Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Generating power through displacement.

  1. Jan 13, 2008 #1
    Hi there.

    I've been looking at whether it's possible to create renewable energy though the use of diplacement and taking advantage of pressure differences. Let me explain.

    Lets say you had a cylinder 100m x 50m. At the bottom of this cylinder you had multiple inlet pipes. The cylinder is then dragged down into the water using a weight of some kind so as to displace the water. The pressure at that depth, if I'm not mistaken would be 145.304 psi. The water is then allowed to pass through the inlet pipes to drive a turbine which then pumps the water out and over the edge of the cylinder. What I want to know is whether the energy created is likely to be greater than the energy required to remove the water from the cylinder?
     
  2. jcsd
  3. Jan 13, 2008 #2

    russ_watters

    User Avatar

    Staff: Mentor

    I think you may already know the answer to the question: The law of conservation of energy applies.
     
  4. Jan 13, 2008 #3

    stewartcs

    User Avatar
    Science Advisor

    No it definitely won't be greater. At the very best, it would be the same if the machine had an efficiency of unity.

    CS
     
  5. Jan 13, 2008 #4
    Energy Can Neither Be Created Nor Destroyed; Can Just Be Transferred From One Form To Another.
    This Idea Is An Illusion Like Perpetual Motion Machines.
     
  6. Jan 13, 2008 #5
    i remember when i used to get out of the box ideas in school and i thought i was a genious ;))
     
  7. Jan 13, 2008 #6
    No. In theory and an idealistic situation, it will be exactly equal. In practice, it will always be less.. less by around 20-30%.
     
  8. Jan 13, 2008 #7

    russ_watters

    User Avatar

    Staff: Mentor

    It's much, much less than that. You might get a turbine efficiency of 65%, then a generator efficiency of 95%, then a motor efficiency of 95%, then a pump efficiency of 65%. That's an overall efficiency of 38%.
     
  9. Jan 13, 2008 #8
    oops.. i stated it wrong.. What i was meaning to say is, "Output energy is 20-30% of input work".
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?