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Hydroelectric power generation

Discussion in 'Alternative Energy' started by Techie7, Dec 12, 2008.

  1. Techie7

    Techie7 Member

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    Hope you experts will help me regarding this.
    In a hydroelectric project water stored in a reservoir pumps to upper hill tank from there rooted to down powerstation through penstockes. I couldn't understand the efficiency of this system. my question is:

    Energy used for pumping lower level water to higher level.
    =?,<?,>?
    Energy generated from taking the higher level water to lower level powestation.
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    What's to understand? - efficiency is fairly low - but it's used to store energy during low power consumption periods, where the electricity would be 'wasted' otherwise.

    Then, during sudden peak demand, the water can be released and very quickly generate multi-megawatts.

    There's a classic example in Wales near Snowden - the power station is built entirely in a mountain, and pumps water to a lake at the top. It's a tourist attraction, you go in on a coach - it's really pretty cool.
     
  3. Techie7

    Techie7 Member

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    so you mean when some power is generated, it should be fully utilized anyway?
    y can't turn off some of the generators when low consumption time and save that wasting of energy.
     
  4. dave

    Dave New Member

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  5. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    There's a point that generators run at where they are most efficient, it makes sense to run them at that level as much as you can - bear in mind you can't stop and start normal power stations in a few minutes. Even the stored power station takes time - although by powering the alternators from the grid (which takes megawatts to do) it can go to full power in a few seconds.

    Have a read about Dinorwig

    First Hydro Electric Mountain Llanberis

    Even if you did turn off power stations during low demand, where are you going to get the sudden high peak demand you might need?.
     
    Last edited: Dec 12, 2008
  6. Techie7

    Techie7 Member

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    but is that applicable to both cases ryt? for not wasting the energy, we start up a storage pump at low demand hours. When a sudden peak demand comes then we have to turn off that pump because the sudden peak demands the energy used by the storage pump :confused:
     
  7. Diver300

    Diver300 Well-Known Member

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    Yes. If the pump is being used to pump water uphill when there is surplus electricity, it can be shut off in seconds if there is a sudden surge in demand.

    The ability to go from 1.3 GW load to 1.3GW of generation in a few seconds is quite neat.

    First Hydro Dinorwig Power Station has some interesting facts and figures. They suggest that the station efficiency is about 75%. That is the total from electricity to rotation to water flow to potential energy to water flow to rotation to electricity.

    That's not bad compared to the approx 60% efficiency of a car alternator and it only goes from rotation to electricity.
     
  8. Hero999

    Hero999 Banned

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    Don't they use the alternators as motors?

    A car alternator is inefficient because it's small (the efficiency of motors and alternators goes up with size) and designed to work at a large range of speeds.
     
  9. Techie7

    Techie7 Member

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    Thanks very much guys.....
     
  10. KMoffett

    KMoffett Well-Known Member

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    Also think of combining wind or solar power generation with the lake as a way of storing their energy in non-peak demand periods.

    Ken
     
  11. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    It's automatic - such sources just feed the grid, if there's surplus on the grid they use it to pump water.
     
  12. dknguyen

    dknguyen Well-Known Member

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    Yeah, I remember when I was in junior high (or was it high school?) and was shocked to learn that they didn't shut down some of the generators during the night because it took too long to start them back up again (like ~10 hours or so?) so they were just left running the entire night doing very little.
     
  13. danielsmusic

    danielsmusic New Member

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    You can compare the lake at the top as one gigantic uber capacitor.
     
  14. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Not really, the lake at the top is like one plate of a capacitor, the lake at the bottom is the other plate.
     

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