Aloha Solar Bozos:
I haven't posted here in ages, and I hope I am cutting out the appropriate
stuff? Probably not, but I will give it a try. I want to reply to Topic 3
regarding backfeeding an off-grid inverter with a grid-tied inverter.
In 2004, I back-fed a SWR-2500U into an Outback FX inverter's back-up power
panel. It required a transformer to step down to 120VAC and a voltage
controlled relay to shut the Sunny Boy off when the batteries were charged.
Greg at OB said that the inverters would regulate the AC output voltage at
~120V, so when the voltage would rise up from the Sunny Boy's production, the
FX was forced to take the power in, resulting in the batteries being charged.
You probably realize that the Sunny Island controls the grid-tied inverter's
output but fluctuating the Hertz, which eliminated that issue for them.
________________________________
From: "[email protected]"
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To: [email protected]
Sent: Monday, August 3, 2009 6:47:22 AM
Subject: RE-wrenches Digest, Vol 2, Issue 818
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Today's Topics:
1. Re: AC Backfeed Battery Over-Charging (Jeff Yago)
2. Broken Modules (Doug Wells)
3. Re: AC Backfeed Battery Over-Charging (Tump)
4. Re: Broken Modules (Jeff Yago)
----------------------------------------------------------------------
Message: 1
Date: Mon, 3 Aug 2009 06:21:56 -0700
From: "Jeff Yago" <[email protected]>
Subject: Re: [RE-wrenches] AC Backfeed Battery Over-Charging
To: RE-wrenches <[email protected]>
Message-ID: <[email protected]>
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Message: 2
Date: Mon, 3 Aug 2009 09:32:08 -0400
From: Doug Wells <[email protected]>
Subject: [RE-wrenches] Broken Modules
To: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset=US-ASCII; format=flowed
Wrenches,
I am curious what other installers are doing with broken modules?
I know some manufacturers are starting recycling programs.
Doug Wells
The Solar Specialists
Morrisville, VT 05661
(p) 802-223-7014
(c) 802-498-5856
www.thesolarspecialists.com
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Message: 3
Date: Mon, 3 Aug 2009 09:39:21 -0400
From: "Tump" <[email protected]>
Subject: Re: [RE-wrenches] AC Backfeed Battery Over-Charging
To: <[email protected]>, "'RE-wrenches'"
<[email protected]>
Message-ID: <cafb0b2ff97b4386bb4ef00df4676...@tumpdggfbh2yn6>
Content-Type: text/plain; charset="us-ascii"
Hey Jeff this was something that Greg @ OB was working on summer of 06.....
Should have it tump, almost got it little problem .... Ahhh sorry we are no
longer working on that! I was in the middle of a large AC Coupled system &
had been waiting for 4 months for this "trick" soft ware to come on line.
Perhaps CF might be able to update us on this software. Kinda of a no
brainier perhaps, John B & the boys @ SMA patented this "trick" software.
<mailto:[email protected]> [email protected] <http://www.swnl.net/>
www.SWNL.net
Solarwinds Northernlights
Serving Mid Coast Maine & Northern California
Me.# 207-832-7574 Cl.# 610-517-8401
Blair "TUMP" May
******** MAINE'S CHARTER ********
NABCEP "Certified PV Installer"
******** MAINE'S CHARTER ********
Trace Xantrex "Certified" Dealer / Installer"
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Jeff Yago
Sent: Monday, August 03, 2009 9:22 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] AC Backfeed Battery Over-Charging
I have a question that may be one of those that everyone wants to know the
answer but feel they are the only one that doesn't know the answer, or
perhaps I am the only one that doesn't know!.
In an AC-coupled system, i.e. the 240 VAC output solar inverter mounted at a
distant array (240 VAC out to reduce long line loss) is wired to the 120/240
VAC output emergency panel supplied from a battery based inverter. This
allows the solar inverter to stay up when the grid goes down since it thinks
the grid is still up on the load side of the battery based inverter. The
battery based inverter will use any excess backfed power from the solar
inverter that is in excess of the other supplied loads to re-charge the
battery. However, when this happens the battery charging process can boil
the batteries when there are no other loads running.
I have been told this is because the battery based inverter does not
regulate its charging of the battery when using backfed power from its
output panel, but I still don't understand why. If the battery charger in
the inverter can provide regulated 3-stage battery charging when the power
is supplied from the grid or a generator, why does it suddenly become a full
output un-regulated battery charger when power is supplied from backfeed and
will keep charging regardless of reaching a high battery voltage?
I would have assumed the battery charger section would charge the same way
regardless of where the power is being supplied from, or perhaps just
shutdown on some kind of backfeed safety. As far as I know, this
over-charging problem in an AC coupled dual inverter system is true for all
battery-based inverters. Any inverter techs out there that can explain
why? Perhaps this would be a nice feature in future high-end battery-based
inverters so we no longer need the custom power relay field wiring to
provide this high voltage cut-out?.
Thanks,
Jeff Yago
_____
Netscape. Just the Net You Need.
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Message: 4
Date: Mon, 3 Aug 2009 06:47:21 -0700
From: "Jeff Yago" <[email protected]>
Subject: Re: [RE-wrenches] Broken Modules
To: RE-wrenches <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="UTF-8"
We have only had one broken module due to shipping damage and this was the
bottom 200 watt module in a shipment where each 2 modules on the pallet were in
heavy cardboard shipping boxes. Of course this not discovered for several
weeks until we worked our way down the stack. However, since suppliers like
Evergreen have switched to the plasic corners that allow stacking modules
without any cardboard packaging, we have had no more breakage in shipment. I
assume the fork truck drivers now see a large stack of glass and take a little
more care whenre thay ram the forks.
As far as what we did with our broken module (which taught a very expensive
lesson about checking shipments), we keep it to show students in our training
classes what happens when things go wrong.
Jeff Yago
_____________________________________________________________
Netscape. Just the Net You Need.
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