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Any amount of power will AC couple. <br><br>
If you use an off grid inverter, such as an Outback, to feed the
protected load panel, the inverter should be fed by grid AC power to
supply loads, when the grid is available. Just feed your grid
tie inverter into the protected loads panel. You will need a
relay to shut off power from the grid tie inverter when the batteries are
full. This can be triggered by the fan relay in the Outback.
<br><br>
The on grid inverter will push power into the grid through the battery
inverter's internal transfer switch during normal operation and AC couple
when the power is out. If your grid tie inverter is 240 volts, you
will need to use a transformer or two inverters. <br><br>
The phantom load of the inverter can be eliminated by using a transfer
switch to send PV power straight to the grid, during normal grid
availability, keeping the inverter turned off. AC coupling seems
much easier than using a charge controller, but there is no conditioning
of the batteries. The charge is just on and off at the voltage set
point. For a back up system, that is not much of a problem, as the
battery inverter can maintain the batteries when power is available.
<br><br>
<br><br>
At 02:04 PM 11/9/2011, you wrote:<br>
<blockquote type=cite class=cite cite="">Nice Find, Drake! Thanks.
<br><br>
What is the minimum system for an AC coupled inverter? <br><br>
Again, the idea is for low cost battery backup of an existing grid tie.
The AC coupled schematics I have looked at require a major rewire and
many components. I would like to hear if someone has a simple add on
solution compared to just switching the array to the high voltage
CC.<br><br>
Larry Crutcher<br>
Starlight Solar Power Systems<br><br>
<br>
On Nov 9, 2011, at 6:14 AM, Drake wrote:<br><br>
<blockquote type=cite class=cite cite=""><br>
I vote for the AC coupled system. But if you need to make a 600 VDC
transfer switch, I think you could likely make one from Tyco relays and
voltage controlled relays.
<a href="http://relays.te.com/datasheets/ev200.pdf" eudora="autourl">
http://relays.te.com/datasheets/ev200.pdf</a><br><br>
At 03:16 PM 11/7/2011, you wrote:<br>
<blockquote type=cite class=cite cite="">Ray,<br>
Yes, the idea was for a low cost way to add battery backup to existing
high voltage PV grid tie systems, not new construction.<br><br>
The second inverter does not need to be able to sell since that is
handled by the grid tie inverter. It simple passes grid power to loads
and maintains the battery. That means any off-grid inverter/charger or
even low cost separate inverters and chargers may be used, a very
economical solution. However, the idea may be of no value because it
appears no one makes a transfer switch.<br><br>
Larry Crutcher<br>
Starlight Solar Power Systems<br><br>
<br><br>
<br>
On Nov 7, 2011, at 11:32 AM, Ray Walters wrote:<br><br>
<blockquote type=cite class=cite cite="">Just curious, what's the
advantage of switching at the array vs. just using a Sunny Island or
Outback system? Seems this would cost more, and have less efficiency,
since you would still have the battery float losses, backup inverter idle
losses, in addition to the 2nd grid tie inverter losses. Are there site
specific conditions driving this that I'm not understanding?<br>
I've done quite a few GT systems w/ battery backup, so I'm always up for
new ideas though.<br><br>
Ray<br><br>
<br>
On 11/7/2011 12:15 PM, Larry Crutcher, Starlight Solar Power Systems
wrote: <br>
<blockquote type=cite class=cite cite="">Hi Glen, <br>
That model is a disconnect switch. What the system needs is a 4 pole
transfer switch, automatic or manual, to connect the PV source to the
charge controller.<br><br>
Hello Gary Willit, <br>
Yes, you've grasped my concept precisely and I agree, getting a high
voltage DC transfer switch may nix this design. Sounds like a product for
Midnite Solar to build.<br><br>
<br><br>
Larry Crutcher<br>
Starlight Solar Power Systems<br><br>
<br>
On Nov 6, 2011, at 1:42 PM, Glenn Burt wrote:<br><br>
<blockquote type=cite class=cite cite="">Siemens makes a line that are UL
listed.<br>
Their VBII series like HNF361PV – 30A<br>
<br>
-Glenn</blockquote></blockquote>
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<font size=2>Drake
Chamberlin<x-tab> </x-tab>
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<x-sigsep><p></x-sigsep>
<font size=2>Drake
Chamberlin<x-tab> </x-tab>
<br>
ATHENS ELECTRIC LLC<br>
OH License
44810<x-tab> </x-tab><br>
CO license 3773<br>
NABCEP Certified PV<br>
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