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Feeding solar power back into municipal grid: Issues andfinger-pointing

M

Malcom \Mal\ Reynolds

Jan 1, 1970
0
Han <[email protected]> said:
I have no idea how it works exactly, but here in North Jersey PSE&G has
been putting up solar panels on their (I think) utility poles. Each one
is maximum 200 Watts at 110V, feeding directly into the grid the poles
carry. This is a link + picture in another town not too far away (1 line):
<http://www.nj.com/hudson/index.ssf/2011/02/pseg_installing_solar_panels_
o.html>
or:
<http://tinyurl.com/3dvgy7r>

I'm willing to take a hit on this, but those panels don't look big enough to
produce 200 Watts
 
D

David Nebenzahl

Jan 1, 1970
0
You are paid 80 cents / kwh for *any* electricity leaving your array (a
billing meter is installed right after your invertors). It doesn't
matter if your own home (AC unit, etc) will suck 100% of that solar
energy with none of it going back into the grid.
and

But still - you can't push more electricity onto a network than the load
is asking for (given that your invertors are functioning correctly I
guess).

Are you sure about that first statement? Pardon me if I misunderstand
what you wrote, but don't you only get paid for the *net current*
leaving your meter? If you're generating 5KW but "sucking" 6KW into your
AC, etc., then you have a 1KW net draw, so you're not gonna get paid
anything, correct?

That second statement is correct: you can't "push" electrons into the
grid. But it doesn't matter *how* your inverters are working; it's a
basic law of physics.


--
The current state of literacy in our advanced civilization:

yo
wassup
nuttin
wan2 hang
k
where
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- from Usenet (what's *that*?)
 
Are you sure about that first statement? Pardon me if I misunderstand
what you wrote, but don't you only get paid for the *net current*
leaving your meter? If you're generating 5KW but "sucking" 6KW into your
AC, etc., then you have a 1KW net draw, so you're not gonna get paid
anything, correct?


.. if the topic is still related to Ontario's micro-FIT program (?)
the solar panels would have their own meter - for metering the solar
output - paid at the high subsidized rate. Any other meters on the
property would be for customer load - billed at those normal market
time-of-use rates. ... otherwise we would not be seeing 5-10 kw solar
arrays sprouying up like dandilions.
John T.
 
D

David Nebenzahl

Jan 1, 1970
0
If you apply more volts to a line than what it is carrying what do you
think happens? I run machines that use regenerative braking. They
draw energy from the line to set things in motion. To slow or stop
them the electric motor acts as a generator producing a higher voltage
than the grid, forcing power back into the grid. An inverter can do
the same thing using solid state circuits. The inverter in my Prius
takes DC current from the battery and converts it to whatever voltage
and frequency is needed at the time to run the variable frequency AC
motor. When slowing down the motor becomes an AC generator and the
inverter converts the output to a DC voltage just a bit higher than
the battery, pumping charge back into it.

Sorry, I don't think you know what you're talking about.

You seem to think that you can "force" or push "voltage" into a line, by
using a higher voltage than what's on the line.

That's not at all what's at work here when one has a photovoltaic system
and an intertie feeding power back into "the grid".

The intertie and the house's power connection are going to be at pretty
much exactly the same voltage. What happens is that the PV system is
connected *in parallel* with the grid; it's dumping more *current* into
the system, not more voltage.

You do understand the difference between current and voltage, don't you?


--
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*?)
 
H

Home Guy

Jan 1, 1970
0
David said:
Are you sure about that first statement? Pardon me if I misunderstand
what you wrote, but don't you only get paid for the *net current*
leaving your meter? If you're generating 5KW but "sucking" 6KW into
your AC, etc., then you have a 1KW net draw, so you're not gonna get
paid anything, correct?

Under the terms of the Ontario microFIT program, you are paid 80 cents
per kwh for any electricity your project generates and "makes available
to the grid".

For about the first year of the existance of the program, a "behind the
meter" connection was allowable, but at some point last year,
Measurement Canada (a federal gov't department tasked with regulating
commercial scales and other forms of measurement devices) published some
sort of guide or position paper stating their disapproval of this
method.

"Behind the meter" meant that your house retained the same single hookup
to the power mains lines (ie - the grid) and the primary meter be
capable of bi-directional current measurement. The meter measuring the
power output of your PV system (which also had to be bi-directional)
could be connected to the grid through your meter. This is also known
as a "series" connection.

Under the new(er) rules, your revenue meter must make a parallel
connection to the grid (in parallel with your load meter). One result
of this is that you will usually be billed an extra $5 or $10 a month
for having a second service connection to the mains grid - even if it's
the same physical wires carrying both services to your home.

As a load customer, you are billed based on what your primary meter is
reading. As a power generator, you are paid for what your PV meter says
you delivered to the grid. This is (and was) the case regardless how
the revenue meter was connected.

The whole point of the microFIT program is to encourage home owners to
fork out the estimated $35k to $55k to put up 3kw to 10kw PV system on
their roof and contractually garantee them a rate of 80 cents per kwh
for 20 years. You need approval all up and down several layers of
burocracy to get your revenue meter plugged in (the last step of the
process) before you start getting paid.

Alternatively, there is nothing stopping you from installing panels on
your own home and basically hooking everything up exactly the same way
as you would under the microFIT program, except there is no revenue
meter. Your load bill would be the net energy you pulled from the
grid. The payback you would get from your investment would therefore
take much longer.
That second statement is correct: you can't "push" electrons into the
grid. But it doesn't matter *how* your inverters are working; it's a
basic law of physics.

Unless your invertors were set to operate at a slightly higher output
voltage. Even just a few volts differential between the mains voltage
and the invertor output would mean that you could push current out into
the grid, and by doing that raise the local grid voltage slightly.
 
G

g

Jan 1, 1970
0
Unless your invertors were set to operate at a slightly higher output
voltage. Even just a few volts differential between the mains voltage
and the invertor output would mean that you could push current out into
the grid, and by doing that raise the local grid voltage slightly.

The grid can be seen as a pretty rigid beast. No small puny inverter in
the sub 1000kW class will much affect the grid voltage as a whole. When
voltage of the converter is attempted to be raised, current will flow
into the grid of course. The voltage increase will hardly be measurable,
as electrical characteristics of the grid will adjust dynamically.

At any one time, there is a certain load on the grid as a whole. When
Mr. Homeowner adds 10Kw from some solar panels, some other power
generating systems connected to the grid will (have to) reduce their
output. As a result the voltage stays the same overall.

If enough homeowners are added to the grid where they are able to affect
the overall power consumption of the grid up to some significant
percentage, it is really important that the inverters are accurate wrt
voltage output and frequency stability.
 
D

David Nebenzahl

Jan 1, 1970
0
<http://www.northjersey.com/news/116938343
_Municipal_officials_throw_wrench_in_PSE_G_s_solar_paneling_program.html>

or
http://tinyurl.com/3tcv4le

1. So what in the world does that have to do with the point I stated?
(Rhetorical question. Answer: nothing.)

2. Y'know, if you used a non-brain-damaged news client that didn't
mangle long URLs (unlike your Xnews), you wouldn't have to dick around
with those tinyurls.


--
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*?)
 
D

David Nebenzahl

Jan 1, 1970
0
The modern grid tie/connected "transformerless" inverter manipulates
the DC output from the panels so that they run on their "sweet spot"
ie the most efficient voltage and current. It self connects/
disconnects to the mains as and when there is sufficient light operate
the panels. I t uses the mains sine wave to generate it's own sine
wave on the AC side. The current delivered is indeed dependant on the
output voltage it dleivers to "push2 that current back into the
mains.
Bullshit.

Bit on the topic here.
http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws
http://en.wikipedia.org/wiki/Grid_tie_inverter

Apparently you didn't even *read* that second article. It says:

The grid tie inverter must synchronize its frequency with that of the
grid (e.g. 50 or 60 Hz) using a local oscillator and limit the voltage
to no higher than the grid voltage.

Re-read that last phrase: "limit the voltage to no higher than the grid
voltage".

You don't "push" electricity from your solar installation into the grid
by raising the voltage, as someone here postulated. It just don't work
that way.



--
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*?)
 
T

The Daring Dufas

Jan 1, 1970
0
Apparently you didn't even *read* that second article. It says:

The grid tie inverter must synchronize its frequency with that of the
grid (e.g. 50 or 60 Hz) using a local oscillator and limit the voltage
to no higher than the grid voltage.

Re-read that last phrase: "limit the voltage to no higher than the grid
voltage".

You don't "push" electricity from your solar installation into the grid
by raising the voltage, as someone here postulated. It just don't work
that way.

I remember a I & V limiting bench power supply I owned back when I
worked as a repair tech at a service depot. Under certain circumstances,
when I cranked the voltage control to raise the voltage, the voltage
stayed put but the current would rise. I wonder if that's the sort of
thing that happens when these grid connected inverters are used?

TDD
 
H

Han

Jan 1, 1970
0
1. So what in the world does that have to do with the point I stated?
(Rhetorical question. Answer: nothing.)

I was agreeing with your statement of parallel systems, and offered a
picture to sort of substantiate.
2. Y'know, if you used a non-brain-damaged news client that didn't
mangle long URLs (unlike your Xnews), you wouldn't have to dick around
with those tinyurls.

Sorry, I'm staying with Xnews for a while longer.

Have a wonderful day, David ...
 
D

daestrom

Jan 1, 1970
0
in message


Got some numbers/calculations to support that? Is that including the
next door neighbors with their PV installation?

daestrom

-------------------

Sure! Basic Ohms lawa and a wire resistance table

http://en.wikipedia.org/wiki/American_wire_gauge

A 200 ampere service running 240 Vac and only considering the straight
resistance of copper (many use AL outside conductors these days).
and considering the street transformer as an infinite current supply (0
Ohms impedance)

The chart shows we would use 2/0 copper (assuming solid copper, but it
won't be)

In a 100 feet of overhead run to a house, down the stack and through the
meter to the main panel, where the fuses or breakers are, not
considering the impedance of the overcurrent devices (that allegedly
cannot handle a fault this big) we come up a with a minimum copper
resistance of

200 feet (has to return) x 0.07793 x 10^-3 Ohms / foot (oh look ...your
old units too) = 0.015586 Ohms

Using 240 Vac as the fault supply (it won't be under a faulted
condition) the max fault current would be

240 Vac / 0.015586 Ohms = 15.4 kA.

Now we haven’t figured in any of the other impedances (very generous)
and any approved O/C device in a panel these days is rated at 100kA.

Only problem with that is that many home service panels use breakers
with an AIR of only 10kA, not 100kA. (my old house, built in 2000 was
10kA, and my new one, built in 2010 is also 10kA, both perfectly correct
by code)

Here's are some modern service panels that come with 10k AIR breakers.
http://static.schneider-electric.us/assets/DIGEST/load-centers.pdf

And how many homes in the utilities service area are even up to current
code? I'd bet many homes in many service areas have only 10kA AIR.

The utility that is being ultra-conservative may have to consider that
older homes in their service area may not even support this.

Can you just imagine the hue and cry when some homeowners are told they
have to spend a couple hundred bucks to upgrade their service panel
because of changes in the utility's distribution?

daestrom
 
V

vaughn

Jan 1, 1970
0
Not he's got it right except for the fact that allr otating electric
lmachinary is AC.

Those two quite common examples seem to refute your
absolute determination that ALL rotating electric machinery
is operated with AC motors...

How so?

Vaughn
 
D

David Nebenzahl

Jan 1, 1970
0
I love how you can state that without any sort of qualification...

.... especially when it's pure BS. But that's our Harry.
You seem to have forgotten about higher end bathroom fans
which use an inverter to operate a DC motor which is much
quieter than an AC motor...

Welll, since this is a.h.r, and since you're picking a nit, let me pick
yours. I've installed several "higher-end" vent fans (Panasonic), all of
which use AC induction motors which are very quiet. Which bath fans use
the setup you described? (Besides which, why in the world would you need
an "inverter" to run a DC motor from an AC supply? Perhaps you meant
"rectifier"?)


--
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*?)
 
I remember a I & V limiting bench power supply I owned back when I
worked as a repair tech at a service depot. Under certain circumstances,
when I cranked the voltage control to raise the voltage, the voltage
stayed put but the current would rise. I wonder if that's the sort of
thing that happens when these grid connected inverters are used?

To "push" power back into the pipe the generator's phase leads the line's, so
in a sense the generator's voltage is greater than the lines (as someone
pointed out Kirchhoff didn't lie).
 
Those two quite common examples seem to refute your
absolute determination that ALL rotating electric machinery
is operated with AC motors...

How so?


Look deeper in the motor. It's all AC on the inside. ;-)
 
M

m II

Jan 1, 1970
0
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S

sno

Jan 1, 1970
0
Look deeper in the motor. It's all AC on the inside. ;-)

I think you are pushing it....the brushes on a dc motor "guide" the dc
to different windings.....it is still dc...

In an ac motor the windings are generally in parallel...all the ac is
applied at one time....

I think I got that right....is a long time since I covered motor
theory..<grin>...the ac is not "chopped up"....or guided anywhere....

You could say that all electric motors operate the same....as they all
depend on magnetism (all generally used motors...there are some operate
on static electricity, etc)
have fun...sno

--
Correct Scientific Terminology:
Hypothesis - a guess as to why or how something occurs
Theory - a hypothesis that has been checked by enough experiments
to be generally assumed to be true.
Law - a hypothesis that has been checked by enough experiments
in enough different ways that it is assumed to be truer then a theory.
Note: nothing is proven in science, things are assumed to be true.
 
D

David Nebenzahl

Jan 1, 1970
0
Yes it does. Electrical current flows from a point of higher
potential to a lower point. The very first thing you learn. Ohm's Law.

How many things are wrong with what you wrote? let's see:

That's not Ohm's Law, not by a long shot. Do you even know what that is?

Yes, electricy flows from a point of higher potential (voltage) to a
lower point. But you're confusing voltage and current here, a common
rookie mistake.


--
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*?)
 
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