Hi all,
A general question about using flywheels for force storage.
Is there a concept of capacity for using a flywheel as a force storage device?
In other words is there a limit for a given flywheel for energy storage? Or is the capacity unlimited? For example I can imagine just spinning a flywheel faster would allow it to store more energy.
Is this similar to voltage vs. amperage?
More volts = faster spinning slywheel
More amps = heavier flywheel
watts = amps x volts
flywheel power = weight x rpm
I ask because I am wondering if a flywheel that I am using in a device just doesn't have the "capacity" to store the energy being pushed into it. I don't think I can push the device to operate quicker, so I think my only choice is to use a larger/heavier flywheel.
@ken_nyus
Just do a Google search for "flywheel designs"
Here's a link that discusses high tech flywheels going from 30,000 to 100,000 rpm.
http://www.testdevices.com/flywheel_article.htm
Also, I put a pdf on flywheel research. Pretty good read.
Regards
wattsup
G'day Ken and all,
One of the problems with flywheels for energy storage has always been the centrifugal (centripetal for the purist) forces that develop. Finding materials that will stand up to incredibly high speeds is the problem and the really good materials that we have are restricted as they are used in centrifuges for uranium enrichment etc.
In other words the limit in practical terms is perhaps more political than technical.
Hans von Lieven
Yep, if you are planning on using one to store energy for a static device it would be okay - but I would suggest that flywheels have serious problems: mainly, to make one really efficient, you need to can it in a vacuum chamber and preferrably mount it on magnetic bearings. plain old flywheels are fine for short- term use but only if you are not moving them around (gyroscopic effects). Batteries are still a better and safer storage method for most purposes - if a flywheel breaks, it makes a BIG BANG wheras a busted battery is only going to lose charge to earth and leave some corrosive liquid.
hope this helps.
G'day magnusx and all,
You are right about the gyro effect.
A number of years ago, perhaps in the early sixties they designed a bus that had a large flywheel in it. The idea was that at every bus-stop an arm would come out and connect to the electricity supply which gave the flywheel a bit of a boost. When the passengers were on board the thing drove on flywheel power.
The system was tried in some African states and was not altogether successful because it was hard to negotiate sharp corners because of the gyroscopic effect.
I can't remember much more about it except that I laughed when I read it.
Hans von Lieven
Hi Ken,
Quote from: ken_nyus on September 08, 2007, 03:00:44 PM
In other words is there a limit for a given flywheel for energy storage? Or is the capacity unlimited? For example I can imagine just spinning a flywheel faster would allow it to store more energy.
Is this similar to voltage vs. amperage?
More volts = faster spinning slywheel
More amps = heavier flywheel
watts = amps x volts
flywheel power = weight x rpm
I ask because I am wondering if a flywheel that I am using in a device just doesn't have the "capacity" to store the energy being pushed into it. I don't think I can push the device to operate quicker, so I think my only choice is to use a larger/heavier flywheel.
The energy stored in a flywheel is proportional to its mass x rpm x rpm x radius x radius, i.e., the rpm and radius terms are squared.
For a flywheel of a given shape, both the stored energy and the centrifugal force that tries to tear it apart are proportional to mass x rpm x rpm, so the amount of energy you can store is limited by the tensile strength of the material that it's made from.
Because centrifugal force is proportional to radius, and energy is proportional the the _square_ of the radius, you can make the most out of a given amount of a given material by shaping it into a thin disc.
Cheers,
Mr. Entropy