Air compressor as energy storage?

[Trygve Lillefosse]

Ok, that makes no sense:

Lake holds water. Water flows down through turbines from lake into
river.

During times of low demand, keep allowing water to flow down through
turbines into river, and then use excess electricity to pump water
BACK up from river to lake?

That's dumb.

During times of low demand, why not throttle back the water flowing
through the turbines and keep more of it in the lake, where it can be
used later during high demand?

They turn of the waterflow and turbines, and pump water into the basin
using electrisity they buy on the electric spot-market. (even though
you get one price on your bill for a given period of time, the price
of electricity fluctates a lot during a 24 hour period, and from day
to day.)

 

[Trygve Lillefosse]

A water turbine can presumably change it's output rather quickly to
meet demand, morseo than a reactor or coal/gas plant.

If a small storage lake is situated to feed a water turbine, then the
turbine's water input must be able to draw from both the main source
of water as well as the storage lake. Which means there is (or there
can be) a connection between the main water source and the storage
lake.

If demand is low, then water could be diverted into the storage lake
instead of going down the turbine.

Instead, what your saying is that the water is allowed to go down the
turbine to generate electricity which is then used to pump that same
water back up to a storage lake. That again sounds stupid.


A hydro-electric plant is always generating power at the same "cost"
all the time. It's the market that puts additional premium on that
power.

Not realy. It has a lower cost per kW the more/faster it produces.
I expect that there is some kind of "sweet spot" where the price per
kW is lowest.

If it is shut down for a few hours due to low electricity prices, you
still got salaries. capital costs etc.

 

[Trygve Lillefosse]

What do you mean no?

If you have a storage lake for excess water, then of course that water
must have a way to get to the intake side of the turbine when called
for. How else is it going to be used?
And if you're going to recharge it, then the most efficient way is to
let water flow from the main source into that lake directly.

You do not have a storage lake, you got one lake where water is
drained. (possibly with connecting lakes, but if so, only to maximise
the area where you can collect rain.

Where is that baseload coming from?

Other utilities. Nuclear, coal and hydro-dams that has to produce
because their storage capacity is full or near full. Or even hydro
plants that rely on rivers without dams.

Why do you need to pump water ->up<- into the storage lake when you
can simply divert it from the main source which (presumably) is at the
same altitude as the storage lake?

The storage lake and main source is the same thing. You pump the water
from other sources. Possibly collection sites at lower altitudes or
from a lake/river.

And remember that these pumps contribute to base load. If they aren't
used, then baseload would fall.

The lower the usage of the baseload(minimum supply of electricity) the
lower the price of the electricity gets. If it is not sold(used), it
needs to be "burned of".

The energy the pumps use is not free, and by rights there should be no
pumps and no excess base-load to run them.

Its not free, but the cost of running them is lower than the price you
get when you are using the pumped water to generate electricity at a
later point.

 

[Trygve Lillefosse]

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.

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.

 

[AJH]

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.

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

 

[andrew heggie]

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.
Yes

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.

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

 

[[email protected]]

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.

Not quite the same, but along similar lines-

Early settlers often relied on "thundermills" for sawing wood or doing
useful work. These mills were on small streams that only had
sufficient power when the stream was full from winter runoff or heavy
storms, hence (I guess) the name derived from mills that operated when
or after there was thunder in the area.

Later mills often employed multiple dams to store as much of the flash
runoff as possible and to accumulate stream flow into a useful burst
of power. One grist mill in the town where I grew up had three dams
on the same stream, yet only the lowest dam had a penstock and pelton
wheel. The upper dams added capacity, but not additional power. The
storage wasn't pumped, but served a similar purpose to pumped power.

Using otherwise wasted storm runoff to power a pump leading to a
storage pond could be an example of where pumped storage makes sense.
As an example, my stream has a relatively low head, but there is a
nearby area about 60 feet above the stream that could be easily and
fairly inexpensively turned into a pond. Would it be cost effective?
Probably not for just power, but if irrigation, fire protection, stock
and wildlife watering, augmenting a later low stream flow to help keep
(stocked) fish in a hole in the stream alive, and other possible uses
are figured in, it might make marginal sense.

I can think of other situations, like a microhydro setup below a power
dam with a regular peak use discharge schedule, where utilizing the
heavy flow might be the only practical method of getting sufficient
power. Would batteries be better for storing it? Possibly, but a
small side canyon or gully that could be dammed would be very tempting
for pumped storage. Such a setup would involve a lot of governmental
meddling though, so it might not be worth it from that aspect alone.

Perhaps the key is similar to co-generation, where instead of heat and
power, the symbiots are water and power. Like this:

<http://gizmodo.com/gadgets/gadgets/waterpressure-powered-lightup-shower-155266.php>

 

[AJH]

Early settlers often relied on "thundermills" for sawing wood or doing
useful work. These mills were on small streams that only had
sufficient power when the stream was full from winter runoff or heavy
storms, hence (I guess) the name derived from mills that operated when
or after there was thunder in the area.

OK I've not come across the same here, though we do have a number of
old tidal impoundment mills, they lead to highly unsocial working
hours.

Using otherwise wasted storm runoff to power a pump leading to a
storage pond could be an example of where pumped storage makes sense.
As an example, my stream has a relatively low head, but there is a
nearby area about 60 feet above the stream that could be easily and
fairly inexpensively turned into a pond. Would it be cost effective?
Probably not for just power, but if irrigation, fire protection, stock
and wildlife watering, augmenting a later low stream flow to help keep
(stocked) fish in a hole in the stream alive, and other possible uses
are figured in, it might make marginal sense.

Well I suspect wildlife and turbines don't go well together but your
points are much the same as mine. I suspect the reaction turbines are
too capital expensive and I haven't any idea how efficient the old
wind powered well pumps are/were but they and pelton wheels are fairly
simple technology. The advantage of a pelton turbine looks like its
ability to follow a synchronous load by simply varying the jet.

power. Would batteries be better for storing it? Possibly, but a
small side canyon or gully that could be dammed would be very tempting
for pumped storage. Such a setup would involve a lot of governmental
meddling though, so it might not be worth it from that aspect alone.

On the other hand a modest pond above and below a decent drop may not
suffer too much regulatory interference??

Perhaps the key is similar to co-generation, where instead of heat and
power, the symbiots are water and power. Like this:

<http://gizmodo.com/gadgets/gadgets/waterpressure-powered-lightup-shower-155266.php>

Saves walking into a cold shower

AJH

 

[HVAC Guy]

wikipedia article on grid energy storage.

The pumped water example given goes like this: At night, buy
electricity at 1.5 c/kwh to pump some water to a high elevation, then
during the day use that water to generate electricity to sell at 4
c/kwh.

(the example given says that the pumping process is 75% efficient,
which I'd like to know how they got that efficiency so high, but
that's another matter).

So even with pumping loss, you're still making maybe 2+ c/kwh.

But the flaw is this. What is the other guy doing burning (or
consuming) his fuel and only getting 1.5 cents at night in the first
place? Why doesn't he conserve it too so that he can make more $$$
during the day by selling it at 4 cents like you're doing?

 

[HVAC Guy]

The other guy might still be making a profit at 1.5 cents if
his costs to produce that kWh is significantly less than that.
The other guy might even be using a generator that takes many
hours to change power levels, works best at a specific level
or which can be damaged by too often changing levels.

Which means that other types of plants that can't scale their output
within a few hours would presumably be looking for technology to be
able to do so, because it's in their interest to be able to scale-back
production so as not to over-supply the market which leads to a low
price for their output.

The supply of cheap electricity at night is a by-product of
operational limitations of current plant design and I'm sure it's not
intentional and perhaps future plants will not have this limitation.

The other strategy to always run the big plants at full output and
convert excess demand into other forms of energy storage (like
batteries, generate hydrogen, etc) is so stupid because of the energy
conversion losses and the infrastructure needed for society to use the
alternate forms. This strategy again is based on the assumtion that
the big plants can't, or won't, or don't want to scale back output to
meet demand. The best solution IS to scale back output so that you're
not burning your main fuel stock when you don't have to.

 

[HVAC Guy]

Because he's already running flat out during the day.

So? What does that have to do with anything?

If he's making money at 1.5 cents, then he's making even more at 4
cents.

And it still isn't enough to meet demand,

That's not his problem.

he may rather stay up and sell at night at 1.5 and during
the day at 4.

Yes, he's a real bonehead. Since he's selling his juice cheap to the
guy running the pumped storage plant, the pump can come on line during
the day and the market price is 4 cents. But if the pump wasn't
there, then the spot price would be 6 cents, and the guy running the
other plant would be making MORE money.

 

[Eeyore]

So? What does that have to do with anything?

If he's making money at 1.5 cents, then he's making even more at 4
cents.


That's not his problem.


Yes, he's a real bonehead. Since he's selling his juice cheap to the
guy running the pumped storage plant, the pump can come on line during
the day and the market price is 4 cents. But if the pump wasn't
there, then the spot price would be 6 cents, and the guy running the
other plant would be making MORE money.

You don't have a good grasp of business and economics do you ?

Graham