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Kg-meter required for 1 MWH generator

  1. Nov 25, 2012 #1
    Dear Friends,

    I need some details to run 1 MW Generator. I found that 3600 Mega Joules/hour (3.6 Giga Joules/hour) required to run 1 MW Generator for 1 hour i.e 1 MWH.

    3600 Mega Joules/hour = 102,000 Kg-m/sec.

    I want to know that Can we run 1 MW Generator (1500 rpm) for 1 hour to supply 1 MWH using this 102,000 Kg-m/sec. Or Only able to run the 1 MW Generator for 1 sec using that 102,000 kg-m/sec?

    Help highly appreciated.

    thank you
  2. jcsd
  3. Nov 25, 2012 #2
    A 1 MW generator, if properly designed, will deliver 1 MW as long as it has fuel. Not just 1 second.
  4. Nov 25, 2012 #3
    102,000 kg-m/sec force enough to run 1 MW Generator (1500 rpm) for 1 Hour? This is what I actually need?
    102,000 Kg-m/sec - required to run 1 MW Generator for 1 sec?
    60 x 102,000 = 6120000 Kg-m/minute - required to run 1 MW Generator for 1 minute?
    60 x 6120000 = 367,200,000 Kg-m/hour - required to run 1 MW Generator for 1 hour?

  5. Nov 25, 2012 #4


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    Power (in Watts) = Torque (in Newton meters) * Angular velocity (in Rads/s)


    Torque = Power/Angular velocity

    at 1500 rpm the angular velocity in rads/s is...

    = 2∏ * 1500/60
    = 157 rads/s


    Torque = 1,000,000/157 = 6369 Nm

    So your generator appears to require a motor capable of producing 6369 Nm of torque at 1500 rpm.

    Edit: Your generator will keep delivering 1MW for as long as your motor keeps delivering 6369 Mn at 1500 rpm.
  6. Nov 25, 2012 #5


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    If I have understood correctly you mean..

    102,000 kg-m/sec = 102,000 x 9.8 = 999,600 Nm/sec


    force (in Newtons) * velocity (in m/sec) = power (watts)

    so what you are saying is that your source is 999,600W.

    Since 999,600W < 1,000,000W the answer to your question appears to be no.

    However even if you decide it's close enough your data still doesn't have enough info to answer the question fully. For example how is your source power delivered? Is it in the form of electrical power? linear motion? rotary motion at the right rpm?

    The generator needs 1MW (6369 Nm, at 1500 rpm) where as you have 0.99MW (?Nm, at ?? rpm).
  7. Nov 25, 2012 #6
    The difference between 999600 W and 1 MW is negligible and stems from rounding errors. The OP converts MW into kg m/sec (I don't know why). I think the word second is the key because it makes pmk69 think the generator would run for only a second.
    On the other hand, perhaps the OP just want to ask the amount of energy needed to run the generator 1 hour, but it isn' so clear.
  8. Nov 26, 2012 #7
    Hi CWatters,

    Thanks for your reply. Available energy is in the form of Linear and it should be converted into Rotary Motion using Gear Box (Like Wind Mill) to give required RPM, For example 1500 RPM, to run a 1 MW Generator. So, I need to know whether the said (1,02,000 Kg-m/Sec) energy can be used to run a 1 MW Generator for 1 Hour to produce 1 MWH?

    Yes Gordianus. This is where I need clarification. Can we run 1 MW Generator for 1 Hour to produce 1 MWH using this 102,000 Kg-m/s?
  9. Nov 26, 2012 #8


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    In my book "Kg-m/Sec" is a ambiguous unit because force isn't measured in kg but Newtons. So can you tell us how you arrived at 1,02,000 Kg-m/Sec ?

    kg.m/sec looks like force (kg) x velocity (m/s) which equals power not energy. So asking how long it will run a 1MW generator is meaningless. It's like asking how long can a 100bhp car engine can deliver 100bhp?

    As I said above..

    102,000 kg-m/sec = 102,000 x 9.8 = 999,600 Nm/sec = 0.99 MW which is less then 1MW so the short answer is no. You can't run a 1MW generator from 102,000 kg-m/sec for any length of time (but it's close if you ignore losses in the generator and gearbox).
    Last edited: Nov 26, 2012
  10. Nov 26, 2012 #9
    This is the URL that I referred. You can also check that:


    Simply to say, How much energy (in Kg-m) I need to run 1 MW generator for 1 hour. I have to store available mechanical energy (Linear) and used that energy to run the Generator.


    Attached Files:

  11. Nov 26, 2012 #10


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    Ah that's a slightly different and easier question...

    First lets assume the generator and gear box are 100% efficient..

    Energy (in Joules) = Power (in Watts) * Time (in seconds)

    = 1MW * 3600 Seconds = 3,600 MJ

    You can then convert that to other units...

    3600 MJ = 3600 M N.m or

    3,600,000/9.8 = 367,346 Kg-m

    Could be done with 367,346 kg of water lifted 1 meter or 36,735 kg lifted 10m etc

    However most generators are going to be less than 40% efficient so in practice you need to store at least 100/40 = 2.5 times that much energy and probably more like 4 times. Plus whatever the pump uses to lift the water into storage.
  12. Nov 26, 2012 #11
    this is what I actually need. If I want to run 1 MW generator (for example, theoretically 100% efficient) for 1 hour is 367,346 kg-m.

    For 24 Hrs = 367,346 x 24 = 8,816,304 kg-m
    For 365 Days(1 Year) = 8,816,304 x 365 = 3217950960 kg-m
    i.e. 3217950.96 tonnes-m or 3.21 million tonnes - m

    Is this correct?

    anyway great thanks to you.

  13. Nov 26, 2012 #12
    how to mark the "Helpful" button?
  14. Nov 26, 2012 #13
    if reply is helpful to solve the issue, we have to mark the reply as "Helpful" and Mark the thread as "Solved"? How can we do it here?

  15. Nov 26, 2012 #14
    Is this conversion correct?

    3600 MJ = 3600 M N.m or

    3,600,000/9.8 = 367,346 Kg-m


    this one is correct?

    3600 MJ = 3,600,000,000 Joules = 3,600,000,000 N-m = 36,000,000 Kg-m

  16. Nov 26, 2012 #15
    EDIT: Nevermind, it all become clear.
  17. Nov 26, 2012 #16


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    The units are different, they are not the same. And even if you add a factor of g, there is one digit missing.

    3,600,000,000 Nm = 360,000,000 kg*m * g
    (with the approximation of g=10m/s^2)
  18. Nov 26, 2012 #17


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    Those features are not enbled here on the PF.
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