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Thread: Power & Energy Help?

  1. #1 Power & Energy Help? 
    Forum Professor scoobydoo1's Avatar
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    Hi everyone. First of all, if I have posted this thread in the wrong forums, I do ask that you folks forgive me.

    I have recently been reading up on power plants; comparing that with how much electricity my country consumes, and I am somewhat confused with the power generated (megawatts coming out of the generators) and the total amount of electricity my country is said to be consuming. I should clarify that this isn't a school project or homework of any sort, and it is something that has peaked my interests from a recent forum discussion.

    A particular power plant generator has a capacity of 2,600MW; making up roughly 25% of my country's consumption. I have also found a source telling me that my country consumes roughly about 6,000ktoe in recent years annually. I have also found another source with a chart showing me that we have generated roughly 45,000GWh in total for one particular year, and has a peak demand of about 6,500MW.

    I must admit, I am very confused by all this. One of the reasons why I am seeking some help in understanding some of these numbers is because I had a conversation with someone recently, and he told me that my country requires a supply of 10.5GW total... which totally does not make any sense to me with the figures mentioned in the above 2 sources. I had thought that to calculate how much electricity is being consumed (or how much we need) takes into account at what % capacity the generators is work at (base load?) and over how long a period of time. And that we can't simply take (2,600MW / 25) x 100 which is how he worked out his "math".

    Now, I know after some of you have read this, it will betray just how "noobish" I am on this subject. It may even irk some of you enough to not reply, but I do honestly want some help in understanding all this. If anyone is kind enough to explain some of this to me or point me in the direction where I can read up more, I would be most grateful.


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    If your 2600 megawatt station supplies 1/4 of the required generating capacity, then it does stand to reason that the total required generating capacity is about 4 times that, or approximately 10,500 megawats. To calculate the required generating capacity, you need to take into account the peak load, and the percentage of time the plant will be available to generate its rated power. Since the plant will be offline at various times for maintenance, either scheduled maintenance or unplanned outages, and sometimes may not be able to produce their peak output, the required generating capacity will need to be greater than the peak load.

    You have stated that the peak demand is 6500 MW, and the required capacity is 10,500 MW. This means that someone has calculated that the plants will be available at their maximum capacity for 6500/10500=about 62 percent of the time.

    The annual power consumption isn't used in these calculations because there is only a limited ability to store electrical energy, so the generators have to be sized for the peak load, unless you can tolerate periodic blackouts.


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    Forum Professor scoobydoo1's Avatar
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    Quote Originally Posted by Harold14370 View Post
    You have stated that the peak demand is 6500 MW, and the required capacity is 10,500 MW. This means that someone has calculated that the plants will be available at their maximum capacity for 6500/10500=about 62 percent of the time.

    The annual power consumption isn't used in these calculations because there is only a limited ability to store electrical energy, so the generators have to be sized for the peak load, unless you can tolerate periodic blackouts.
    Erm, actually the required capacity of 10,500MW wasn't stated in any of the sources I could find, and the figure of 10,5000MW was a result of how this fella worked out the math. I was hesitant in taking his word for it, since I figured I could work backwards from the annual consumption and arrive at what I assume to be a more accurate reflection of electricity my country consumes and how many power plants generators of varying MW capacities we would require.

    45,000GWh annually / 12months = an average of 3,750GWh per month

    I honestly do not know if I wrong in taking this approach. If I am wrong, I guess I may owe this fella an apology for doubting his methods.


    * but I wasn't sure how an average of 3,750GWh per month would help me in calculating how many megawatts generators we would need, since there is a plan for my country to have more power plants in operation within the next 1-2 years.
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    Moderator Moderator Janus's Avatar
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    Quote Originally Posted by scoobydoo1 View Post

    45,000GWh annually / 12months = an average of 3,750GWh per month

    I honestly do not know if I wrong in taking this approach. If I am wrong, I guess I may owe this fella an apology for doubting his methods.


    * but I wasn't sure how an average of 3,750GWh per month would help me in calculating how many megawatts generators we would need, since there is a plan for my country to have more power plants in operation within the next 1-2 years.
    3750Gwh per month is ~3750Gwh per 730 hours means an average power usage of 5137 Mw.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  6. #5  
    Forum Professor scoobydoo1's Avatar
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    Quote Originally Posted by Janus View Post
    3750Gwh per month is ~3750Gwh per 730 hours means an average power usage of 5137 Mw.
    If that is reliable way of estimating how much MW power would be needed from generators; 5137MW. Am I wrong to assume that it is about half of the 10,500MW capacity mentioned, which I think takes into account what Harold said about the offline periods of power plants and not necessarily working the generators at 100% capacity?
    Last edited by scoobydoo1; October 15th, 2011 at 11:55 PM.
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    Quote Originally Posted by scoobydoo1 View Post
    Quote Originally Posted by Janus View Post
    3750Gwh per month is ~3750Gwh per 730 hours means an average power usage of 5137 Mw.
    If that is reliable way of estimating how much MW power would be needed from generators; 5137MW. Am I wrong to assume that it is about half of the 10,500MW capacity mentioned, which I think takes into account what Harold said about the offline periods of power plants and not necessarily working the generators at 100% capacity?
    Yes, that is the general idea. For more information, see these Wikipedia articles.
    Availability factor - Wikipedia, the free encyclopedia
    Capacity factor - Wikipedia, the free encyclopedia
    Capacity factor - Wikipedia, the free encyclopedia
    Demand factor - Wikipedia, the free encyclopedia
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    Forum Professor scoobydoo1's Avatar
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    Thanks for the links, they were most helpful in helping me understand more about the subject and how to derive a more accurate figure from the numbers I have gotten from the sources I had found earlier. Although it did take a couple of tries before I managed to work out the math to get a capacity factor % to understand what you said before about the generators not working at 100% capacity all the time.
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