AC COUPLE

AC Coupled Systems

• Growing market segment• Can be confusing!• Can be complicated!• Numerous ways to go• MidNite has taken most of the mystique

out of the equation

One inverter capable of AC

coupling

The SMA Sunny Island is the most difficult inverter to hook up to pass

inspection

More on that later

OutBack inverters were the first to AC couple, but each inverter is only 120VAC• Grid tie

inverters are 240VAC

• 2 inverters required in this setup

It is interesting to note that 90% of this system would be the same for off-grid or battery backed up grid tie.

Can you tell which type this is?

120V Magnums are also not easy to AC couple

Yes, you can even screw

up a MidNite E-Panel for

the XW inverter.

This is functional, but messy

Before we show how to make AC coupling easy, let’s see just what AC coupling is

Why AC Couple1. a way to use those expensive grid tie

solar panels during a power outage2. Provides limited power during a power

outage3. Allows the installer to go visit their grid tie

customers with something useful to sell

What is AC Couple• AC Coupling is a controlled back feed to a

battery based inverter• A back feed is hooking up AC to the output

of an inverter• Normally when you back feed an inverter,

they blow up (try it sometime, smile)• AC coupling is a synchronized back feed• The grid tie inverter shifts frequency to

match the battery based inverter before connecting. This makes it ok to do

AC Coupling of inverters

• Battery-less grid tie inverters require a grid to be connected before they will turn on. The grid must meet certain voltage and frequency parameters.

• You have all heard about anti-islanding requirements that the inverters must meet

• Battery based sinewave inverters can meet these requirements

• Inverters do not need to be grid tie listed

AC Coupling of inverters

• Not all battery based sinewave inverters are capable of backfeed.

• Your choices in North America are:• SMA Sunny Island• Outback FX, VFX and Radian• Magnum PAE series• Schneider XW series

SMA Sunny Island

AC Coupling of Inverters

• The Sunny Island and Sunny Boy communicate with each other to insure proper battery charging during a power outage.

• No other inverter combination can claim this

SMA Sunny Island

Since the Sunny Boy output is

240VAC and the Sunny Island

input is 120VAC, a step down autoformer is

used

SMA Sunny Island

Notice that the output of the SB connects to the output of the SI

The autoformer changes 240V to

120V

SMA Sunny Island

The SI inverter has only one AC

input. We provide an

optional ATS that5 fits inside

our SMA E-Panel

The Sunny Island/Sunny/

Boy combination was designed to be AC Coupled

They thought of everything

(from a European point

of view)

SMA in Germany still has problems with the US

NEC code. The Sunny Island is

not easy to install to meet

code

SMA had been requesting that MidNite Solar make them an

E-Panel for years. We finally

did

We did not realize how big a deal this was

going to be!

The pre-wired system shown

here is as plug and play as they come

The top piece is the autoformer

Battery box and cabling is included

and drop ships where you want it

E-Panel with ATS

option installed

All SMA E-Panels

come wired for 240VAC

(2 SI inverters)

E-Panel shown with AC bypass switch, 500 amp shunt

and sub panels

breakers installed

Dual systems do not require an autoformer

Need a large AXC coupled system?

We even designed a 1000 amp battery combiner for this system

SMA AC Coupled systems

• SMA AC Coupled solutions for 1 to 4 inverters

• 4,500 watts to 24,000 watts• Purchase pre-wired and tested or parts• Remember those tech service people we

mentioned? You may need to involve them on your first system.

Enphase AC Coupled systems

• Enphase systems are pretty much the same as all others

• When using a Magnum PAE inverter, you must limit the PV array to less than 4000 watts.

• Failure to do this will result in inverter failure

• Magnum is the easiest for Enphase AC coupling

This exact

system is now on our

price list and

available for order

The disco combiner is

there for reference only

We do have a three string AC disco combiner

The Grid Tie inverter

shown can be Enphase or any 240VAC grid tie up to 4000 watts of actual output

Since the two different

inverters have no

communication, we install a SSR

to knock the grid tie off line

as required

This is a pictorial wiring diagram

Uncontrolled battery charging

• Magnum and OutBack inverters charge batteries from AC connected to their outputs

• The inverters sense circuits that control charging are on the AC inputs not the output, therefore cannot control charging

• These inverters charge wide open and cannot taper off.

• A relay is required to disconnect the GT

Uncontrolled battery charging

• SMA has controlled battery charging and tapers off as the batteries get charged

• This requires that the AC coupled system is comprised of a Sunny Island and Sunny Boy. They were designed to work together.

• No external relay required

Uncontrolled battery charging

• Schneider WX shifts frequency to knock the grid tie inverter off line for 5 minutes.

• The XW does this with any brand grid tie inverter, but battery charging does not taper off.

• No external relay required

Uncontrolled battery charging

• OutBack inverters do not taper off like the SMA, nor do they shift frequency like the XW

• You must add an external relay between the grid tie inverter and the battery based inverter

• The OutBack aux output can supply the power & control to drive an external relay

Uncontrolled battery charging

• Magnum inverters do not taper off like the SMA, nor do they shift frequency like the XW

• You must add an external relay between the grid tie inverter and the battery based inverter

• The Magnum router can supply the control to drive an external relay, but not the power

The solid state relay eliminates battery over charging

Hook up the output from your grid tie inverter here

Hook up the sub-panel hereThis is the AC output of the

inverter

Hook up the mains utility connection here

Hook up the neutral and ground connections from the main

distribution panel here

4000 watt limit

• This limit only applies during power outages

• We have another method that allows larger arrays, but reduces the array power during outages

• This is a radical modification, but works

A solid state relay is placed inside the combiner to reduce quantity of strings

This is a self contained pre-wired AC coupled system

All wiring is behind the breaker panel

All required over current and disconnects are in place, wired

and tested

Multiple battery configurations available. Shown is just one

The enclosure

for this system is

made from aluminum

and is suitable for

outdoor locations

Nice looking AC coupled addition

to an existing grid tie system

OutBack and Schneider

• 2 OB inverters are required for AC Coupling.

• OB offers superior regulation during outages and has a built in aux circuit

• Schneider offers a good inverter for AC coupling. The XW will shift frequency to knock the GT offline

Install responsibly, always use protection

SPD 600’s installed in Montana

The MNBCM is very inexpensive ($69 list)It offers at a glance assurance that the

batteries are full.Do not waste your money on a shunt based battery monitor for an AC coupled system.

The batteries are always full.

Three technical support people

• All three will be able to help answer your questions. Ryan, Tom and Kim

• Beware, Kim will try to sell you something

MADE IN USA

The MidNite kitty