Hybrid Car – More Fun with Less Gas

Use a SMA Sunny Boy "off-grid" with OutBack FX inverter/chargers

register ::  Login Password  :: Lost Password?
Posted by Christopher Freitas on January 6, 2004, 12:26 am
OutBack Power offers a line of inverters already that can and are
being used with Sunny Boy Grid-tie inverter systems for these types of
"micro-grid" applications.  Its the same inverter system that we
already are offering and does not require any other changes - it uses
a 48 vdc battery system.  The Sunny Boy is simply wired up on the same
output as the loads.

With this configuration you can create a micro-grid system with PV,
battery and even wind-turbines with or without a utility connection.
Or you can just add battery back-up to an existing Sunny Boy system.

This is an expensive solution for doing off-grid systems compared to
simply using a 48 vdc PV array and battery bank solution. There are
some systems where havign the PV array at higher voltage might be
advantageous - but it gets expensive compared to larger wire or a few
more PV panels.

If you are interested, please email me directly and I will put you in
contact with our distributor that has been working on these types of

Christopher Freitas
OutBack Power Systems
tel 360 435 6030

Posted by William P.N. Smith on January 6, 2004, 1:39 pm
cfreitas@outbackpower.com (Christopher Freitas) wrote:

That sounds like a great way of getting around the "charge balancing
on battery&grid systems" but does it still charge the batteries when
the grid goes out, and sell to the grid when the grid is on?

I'm having a hard time wrapping my mind around how you start selling
power when the batteries are charged, is it just based on battery
voltage, or do you need something like the Smart Shunt to determine
battery state?

William Smith
ComputerSmiths Consulting, Inc.    www.compusmiths.com

Posted by Christopher Freitas on January 9, 2004, 4:27 am
I think your question is in regard to the OutBack inverter/charger
with the PV array connected to it and not going through a Sunny Boy
SMA high voltage inverter...

So with the OutBack System - which is made up of an inverter/charger
and our MX60 PV MPPT charge controller:

We actually do the typical bulk-absorb cycle where we hold the battery
at a voltage (adjustable) for a time period you program in.  Once this
is completed we then lower the "battery" voltage down to a level just
above the rest voltage of the battery back - which eliminates the
losses caused by floating the batteries all the time (such as with the
Xantrex SW series). During both the initial ABSORB cycle and while
holding the batteries at the lower voltage, we sell the excess power
from the PV array which is not going into the battery. The MX60
controller just stays in the MPPT mode during all of this.

If there is not a power outage, or if a power outage occurs but is so
short that no real discharge from the battery has occurred,  the we
simply go back to selling power from the PV array with the battery
held just above its rest voltage when the utility grid returns.

When a power outage occurs and the power output of the PV array
exceeds the power consumption of the AC loads - then the MX60
controller limits the power output of the PV array to keep the battery
voltage at the float voltage level.

The Smart Shunt (under development) will improve the operation of the
system by providing a value for the amount of power removed and put
back into the battery after an outage has occurred.  This is not
essential - but is very nice and will improve the performance IF
outages are frequent.

At night we not only turn off the inverter - but we also disconnect
the transformer of the inverter as well. This eliminates an additional
10 watts or so of idle power consumption from the utility grid.  If an
outage occurs, we are able to turn on the inverter in less than 20
milliseconds to keep the loads running.

Christopher Freitas
OutBack Power Systems
tel 360 435 6030

Posted by William P.N. Smith on January 9, 2004, 1:30 pm
 cfreitas@outbackpower.com (Christopher Freitas) wrote:
[I wrote]

Yes, it was, thanks!

The conceptual part I was having trouble with is that you've got one
device (the MX60) putting current into the batteries, and one (the
inverter) taking power out and selling it to the grid.  How do the two
communicate so that the inverter "knows" how much power is surplus and
can be sold, or is there a separate feed from the MX60 to the inverter
that gives it what might otherwise be lost "shunt" current from the

[Count me amongst those who are very positively impressed by Outback's
involvement in this forum!]


William Smith
ComputerSmiths Consulting, Inc.    www.compusmiths.com

Posted by Robin Gudgel on January 11, 2004, 4:40 am
 I'm just the mechanical engineer at OutBack, but I'll give this a try
since Bob and Christopher are away.
The inverter will sell excess power that would have caused the
batteries to rise over the "SELL" voltage. That "SELL" voltage is
programmable, but we suggest around 13.0 VDC. (I have to think in
terms of 12v batteries). The MX60 does indeed communicate with the FX
inverter during selling to coordinate for maximum power. This is not
required, but we find it helps a bit. The MX60 is set for a higher
voltage charge than what the inverter sell voltage is set for. The
inverter has no choice but to sell to the grid in order to maintain
the SELL voltage. Seems simple.

William P.N. Smith <> wrote in message

This Thread
Bookmark this thread:
  • Subject
  • Author
  • Date
please rate this thread