Help adding flexible battery storage to existing net-metered solar w/ generator

[tabula_rasa]

Looking for help with a system re-design for adding super flexible battery storage to a non-standard net-metered micro-inverter solar install with backup generator.

End Goals:

• Grid-tied time of use storage arbitrage
• Immediate battery fail-over w/ grid forming during outage
• Ability to charge batteries w/ grid during off-peak hours
• Ability to charge batteries using generator without grid
• Ability to charge batteries w/ solar with or without grid
• Bonus: Ability to charge batteries using solar and generator simultaneously without grid
• Bonus: Ability for generator to start on-demand to supplement the battery inverters + solar output without grid (Would consider only 2 inverters if this is possible)

Constraints:

• Batteries must be located in detached garage located ~80 ft away
• Avoid deep 18-24" re-trenching to detached garage (shallow low voltage re-trench begrudgingly acceptable)

Existing Equipment:

• 22kW Generac Generator
• 2x 200A Generac RXSW200A3 ATS
• Enphase IQ Combiner 3-ES
• 25x Enphase IQ7+ (340w panels)

Existing Layout:

120/240 split-phase 200A meter w/ primary disconnect feeds a tap box with 3 downstream connections to (1)Enphase IQ Combiner 3-ES, (2)House ATS, (3) Detached Garage ATS which are all co-located with the generator which is connected to both ATS switches. Each ATS then feeds a 200A load center with an 80ft trenched conduit to the detached garage load center. When grid goes down solar goes offline and generator picks up full load.



Proposed Equipment:

• 22kW Generac Generator
• Enphase IQ Combiner 3-ES
• 25-33x Enphase IQ7+ (340w panels)
• Enphase IQ System Controller 2
• 4x Victron MultiPlus-II 2x 120V 3kW
• 6x Vestwoods LiFePO4 100Ah 48v

Proposed Layout A:
200A 120/240 split-phase meter w/ primary disconnect along with 22kW Generac Generator each feed new Enphase IQ System Controller 2 which then feeds a tap box with 3 downstream connections to (1)Enphase IQ Combiner 3-ES, (2)Home Load Center, (3)Garage Load Center (~80ft away via trenched conduit). Garage load center connects to 4x Victron MultiPlus-II 2x 120V 3kW's operating in parallel split phase mode which are connected to rack mounted batteries.




Alternative Layout B:
200A 120/240 split-phase meter w/ primary disconnect along with 22kW Generac Generator both feed 4x Victron MultiPlus-II 2x 120V 3kW's operating in parallel split phase mode which feed tap box with 3 downstream connections to (1)Enphase IQ Combiner 3-ES, (2) Home Load Center, (3) Garage Load Center (~80ft away via trenched conduit). Batteries in garage connect back to inverters via new 80ft shallow low voltage trenched conduit.



The difference being layout B does away with Enphase IQ System Controller 2 and moves inverter location to serve as "smart ATS" instead but would require a new (hopefully shallow?) ~80 ft low voltage DC trench to detached garage where batteries are located.


Questions/Concerns:

• Not confident that Victron inverter can actually operate like I've laid out.
• Not at all confident that Enphase IQ System Controller 2 is right choice for my "smart ATS" or that it will be compatible with Victron inverters? Any good alternatives for either?
• Concerned about back-feeding and overloading generator with solar / inverter output.
• How exactly will generator know when to start or stop? Assume low voltage comm wires will need to be run between generator and Victron inverters or can Enphase IQ System Controller 2 (or similar "smart ATS") signal the generator?
• I've seen threads in experimental section of forums discussing how Victron inverters can frequency shift control IQ7+ (on/off at least, maybe not stepped?) but perhaps only when operating in full off-grid mode?
• If layout B, DC voltage drop between batteries and inverters may be rough over ~80ft?
• With layout A, would it be possible to use Enphase IQ8X-BAT as my battery inverter instead with non Enphase battery rack?

Thank you all very much for your help sorting through this complicated mess!

Edit: Added revised graphical summaries of layouts.

 

[sunshine_eggo]

Too much info, and there are several portions outside of what little expertise I may possess. Some comments:

Run the voltage drop calculations for 80' of battery cable and calculate the $ to keep it reasonable. Okay, the link will take you to it. Have you priced out 480' of 1/0 awg? Probably north of $1800 in copper.

You absolutely, positively do not need the 2x units. Those are purpose built for 50A RVs to allow for easy switch between 30 (120V) and 50A (120/240V split phase) shore power. They are not split phase and add a layer of complexity at an increased cost for no benefit to your situation.

You simply want the standard 4X MP-II 48/3000 units instead.

By your choice of Victron, I assume code compliance is not important at all. Victron inverters are not UL listed and depends on the AHJ accepting your non-listed equipment.

 

[tabula_rasa]

Thanks for the help!

I ran a calculator for 80 ft of 3/0 copper which works to $1100.

Good call on the inverter model, I should have specified the model you listed not the 2x. UL compliance would be nice for extra peace of mind but not required. If anyone can point out other suitable inverters that meet goals I'm all ears!

 

[sunshine_eggo]

You would need two pairs of conductors or a total of 320 ft of 3/0 to keep voltage drop under 3%.

Any of the Teir 1 inverters, Outback, Magnum, Schneider, etc. should work with AC coupling.

 

[tabula_rasa]

Just realized 4/0 can be had for same price as 3/0 oddly and doubling conductors up would mean $2150 in copper to see sub 2.5% drop which is certainly pricey but better than batteries in home. Conceivable at least a few feet could be shaved off the run as well as I'm overestimating.

Of inverter brands you listed seems these models may be of interest for consideration:

• Outback Radian GS4048A/GS8048A
• Schneider Electric Conext XW Pro 6.8 kW Hybrid Inverter
• Magnum MS4448PAE

Will look into inverter specs in the AM, thanks for your help everyone!

 

[timselectric]

Constraints:

• Batteries must be located in detached garage located ~80 ft away

IMO
This is a horrible constraint.
You will be better off buying a larger fuel tank for your generator. And forgetting about batteries, all together.

 

[sunshine_eggo]

Just realized 4/0 can be had for same price as 3/0 oddly and doubling conductors up would mean $2150 in copper to see sub 2.5% drop which is certainly pricey but better than batteries in home. Conceivable at least a few feet could be shaved off the run as well as I'm overestimating.

Of inverter brands you listed seems these models may be of interest for consideration:

• Outback Radian GS4048A/GS8048A
• Schneider Electric Conext XW Pro 6.8 kW Hybrid Inverter
• Magnum MS4448PAE

Will look into inverter specs in the AM, thanks for your help everyone!

It's worth looking at locating the inverters at the battery and comparing the cost/efficiency of running AC that distance.

 

[400bird]

Where's the generator?

If it is close to the main house, could you build a nice little shed next to it for the batteries and avoid the ridiculous 80' battery run?
Is there anywhere near the house panel/Enphase equipment that could could build a nice little dedicated battery shed?

Schneider specifically calls out a max battery cable length of 10' one way for the XW pro.