Buffer in power grid?

Hi -
I'm trying to learn about how AC power flows through "the grid" from generators, through tranmission lines, down to distribution stations
and eventually our homes, but I can't get past a fundamental question: Are huge battery banks part of the grid?
I haven't run across anything that says there are, but if not then does that mean that the demand for power is EXACTLY equal to the power that is being generated? I find it hard to believe that at the instant i turn off my light a generater ramps down a tiny bit. I just can't visualize all of this working unless there's some kind of buffer, like a water tower, that keeps the flow constant.
Especially since I've learned that it takes time to ramp generators up and down, so where does the power come from as it's gearing up? and is power thrown away as it gears down?
Thank you in advance for your help.
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On Mon, 15 Oct 2007 15:38:25 -0700, snipped-for-privacy@lmco.com wrote:

Absolutely. Including all line losses and other losses along the way.
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snipped-for-privacy@lmco.com wrote:

No.
No, its not.

Inertia. The system has a huge amount of inertia. In fact, all of the connected generators, together with other spinning equipment like motors, behave exactly like a huge flywheel.
The system operators monitor the load on the system and attempt to keep the generation close to the demand by starting and stopping generation. The error between their control and the actual system ends up either speeding the system up (too much generation) or slowing it down (too much load). At certain times, they bring the system frequency (actually, the number of cycles per day) back in line with precision time bases by tweaking the generation as required.

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On Mon, 15 Oct 2007 15:38:25 -0700, snipped-for-privacy@lmco.com wrote:

You and your light bulb is like a gnat against an aircraft carrier.
The generator load doesn't change one iota. However, when a huge industrial plant that heats vats of chemical electrically, or a steel mill's induction driven blast furnace fires up or shuts off, you can bet compensation is involved.
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Very interesting. Ha, and thanks for the gnat comment ;-) That puts things in perspective.
Ok, so then pretend there is a group of generators producing 100MW. Then a loud rock concert starts and it draws (for simplicity sake) one more MW. Where does that 1 extra MW come from during the time it takes for the power operators to sense the extra load and the group of generators to speed up a bit to produce 101MW?
I think Paul is close to what I'm getting at: "The error between their control and the actual system ends up either speeding the system up (too much generation) or slowing it down (too much load). " In the case of too much generation is electricity 'thrown away'? And when there's too much load is there a black (or brown) out?
Thanks so much, Shane
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Two things happen when you initially apply the extra load - (1) the voltage drops, and (2) the frequency drops.
How much the voltage and frequency drop depends upon the characteristics of the system, including as one other poster has pointed out - the inertia of the alternators.
At the power station they simply apply more steam to the turbines to compensate for the higher load.
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Got it. Makes total sense now. Thank you!!!!
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snipped-for-privacy@lmco.com wrote:

Neither. Think of the power grid like your car. You try to maintain a constant speed with the throttle. But you can't be that precise. The error in your throttle setting results in the car speeding up slightly or slowing down slightly. In either case, power isn't 'thrown away'. It is either added to or subtracted from the kinetic energy of the vehicle's motion.
As long as you are reasonably close with your throttle control, the speed (frequency in the case of the power system) will remain within acceptable limits. The energy you put in when the throttle was set a bit high can be taken out when you back off and coast.
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Not quite but here in the UK we have:
http://home.clara.net/darvill/altenerg/pumped.htm
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Stuart Winsor

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wrote:

Now if you used the tides to do the pumping, you would have a lot of free, readily available demand stores.
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At the time Dinorwig was built, it used the excess night electricity from the nuclear power stations, so the energy was in effect free. (Nuclear power plants can't crank down for just 6 hours overnight.) I don't think we have excess unused power generation at night anymore in the UK now though.
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They exist in the states too, Smith Mountain Lake in Virginia for one, about 560MW capacity. Went on a tour and actually stood in a generator while the rotor spun just about a foot above my head.
jh
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Which is why I suggested using tidal energies to do the pumping over a long term basis for no pumping cost, and no need to perform it only during off peak hours.

Tidal forces. Do not pump salt water. Use salt water to make small energy gains that are used to pump standard fresh water to the reservoirs.

I think salt domes also could yield other benefits. Deep into the salt dome center spike, there is a LOT of heat, and it is VERY stable. More so than lava beds or geothermal even. This heat could be used to pre-heat water for boiler purposes, thus reducing the heat requisite to boil the water.
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wrote:

---------- Tidal energy is cyclic and the cycle changes independently of man's need for energy. Actually you will gain more from using tidal to supplant other generation-- independent of pumped storage. It can be used for pumping IF it is available at off peak times but generally it makes economic sense to use it directly. Since it is predictable the rest of the system can adapt (as in France where it has been used for many years). --------------

------------ Again- dedicating tidal energy to provide pumping energy is generally a fool's game. If there is a need for energy at the time that tidal energy is available- use it directly. If you have 100MW of tidal and feed it into the system you get 100MW into the system- If you dedicate it to pumping, you get 80MW at the same or more cost. Pump when you have cheap off peak energy and this has nothing to do with the source of the energy-just the cost. This has nothing to do with the salinity of the water being pumped. ------------------------------

-- Not really in most cases. Definitely not in the German case.
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Which is what makes it perfect for performing reservoir filling operations WHENEVER it is in action. It has nothing to do with the chronology of any demand.

Not really. At that point, it ONLY becomes useful if it is active during the same interval as the demand.

And I'll bet they use it to pre-fill a storage mode system for LATER demand period use.

Not the pumped energy. That is what should be done on the cheap, as in free with tides. The UTILIZATION of that stored energy is what should be governed for use only during peak needs intervals.

I think you have it ass backwards. Wind mils only pump electricity when the wind is up.

Too sporadic. Even if a tide is known chronologically, they are rarely known as to the magnitude they will operate at.

That's another point. That is not the level at which they operate. If it were, you would be right, and we would ALREADY be using them. They make much smaller bits of juice. Using them whenever they arrive to fill a storage based system, then using that system is a far better choice, regardless of any losses incurred.

There is NO cost, and those numbers are wrong. When one dumps a filled reservoir during a peak demand interval, one gets EXACTLY the level of power one needs from the system. The minimal "losses" in using a tidal force to operate a middle man pumping system do not have direct costs attached to them as the tides are free. You need to grasp that fact.

Yes, your idea of using cheap off peak electrical power to operate fill pumps does indeed have a COST. My idea of using the tides to do it, albeit a bit more slowly has NO cost attached to it, and MAXIMIZES the efficiency of the on demand reservoir system, and minimizes the pumping cost.

AGAIN, you do NOT pump saline water. The sea is just the motive force. The water that gets pumped into the reservoirs is fresh water.

That's more than a bit ambiguous. What are you referring to? Salt domes? Tides?
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wrote:

------------ It has a hell of a lot to do with both the load demand cycle and the tidal cycle. Pumped hydro is an economic choice (including ecological costs). Pumping is done when fuel costs are low- i.e. off peak by whatever sources do the job best at that time. These sources would include tidal plants. However at times of high demand, if tidal energy is available it is beneficial from economic and environmental bases to feed the grid (each MW of tidal energy supplants 1MW from gas turbine or other high fuel cost source where if it is used for pumping it only supplants 0.8MW of such sources. IF the tidal energy is available at off-peak periods, it may, but not necessarily, be the best pumping source. .>

-- Not so. Look up "Economic dispatch" and "unit committment" as well as more difficult to find subjects as system planning. I see nothing useful in dedicating a tidal plant of , say 100MW output, to pump and recover 80MW only at peak times. It is far better to feed the system whenever possible and use the system, at off peak times to do the pumping- if tidal energy is available at those times- then it "may" be a large factor in the pumping. At other times why take the 20% energy hit? ------------------>

------- They don't - they arent that stupid when it comes to engineering and economics. They simply cut back on the load on other sources with higher fuel costs. It is not a problem as tidal energy can be predicted accurately for years ahead.

-------- First of all, tidal plant energy is not free. The operating cost is low but the capital cost is high. Both enter into the cost of energy. Pumped storage is not free for the same reason. You would find, on a hard nosed analysis that tidal plant and pumped storage each may be viable on their own as part of a system. but a dedicated tidal/pump storage system would (if suitable sites were available) not be viable. In addition there is the efficiency factor. Even if operating costs including fuel were zero, building a tidal /pumping scheme would result in recovery of only about 80% of the energy of the tidal plant. Assuming that the tidal and pumped storage plants are about the same cost/Kw capacity this means that the base cost/kw capacity of the combo is about 220% that of the tidal plant only. This has a considerable impact on the cost of energy produced.
--
>
>>> Tidal forces. Do not pump salt water. Use salt water to make small
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In the particular case I quoted, there was a nearby nuclear plant which, by its very nature, needed to be kept running continuously. That plant is now being de-commissioned but the pumped storage facilty is still a very useful operation and is still in use.
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wrote:

Certainly it is useful. All it needs to do is supply peaking energy at less cost than the best of the available alternatives. In this case, if the plant has not been fully amortised- its capital costs are still there whether it is running or not- in that case it may still be cheaper than the alternative . If it has been fully amortized, then its costs are simply operating costs and there is a greater margin between the cost of its energy and the next best peaking source. As it is a hydro plant, it has a long useful life-more so than any thermal plant. It still comes down to an economic choice (biased by ecological considerations and subject to periodical review as the system grows and the mix changes.
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