Could tide-powered buoyancy be a viable source of energy?

[BethNB]

Hi all, this is my first post. It seems around eight years ago I was on a similar brain-wave-length as Laurence Kemball-Cook, with his idea to create a power generating flooring surface... only he had the know-how to bring the idea to market, so credit where credit is due. (though now I wonder couldn't the insides of shoes simply have this and save on the manufacture of area that may never get stepped on? Or maybe that's been done already too)

Anyway, on to the next idea I don't have the know how to bring to market, but I'm curious to learn about the feasibility of the idea in terms of forces involved... it's based on an idea I had watching the footage of ice going down in low-tide and being lifted in high-tide in this clip from BBC Human Planet: (around the 1:10 minute mark is where the ice goes down). What immense power is demonstrated there, in lifting such heavy ice!

I can't help but wonder if the two ideas for energy conversion were to be married:
That of buoyancy and that of weight pressing down... could the up-down motion, buoyancy and weight of an object lifted and let down by tides, be part of an equation that allows us to convert that energy into something we can use? I'm NOT talking about a PMM or Free Energy because nothing is free and nothing is perpetual I understand very well.

I've seen tidal power plant concepts but nothing that utilizes an up-down motion, with a buoyant but heavy object when it's being pulled up, or the weight of the same object when it's released down, to generate electricity. Am I way out there with such a marrying of ideas?

What forces are involved (that aren't immediately apparent i.e. Gravity & buoyancy... or I haven't already mentioned) and what mechanisms/engineering principles would I need to get schooled in, in order to learn more about the principles involved?

And it also makes me think of the up down motions of elevators... I wonder if there are any elevators that are geared towards self-charging when it's the case that the elevator is going down? Like a hybrid car that is half electric and half self-charging?

Thanks in advance for any kind and patient input you could give or directions you could point me in.

 

[BvU]

Hello Beth,

I've seen tidal power plant concepts but nothing that utilizes an up-down motion

Seems to me you've seen them but not understood them ? If something works on a back and forth motion it just might be that such motion is in fact caused by an up/down force...

 

[BvU]

I wonder if there are any elevators that are geared towards self-charging when it's the case that the elevator is going down

Ever seen counterweights at the side of elevator shafts ?

 

[Lord Jestocost]

I can't help but wonder if the two ideas for energy conversion were to be married...

Your idea reminds me, for example, of the "NEMOS Wave Energy Converter" (https://www.nemos.org/waveenergy/).

 

[BethNB]

Ever seen counterweights at the side of elevator shafts ?

I'm aware of the role the counterweight plays, to some degree, but would the up and down motion being carried out through everyone's daily comings and goings not be something that an ulterior tailor made energy conversion/power generating system could "plug" into?

 

[BethNB]

Your idea reminds me, for example, of the "NEMOS Wave Energy Converter" (https://www.nemos.org/waveenergy/).

Thanks for mentioning that... I am looking into it

 

[jbriggs444]

I'm aware of the role the counterweight plays, to some degree, but would the up and down motion being carried out through everyone's daily comings and goings not be something that an ulterior tailor made energy conversion/power generating system could "plug" into?

Suppose that a person comes into the building on the ground floor in the morning, rides the elevators for most of the day and exits from the ground floor in the evening. How much energy can be harvested from the difference between that person's potential energy upon arrival and upon exit?

 

[sophiecentaur]

I am amazed that the message "you don't get anything for nothing" is not instilled into kids of all ages at school and at home. It works in all of life and not just Engineering.
If people all climbed the stairs and then rode down in the elevator there could be some mileage in the idea. (Tongue in cheek)

 

[BethNB]

I am amazed that the message "you don't get anything for nothing" is not instilled into kids of all ages at school and at home. It works in all of life and not just Engineering.
If people all climbed the stairs and then rode down in the elevator there could be some mileage in the idea. (Tongue in cheek)

Yet elevators ride empty all the time. I'm talking about viewing an up and down motion, that's happening anyway for other reasons, as a sort of engine that we can plug into. Same as the tide and anything that the water happens to hold up or let down, as an engine to plug a power generator into.

 

[BethNB]

Suppose that a person comes into the building on the ground floor in the morning, rides the elevators for most of the day and exits from the ground floor in the evening. How much energy can be harvested from the difference between that person's potential energy upon arrival and upon exit?

How do we factor in the empty elevator that travels to pick people up when they call for it? It's moving up and down through the day and it's the motion of it moving up and down I'm interested in figuring out how to "plug" into.

 

[jbriggs444]

How do we factor in the empty elevator that travels to pick people up when they call for it? It's moving up and down through the day and it's the motion of it moving up and down I'm interested in figuring out how to "plug" into.

What is the difference in potential energy between an empty elevator on the ground floor first thing in the morning and an empty elevator on the ground floor at evenings end?

You can't pull energy out of the elevator that the elevator's motors did not put into start with. It's a losing game.

 

[BethNB]

What is the difference in potential energy between an empty elevator on the ground floor first thing in the morning and an empty elevator on the ground floor at evenings end?

You can't pull energy out of the elevator that the elevator's motors did not put into start with. It's a losing game.

Elevators are run on electricity and counterweights so yeah it would only be getting out a portion of what was put it. But the concept of how to do that with an elevator, would be the concept or principle that I would want to apply to an object being lifted and let down by rising and lowering tide waters.

 

[BethNB]

Suppose that a person comes into the building on the ground floor in the morning, rides the elevators for most of the day and exits from the ground floor in the evening. How much energy can be harvested from the difference between that person's potential energy upon arrival and upon exit?

We've all also seen boats left sitting on a dry coastal sea floor, when the tide is out. So what is the potential energy of such a large item when it has been lifted up to 15 meters?

 

[jbriggs444]

We've all also seen boats left sitting on a dry coastal sea floor, when the tide is out. So what is the potential energy of such a large item when it has been lifted up to 15 meters?

http://lmgtfy.com/?q=potential+energy+formula

 

[BethNB]

http://lmgtfy.com/?q=potential+energy+formula

Thank you for pointing me to that. Let's suppose the floating object is usually 200 kg. And let's say the height at high tide is 15 meters... but now I'm having a hard time figuring it's SI, or acceleration due to gravity, because it's not free falling... not like in the illustration that shows up in the following search: acceleration due to gravity

 

[BethNB]

It's buoyant weight is different I'm sure but as it's let down imagine if there were mechanisms offering resistance, designed to generate electricity as its lowered? Like the electricity generating flooring surface that Lawrence Kemball Cook came up with?
Or if the object's height could be maintained til the tide has gone out, and then let the object free fall? Would that work better?

 

[BethNB]

I am amazed that the message "you don't get anything for nothing" is not instilled into kids of all ages at school and at home. It works in all of life and not just Engineering.
If people all climbed the stairs and then rode down in the elevator there could be some mileage in the idea. (Tongue in cheek)

I did acknowledge nothing is free. I think what I'm trying to say is that tide waters lifting heavy things up for us for 'free', is the same idea as people climbing the stairs but taking a power-generating-elevator down, if only we could plug into the potential energy of those raised heavy objects, and then maybe even also plug into their natural desire to stay buoyant, as the waters raise it again...

 

[jbriggs444]

It's buoyant weight is different I'm sure but as it's let down imagine if there were mechanisms offering resistance, designed to generate electricity as its lowered? Like the electricity generating flooring surface that Lawrence Kemball Cook came up with?
Or if the object's height could be maintained til the tide has gone out, and then let the object free fall? Would that work better?

If you offer resistance as the object is lowered, you can harvest energy. How much energy you can harvest depends on how much resistance you can offer and how far the boat will move against that resistance.

What is the maximum resistance you can offer?
If you offer this much resistance, what effect does it have on the distance the boat can be allowed to fall?

 

[BethNB]

If you offer resistance as the object is lowered, you can harvest energy. How much energy you can harvest depends on how much resistance you can offer and how far the boat will move against that resistance.

What is the maximum resistance you can offer?
If you offer this much resistance, what effect does it have on the distance the boat can be allowed to fall?

Those are good questions. I don't know anything about offering resistance but what if the whole thing was designed abit like an elevator with a counterweight on a pulley? (The counterweight would need a water-free shaft maybe so that the water doesn't influence the freedom of its up and down movement?)

 

[jbriggs444]

Those are good questions. I don't know anything about offering resistance but what if the whole thing was designed abit like an elevator with a counterweight on a pulley? (The counterweight would need a water-free shaft maybe so that the water doesn't influence the freedom of its up and down movement?)

A counterweight is going to do no good at all. The point of a counterweight is to allow a mechanism to operate with minimum external force applied. For instance, in a properly balanced elevator, a two ton carriage balanced by a two ton counterweight can be moved up and down with (ideally) no effort at all.

If you are attempting to generate power, you want to maximize the external force. You want to harvest energy on the upstroke (if freeboard permits). You want to harvest energy on the downstroke. A counterweight that reduces the force presented to the generator is counter-productive. A counterweight that makes the force higher in one direction than in the other would mean that you have to over-engineer your generator to deal with the increased maximum force.

One simple-minded approach would be to hook the boat up to some chains or cables on a winch and let the winch run a generator as the cable plays out. Not very efficient though. It would make far more sense to use turbines and a huge reservoir instead of cables and a small boat.

 

[BethNB]

A counterweight is going to do no good at all. The point of a counterweight is to allow a mechanism to operate with minimum external force applied. For instance, in a properly balanced elevator, a two ton carriage balanced by a two ton counterweight can be moved up and down with (ideally) no effort at all.

If you are attempting to generate power, you want to maximize the external force. You want to harvest energy on the upstroke (if freeboard permits). You want to harvest energy on the downstroke. A counterweight that reduces the force presented to the generator is counter-productive. A counterweight that makes the force higher in one direction than in the other would mean that you have to over-engineer your generator to deal with the increased maximum force.

One simple-minded approach would be to hook the boat up to some chains or cables on a winch and let the winch run a generator as the cable plays out. Not very efficient though. It would make far more sense to use turbines and a huge reservoir instead of cables and a small boat.

Ok, well I definitely need to understand more about counterweights then. I really appreciate your descriptions and using better terminology than I'm able to, to describe what it is I am trying to describe, this is great! And I'm totally open to understanding that it's a naf idea but understanding why is a great learning process. What kind of generator do you think would work in the low-efficiency scenario you described? Are there any books on those principles I could read? It might make more sense on a big scale to use turbines and a huge reservoir (based on your more educated prognosis) ... but what about for a small scale town of fishermen who own boats... I wonder if they couldn't set something up on a small scale, for whatever it would be worth...

 

[sophiecentaur]

maybe even also plug into their natural desire to stay buoyant, as the waters raise it again...

That's a bit too anthropomorphic if you want a good understanding of Science. "Things" don't "desire" anything.
The point is that you have to ask the question "Who or what is responsible for the rise and fall of the tide and where does the energy come from?" Nothing happens without Energy being transferred in some way.

if only we could plug into the potential energy of those raised heavy objects,

But we can. The devil is in the detail, though. Making use of the 'up and down' motion of the tide directly by mechanical means (levers / chains / masses) tends to be highly inefficient and very poor payback for any investment of money. The most successful way, so far, to use the tide is to allow a suitable estuary or inlet to fill and empty through a hole in a dam. The flowing water can be used for electricity generation during a substantial part of the ebb and flow periods. The Range Tidal Scheme is described in this link. Larger schemes have been planned or built. You may notice that the power output of the Range scheme is extremely small in terms of modern power stations and there have been ecological repercussions. Whether or not it was overall a worthwhile project is probably a matter of opinion. At least there is no air pollution.
You should Google "Alternative Energy Resources" and read all you can. But beware of some of the "snake oil" systems that litter the web.

 

[BethNB]

Making use of the 'up and down' motion of the tide directly by mechanical means (levers / chains / masses) tends to be highly inefficient and very poor payback for any investment of money.

Thanks for the pointers!
I'm curious if anyone has actually tried though? or even if the physics/math could be figured theoretically...
Is there a guideline for power generation/outputs that are generally considered "efficient" or otherwise, in proportion to the money/effort put in + lack of negative effect on the environment?
And it's funny to me that something being a losing game or bad investment for money is mentioned so often... we humans do a ton of things that don't exactly "pay off" in the long run, but we still do them even if just for fun...

 

[sophiecentaur]

Is there a guideline for power generation/outputs that are generally considered "efficient"

If you can estimate or predict the total Energy available over the life of an installation an compare it with the capital / running cost, that will give you an idea of whether something is worth while. This may be modified if, for instance, you have no other handy alternatives.
Another criterion is continuity of supply and this particular system would, at least be regular (unlike solar and wind).

but we still do them even if just for fun...

The 'fun' subset of projects has to be cheap enough not to break the bank if it fails. I think this idea would need a fairly large scale model to make it work. Perhaps a boat of a few tons, floating in a calm marina could use the energy to some effect. I have to say, of all the odd methods available for providing leisure craft with non-mains electricity, I have never come across this. @anorlunda would, perhaps know of something(?).
Wave power can work on the same principle and has the advantage that the short term oscillations are a bit more usable than a 12 hour cycle is likely to be.