/batteries at main house (I'm a fan of inside the garage placement, as more temperature controlled, vs outdoors ... but it depends), and do minor re-wire a the pole (per local code requirements) and run full 200A service feed to hybrid inverter at main house... then run 1 or 2 feeds for the other building sub-panels from Hybrid Inverter (or associated panels) back to service entrance power pole. I'd be inclined to move service entrance breaker to main house... BUT, that may not be ok per local code requirements, PoCo rules, etc... and means needs to cut power at meter (unless you have a separate cut-off switch between meter and service entrance breaker?), vs being able to do all work without touching the meter service entrance wiring to main breaker

My default thought would be to bring garage and guest house sub-panel feed wiring to main house. Whether you do that via new direct wiring, or extend the 2 outbuilding wiring feeds from the meter pole back to house... your choice/it depends.

Anyway... from a non-electrician, but decently educated solar noob, with some food for thought
 

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