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

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On 17/04/2011 14:27, snipped-for-privacy@optonline.net wrote:

Well, I was just teasing him, did not really expect any answer.
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by the GymmyBob troll.. another of a few hundred of his 'victims'. Deservedly so on this occasion.. you prove a clueless dolt.
Get yourself educated on "how to" in reading news, rube. netscape.public.mozilla.general
Then go check out your 'victor' :-/
.. mind how you go. Don't want you bleeding all over the place:-D
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On 18/04/2011 05:44, no spam wrote:

You apparently have spent a lot of time "checking out" people. Well, it is your time, waste it as you see fit. Better you than me.
Your tone of language though is one that tell much more about you than you understand. Maybe you and Mho can waste each others time checking each other out. For all I know you are one and the same.
Hopefully you will be so busy name-calling each other that the rest of us can forget about you. :)
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Especially since you answered your own questions in your response.
-------
"g" wrote in message
Well, I was just teasing him, did not really expect any answer.
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there is a VERY slight increase in local voltage.
If you want to push 5 kW back into the gird, the local voltage rises by the amount of voltage drop in the wires leading to the grid with 5 kW flowing through them. Its the same amount as it drops when 5 kW flows out.
For example, if the grid is 120.0 and your house is pulling 5 kW, then the local voltage at your house may drop to 119.9.
If your house pushes 5 kW into the grid the local voltage at your house may rise to 120.1.
The 5 kw is not wasted, the rest of the grid reduces its generation by that 5 kW to keep the grid at 120.0.
Another analogy is tandem bikes. If the back person pushes harder, the front person has to push less to go at the same speed. For synchronous AC motors and generators this is really a good analogy, they are all running at exactly the same speed and the PHASE slips ahead or behind slightly depending on which way the power flows. You can think of it as a bit of stretch in the bike chain one way or the other.
A lot of the engineering of power systems goes into how the load is shared among multiple sources.
But in any case, a 5 kW load or source is very small compared to the overall power flow in the grid.
Mark
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test

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Why would there be a local increase in the voltage?
The grid is filled with tapchangers and capacitors to adjust the voltage to a constant level, loads on a complex grid can shift load continuously to another place. A small PV source may increase the voltage up to the next house and would never be noticed.
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"Mark" wrote in message
there is a VERY slight increase in local voltage.
If you want to push 5 kW back into the gird, the local voltage rises by the amount of voltage drop in the wires leading to the grid with 5 kW flowing through them. Its the same amount as it drops when 5 kW flows out.
For example, if the grid is 120.0 and your house is pulling 5 kW, then the local voltage at your house may drop to 119.9.
If your house pushes 5 kW into the grid the local voltage at your house may rise to 120.1.
The 5 kw is not wasted, the rest of the grid reduces its generation by that 5 kW to keep the grid at 120.0.
Another analogy is tandem bikes. If the back person pushes harder, the front person has to push less to go at the same speed. For synchronous AC motors and generators this is really a good analogy, they are all running at exactly the same speed and the PHASE slips ahead or behind slightly depending on which way the power flows. You can think of it as a bit of stretch in the bike chain one way or the other.
A lot of the engineering of power systems goes into how the load is shared among multiple sources.
But in any case, a 5 kW load or source is very small compared to the overall power flow in the grid.
Mark
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On 4/18/2011 12:05 PM, Mho wrote:

Like he said, if there is a change in the current flow there is a change in the voltage drop across each component between you and 'the grid'. The impedance of these components is small, but nevertheless it exists.
Besides, grid voltage regulation is not perfect. Those tap-changers you mentioned have discrete steps and most have time-delays in them with a dead-band around their set-point. These are designed so the thing doesn't wear out constantly stepping up and down when the voltage set-point is 'between' the tap settings.
daestrom <snip>
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Would the contacts be the tungsten (heavy) cylindrical slugs sometimes found below equipment-laden power poles?
jsw
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.. twould be a strange grid/retic system indeed were tap change contacts found in the environment. Then again I am not surprised at anything uttered from those who feed the Gymmy Bob troll.
GB will be very busy searching his digests of "Popular Mechanics" for the term "dead-band" just to be sure it isn't an old Bob Marley joke:->
.. mind how you go. Don't want you bleeding all over the place:-D
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On 4/19/2011 17:28 PM, Jim Wilkins wrote:

The few tap-changers I've seen 'up close and personnel' are in sub-stations, not pole-mounted. The contacts are in oil-bath and arranged such that they don't open under appreciable current (multiple contacts, a center-tapped inductor and ingenious mechanism).
daestrom
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Similar experiences here.The contacts are usually just copper or copper plated with silver.
Many schemes are contrived to save the wear and tear on the contacts. On larger capacity units there are two sets of contacts, ones that take the arc and are easy to replace and a second set that can carry big currents, close last and open first.
Some use vacuum bottled contacts to eliminate arcing and most use an inductor or resistance not as good) to afford tap changing without ever breaking the circuit.
Oh, I have dealt with a few pole mounted units for inline use in the rural long lines to boost it back up a bit. --------------
"daestrom" wrote in message The few tap-changers I've seen 'up close and personnel' are in sub-stations, not pole-mounted. The contacts are in oil-bath and arranged such that they don't open under appreciable current (multiple contacts, a center-tapped inductor and ingenious mechanism).
-------------- On 4/19/2011 17:28 PM, Jim Wilkins wrote: Would the contacts be the tungsten (heavy) cylindrical slugs sometimes found below equipment-laden power poles?
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With Free Energy extant throughout appliances there will be no requirement for a HV Grid anyway.
So long
Old Timers
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Oh, I dream alright!

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Dribbling too eh?
wrote:

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harry wrote:

That's exactly what I've been saying - that you "turn it up" (the inverter's voltage output) to maximize the PV's current (I) supply into the grid.
But everyone else (or most everyone else) is saying no - that simply matching the grid voltage (as measured at your service connection) is all that happens (and is all that needs to happen) for the entire PV current (I) capacity of the PV system to be "injected" into the grid.
So now that we agree that PV systems need to raise the grid voltage if they're going to "force" their maximal available supply capacity into the grid, it's a moot or academic question as to what exactly their supply situtation would be (how much current they'd supply into the grid) if the invertors simply matched the grid voltage.
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You can only guess at what the inverter is forcing and sensing without looking at the schematic and uP code or a technical explanation of it. The Wiki type explanations are oversimplified for general readers, engineers have better sources.
I was hired to decipher and troubleshoot several lead-acid and lithium battery charging circuits after the designers quit, and found a couple of different approaches in use. Generally they compared voltage and current measurements to a model and used the result to pulse-width- modulate the output control.
Power factor control is similar to the design issues of a grid-tie inverter, with a large enough market to support custom ICs: http://focus.ti.com/lit/an/slua144/slua144.pdf
jsw
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Motors aren't the only things that need PF correction. Capacitors aren't the only, or often the, way of doing it.
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An incorrect assumption. Those are for more complex loads like switching power supplies with rectifier inputs.
jsw
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On 12/04/2011 07:33, Home Guy wrote:

1) The actual voltage increase will relate to the ratio of grid impedance vs local impedance, i.e. your local power consumers (fridges, heaters etc) has a much higher impedance relatively, thus the grid will "take" the majority of the generated power. The _only_ increase in voltage you will see results from the voltage drop in the grid components.

2) Pretty complex calculation, but yes, _somewhere_ one or more generating pieces of machinery will reduce its output. Makes sense intuitively, does it not?

3) You just set your PV system to operate at max power, the grid system will balance out automatically. See 1) above

4) The grid voltage does actually fluctuate a bit, depending on load. Power companies have means of adjusting line voltages depending on load fluctuations. The average subscriber never knows this.

5) That will be a very inefficient way to utilize your PV system.
A simplified way is to look at the grid as a battery. When your PV system generates more power than your local consumers, the surplus will flow into the grid. At all other times the grid and the PV will both supply the needed power to the local consumers.

6) Fairly close to impossible. How do you match local power consumers to hit the 100% PV capacity?
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