hybrid grid tie - SMA / OutBack [RE-wrenches]

[Nick Nicholas, APS]

Hi wrenches:
    I have a Sunny Boy System backfeeding an FX-2024 inverter at a
customer's grid-tied home here in California.  The system has been operating
for over six months, and has worked flawlessly.  We use the FX's voltage
controlled 12V power supply to switch the Sunny Boy off if batteries ever
get too high.  We first tested the system at our store.


            Nick Nicholas
            Chief of Engineering
            Alternative Power Systems, Inc.
            135 Colfax Ave. Grass Valley CA 959545
            530-274-0588 530-274-0589 530-913-5605
            aps at sbcglobal.net alternativepowersystems.com



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Alternative Power Systems
www.alternativepowersystems.com
aps at sbcglobal.net
135 Colfax Ave.
Grass Valley, CA 95945
(530) 274-0588 phone
(530) 274-0589 fax
----- Original Message ----- 
From: "Christopher Freitas --- OutBack Power" <cfreitas at outbackpower.com>
To: <RE-wrenches at topica.com>
Sent: Tuesday, February 10, 2004 6:28 AM
Subject: RE: hybrid grid tie - SMA / OutBack [RE-wrenches]


> Jeff at GlobalResourceOptions.com wrote:
> > If you're talking about back-feeding the AC out on the inverter, this
> > sounds like a smoke producing situation to me. Cannot put AC back in
> > where it comes out on any inverter I know of.
>
> Actually this has been done already and it does work - this is the same
> idea as what SMA calls the "sunny island" system.  The inverter's AC
> output becomes the utility grid to the SMA inverter - keeping it
> operating during the power outage. The AC transfer switch in the OutBack
> inverter keeps the house isolated so we don't cook any lineman.
>
> If the AC loads are large - then the OutBack inverter adds power from
> the battery automatically to the power from the Sunny Boy inverter.  If
> the loads are small,  then the OutBack inverter will "absorb" the power
> produced by the Sunny Boy inverter - converting it into DC and charging
> the battery.  The issue is what happens when the battery gets full?  Use
> the AUX output of the OutBack inverter to disconnect the Sunny Boy
> momentarily or use one of those antique PWM charge controllers laying
> around to divert the excess power to a dump load (or do both options for
> redundancy).
>
> Credit goes to Dave Katz at AEE for being the first brave soul to try
> this on his own house.  He reported that he was even able to manual drop
> the grid by throwing the AC disconnect for the house without the SMA
> tripping off - the transfer time of the OutBack inverter/charger was
> fast enough to not trigger the SMA islanding protection...
>
> So - who's ready to use this in a real off-grid system?
>
> > I would recommend using (3) 24V modules in series if this is a warm
> > weather application (cannot do this in cold regions as you violate the
> > 145VOC limit on the MX60). With this voltage level, you can get down to
> > a "reasonable" wire size. This is much easier than inventing a custom.
> > And MX60's cost less than SunnyBoys as a charge controller. If you were
> > 400' away, I might feel differently, but I'd go for the standard system.
>
> We have had good feedback on using the MX60 with three 24 vdc modules in
> series even in some pretty cold locations.  Some reports of the
> controllers staying off in the morning until the panels warmed up a
> little and the VOC dropped below 140 vdc.
>
> As fun as the micro-grid SMA/OutBack hybrid system sounds - I agree that
> the MX60 and some fairly big wire might be the best option.  The 3200
> watts DC (nameplate) on the SMA might also cause a bottle neck - and
> there is two complete conversions occurring when battery charging (but
> only one when the AC loads are being powered directly from the SMA).
> The MX60 has about 1/2 the losses of the Sunny Boy (97% versus 94%) and
> can handle the 3200 watts DC from the PV array (barely).
>
> Christopher Freitas
> OutBack Power Systems, Inc.
> cfreitas @ outbackpower.com
> www.outbackpower.com
> Arlington WA USA
> Tel 360 435 6030
>
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