14 Responses to “Storing the wind”

1. twotexastravelers Says:
   September 20th, 2008 at 2:36 am

   Your ideas to store the energy is great, and they solve one of the problem of energy storage. You can trickle the water back down through a turbine, or use the total weight of the volume of water to push hydraulics or or air. A third solution (other than pumping water or compressing air) is to use a low gear to raise a very heavy solid weight - a very old solution used in England to harness tides and power pumps in a system of canal locks.

2. nottinghamscience Says:
   September 20th, 2008 at 2:36 am

   Part 8

   In a full-scale implementation, we do not use holes. Controlled valves at the blade ends allow air to leak out freely until just the right amount of air is left for the piston to be able to bring up to the reservoir pressure.

   SDG

   (end)

3. nottinghamscience Says:
   September 20th, 2008 at 2:36 am

   Part 7

   You can either have a large amount of low-pressure air or a small amount of high pressure air. There are trade-offs both ways. High pressure causes high thermal losses. Low pressure makes it very difficult to store energy economically if you want to store it and makes the expander machinery more expensive. The holes in the tube were to allow the pistons in the demonstrator to compress only towards the end of stroke so that we could produce a small amount of high-pressure air. (cont)

4. nottinghamscience Says:
   September 20th, 2008 at 2:36 am

   Part 6

   The combination of these two makes the whole thing absolutely practicable. In the case of (a), you might think that you are sacrificing some compressed-air energy but this is not so. You get the energy back at the end of stroke (less some small losses). Now about those holes. The energy-per-blade-per-stroke isn’t something over which you can exert much influence (if turbine diameter has been decided). However, the pressure of air that you get out is absolutely within your control. (cont)

5. nottinghamscience Says:
   September 20th, 2008 at 2:36 am

   Part 5

   However, even at 200m the mass does not fall fast enough. Remember that as diameter increases, the mass has further and further to travel in one stroke!
   So you have to do one or both of these things: (a) allow a small amount of compressed-air back into the blade to help to “kick the piston off” on its downward journey from a blade tip near to top dead centre, (b) use a direct mechanical tie between the mass in two diametrically-opposite blades. (cont)

6. nottinghamscience Says:
   September 20th, 2008 at 2:36 am

   Part 4

   For small turbines, CF is many times greater than g at the blade tips and any free-running mass near to the tips will not naturally fall. As turbines become larger, the CF at the blade tips falls in proportion to the diameter, D, - basically because CF is proportional to W squared and W is inversely proportional to D. So, in very large turbines, (order of 200m diameter and above), masses will start to fall naturally when blade reaches “top dead centre”. (cont)

7. nottinghamscience Says:
   September 20th, 2008 at 2:36 am

   Part 3

   The product (2Mgh N (W/60)) is the total power that you can convert where M is the mass of the piston in one blade, N is the number of blades, h is the stroke achievable within one blade, g is the acceleration due to gravity and W is the rotational speed in revolutions per minute.

   Now, you are right that the rotational speed does produce centrifugal force (CF) concerns. (cont)

8. nottinghamscience Says:
   September 20th, 2008 at 2:36 am

   Part 2

   The rotational speed tells you how many times per minute each blade will pass through a full cycle and the power then tells you how much mass there must be falling within each blade. You can choose how far the mass can fall. Obviously, the piston will not be able to reach all the way to the blade tips but we probably want it to reach more than 70% of the way. (cont)

9. nottinghamscience Says:
   September 20th, 2008 at 2:36 am

   Posting a (lengthy) reply on Seamus’s behalf…

   Part 1

   Relating to holes in the plastic tube and centrifugal force, there are some inter-linked design decisions. To understand the linkage, you first start with what you cannot change. The optimal rotational speed of the turbine and the total power that is extracted from the wind are the “unchangeables”. These have to do with fundamental aerodynamic issues that are the same no matter how you convert that power into a transportable form. (cont)

10. alastair78 Says:
    September 20th, 2008 at 2:36 am

    A couple of questions. I noticed your plastic tube has holes to release the air faster, wouldnt the piston take longer to compress the air without these holes thus getting only 1/2 a stroke or less in before the piston falls outwards again? It seems to compress at a higher PSI, the piston will need to weigh more slowing the blades. Also it wont work if the blades spin too fast because centrifugal force will throw the pistons towards the ends of the blade.? No?

11. joeyboudreau Says:
    September 20th, 2008 at 2:36 am

    I like this idea…..hmmm …will this “storing of wind” for energy overcome the fact that you are constantly changing the centre of gravity of the blades?…the center of gravity becomes lower than the center of rotation, this of course makes continuous rotation more difficult to achieve,demanding higher wind velocities….hmm. I really like this idea…like you say calculations and further experimentation will tell the tale….very nice conception and Good luck!

12. dcsproject5 Says:
    September 20th, 2008 at 2:36 am

    Very clever idea, well explained for the slower among us (me hehe). Good work professor, this could be an excellent prospect for the environment.

13. CaptAhab1 Says:
    September 20th, 2008 at 2:36 am

    fgbj

14. Sepero1 Says:
    September 20th, 2008 at 2:36 am

    Thanks for posting. Nice vid.

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