And to add further explantaion, the weight of the flywheel (and as mentioned the mass distribution) with the rpm, gives the momentum of the flywheel. And the momentum gives us how much energy it has stored.

The transfer of this stored energy to electricity through the generator, depends on the size of the generator and the efficiency of the generator (at various rpm - as mentioned the rpm will slow as the energy stored in the flywheel reduces).

So in the perfect world, the mechanical energy in, will equal the electrical energy out, allowing for efficieny losses in the generator and in the mechanical transfer of the energy to the generator.

My advice; start with how much energy you need (ie how many kW?) Then size the generator, and obtain the efficiency / rpm curve. Then you can calculate the energy requirements of the generator to achieve the outputs you need.

Hope this helps,

Anthony

Thanks for the start. To be a little more clear, I have a 7kw portable generator that I would like to run off a flywheel instead of the motor. I am aware of the dangers of high speed failures so I would like to turn the flywheel at lower speeds thus the heavy weight The generator came with a 5 hp motor that no longer works and the little boy in me wants to see if I can get it to produce 7 kw for one hour using a flywheel.

The speed would be in a curve, the flywheel under no load would begin to slow on its own once the force driving it was removed.....a generator generally speaking, must be run at a constant speed to be useful, unless you are storing the energy say for instance in a battery...A 7kw generator would require about 12hp, this would require a force of 12 x 550 ft·lb_f/s = 6600 ft·lb_f/s.... this would take a flywheel that weighed several million tons....

His 7 kw generator came with a 5 HP engine. Something doesn't compute.

Is that under continuous load or just peak load?

Point taken.

However the OP wants 7kw continuous, I believe. Or, at least he's under the impression that his generator is capable of this.

A tall order for a 100RPM flywheel in either case.

Much better than 33 1/3 rpm. :)

There's a whole generation out there going, "What's that?"

I was shouting at the radio last night as I listened to Eddie Izzard saying that whale song was "on 78...if you put it on 45" and he demonstrated that the frequency of the sound would rise and the words would run together to be intelligible as English.

A good joke ruined....

I think I have that song on an 8-track tape, somewhere.

Half-heard that - didn't believe my ears. <sad face>.

And F1 stores energy at about 22,000 rpm. The F1 kinetic energy recovery system generates up to 50+ kW of energy.

Second, any transmission introduces loss in the way of friction.

Re: transmission losses - I quite agree, and have never suggested otherwise.

Good points!

Thanks for being helpful. I am a firefighter by trade and have spent my life helping random people that needed a helping hand for no other reason that I could. So with that said. Thanks I understand that increasing the speed is more efficient than increasing the weight is this correct?

There is a whole bunch of necessary information missing from the original post, which displays no understanding at all of relevant physics relationships.

On a very wild guess, such a flywheel might need to weigh a few tens of tons.

Where will the energy come from to "spin up" said flywheel?

He's cranking it by hand?

Or... just run on top of it like a Flintstone tread mill.

Thanks JohnDG for providing an answer that presents the OP with some elucidating information related to his question.

To simplify things a little more for someone who has little exposure to physics / engineering, JohnDG's equation of Energy Stored in the Flywheel = ½Iω² boils down to:

Energy ≈ rpm² * mass * diameter²

So Chuck, you can see that the mass of the flywheel, which is what you originally asked about, has less of an impact on the energy stored in the flywheel than the rpm or the diameter.