Clean energy might be easier than expected

[Iggyz]

1. Is it correct that the maximum output electrical power of a generator is equal to the maximum input mechanical times the generator efficiency?

2. Assuming this is correct. Does that imply 1 kW of mechanical input power yields 0,95 kW of electrical output power?

3. Also, is the correct answer to the question asked in the attached picture is 'more energy'?

4. Meaning it is more efficient to power the disc at its edge.

If the answer to all four questions is yes, than it might be possible to build a perpetuum mobile. Depending on how more efficient it is to power the disc at its edge.

Imagine the disc is a 20 meter in diameter rotor of a direct drive 10 MW generator with an efficiency of 95%. The weight of rotor is 50.000 kg and it has to spin at 12 rpm to generate its maximum electrical output.

It would take 10 MW of mechanical input applied to the shaft of the rotor to generate an electrical output of 9,5 MW.

How much mechanical energy is needed to drive the rotor at its edge in order to generate an electrical output of 9,5 MW?

If it is substantially less, say 7 MW, an electrical motor can supply the mechanical input and we can generate a net electrical output of ~ 2 MW.

Can someone please do the math to find out how much energy is needed to drive the rotor via its edge and how much energy is needed to drive the rotor its via shaft? In a way a layman can understand please. Many thanks in advance!

[edzieba]

You're making very basic errors, mixing up "power" and "energy" and ignoring mass.

If you think you've designed a perpetual motion machine, the answer is "no".

[laszlo]

No math is needed to answer your questions, just an understanding of the system and basic physics. You are basically asking if driving a shaft through a gear instead of directly will allow you to make a perpetual motion machine.

First, nothing will ever let you make a perpetual motion machine. Thermodynamics disallows this. As soon as you think you can make one you know that you've made an error.

Second, driving the shaft through the disk instead of directly simply changes the amount of torque required to drive the shaft at a specific rotation rate. Any changes in energy are the result of the efficiency of the prime mover at various rotational speeds. If driving the generator through the disk instead of directly at the shaft allows the prime mover to operate at an RPM that produces maximum torque, you'll get more energy from the generator for the amount of energy you're putting into the prime mover. In effect, driving the disk at the edge could match the maximum torque RPM of the prime mover to the maximum electrical generation RPM of the generator. Congratulations, you've invented the transmission.

But, as has been proven by over a century of automobiles, a transmission does not result in a perpetual motion machine, otherwise we could have closed all the gas stations decades ago.

[daedalus1]

This is deja vous.

[laszlo]

Yep, expecting this thread to disappear at any moment. The only reason to leave it is as a teaching moment for the OP. Maybe we ought to have a thread with sticky posts called Basic Physics for People Who Believe in Perpetual Motion, FTL and Reactionless Drives. Probably wouldn't slow down the silly posts much, but it could help those with open minds and incomplete educations.

[Crispy]

I think this is infinite energy machine no.7
Still making some very basic physics mistakes, I'm afraid.

[Iggyz]

Most of the weight of the rotor / disk is situated near its edge (correct?). That's why I think it is more efficient to drive the rotor at its edge.

If it is correct, how much less energy is needed to give it the same rpm and generate the same electric output?

[Jim]

Most of the weight of the rotor / disk is situated near its edge (correct?). That's why I think it is more efficient to drive the rotor at its edge.

If it is correct, how much less energy is needed to give it the same rpm and generate the same electric output?

No and no. And it is the same energy needed.

[Jim]

Can someone please do the math to find out how much energy is needed to drive the rotor via its edge and how much energy is needed to drive the rotor its via shaft? In a way a layman can understand please. Many thanks in advance!

It is the same

[Iggyz]

Thank you Jim.

An generator's rotor can be engineered by using spokes like in the attached picture.
Will these make a difference?
Also, is it possible to use a light weight material like carbon fiber for the spokes?

[rubicondsrv]

Thank you Jim.

An generator's rotor can be engineered by using spokes like in the attached picture.
Will these make a difference?
Also, is it possible to use a light weight material like carbon fiber for the spokes?

it does not matter what the rotor is made of, the best possible output equals the input and it will never quite reach that. 

[Lar]

Yeah we're done, this is a perpetual motion machine proposal.

Locked. Don't restart it....