Posted by krw@att.bizzzzzzzzzzzz on April 18, 2011, 1:33 am
wrote:
>> No, you can't get on the "freeway" unless you're going faster than 60.
>> If you're going slower (or the same speed as you say,)
>> they're actively pushing you off.
>I've chewed this over a bit, and I still don't like it, and here are my
>reasons:
Again, physics doesn't care what you like and don't like. It is.
>1: Voltage sources in parallel do not push *against* one another.
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.
>2: If no voltage source can join the grid without being at a higher than
>grid potential, then every contributing power station would have to be
>at a higher potential than every other one, and that's impossible.
You assume wire has zero resistance. Bad assumption.
>3: While voltage might *push*, it's the load that it said to *pull* the
>current. If there's a demand, current will flow whether the supply
>voltage is 119, 120 or 121.
That is "said" has little bearing on physics.
>Where is my thinking flawed?
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
wrote:
>> wrote:
>>
>> >
>> >> No, you can't get on the "freeway" unless you're going faster than 60.
>> >> If you're going slower (or the same speed as you say,)
>> >> they're actively pushing you off.
>> >
>> >I've chewed this over a bit, and I still don't like it, and here are my
>> >reasons:
>>
>> Again, physics doesn't care what you like and don't like. It is.
>>
>> >1: Voltage sources in parallel do not push *against* one another.
>>
>> 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.
>>
>> >2: If no voltage source can join the grid without being at a higher than
>> >grid potential, then every contributing power station would have to be
>> >at a higher potential than every other one, and that's impossible.
>>
>> You assume wire has zero resistance. Bad assumption.
>>
>> >3: While voltage might *push*, it's the load that it said to *pull* the
>> >current. If there's a demand, current will flow whether the supply
>> >voltage is 119, 120 or 121.
>>
>> That is "said" has little bearing on physics.
>>
>> >Where is my thinking flawed?
>>
>> 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". ;-)
>None of the things you just said mean anything. Saying it's "due to
>physics" is meaningless. I know wire has resistance, so what? And I'm
>sure you know that when I said "I don't like it" I meant "I don't agree
>with it."
Let me say it again, perhaps you'll catch on. Physics doesn't care what you
like. It is what it is.
>And, uh, rivers don't fight against tributaries, last I
>checked, but you shouldn't be using analogies if you don't think they
>hold water. So to speak.
Because, like electricity, water always flows "down hill" - high to low.
>You are billed by how much current you draw. Let's say your normal
>consumption is a steady 1 kw. Now you start generating 100 watts. So now
>you're only drawing 900 watts from the rest of the grid, and that,
>multiplied by hours, is what you get charged for.
OK.
>OTOH, let's say you install some bigger panels, and you can generate
>1500 watts. Now your net consumption is *minus* 500 watts, so you're
>pumping 500 watts into the grid, and, hopefully, being compensated for
>that by the power company. You're using 1 kw locally, and delivering the
>rest where it's needed elsewhere.
OK.
>I seriously fail to see where the resistance of the wire has anything to
>do with it. Please don't tell me "that's just the way it is." If I'm
>wrong, give me a reasonable and logical argument.
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
> ...
> Where is my thinking flawed?
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
resistance.
http://en.wikipedia.org/wiki/Current_source
jsw
Posted by David Nebenzahl on April 18, 2011, 3:40 am
On 4/17/2011 7:19 PM Jim Wilkins spake thus:
>
>> ...
>> Where is my thinking flawed?
>
> 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
> resistance.
>
> http://en.wikipedia.org/wiki/Current_source
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:
yo
wassup
nuttin
wan2 hang
k
where
here
k
l8tr
by
- from Usenet (what's *that*?)
Posted by krw@att.bizzzzzzzzzzzz on April 18, 2011, 3:49 am
wrote:
>On 4/17/2011 7:19 PM Jim Wilkins spake thus:
>>
>>> ...
>>> Where is my thinking flawed?
>>
>> 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
>> resistance.
>>
>> http://en.wikipedia.org/wiki/Current_source
>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".)
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.
>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.
You're throwing around the pseudo-science. If you don't like the treatment,
you can easily leave.
>> If you're going slower (or the same speed as you say,)
>> they're actively pushing you off.
>I've chewed this over a bit, and I still don't like it, and here are my
>reasons: