Air compressor as energy storage?

[Taunto]

I'm just trying to figure some efficient, cost effective ways to
"time-shift" energy usage, for charging at night when rates are cheap,
and discharging when not.

Seems like battery storage is to inefficient. Flywheels are expensive,
and liable to fly apart.

What about pumping air into a tank, and then running it backwards when
needed? Would need some sort of motor that runs on compressed air.

What are the inefficiencies of this route?

 

[Eeyore]

I'm just trying to figure some efficient, cost effective ways to
"time-shift" energy usage, for charging at night when rates are cheap,
and discharging when not.

Seems like battery storage is to inefficient. Flywheels are expensive,
and liable to fly apart.

What about pumping air into a tank, and then running it backwards when
needed? Would need some sort of motor that runs on compressed air.

What are the inefficiencies of this route?

Fairly significant. Using compressed air is lossier than batteries.

Graham

 

[Vaughn Simon]

I'm just trying to figure some efficient, cost effective ways to "time-shift"
energy usage, for charging at night when rates are cheap, and discharging when
not.

Seems like battery storage is to inefficient. Flywheels are expensive, and
liable to fly apart.

What about pumping air into a tank, and then running it backwards when needed?
Would need some sort of motor that runs on compressed air.

Actually, that could be the easiest part. With a proper design, the
compressor could easily be the motor. By the way, you would need a very large
storage tank and/or very high pressures.

What are the inefficiencies of this route?

Terrible. There are good reasons why compressed air energy storage is not
common.

Besides the usual things (friction, motor losses, generator losses) you
have a special kind of thermal loss. Simply put: When you compress air, it gets
hot, and you supply the energy to make that heat. Unless you recover that heat
somehow, it is energy lost to you forever. When you expand your air to generate
power, it suddenly gets cold. This reduces the expansion (and the power you
extract) and creates problems for your motor. It can end up encased in a big
block of ice!

Vaughn

 

[HVAC Guy]

I'm just trying to figure some efficient, cost effective ways to
"time-shift" energy usage, for charging at night when rates
are cheap, and discharging when not.

That would only work assuming you are charged based on time-of-day
use. Not many people are.

What about having a situation where you would mechanically lift some
large mass using excess energy (solar, wind, low-cost utility power,
etc) and then use the stored kinetic energy when you need to convert
it back to electricity by running a generator as the mass is lowered.
Efficiency would depend on how much you could reduce friction I guess.

See these:

http://www.columbia.edu/~zk30/gravity.html

http://www.halfbakery.com/idea/energy_20storage_20gravity

 

[Eeyore]

ARe there major appliances that run on both AC and DC?

Resistance heaters.

Graham

 

[[email protected]]

If you want to store heat energy then phase change storage (substances
that melt and freeze) is a very effective solution. Paraffin (wax,
the US kind, not UK kerosene) is a very good medium. It has a decent
heat of fusion and melts at a convenient temperature (~140 to 180 deg,
depending on blend). There are companies that sell phase change media
encapsulated in convenient balls that can simply be poured into a
water tank to more than double the heat storage capacity of a tank
full of water alone.

I'd like to double the heat in a 957-gallon 170 F STSS tank.

Got any brand names?

Nick

 

[Eeyore]

I'd like to double the heat in a 957-gallon 170 F STSS tank.

Got any brand names?

Googling "wax balls" gives a rather less than useful result !

Graham

 

[[email protected]]

Something that melts at 100 F might be nice, eg the C20 material on
the site Anthony found, but their "macro" spheres are 4 mm max...

Ball? (you know, as in Ball jars and canning wax..)

I didn't see PCMs among the aerospace and packaging products on their site.
Maybe they stopped making them.

Look for "phase change heat storage balls" to start with...

Lots of patents and studies and companies who might make custom products,
but Googling didn't turn up any standard stuff.

Unless you have a need for the sealed media, however, I suggest looking
at plain old paraffin. A tank of paraffin with sufficient copper coils
inside to effect the heat transfer to the water would do the job.

The tank has an EPDM liner. I can picture paraffin clogging the draindown
"solar collector," 64' of fin-tube pipe near the top of an air heater.

Nick

 

[[email protected]]

I'm just trying to figure some efficient, cost effective ways to
"time-shift" energy usage, for charging at night when rates are cheap,
and discharging when not.

Seems like battery storage is to inefficient. Flywheels are expensive,
and liable to fly apart.

What about pumping air into a tank, and then running it backwards when
needed? Would need some sort of motor that runs on compressed air.

What are the inefficiencies of this route?

WHAT?!? We can't hear you! The sound of the air compressor is
too LOUD!!!

Ever worked in a place with one of those things?

 

[HVAC Guy]

Actually much mo-betta is pumped storage, like NE utilities have
been doing since the forties. Pump from river up to lake during
low demand; flow down to river through turbines for peak demand.

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?

 

[Eeyore]

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.

That's not what he said.

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?

And put more in the lake by pumping it there with electricity from baseload
generation.

Graham

 

[EXT]

There are two "pump up" installations just north of Niagara Falls, one on
the Canadian side and one on the American side of the Niagara River, each
with their own small lake for storage.

 

[Vaughn Simon]

These plants change power output only very
slowly. A PRW nuke that uses dissolved boric acid neutron absorber
for power control can take days to make a major load change and settle
down.

You are correct that those plants like a steady load, but technically
speaking the boron does not control the power level in the short term. In a
PWR, power level is controlled by the negative temperature coefficient of
reactivity. As the water cools, it becomes denser and serves as a more
efficient moderator, increasing the power level. As it heats up, the opposite
effect occurs. Back when I was a reactor operator, I could watch a large change
in power without ever touching the rod controls.

What the boron does is allow the rods to be withdrawn more fully, which gives
more even fuel burn and (incidentally) allows a greater shutdown margin. After
a sudden shutdown, the boron can indeed prevent restart until it is either
removed or poisons (mostly xenon) allowed to decay. That is an effect called
"xenon precluded startup".

(Just thought I would add a bit to the group's base of useless knowledge)

Vaughn

 

[HVAC Guy]

There are two "pump up" installations just north of Niagara Falls,
one on the Canadian side and one on the American side of the
Niagara River, each with their own small lake for storage.

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.

Not demand, cost.

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.

Pump up during low cost, drain down during high cost

cost to who?

The consumer, or the operator of the plant?

But that still doesn't address the issue of why let the un-needed
water drain down the turbine in the first place instead of diverting
it into a storage lake. Why let it go down, then turn around and pump
it straight back up?

 

[Taunto]

EXT wrote:




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.




cost to who?

The consumer, or the operator of the plant?

Cost of electricity to the utility.

But that still doesn't address the issue of why let the un-needed
water drain down the turbine in the first place instead of diverting
it into a storage lake. Why let it go down, then turn around and pump
it straight back up?

Dude, I didn't invent it, I'm just citing to installations that use it.
If you have questions, I think you should ask it of the people who
make it work.

 

[Eeyore]

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

Indeed. That's the whole point. It's used for peaking generation.

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.

No. Why did you introduce such a silly complication ?

If demand is low,

Nightime typically....

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.

He's not saying that at all.

When you're pumping water 'uphill' the turbine is off. You're using baseload
generation to do it.


Graham

 

[Eeyore]

Or google 'Ludington Pumped Storage'

http://en.wikipedia.org/wiki/Pumped_storage Complete with pretty pictures.

Graham

 

[HVAC Guy]

No. Why did you introduce such a silly complication ?

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.

He's not saying that at all.

When you're pumping water 'uphill' the turbine is off. You're
using baseload generation to do it.

Where is that baseload coming from?

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?

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

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

 

[Eeyore]

What do you mean no?

No connection between 2 supposed sources of water.

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?

Why do you think you need 2 sources ?

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.

Good Lord. You just don't get it do you. The 'main source' has limited flow
therefore a limit on power capacity. By pumping water up into the lake /
reservoir you generate extra capacity for peak demand. It's all about peak
demand you see which is more expensive to provide.

Pumped storage is way to provide peaking power for little more than the price of
baseload.

Where is that baseload coming from?

Coal and nuclear mainly.

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?

In the examples I know of the 'main source' *is* the lake.

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

A reduced baseload isn't much use since large power stations (esp nuclear) like
working at fixed and a high percentage of full output power.

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

Peaking power generation is significantly more expensive than baseload. The
whole point is that it doesn't result in 'excess' baseload. It takes advantage
of the lower cost baseload generation when it's not fully stretched.

Graham

 

[Trygve Lillefosse]

I'm just trying to figure some efficient, cost effective ways to
"time-shift" energy usage, for charging at night when rates are cheap,
and discharging when not.

If you by energy means heat, to heat your house. Something as easy as
a timer on your boiler would be a good start. Then insulate the boiler
for even better effect.

If you have central heating, you should be able to save quite a bit by
doing this.

Even more if you could get a realy big and rely well insulated tank.

And even better still if you use a heatpump (air/water* or geothermal)
to heat the water at night.

*This may depend on the COP at night compared to the COP at daytime.
Since the outside temperature is lower at night - The price-difference
may be smaller than with geothermal..