Adding battery backup to grid tie array... high voltage DC xfer switch?

[Chris_NH]

Hi. I installed my own small grid tied system myself on the garage roof 15 years ago. I want to add a small battery backup to utilize the solar panel power generated when grid down in order to run a few critical circuits when the power is out.

Current array is twelve 220watt 24v panels in series sending 330ish volts to a dsquare disconnet, then to the Sunny Boy GTI to a 100a subpanel in the garage to our main 200a house panel.

I think I want to add a DC transfer switch just after the dsquare mechanical DC disconnect so that when power goes out I can redirect the 330v array to an all-in-one inverter/small battery bank. Don't know if I'd go auto or manual transfer switch.

What products are available to make this all happen? What's available on the market for a transfer switch that can handle 400volts DC?

I also have ten 100w 12v panels that have not been utilized in a number of years and I think I want to mount them to keep the battery bank topped off and run the few things I run in the garage where all this will be mounted.

I was thinking a EG4 3000EHV-48 since it can handle 500v and 1 or 2 of the EG4 Lifepower4 48v 100ah server rack batteries to keep it budget friendly, but not sure yet.

All input welcome and appreciated.
Chris

 

[12VoltInstalls]

was thinking a EG4 3000EHV-48

want to add a small battery backup to utilize the solar panel power generated when grid down in order to run a few critical circuits when the power is out

Don't know if I'd go auto or manual transfer switch

Does not the EG4 have a built-in transfer switch?

Most AIO’s do.

So you’d set the aio to pass through grid power and run your critical loads fulltime on that; when power goes out it turns off ‘grid’ and switches to battery in a few milliseconds.
That’s what I might do.

 

[CRenner]

Can the Sunny Boy handle batteries?
The EG4 is only 120v.
Do you want this automatic or manual? Meaning you would have to flip breakers and turn it on.

 

[Chris_NH]

Can the Sunny Boy handle batteries?
The EG4 is only 120v.
Do you want this automatic or manual? Meaning you would have to flip breakers and turn it on.

The Sunny Boy is just grid tie.

I would only activate/transfer to single pole 120v critical breakers. Wouldn't think of using the clothes dryer or hot water heater on the batteries. For long outages I'd wheel out and plug in the generator like I've been doing right along. The hookup for that is on the main house right into the main 200amp services where the panels and Sunny Boy are on the detached garaged, feeding the 100amp subpanel there.

Not really sure if auto or manual is preferable to me. I guess I wouldn't mind it done auto, but I kinda figured it'd be manual to keep the cost down and safety factor up.

 

[Chris_NH]

Does not the EG4 have a built-in transfer switch?

Most AIO’s do.

So you’d set the aio to pass through grid power and run your critical loads fulltime on that; when power goes out it turns off ‘grid’ and switches to battery in a few milliseconds.
That’s what I might do.

I'm not sure if it has built in xfer switch, but I'm not the type to trust tech in this lower price range to something like that even if it did.

If it worked like you described reliably it would be great.

 

[CRenner]

I put an hybrid inverter and batteries on an interlock device in the main panel.
When the grid goes down, I have to turn on the batteries, inverter, disconnect the main breaker and connect the inverter ( that all take 15 seconds).
All circuits are powered and it is up to me to disconnect any I don't want.

 

[12VoltInstalls]

I'm not sure if it has built in xfer switch, but I'm not the type to trust tech in this lower price range to something like that even if it did.

If it worked like you described reliably it would be great.

My tiny 1012LV-MK works great and has for ~2 years now. The ATS feature gets used whenever I pull the generator cord.

I’d call it quite reliable.

 

[Chris_NH]

I put an hybrid inverter and batteries on an interlock device in the main panel.
When the grid goes down, I have to turn on the batteries, inverter, disconnect the main breaker and connect the inverter ( that all take 15 seconds).
All circuits are powered and it is up to me to disconnect any I don't want.

Sounds simple enough. Do you have grid tie also? And if so, do you have a manual transfer switch to redirect the array to the hybrid inverter, or does the inverter handle the switch?

 

[Hedges]

The way I transfer PV DC between two inverters is turn off DC disconnect, unplug MC3 cables, swap them to other MC3 connections.
I use MC3 because they have no locking mechanism. You could cut latch off MC4. Just make sure fully mated when in use.
My plan was to have the connectors inside box of a visible blade disconnect; cover is latched while switch is on. I haven't done that yet.
This is for two 600V SMA inverters, you could do similar with multiple connections for lower voltage input of a hybrid.

Panels are cheap enough today that separate array for offgrid inverter is an option.
You could get a hybrid that backfeeds the grid to use power from those panels all the time.
Could replace GT PV inverter with hybrid.

Which model Sunny Boy?
Probably not one that supports offgrid mode, but if it does then you could AC couple to a battery inverter. More involved and more expensive than cheap off-grid inverter, but makes a very capable system.

 

[CRenner]

Sounds simple enough. Do you have grid tie also? And if so, do you have a manual transfer switch to redirect the array to the hybrid inverter, or does the inverter handle the switch?

My Enphase is grid-tied to the main panel.
The inverter is off 99% of the time.
Interlock device is manual.