Outback with Sunnyboy [RE-wrenches]

[Brian Teitelbaum]

Jeff,

In this arrangement, the OutBack's are acting just like the Sunny Island
does.

The Sunny Boy is connected to the "output" of the OutBack inverter (in the
emergency load sub panel that the OutBack powers during a grid failure). The
grid is connected to the OutBack's "input". When the grid goes down, the SB
automatically shuts down, but then the OutBack's internal transfer switch
throws and powers up the sub panel. The SB now "sees" the output of the
OutBack and thinks that the grid is back up. After the 5-minute delay, the
SB comes back on, and can power AC loads directly. PV power not used by the
loads in the sub is sent to the battery for charging.

The relay is used to prevent overcharging. When the batteries are full, the
relay opens the AC circuit to the SB, and it shuts down again, stopping the
charge. When the battery voltage drops, the relay closes, and after another
5-minute delay, the SB comes on again to charge batteries or run loads. The
SB will go on and off like this until the grid comes back on.

When the grid does come on, the OutBack provides the 5-minute delay before
"selling" power to the grid (remember, the SB is connected to the OutBack's
"output", not the "input" wiring that is connected to the grid).

In normal operation, the PV power from the SB goes into the OutBack's
"output", through it's transfer switch, and right back out to the grid, with
no additional loss.

Although this all works fine, I don't think that it is quite as elegant as
the Sunny Island system. The advantage of the SI is that it can communicate
with the SB. It regulates the charging of the batteries by tapering the
output of the SB (through frequency shift), providing a tapering charge, not
just an "on-off-on" process. The really neat thing is that the SI counts the
degree of frequency shift that occurred during the outage, and corrects the
cycle count over the next few hours to make sure that the clocks in the
house stay accurate. How German of them!

Brian Teitelbaum
AEE Solar



 
-----Original Message-----
From: Jeff Yago [mailto:jryago at netscape.com] 
Sent: Wednesday, December 06, 2006 4:34 AM
To: RE-wrenches at topica.com
Subject: RE: Outback with Sunnyboy [RE-wrenches]



I seem to be missing something.   You are using the SunnyBoys in typical
gridtie like a solar charge controller (without batteries) and putting all
output to grid?  You have Outbacks with batteries also installed to charge
battery bank and provide emergency backup power?   During a power outage you
have a power relay controlled from Outback system to dis-connect SunnyBoys
from grid connection?   The SunnyBoys "see" battery charging load and
continue to provide AC to Outbacks?

1.  I thought the whole purpose of the UL and IEEE listing for Gridtie
inverters was to stop their output to the grid if they could not "couple" to
the grid AC sinewave during an outage.

2.  If you use a relay controlled from Outback Inverter to "dis-connect" the
SunnyBoys from grid so they continue to supply AC output back to Outback
inverters to charge batteries and supply load, why dosn't the SunnyBoy shut
down output as soon as it no longer can "see" the dis-connected grid?

I understand the wiring, but not how you get around islanding issues or
automatic shutdown if grid is lost.

Thanks,

Jeff Yago

_____________________________________________________________
Netscape.  Just the Net You Need.


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