Compressed liquid energy storage?

[cato]

hey all,

I watched a show recently (probably on discovery or something) about a company producing compressed air powered cars. I thought that was a novel idea, so I looked up the energy density of typical compressed air, and noted that it is at least an order of magnitude less than plain-o'l gasoline.

that got me thinking, why not compress something with more... potential, like water.

does anyone know how practical it is to compress water and release the energy into a small turbine or cylinder for propulsion?

I would think water could achieve higher energy densities, but I could be wrong. not my area of expertise. I am an expert at pushing bits around :P

[mathman]

For all practical purposes, such as the application you are suggesting, liquids are incompressible.

[cato]

well, if a liquid contains gases (like water does) it will be compressible. so, I am basically talking about pressurized water. one wouldn't really need to significantly alter the density of the water, as long as it stores useful energy.

I was just thinking that the water would not be as susceptible to diabatic inefficiencies, like air is. however, I have very little chemistry under my belt, so i was hoping someone could shed some light for me.

[TBodillia]

http://www.physlink.com/Education/askExperts/ae15.cfm

Question
Can you compress a liquid (water)?

Answer
The answer is yes, You can compress water, or almost any material. However, it requires a great deal of pressure to accomplish a little compression. For that reason, liquids and solids are sometimes referred to as being incompressible.


Almost sounds like you are asking about an over unity contraption: using energy to pressurize water, release it to spin a turbine, and use that to produce energy.

[TBodillia]

Not exactly on point, but close...I forgot about pumped storage hydroelectricity. Hydroelectric plants use pressurized water (the falling water is channeled into smaller pipes, gaining speed & building pressure) and that is used to spin turbines.

At several facilities in the US (and worldwide), when demand for electricity is low, they use excess electricity to pump water back up into the reservoir or into a separate lake to hold for a later use (when demand is high and they can sell the electricity for more money).

http://www.ferc.gov/industries/hydro...ation/pump.asp

http://en.wikipedia.org/wiki/Pumped-...droelectricity

[spidergoat]

Water is very heavy and air is light, making air a better choice. Also air powered tools are commonplace. Any vessel to contain highly pressurized water would also be extremely heavy. A better choice might be a flywheel spinning at high RPM.

[Diode-Man]

hey all,

I watched a show recently (probably on discovery or something) about a company producing compressed air powered cars. I thought that was a novel idea, so I looked up the energy density of typical compressed air, and noted that it is at least an order of magnitude less than plain-o'l gasoline.

that got me thinking, why not compress something with more... potential, like water.

does anyone know how practical it is to compress water and release the energy into a small turbine or cylinder for propulsion?

I would think water could achieve higher energy densities, but I could be wrong. not my area of expertise. I am an expert at pushing bits around :P

India has alot of compressed air motorcycles running around, thats whats up! Compressed air motorcycles are the way!

[spidergoat]

As far as I can tell, there are only a few made by engineering students that go about 2 miles per charge.

[cato]

Question
Can you compress a liquid (water)?

Answer
The answer is yes, You can compress water, or almost any material. However, it requires a great deal of pressure to accomplish a little compression. For that reason, liquids and solids are sometimes referred to as being incompressible.

right, it would not need to compress a lot, just enough to store energy useful for power a small vehicle.

Almost sounds like you are asking about an over unity contraption: using energy to pressurize water, release it to spin a turbine, and use that to produce energy.

nothing over unity, but you have the basic idea. similar to the air powered cars, one would compress it at home, then use the energy to drive.

Water is very heavy and air is light, making air a better choice. Also air powered tools are commonplace. Any vessel to contain highly pressurized water would also be extremely heavy.

good point about the weight, but I was thinking little more than 5 gallons/20 liters, so it wouldn't be considerable with respect to a vehicle. although, any weight gained in a green vehicle is important.

A better choice might be a flywheel spinning at high RPM.

a flywheel has similar problems. heavier flywheels store more energy per RPM than lighter ones. moreover, you have the problem with it slowing down while you are no using it. an air powered car would be able to hold a charge in an idle state for a much longer period of time. that's one of the reasons I like the idea of compressed air vehicles (that and lack of chemicals), but their energy density is pretty low.

compressed air motorcycles? that sounds cool. has anyone produced one with decent range?

[spidergoat]

For all practical purposes, water does not compress. When water gets into the piston of an engine, it doesn't compress and the piston blows up. A spring would be more efficient.