DIY ac/dc coupling mess

[owner124]

Hi all, ive been reading threads till my eye balls bled. and hopefully someone can confirm or point me in a better direction.
I have a 6kw 24panel with solaredge optimizers feeding a solaredge gridtie inverter. I originally put the solar in to use a backup power source for hurricane season here in florida. but being i still have use for both of my kidneys i didnt want to sell one to buy a powerwall. a few months ago i bought Samsung SDI ESS Energy Storage Battery 16S 60 Volt - Used 13.2 kWh Rack Mount. However my solaredge inverter will only communicate with a LG chem pack or the powerwall. according to solaredge (they refuse to help me) ugh!
So here is my down and dirty plan. have the battery bank feed a 48vdc - 240ac inverter, use a disconnect to mains from solaredge and feed the 240 back into solaredge. so in theory the panel optimizers will see the signwave and turn on, feeding the solaredge inverter which will go to a critical sub panel. and here it gets even crazier, use a 110vac prismatic battery charger for my 60v battery bank while the sun is out?

Is any of this possible? or should i just give up and find a good surgeon.

 

[SolarQueen]

Here's a very detailed white paper with schematics from Outback on how to wire up an AC Coupling system. https://www.altestore.com/static/datafiles/Others/Outback_AC_Coupling_AppNote.pdf

 

[owner124]

thx solarqueen. that solution does looks nice. however it comes with a $4k price tag with it. and unfortunately above my budget for this project.

 

[SalckwareRobert]

Have you thought about maybe selling a part of your liver? It grows back in 6 months. LOL

 

[svetz]

Sadly the Outback solution works with Outback gear and is engineered for their devices, can't just swap components willy-nilly.

... solaredge gridtie inverter...Samsung SDI ESS Energy Storage Battery 16S 60 Volt - Used 13.2 kWh Rack Mount. However my solaredge inverter will only communicate with a LG chem pack or the powerwall...

Just throwing this out there... could you get a powerwall or LG Chem pack "front end" off eBay for communication (e.g., no or dead batteries) and use your batteries on the back end?

 

[Ampster]

Unless the OP has a StorEdge model of Solaredge inverter his only way to do what he wants is with AC coupling. Outback, Powerwall and others do that but as he found out they are expensive. My Outback Skybox AC couples with Enphase microinverters seamlessly and I anticipate it will also work with my Solaredge GT inverter when I rewire my sub panel.

 

[Paul_in _Berkeley]

thx solarqueen. that solution does looks nice. however it comes with a $4k price tag with it. and unfortunately above my budget for this project.

What are you spendings $4k on? 4kW of Radian inverter is closer to half that... even less used.

 

[SolarQueen]

What are you spendings $4k on? 4kW of Radian inverter is closer to half that... even less used.

The problem is the battery inverter has to be larger than the grid tied inverter, as it has to handle all of the power going through it. So with his 6kW inverter, he'd need the more expensive 8kW Radian.

 

[SolarQueen]

So here is my down and dirty plan. have the battery bank feed a 48vdc - 240ac inverter, use a disconnect to mains from solaredge and feed the 240 back into solaredge. so in theory the panel optimizers will see the signwave and turn on, feeding the solaredge inverter which will go to a critical sub panel. and here it gets even crazier, use a 110vac prismatic battery charger for my 60v battery bank while the sun is out?

Is any of this possible? or should i just give up and find a good surgeon.

The reason you can't do this as described without a battery based inverter, is grid tied inverters like your SolarEdge don't generate a sine wave. They just ride on top of the existing grid wave. If you remove the grid, there is no wave to ride on. That is why AC coupling is required. Battery based inverters do create the sine wave, and when you feed it back to the grid tied inverter, it can sync up and go along for the ride. Unfortunately, there is no cheap solution for what you have.

 

[Hedges]

The problem is the battery inverter has to be larger than the grid tied inverter, as it has to handle all of the power going through it. So with his 6kW inverter, he'd need the more expensive 8kW Radian.

Does his SolarEdge grid-tie inverter respond to frequency shift and reduce power output (so it can be adjusted to match load)?
If not, then yes the battery inverter has to swallow all power not used by the house. (Hmm, just need a couple space heaters as "dump load"?)

If it does respond to frequency, Sunny Island can manage twice its rating in AC coupled loads. E.g. two, 6kW Sunny Island can work with four, 6 kW Sunny Boy.
(but even one would break the bank for him. Unless he gets one on eBay for $1500 and adds a 120/240V transformer)

 

[Hedges]

How about selecting a low priced hybrid inverter capable of using your battery pack.
Rewire some quantity of your existing PV panels onto the hybrid inverter.
You should then have a battery-backed UPS with PV charging.
Depending on the inverter, it may also be able to backfeed surplus PV into the grid. But most economical ones may only use PV for downstream loads.

If you just want to PV/Battery backup selected loads like refrigerator, this may be a reasonable compromise option.