the first power tool

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says...

Some convenient natural or man-made feature that is above the surface level of the reservoir that feeds the main dam.

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On 8/18/2015 8:13 PM, krw wrote:

I was thinking - and I think John McCoy (and perhaps another poster) - of a different reservoir. It's not as if you were just standing there pouring water back and forth into the same two glasses.
If you view the water as fuel to run the generator (turbines) or ???, then by using the electricity generated which is in excess of that currently needed (low demand period at night?) to pump fuel (water) to that other reservoir which may not be filling by itself as quickly you now have an expanded source of "fuel" with which to run a different generator turbine or divert the water for irrigation purposes. Somewhat analogous, I think, to a storage battery. Electric "fuel" is stored in a cell, water "fuel" is stored in the reservoir.

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On Tue, 18 Aug 2015 21:52:42 -0500, Unquestionably Confused

It's exactly analogous to a storage battery. The voltage on the battery corresponds to the height of the reservoir (both represent potential energy) and the flow of water to the current (kinetic energy). In both systems there are losses converting potential energy to kinetic energy and verse visa.

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On 8/18/2015 10:52 PM, Unquestionably Confused wrote:

Jumping in this very late in the thread, Just came back from Alaska 2 weeks ago. I thought they had a great use of water. Alaska is a rain forest in many areas (not all). They would run a pipe down from the high lakes only about 10-12" pipes and be able to power many homes from the force of the water in that small pipe. I imagine had a very good impeller design too. Very efficient.
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Jeff

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It's generally the case with steam plants (coal fired, nuclear, whatever) that they can't be run efficiently at lower power outputs. So where possible, it makes sense to size the steam plant at, say 90% of maximum demand, run the steam plant at 100% capacity all the time, and save 10% at night so you can provide 110% capacity when demand is at maximum.
(to Unquestionably's point, yes, hydro is easily controlled. Unlike a steam plant where there's typically only one turbine, hydro plants usually have multiple turbines that can be cut in and out, and running them at less than full capacity isn't as inefficient as it is with a steam turbine).
John
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On 8/18/2015 9:46 AM, John McCoy wrote:

How would you suppose the 10% is stored, batteries?
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On 08/18/2015 08:21 AM, Leon wrote:

For solar, one method is salt - not table salt, but salt:
<http://phys.org/news/2013-10-arizona-solar-hours-sun.html
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gospel of envy, its inherent virtue is the equal sharing of misery"
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On 8/18/2015 11:41 AM, Doug Winterburn wrote:

That is pretty cool, not photovoltaic. I missed the salt part. I could see how rain during the night might hamper but there is probably not much problem with that considering where it is located.
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On 08/18/2015 11:22 AM, Leon wrote:

There's a link at the bottom of the page that gives more on the tanks of "molten salt" at 700+ degrees...
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On 8/18/2015 5:24 PM, Doug Winterburn wrote:

Gotcha thanks
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wrote:

Um, if you read upthread a bit, you'd see it's stored by pumping water uphill, and then letting it flow back down thru hydroelectric generators when it's needed.
Batteries, while theoretically possible, in practice are a lot more complicated than using water. They're used in a few places on a small scale. Other small scale storage mechanisms include compressed air, and electrolizing water into hydrogen and oxygen (later recombined in a fuel cell).
I'd guess pumped water makes up 99% of the electric utility energy storage capacity.
One of the problems with solar energy is that places which are good for large-scale solar tend to be flat, meaning that pumped water storage (for night time use) isn't possible. There's a fortune to be made for whoever figures out a good alternative.
John
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On 8/18/2015 11:46 AM, John McCoy wrote:

Yeah I saw that.... but, If you run at 100% capacity/output, having 10% more water/fuel is not going to increase capacity. You still have the bottle neck of 100% capacity. Maybe I am mixing two different explanations here. And, it seems that if capacity is only 90 percent of demand, taping into 100% capacity to pump water back the the reservoir that it would be counter productive. Certainly there is a loss of capacity pumping the water back up stream than it produces.

Understood but batteries supplement/add to output. Recycling water does not add to on demand capacity, unless the lake is about to go dry.
Not arguing with you here, just kicking thing around.
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I think I wasn't clear there.
Suspose the peak demand is 100MW - daytime, AC running in the summer, heat in the winter, businesses have all their machines and computers and whatnot running. And at night the demand is only 70MW, because people are sleeping, not using much electric equipment.
Now, suspose we design a powerplant with maximum capacity of 90MW. We're 10MW short of what's needed for peak demand, but we have 20MW extra at night. So we use some of that 20MW to pump water uphill at night, and in the daytime we let it run back thru a 10MW hydro generator. Thus we get the extra 10MW we need at peak demand times.
This all makes sense because:
a) powerplants are expensive, and the savings from building a 90MW plant instead of a 100MW plant pretty much covers building the pumping plant.
b) running a 90MW powerplant at 70MW is inefficient, and will consume almost as much fuel as running it at 90MW, so the power used for pumping is almost free.
John
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On 8/18/2015 2:27 PM, John McCoy wrote:

But unless I am missing something here, It does not matter how much water is in the reservoir/lake because whatever water is there to begin with is enough to operate the power plant at capacity.
Unless the water goes to a different reservoir that does not naturally refill itself to power the smaller generator.
And FWIW I am picturing Lake Mead as the reservoir.
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wrote:

There was a hydro plant in Missouri that was man made reservoir that failed, it was filled from a river.
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Ah, I see the problem.
The site I'm familiar with, Cabin Creek in Colorado, is typical. There is one lake/reservoir above Georgetown, and another one about 800 vertical feet further up the mountain. They pump water from the lower one to the upper at night, and let it flow from the upper to the lower (thru the generator turbine) in the daytime.
The upper reservoir does get a little water from snowmelt, but that's lagniappe. Mostly it's the same water being pumped up and down every day.
John
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On 8/18/2015 7:45 PM, John McCoy wrote:

Gotcha.
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On Mon, 17 Aug 2015 13:15:56 -0700, Electric Comet

Pump storage is not unique to the South Pacific. It's not unheard of in the US.

No, water power is really solar power.
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says...

Yep. Perhaps the ox-drawn plow was the first "power tool" by that definition, around 3000 BC.
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On Sun, 16 Aug 2015 10:38:02 -0400, "J. Clarke"

I was thinking about the (grain) mill, but you're probably right. The grain likely came before the mill. ;-)
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