Flywheel Generator - Need help understanding

[Spadez]

Hi,

I was wondering could help me explain how these flywheel energy storage systems ive been reading about convert their mechanical movement and feed it back into the grid.

I understand that a generator is used, but is the generator simply plugged into a battery or is it a lot more complicated than that? I dont know if super-capacitors are used to store the bursts of power, then have it fed back into the battery from there?

 

[ericgibbs]

Hi,

I was wondering could help me explain how these flywheel energy storage systems ive been reading about convert their mechanical movement and feed it back into the grid.

I understand that a generator is used, but is the generator simply plugged into a battery or is it a lot more complicated than that? I dont know if super-capacitors are used to store the bursts of power, then have it fed back into the battery from there?

hi,
The French railway system has used flywheel energy storage devices for many years.
**broken link removed**

 

[Spadez]

Thank you very much, ill read through the article. However, it doesnt seem to explain how the generator on the flywheel has its electrical output stored, thats the bit im really interested in.

 

[sandeepmulay]

flywheels are heavy metal wheels connected to engine or prime mover,and shaft of engine rotates armature of the alternator or generator.

when engine runs kinetic energy is stored in flywheel ,as heavy load is put on the alternator ,stored energy in flywheel is transformed to alternator shaft, giving pulseof energy.
oposite of this happens when load on alternator is removed or decreased.

sandmulay

 

[Spadez]

Ok, but is the generator connected directly to the battery to store energy, or is there complicated circuity to regulate the power and stop the battery power flowing back into the generator. This is the bit I dont understand very well.

 

[Spadez]

I found this thread as a starting point:

Regenerative braking, how? - All About Circuits Forum

 

[Hero999]

The generator can act as both a motor and a generator.

A synchronous motor/generator connected to a huge flywheel can simply be connected to any part of the grid and it will hold the voltage up when there's not enough power from the power station and will absorb excess voltage when power station generators too much power. It's like a huge decoupling capacitor on a DC system but for AC.

 

[Spadez]

Thank you for the reply. I don't really understand how the flywheel can be plugged straight into the grid then. Wouldn't the generator act as a motor, using the grid power? Also, the grid is ac, but the generated power would be DC. Finally, the generated voltage would undoubtably be much smaller than the grid voltage.

I'm assuming there must be some kind of diode / rectifier / converter circuit? If so, can someone explain what is involved in this circuit.

 

[Hero999]

Yes, when the flywheel is connected to the grid, the generator will act as a motor, drawing power from it to bring the flywheel up to speed.

Once the flywheel is up to speed, a tiny amount of power will be used to make up for the losses in friction caused by the bearings and air resistance.

No, the generated power will be AC since it's an AC motor/generator.

The generated voltage will only be very slightly lower than the nominal grid voltage due to the losses in the generator, possibly a volt or so? This makes very little difference because when the grid voltage drops below the generator's voltage, the energy from the flywheel will be put back into the grid.

No, there is no need for a converter circuit, all that's needed is a synchronous motor with a huge flywheel connected to its shaft. Having said this some circuitry may be required to limit the current surge created in starting the flywheel but it certainly isn't required once it's up and running or when energy is taken from it.

I imagine that putting the flywheel in a vacuum and supercooling the motor/generator will minimise the losses but it probably isn't worth it.

 

[flywheelguy]

Actually a FESS (flywheel energy storage system) can store in both AC & DC by simply changing the motor type. The only drawing back to using flywheels in grid support is that they cannot slow discharge; with one exception (**broken link removed**). The Tribology design does not use mag.lev bearings; which all other FESS Mfg's must use and therefore can slow discharge all of the stored energy over any given period of time.

 

[RCinFLA]

The ones used as temporary supply to allow time to start a backup diesel or propane generator use DC-AC inverter. Two problems with just spinning from a flywheel coast down grid freq motor/alternator. 1) The frequency of output would decrease and quickly fall outside of grid backup freq tolerance allowing very little of the stored kinetic energy to be extracted from the flywheel. 2) Once the backup generator is started, a coast down grid freq motor/alternator would not have the ability to adjust its freq/phase to match the generator.

 

[Hero999]

What about connecting the flywheel via a continuously variable transmission, or would the power losses be too great?

How about connecting the diesel backup generator via a clutch so it can connected when needed and brought to to synchronous speed with fluctuations being smoothed by the flywheel?