Question Dual Gridboss with single 48KWh Generator

As of now, you will need 2 generators. 1 for each Gridboss. I don't believe it is possible for 2 Gridboss' to control 1 generator. 

I don't understand why you couldn't parallel the start relays to control the generator. Any gridboss calling for the generator to start then gets power from the generator, transfers load and starts charging the connected battery. The other one will just transfer the load, but not necessarily charge the batteries. 

Posted by: @envisionit

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I am doing research for my setup.  I have dual 200A panels from a 400A meter.   I am planning on dual Gridboss one for each panel each with dual Flexboss21.  Each panel would have 10KWh of Solar and it's own battery backup.  Essentially, two separate units.  I want to add a generator backup.  I was planning on getting a single 48KWh Generac generator which outputs 200A that feeds to both Gridboss units...  Is this possible?  Or do I have to get 2 generators at 24KWh each?  I was hoping to only have to get a single generator vs having to maintain / service 2 of them.

Am curious if both Gridboss units can control a single generator and tell it to turn on / off when the grid is down.   

Your panel and meter base setup sounds exactly like mine, 2-200 amp panels and 1-400 amp base. But, my house doesn’t require 400amps, not even close, I could have gotten away with 1-200 amp service but there’s way too many circuits for 1 panel so we were forced to go with this setup. If you can get away with using 1 of those 200amp feeds for your inverters/Grid-Boss it will give you a ton of options. 

I just installed a very similar architecture. I have a 400 amp split SE with two 200A breakers immediately after the meter, all combined in the SE panel.  The load panels are two 200A panels. I just installed dual Gridbosses, dual Flexboss21's ( one feeding each GB) and four 314 Ah wallmount batteries (2 in parallel with each Flexboss).  I just converted my 24kW Generac to 2-wire start which seems to be working fine from the Gridboss #1 included inwhat I will call system #1 (Gridboss/Flexboss/2 batteries). This serves most of my critical loads.

According to an EG4 document the Gridbosses/Flexbosses can be set up in a dual fashion sharing what appears to only be the RSD external switch for shutdown, the generator and the grid. It does show the generator output coming into both system #1 and system #2. My 2-wire control through the dry contact #1 NO1 and COM1 controls the generator to initiate starting. I have a splice in a junction box that then feeds to the generator port in each of the 2 Gridbosses.

My question is if I lose Grid and the generator conditions are met to introduce it to the system for load/charging is, what happens to the other Gridboss (system #2) when the GB #1 relay switches out the grid on system #1? The grid is still technically connected through system #2 (at the meter common) if Gridboss #2 does not initiate the relays to switch out grid / switch in generator.  How does Gridboss #2 know to trip the relay?

The EG4 document is attached.  (DRAWING #GB-V2-1L-1, VERSION 1.2 ©2024 EG4 ELECTRONICS, LLC. ALL RIGHTS RESERVED. )

I have a 600A SE with three 200A disconnects below the utility meter to panels A, B, and C.  Panels A and B each have a 60 amp breaker feeding other panels (E & F).  Panel D is right next to B without a service disconnect or feeding breaker, so assume it is connected via shared 200A service with B, which is completely full with breakers.  Panels are all located far apart from each other, and from the SE.  

For whole house backup, it looks like I need three separate systems - one for panels A/E, one for panels B/D/F, and one for C - each with Gridboss, Flexboss 18/21 inverter(s), PV, and batteries.  I checked my usage over the past year, peak 1hr was 25kW and peak daily was just over 400kW.  So I'm not using anywhere near the 600A grid limit, but there are 7 Trane AC units with high LRA so will need to get soft starts for them; four are in panel B and three are in panel A, so those systems will almost certainly need parallel inverters.  C doesn't have any particularly heavy loads, except for EV charger but Tesla was sold last year so not currently used.  Primary water heaters, furnaces, dryer, and oven are gas which helps reduce total demand.

I am interested in adding a ~ 25kW natural gas generator, but they are neither cheap nor small, so probably would be a single unit connected to only one system (for panels B/D which covers the west wing of the house, including the kitchen.

PV is going to be a challenge because of space as I don't want to put panels on my Mexican terra cotta tile roof.  I have a large L-shaped flat roofed area over some patios that can accommodate ~ 25kW, and I have a couple small ground arrays I built for a power station ~ 2kW, all south facing.  I have space for more ground arrays but they would mostly be east/west rather than south facing. My wife wants to build another structure in the backyard ~ 1800 sq ft and I could mount more panels on its roof, if it gets built.  I'll don't forsee ever generating 400kW per day but if even 75kW will slice my bill since I could run the house 4-7pm peak hours from PV removed link