AC Coupled Systems
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Growing market segment
Can be confusing!
Can be complicated!
Numerous ways to go
MidNite has taken most of the mystique
out of the equation
Before we show how to make AC coupling easy,
let’s see just what AC coupling is
Why AC Couple
1. a way to use those expensive grid tie
solar panels during a power outage
2. Provides limited power during a power
outage
3. 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 EPanels
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 here
This 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 prewired 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
The MidNite kitty