Any amount of power will AC couple.
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.
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.
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.
At 02:04 PM 11/9/2011, you wrote:
Nice Find, Drake! Thanks.
What is the minimum system for an AC coupled inverter?
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.
Larry Crutcher
Starlight Solar Power Systems
On Nov 9, 2011, at 6:14 AM, Drake wrote:
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. http://relays.te.com/datasheets/ev200.pdf
At 03:16 PM 11/7/2011, you wrote:
Ray,
Yes, the idea was for a low cost way to add
battery backup to existing high voltage PV
grid tie systems, not new construction.
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.
Larry Crutcher
Starlight Solar Power Systems
On Nov 7, 2011, at 11:32 AM, Ray Walters wrote:
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?
I've done quite a few GT systems w/ battery
backup, so I'm always up for new ideas though.
Ray
On 11/7/2011 12:15 PM, Larry Crutcher,
Starlight Solar Power Systems wrote:
Hi Glen,
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.
Hello Gary Willit,
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.
Larry Crutcher
Starlight Solar Power Systems
On Nov 6, 2011, at 1:42 PM, Glenn Burt wrote:
Siemens makes a line that are UL listed.
Their VBII series like HNF361PV 30A
-Glenn
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