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B How much power/Electrical energy would this device produce?

  1. Jan 13, 2019 #1
    Hey, i don't know much about physics but i have heard that gravitational energy is non efficient since it needs a lot of power.

    So this is what i had in plan..

    Average household has 2 to 3 members with each waiting average 50 kilos.
    You would use their combined weight force to pull up a 1000 kilo weight up in the air 5 meters using a 1:5 lever, two pulleys, wheel and a cabel.

    About the force applied: 3 times 50 kilos if they stand on the lever, + they could use additional force pulling with their hands a rope that's tied to the ground.

    The system i am talking about is down on the picture.

    robi struja pokaz.jpg
    About the wheel: The levers on the wheel can move in one direction letting the lever on wich force is applied go down and pus the wheel again.

    Whats the use?

    So you have two small wind turbines.. two small solar collector.. And you are short of some extra power for your house to be fully independent.

    Can someone brainstorm this quickly with me, or do the "calc"?
  2. jcsd
  3. Jan 13, 2019 #2


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    Staff: Mentor

    People are more efficient pedaling bicycle generators instead of pulling up weights. Maybe look at ways to store that energy (electrically in batteries or gravitationally with pumped water into a water tower).

    BTW, maybe this is a good way to keep your teenagers from watching so much TV. "You want to watch an hour of TV? Okay, go pedal the exercise bike for an hour first to store the energy..." :wink:
  4. Jan 13, 2019 #3
    I don't know if you red the post, but, the people use their weight, 3, 4, 5 people... and the aditional pull force to lift this.

    So it's not just pulling weights.
  5. Jan 13, 2019 #4


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    Staff: Mentor

    Yeah, but a bicycle style generator is still more efficient than a Stairmaster style generator. You want the people to keep climbing up on that lever thing, right? The energy has to come from somewhere (from sweaty people in this case)...
  6. Jan 13, 2019 #5
    It's not the same force. I believe this produces more power :D

    Edit:Anyway, pedaling is boring.
  7. Jan 13, 2019 #6


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    Staff: Mentor

    Well, we can do a quick calculation to see...

    75kg person rising up 0.25m each second is E = mgh, P = E/t

    E = 100kg * 9.8m/s^2 * 0.25m = 184J/s, so Power = 184W. That's about the same as pedaling for a reasonable bike rider. I know which one I'd rather do for an hour straight... :smile:
  8. Jan 13, 2019 #7
    How much time for the 184 w? An hour?
  9. Jan 13, 2019 #8


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    Staff: Mentor

    As long as you keep stair climbing or pedaling. You only put power into the storage mechanism while you are doing work on it.
  10. Jan 13, 2019 #9


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    Science Advisor
    Gold Member

    We should get some actual figures from the original scenario. However you go about lifting the weight, you will require the same amount of Energy.
    The work needed to lift 1000kg by 5m is 50kJ plus whatever losses there are in the mechanism - perhaps double that requirement. That's the maximum energy you could get back out (assuming everything is 100% efficient.
    That would drive a 50W lamp for 1000seconds (17minutes) or a 5W lamp / radio / motor for 170 minutes or 2.8hours. Allowing for a realistic figure for overall efficiency, you could probably call it 2 hours. So that's the ball park figure for what the proposed system could give you back.
    Bearing in mind that you would need to use electricity in order to make use of the mechanically stored energy then why not use a battery and a commercially available pedal power dynamo system?
    Health and safety would need to be considered for the proposed system - use something that's intrinsically safe and off the shelf.
  11. Jan 13, 2019 #10
    @sophiecentaur Its just gravitational battery, i was very disapointed when i found out its not efficient. Do you know anything about Compressed air energy storage?

    I stumbled upon it couple minutes ago.

    Its 99 % green.
    Low cost.
    Only takes up a lot of space.

    But i am developing a system where i have a lot of sun, wind, water flow and a lot of space.

    My main problem is the parts.

    For sun i was planning on making two parabolic dish stirling generators, for wind, a vertical axis wind turbine with a blocker

    Picture 2..jpg

    And since i have a river by my house, i was planing on putting some water turbines inside.

    For solar i have the satelite dishes and mirrors for free, for wind and water turbine i have a lot of motors and parts, and for compressed air battery i was planning to use old boilers and dig them underground, i just need to check the pressure.

    So the problem is manufacturing stirlings, They are actually not that complicated, but i am not skilled in making.

    There is other problem, with water, and insulating underwater generators.

    About the compressed air battery, it actually wouldnt have to be so big, because we have 250 sunny days in croatia, a lot of wind and probably the river too.
    So the compressor would be used as a backup, and for apliances that are being used over night when there is no sun and no wind.

    How does it feel?
  12. Jan 13, 2019 #11
    "Several research groups have designed, modeled and built small-scale combined heat-and-power CAES units which provide heating and cooling as well as electricity. The high pressure system with a storage volume of only 0.55 m3 that we mentioned earlier, is an example of this type of system. [9] As noted, its electrical efficiency is only 11-17%, but the system also produces sufficient heat to produce 270 litres of hot water per day. If this thermal source of energy is also taken into account, the “exergetic” efficiency of the whole system is close to 70%. Similar "exergy" efficiencies can be found in other studies, with systems operating at pressures between 50 and 200 bar. [11-21]

    Heat and cold from compression and expansion can be distributed to heating or cooling devices by means of water or air. The setup of an air cycle heating and cooling system is very similar to a CAES system, except for the storage vessel. Air cycle heating and cooling has many advantages, including high reliability, ease of maintenance, and the use of a natural refrigerant, which is environmentally benign. [11]"

    : https://www.lowtechmagazine.com/201...f-the-grid-compressed-air-energy-storage.html
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