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.
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.
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.
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).
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.
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
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.
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.
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.
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 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.
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