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On/Off grid inverters

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David Lesher

Jan 1, 1970
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I'm looking for make/models of inverter systems that can work in
two different cases:

a) Grid-tie; when excess PV output is sold back to the utility.

b) Offline backup: When the grid's dead; you draw down on
battery backup, and/or generator.

While some folks talk about doing both in one box, it appears
both regulatory and technology issues generally preclude same,
at least in the 15KW/3ph. and up PV range.

Further, we want to take advantage of the PV capacity
whenever. In other words, in b) mode, we want the PV output to
supply loads, including battery recharge. Most of the vendors
I've looked at fall down in that regard.

(At first, I thought it could be done at the DC level, but no
joy there; the grid-tie inverters want DC strings in the hundreds
of volts; the stand-alone ones are expecting 48V or other lower
voltage DC inputs.)

Sunny/aka SMA tells me they can not only recharge the battery
plant from the PV inverter, but if the array can't keep up; it
will request a generator start and all three 60 Hz. sources will
play, in tune as needed.

So my questions:

1) Has anyone here used such a system?
2) Know of any other venders of such cooperative systems?
 
B

Bill

Jan 1, 1970
0
Well the idea of grid tie (called net metering) is that you don't need
batteries. The grid acts as a battery. This is what is attractive to me, I
would not need batteries. And I like that because batteries are expensive
and don't last forever.

I think Xantrex makes one that will also work off-grid? Then you could use a
battery charger I would assume...

Xantrex which now seems to be "Schneider"...
http://www.schneider-electric.com/c...&f=F13:Renewable+Energies&p_function_id=15210

Then there are plenty of 120 volt AC or 240 volt AC battery chargers.

And you can get a transfer switch for the generator.



"David Lesher" wrote in message
 
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David Lesher

Jan 1, 1970
0
Bill said:
Well the idea of grid tie (called net metering) is that you don't need
batteries. The grid acts as a battery. This is what is attractive to me, I
would not need batteries. And I like that because batteries are expensive
and don't last forever.

And when the grid fails?
I think Xantrex makes one that will also work off-grid? Then
you could use a battery charger I would assume...
Xantrex which now seems to be "Schneider"...
Then there are plenty of 120 volt AC or 240 volt AC battery chargers.
And you can get a transfer switch for the generator.

If only it were that simple. One big goal is: use solar power
when both on and off grid. I've seen several schemes that just
shut down the PV input when offgrid.
 
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David Lesher

Jan 1, 1970
0
Using the grid as your battery doesn't help you when th grid is down.
We went 30 days with no grid in the Ice Storm of '98.

Bingo. We'll have a propane generator, but it's big, noisy and $$$$ to run
for long.
 
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David Lesher

Jan 1, 1970
0
It's easy to do 3 phase with outback inverters, just takes 3 units to
do so. I've done it, so I know it works, both 3 phase and grid tie.

I spoke to them today, and they stopped me at the "208 3phase"
line in my query.

Further, they seem to be trailing the pack re:
monitoring/control software. They have no networkable
scheme. There's a "Mate" but it's USB, not Ethernet.
 
D

David Lesher

Jan 1, 1970
0
It is that simple. Outback and xantrex offer PV/battery primary, grid
optional, and PV/grid primary, PV/battery backup modes. In the pv/
battery primary role, the idea is that power is only taken from the
grid if the batteries are low due to low sun conditions, and only long
enough to bring the batteries up to a specific SOC. Outback calls it
their HBX mode.

Finally found a human at Xantrex [in Vancouver] who was helpful, but could
not find any references to 3ph 208 Wye systems that they offer. I sent her a
note to forward to apps engineers.

We want grid-tie such that ONLY PV output is sold,, never battery->grid.
Interestingly, PGE swears upsidedown and sidewise that they NEVER allow
a grid-tie with batteries attached; while both Xantrex and Outback say theirs
have same; and one, ISTM Outback, said that's how they think battery->grid,
with PV being battery recharge.
 
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