Air compressor as energy storage? - Page 6

 

Pumped *storage*, does not mean you have a lot of water at a high place and
are 'letting it down' just to pump it up again.

For example, one installation in western Michigan had *no water* at the high
end originally.  But the geography was such that they could create a large
basin a few hundred feet above Lake Michigan with little expense.  The
pump/turbines are powered by base-load generation (coal plant) at night to
pump water from Lake Michigan *up* to the basin at night.  Then, during the
day, they let the water back down, spinning the pump/turbine to make
electricity.

You don't gain energy, but you shift time-of-use (and indirectly, the cost
of the energy you produce).  When there is less demand than the coal plant,
the coal plant still runs at full capacity, storing water at elevation.
When demand is greater than the coal plant, you don't need to start another
plant (say, natural gas fired unit), because you get to recover the stored
energy in the water by letting it down.

At Niagara it's a bit more complicated.  The agreements between US and
Canada about using the water in the Niagara river include such details as
not drawing so much water away from the river that the falls dry up during
the day.  Believe it or not, the tourist attraction aspect is that important
to them.

So at night, they divert a lot more water from the river to the turbines at
the power plants.  Also at night, they run the pumped-storage units in
'pumping' mode to pump water from the Niagara river into storage.  The
intake for this pumping is upstream of the falls, and the water is pumped
higher than Lake Erie (the headwaters for the falls).  During the day, water
from this reservoir flows back down through the pump/turbines at the
Lewiston site, then flows down the turbines at the Niagara Project.  So the
reservoir water flows through two turbines during the day.  And the Niagara
Power plant turbines can run closer to full capacity during the day without
diverting too much water from the falls scenic beauty.
http://www.nypa.gov/facilities/niagara.htm

Another one in the Catskill Mountains, is Blenheim-Gilboa
http://www.nypa.gov/facilities/blengil.htm


daestrom

  On Wed, 21 Feb 2007 19:04:17 -0500, "daestrom"

I am a bit uncertain about the usage of the term pumps/turbine here.

Even though you may use a pump as a turbine by reversing the flow, I
belive that the utilities uses blade/spoon turbines than are more
effective, but cannot be used to pump water.

Offcource, it may be cost effective to use pumps as turbines in this
setting (lower capital costs). But without beeing completely sure, I
would put my bet on seperate pumps and turbines.

--
SEE YA !!!
Trygve Lillefosse
AKA - Malawi, The Fisher King

 On Thu, 22 Feb 2007 22:44:40 +0100, Trygve Lillefosse


The pumped storage system in Dinorwig, Wales uses the same reaction
turbines both for the generation and pumping, they're vertical axis
with inlet guide vanes, I was astonished they had the ability to pump
600metres head in a single stage.

I cannot see it being viable for domestic use but I can envisage a
high head water reservoir being pumped by a direct driven wind turbine
as being feasible on the 30kWhr/day scale.

AJH

 wrote:


Similar with Racoon Mountain.  Single pump/turbines and
motor/generators.

When I was in college and working for TVA as a heavy equipment
operator, I had the distinction of operating the locomotive that
hauled all the Racoon Mountain turbine wheels and scroll pieces from
the Southern Railway to the dock at Sequoyah nuclear plant where they
were put on barges and barged to Racoon Mountain.  Also had the
dubious distinction of derailing one turbine wheel car but that's
another story :-)

Losses don't scale linearly with size which is what makes the large
scale units feasible and small ones not.  Plus, the marginal cost of
off-peak power is so low for nuclear plants that even inefficient
storage makes economic sense.  Especially when compared to peak
shaving plants like gas turbines.

Other than high losses, the problem with small plants is that the cost
of energy is still quite high.  The marginal cost may be zero (for
solar, hydro and wind) but the extremely high cost to performance
ratio of the equipment means that even the armortized cost per KWh is
significant.  

If one needs a certain amount of power and the demand is being met
with the existing equipment most of the time then that equipment would
have to be more than doubled to account for the storage losses.  That
would probably make the cost prohibitive and in the case of hydro or
wind, might exceed the available energy source.

Batteries are expensive and somewhat pesky to maintain but they're the
only choice right now for the small operator, unfortunately.

John
---
John De Armond
See my website for my current email address
http://www.neon-john.com
Cleveland, Occupied TN
Don't let your schooling interfere with your education-Mark Twain

 

On Fri, 23 Feb 2007 14:18:45 -0500, Neon John wrote:


Again there's no disagreement, the sum is quite simple, the cost of
grid power is made up of capital charges, fuel cost and
operation+maintenance cost. So large simple plants with low fuel costs are
favoured other than for your peak shaving. The pumped storage schemes
profit on the difference between the two costs.

There is scope for the domestic owner to save though because, in UK at
least, the bulk of the delivered cost of grid electricity is the
distribution cost, not the generation cost. In fact the difference seems
to be about a factor of 4.

So if you had a cheap means of generating electricity or direct pumping
and the right site, then storing the water at high head and generating
through a pelton wheel may bear looking at the figures. I've not satisfied
myself of any circumstance where it would be competitive with grid power,
yet.

AJH