Is weight a better way to derive energy than flow?

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Discussion Overview

The discussion centers on the potential energy generation from a system of falling buckets compared to traditional turbine systems in hydroelectric applications. Participants explore the mechanics of energy calculation, efficiency, and the feasibility of using buckets as an alternative to turbines.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes using the mgh formula to calculate energy from falling buckets but expresses uncertainty about incorporating the radius of the pulleys.
  • Another participant highlights the challenge of calculating efficiency, noting that energy is lost when water empties from the buckets, which complicates the efficiency comparison with turbines.
  • Some participants discuss the efficiency of modern turbines, suggesting they can achieve around 90% efficiency, which may be difficult for bucket systems to match.
  • Concerns are raised about inefficiencies due to friction and potential spillage if buckets are not operated at the correct speed.
  • Participants question the theoretical limits of turbine efficiency, with some suggesting that water turbines could theoretically reach 100% efficiency, unlike wind turbines, which have lower theoretical limits.
  • There is a discussion about the GGS model predicting lower peak efficiency for wind turbines, with some participants questioning the model's accuracy based on operational turbine performance.
  • One participant notes the importance of defining efficiency in terms of the kinetic energy of the air passing through a turbine, raising questions about how this is measured.

Areas of Agreement / Disagreement

Participants express varying views on the efficiency of bucket systems versus turbines, with no consensus on which system may be superior. There are also differing opinions on the implications of theoretical efficiency limits and the accuracy of models used to predict turbine performance.

Contextual Notes

Participants note that the efficiency calculations depend on various factors, including implementation details, water flow rates, and the mechanics of the systems being compared. There are unresolved questions regarding the assumptions made in the calculations and models discussed.

  • #31
CherryB said:
Ah. So there’s the tie-in to momentum. So if it traveled the 30m in 1 minute then it would be 294.3 mw divided by 60?
Yep. It's worth noting that this is per bucket as well, so if you had 10 full buckets descending at once, it would be 294.3/60 per bucket * 10 buckets for a total of around 50 MW.
 
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  • #32
russ_watters said:
As demanded by conservation of energy, yes.

Yes, mgh... but I don't see why pulley radius matters. bucket speed insofar as it tells you mass flow rate, yes.

It depends where the water level is at the bottom. If the buckets are submerged they act like paddles. If not, they drop the water and you aren't using all the available "h".
I guess I'm confusing moment with force, and translating that conflation into energy, because I can definitely hold a 10 lb barbel in my hand indefinitely if it's close to my body, but I can't do the same if my arm is outstretched. Seems to make some sense for me viscerally
 
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  • #33
cjl said:
Yep. It's worth noting that this is per bucket as well, so if you had 10 full buckets descending at once, it would be 294.3/60 per bucket * 10 buckets for a total of around 50 MW.
Right. So that's quite a bit of power, but it just seems like an awfully fast rotation to keep up with mechanically. I'm guessing that I would have to utilize a gearbox like the ones they use for wind turbines. I saw something about a 600 shaft rpm turbine gearbox yielding 8mw, but I'm not sure how to calculate the shaft input power needed to turn the gearbox
 
  • #34
 
  • #35
A full minute of descent time to cover 30m seems fast to you? Sure, you can gear them however you want, but if anything, I'd actually expect you'd want to gear it up, since generators are smaller, cheaper, and more efficient if spun faster.

EDIT: Also, the power you get out of a gearbox is the same as the power you put in (minus losses). If the gearbox is outputting 8MW at 600 RPM, the input will also be 8MW (at some other RPM - probably around 9RPM for a turbine that size).
 
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  • #36
What I meant to say is that maybe a gearbox like that could be used, just to slow things down, then connect it to the near 50mw input from buckets. The speed of 30 meters per minute seems large to me, only due to the buckets having to turn around the sprocket, and how much destructive force will be acting on the chain and buckets. But I may be overly conservative about that
 

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