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Feeding solar power back into municipal grid: Issues and finger-pointing - Page 19

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Posted by krw@att.bizzzzzzzzzzzz on April 18, 2011, 1:33 am

Again, physics doesn't care what you like and don't like.  It is.

Well, I guess you could say that "currents" push against each other, but it
requires a difference in voltage to have a current.  Think of the intersection
of two rivers.

You assume wire has zero resistance.  Bad assumption.

That is "said" has little bearing on physics.

The biggest flaw is that resistance is not zero and you take what people "say"
too literally.  Analogies are always flawed.  That's why they're called
"analogies".  ;-)

Posted by krw@att.bizzzzzzzzzzzz on April 18, 2011, 3:31 am

Let me say it again, perhaps you'll catch on.  Physics doesn't care what you
like.  It is what it is.

Because, like electricity, water always flows "down hill" - high to low.

Voltage is dropped across a resistance.  Not all points in the grid go up
because your solar cells output more voltage because there is non-zero
resistance between all points.  If you're generating electricity, your house
will be at a *higher* voltage than the pole.  If the resistance of the wire
were zero this couldn't happen.

Posted by Jim Wilkins on April 18, 2011, 2:19 am
It makes more sense if you think of the inverter as forcing a constant
CURRENT and let the voltages be whatever the source (wire etc)
resistance makes them at that current.

The grid may or may not act like an infinite sink. The continual load
variations will probably swamp out any voltage measurement you might
make, so it's reasonable to consider it an infinite sink unless you
have a very large inverter. The GTI wants to dump all the current from
the array onto the line and will adapt itself to the line voltage,
whatever it may be.

If you connect a PV panel to a 12V battery the panel will source as
much current as the sunlight produces, at the voltage of the battery
even if the panel's open circuit voltage is above 20V. The battery
voltage will rise a little because of the IR drop in its internal



Posted by David Nebenzahl on April 18, 2011, 3:40 am
 On 4/17/2011 7:19 PM Jim Wilkins spake thus:

It *sounds*--and I'm sure you'll correct me if I'm wrong--as if you're
agreeing with me, and with Smitty, and others when we say that it is
*not* required that the photovoltaic inverter supply a higher voltage in
order to transfer current to the grid. (I take this from the last
sentence in the next-to-last paragraph, where you say " ... will adapt
itself to the line voltage, whatever it may be".)

The arguments against this, with all the pseudo-science being thrown
around (most of it by the ones who are also slinging insults) are
getting quite tiresome here.

The current state of literacy in our advanced civilization:

   wan2 hang

- from Usenet (what's *that*?)

Posted by krw@att.bizzzzzzzzzzzz on April 18, 2011, 3:49 am

No, the voltage will STILL be higher if you're supplying current to the grid.
Wires have resistance.  Current sources don't go against physics and really
are the same thing as voltage sources (Norton/Thevenin duality).  Physics
doesn't lie.  

You're throwing around the pseudo-science.  If you don't like the treatment,
you can easily leave.  

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