Author Topic: Why can't a gravity powered generator work?  (Read 33545 times)

Offline mangyhyena

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Why can't a gravity powered generator work?
« on: June 16, 2012, 07:31:08 PM »
Right out of the gate, I realize this probably isn't viable.  For the physisists here, I'm NOT talking about free energy.  What I want to know is, why can't we use gravity, or I guess suspended weight, as our energy storage medium?

We have a cuckoo clock with a swinging pendilum at my home.  I pull the chain, raising two weights, then it keeps time for about a day, keeping the pendilum swinging the whole time.

Could a few rechargable AA batteries be charged in a day or two if the pendilum were a magnet and, say, 2 coils were placed at each side of the pendilum?  Or would it not produce enough electricity for even that?  Could a capacitor be loaded and periodically discharged into the batteries to overcome the small amounts of electricity produced during each swing?

Next question:  if a larger pendilum were set up with much heavier weights, could it produce a respectable amount of power in a 24 hour period, enough for a small battery bank?  Could it charge a a small battery bank in a week's time, assuming the weights were reset each day?  No, it would not produce more energy than it takes to raise the weights, so using power equipment to raise the weights would result in a net loss of energy.  However, those weights could be raised using human or animal power.  If I can lift my vehicle with a jack, I can reset the weights for the pendilum, even if they weigh 1,000 pounds each.  Pain in the butt, I'm sure, but I could manage it.

I guess the question isn't whether or not this setup would produce electricity.  Rather, would it produce a usable amount of electricity?  How much or how little?

I'm assuming solar and wind are more productive.  It's just curiosity that drove me to ask about this.

Offline cmxterra

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Re: Why can't a gravity powered generator work?
« Reply #1 on: June 16, 2012, 07:59:35 PM »
Someone smarter than I will come along and make more sense.

My understanding of the way energy generation works is that the energy density of whatever power source you are using has to have enough potential energy before it is converted to electricity to be a viable energy source. Be that fuel, water, sunlight or wind.

With a gravity driven system the amount of energy you would need to exert to set your weight up would at BEST equal what you might get out of it (and that would never happen as you can not have a perfect conversion of energy)

So to get enough energy to do any useful work with a gravity system you would have to put more energy into it than you would get out of it. At least with solar, wind and hydro nature is putting in the work for you.   

Offline Entity

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Re: Why can't a gravity powered generator work?
« Reply #2 on: June 17, 2012, 01:42:29 AM »
taking energy from the pendulum would damp and eventually stop the pendulum. The gravitational potential energy that is converted to kinetic by the bottom of the swing is re-converted to potential to get it up the other side.

taking energy of the falling weight (and simply modulating the rate at which that weight falls), is ... exactly how your clock works

Offline Jeff NH

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Re: Why can't a gravity powered generator work?
« Reply #3 on: June 17, 2012, 06:16:27 AM »
Note that you might also be using the wrong terms here. What you are describing (both in terms of desired device and your example device) is a energy storage device (like a battery) and really less of a generator. You pull the weight to the top, and it falls down slowly. The pendulum is there to keep time and is getting energy needed to overcome friction from the energy you stored in the weight system.

Given a significant enough weight, you could store energy in a system like this as an alternative to a battery. Not sure what the efficiency of such storage would be. It would be a fun project. To get any significant/useable amount of electricity, you'd need much more weight than the clock.

Offline mangyhyena

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Re: Why can't a gravity powered generator work?
« Reply #4 on: June 17, 2012, 07:29:19 AM »
The much-more-weight challenge could be met, I think.  My real question is can that weight be converted to a usable amount of electricity.  If it can, great.  It'll be time to start figuring out how to elevate the weights.  If not, why bother?

If I wanted a sidnifigant amount of weight raised, so when it falls it generates electricity, I'd have horses or cows walk up onto a raised platform, where they would stay until the platform came back down.  4 horses or more would seem to present a respectable amount of weight.  And, the animals could walk themselves up to the correct elevation at feeding time.

I've got 2 horses, but neither is in any shape to do work.  One is lame with ringbone, the other is old.  Both, however, could easily walk up to a raised platform at feeding time and stay there as the platform "falls" (slowly) and produces electricity.  We would take in and care for more so-called useless animals for this purpose, if it could work to produce a usable amount of electricity for my home.

The pendilum approach came from me looking at that cuckoo clock, but if there is a better way to harness the energy from the falling weight, I'd be all for it.

Offline Mr. Bill

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Re: Why can't a gravity powered generator work?
« Reply #5 on: June 17, 2012, 09:42:12 AM »
I was just reading an article about energy storage at the "large electric utility" scale, where batteries aren't feasible.  Many systems involve some sort of gravity/weight system, e.g. pumping water into a reservoir or tower when solar or wind energy is available, and then letting it run back through a turbine when the energy is needed.  One system even involves using railcars on a sloped railroad track.  So it's not an unrealistic idea, but I'm not familiar with homestead-scale systems using it.  I'm guessing the biggest challenge would be in not losing a bunch of energy to friction.

Offline mangyhyena

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Re: Why can't a gravity powered generator work?
« Reply #6 on: June 17, 2012, 04:18:36 PM »
There is another thread I got going about animal power, which was more about using the animal's muscles to generate power, be that a generator or a water pump.  Running both these threads at the same time made me wonder if they could be combined.  Using the animal's weight for power generation seems doable, since the animal is mobile and can put itself in a position to "fall" (slowly/humanely) without extra energy input from people or oil/coal.  Build a gravity motor & use the animals as the "resettable" weights.

Sounds good, but a setup would need to produce a usable amount of energy and for a long enough period of time for it to be feasabile.  And that is where this whole idea could be all wet.

But, just think of the multiple benefits toward self sufficiency if it could be made to work.  Animals produce power, and/or pump water, using their muscles, weight on a gravity motor, or both.  Manure from animals goes to a methane digester first, then to fertilize crops.  If pumping water for energy storage, the water goes to irrigation and watering animals after producing power via hydro generator. At some point, the animal winds up on the dinner table.

If you have the land for it, you could board other people's animals, for a fee, and have their animals generate power; in essence, having other people pay for your energy production.

Again, depends on whether or not a usable amount of energy can be produced and stored in this manner.  That is a big IF.

Offline Philip

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Re: Why can't a gravity powered generator work?
« Reply #7 on: July 15, 2012, 09:02:06 AM »
I don't know how accurate this would be but if you took the calculations from a theoretical hydro setup www.powerspout.com (use their calculator)  and figure the weight of the water over time at x-fall you might get a rough estimate.

Offline fritz_monroe

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Re: Why can't a gravity powered generator work?
« Reply #8 on: July 15, 2012, 10:01:54 AM »
Back to your weights.  How about pull the weights to the top and as they slowly fall, they turn a gear.  Step this up to the point where it is turning an alternator fast enough to charge your batteries.  I guess that would be a generator using weight as the fuel source.  I have no idea how long it would run for on each lift of the weight or any other details.  Someone much smarter than I am would need to figure that stuff out.

Offline LdMorgan

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Re: Why can't a gravity powered generator work?
« Reply #9 on: July 15, 2012, 02:58:22 PM »
The problem with animal power is that it takes much more feed to keep the animal at its normal weight when it's put to work. Just standing around the stable doesn't require much energy, or much feed to provide it.

You don't need to invent a gravity motor for  animals--just check out some of the existing technology.

Example: http://www.fao.org/wairdocs/ilri/x5455b/x5455b0z.htm

That's a pretty poor engine, BTW. Even at a glance I can see a much better & cheaper way to get the job done.

For gravity power, the trick is just to find something heavy uphill and send it downhill.

You could throw a 5 lb rock off a 100-ft cliff--tied to a rope that spins a generator as it pays out. Wind it back up empty, and then drop another rock.

When you cut a tree down, why waste the energy of position? A 50 lb limb falling 10 ft would do the same job as the 5 lb rock.

If thinking outside the box is fun, go the other way: Send a passive hot air balloon up on that same rope. All you need is a balloon and a campfire. 5lbs of lift and 100 ft of rope--voila! Then just reel it back in when it cools and starts to drop. Better yet, 50 lbs of lift and a long enough rope to use it all.

Or send up a kite and let the wind pay out the rope. Then untrim the kite, reel it back in, and repeat.

Of course, if you have a 100-ft cliff in the first place, why not just drop a bare copper wire over the edge and pull a perpetual voltage out of the bottom end? Cheap, no moving parts, and you can double the power just by adding another wire.




Offline tamo42

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Re: Why can't a gravity powered generator work?
« Reply #10 on: July 16, 2012, 12:39:02 PM »
The easiest way that I'm aware of to do this kind of thing is to pump water uphill into a holding tank/pond, which would then be available for hydroelectric (or hydrothermal or whatever) applications. Depending on your available resources, you might use solar power, wind power, water power (ram pumps for example) to get the water uphill in a "free" way.

Offline ToMegaTherion666

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Re: Why can't a gravity powered generator work?
« Reply #11 on: July 16, 2012, 01:12:46 PM »
You can hook the clock up the cubbord, and wind it everytime you eat. Id imagine there are a hundred little things you could do if you wanted to generate a small charge.

a pull rope in teh bathroom that works a dynamo on the way down and on a geared/weighed release (you could likely make a working modle with the guts of a hand crank flashlight, some rope, and an old bicycle) - so you pull the rope a little and the light comes on and because of the mechanical amplification the light will continue to run and charge for some preset amount of time.

which might be a more efficient solution than using several methods to maintain battery across a grid.

on the high tech end.. floor pressure plates are being tested to take energy from people walking across them to generate light etc


Offline markl32

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Re: Why can't a gravity powered generator work?
« Reply #12 on: July 16, 2012, 06:17:18 PM »

http://www.activepower.com/

Fly wheel.  Power keeps the flywheel spinning.  Power goes down, flywheel becomes a generator, for a while. 


Offline mangyhyena

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Re: Why can't a gravity powered generator work?
« Reply #13 on: July 18, 2012, 07:28:19 PM »
I knew other people wondered about strange contraptions, too. 

Isn't the flywheel a power storage option?  I thought I read they're using them to supply immediate power to computer servers at the onset of a power outage, giving the generators time to kick in.  I could easily have that wrong, though.

The hot air idea is a fun one.  Who wouldn't want to play with fire while flying a balloon?

Offline Bradbn4

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Re: Why can't a gravity powered generator work?
« Reply #14 on: July 18, 2012, 07:57:30 PM »
The easiest way that I'm aware of to do this kind of thing is to pump water uphill into a holding tank/pond, which would then be available for hydroelectric (or hydrothermal or whatever) applications. Depending on your available resources, you might use solar power, wind power, water power (ram pumps for example) to get the water uphill in a "free" way.

A quote from an old Professor when I was going to school and asked this question:

Pushing water up hill is the best way to store energy. 

When I was over seas on my big European vacation, we took a tour of a man made "lake" at the top of a good size hill.  During the day they would use water to help support peak electric loads while at night they used excess energy to pump the water back up the hill. 

Offline joeinwv

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Re: Why can't a gravity powered generator work?
« Reply #15 on: July 18, 2012, 08:47:30 PM »
As long as the weight, water, animals, etc magically finds its way to the top - it all works. By the time you factor in the time,  work and materials it takes to set all this crap up, you almost certainly end up with a negative gain. Especially when you factor in the crappy battery technology we have now.

Your clock works because you spend energy winding it - the flywheel and springs slow down the release of that energy, but it's not making any power. It's storing / releasing the power you put into it.

Offline Jerry D Young

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Re: Why can't a gravity powered generator work?
« Reply #16 on: July 19, 2012, 12:16:43 PM »
I think a gravity engine will work. I have a design for one, but I just haven't had the time or money to follow up on it.


Offline fritz_monroe

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Re: Why can't a gravity powered generator work?
« Reply #17 on: July 20, 2012, 07:33:58 AM »
As long as the weight, water, animals, etc magically finds its way to the top - it all works. By the time you factor in the time,  work and materials it takes to set all this crap up, you almost certainly end up with a negative gain. Especially when you factor in the crappy battery technology we have now.

Your clock works because you spend energy winding it - the flywheel and springs slow down the release of that energy, but it's not making any power. It's storing / releasing the power you put into it.
All true, but the OP seems to want to be able to charge some batteries in event of a catastrophe.  Can't run a radio, flashlight or any other small electrical item off the muscle power of an animal.  But convert that to an electrical charge by having that animal run a pump to pump water uphill to run a micro hydro set up and now you're cooking.

Just because it's a negative gain doesn't make it useless.  In event of a major power outage, that animal could just be wasting that energy wandering around the paddock.  Putting it to work to run the pump, generator, etc is generating an energy source that is usable to the OP.

Offline donaldj

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Re: Why can't a gravity powered generator work?
« Reply #18 on: July 20, 2012, 07:56:48 AM »
Yes. One of the biggest misunderstandings of conservation of energy is people assume things are working with 100% efficiency to begin with, and any new load on the system means more power.

Animals are absorbing energy just living. Getting them to expend some more energy may get you a lot of usable energy.

A single duck flying south for the winder uses a lot of energy. All his buddies making the duck formation are NOT adding their 'weight' to the first duck's load, they're using the benefits the first duck already created (high pressure zone) more efficiently.

A truck going down the road has to bludgeon it's way through the air (wind resistance) to get from point A to B. The myriad of other trucks and cars that draft the truck are not increasing the load on the first truck, they are using the already expended energy (the low pressure zone behind the truck).

A car's turbocharger is using already created exhaust gas flow to spin a compressor. For only minor reverse pressure, the car can make additional horsepower from this energy. It's not sapping the system, it's using already expended energy more effectively.


As for the water thing, isn't there a model that uses high tides?  High tide creates a reservoir and turbines are run as the water enters, and low tides run the turbines as the water leaves.


Offline mangyhyena

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Re: Why can't a gravity powered generator work?
« Reply #19 on: July 20, 2012, 07:36:50 PM »
I think that if teotwawki actually happens, the survivors will figure out what works best for them in their particular circumstances, in terms of generating and storing power.  The survivors will not give a crap about what academics say is inefficient, impractical, ect.  They will care only about getting results to power their lives.  They'll do what works.


Offline fred.greek

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Re: Why can't a gravity powered generator work?
« Reply #20 on: July 20, 2012, 08:57:19 PM »
PLEASE, check my numbers... I babble a lot....

Turning generators with moving water, caused by the sun (natural, and artificially induced means to move water to a higher location, or from a pressurized container.) Power can be constant and regulated.  Most naturally occurring cases of water in a high gravity location have already been exploited.

Where tanks can be positioned at significant differences in altitude (i.e. 100'+) water pumped by windmill to the higher tank can bank the energy (serve as a battery) for later expenditure by turning a generator when dropped again thru a turbine. Think outside the box… Can you modify a turbocharger from a car to serve as the driving turbine in a micro-hydro generator?   

Factors:

1kw = 1.3 hp
Water flow in cubic feet/second x height difference in feet divided by 8.8 = hp
1 cubic foot = 7.48 gallon
Assume two 10,000 gallon tank, one 100' higher than the other.  To generate 1kw of power
1kw = 1.3hp = flow/second x 100 / 8.8
1.3 x 8.8 = flow x 100
11.44  = flow x 100
11.44 / 100 = flow
.1144 cubic feet = flow
.1144 cubic feet = .856 gallon/second
10,000 gallon tank / .856 = 11,682 seconds / 60 / 60 = 3.24 kilowatthours for this "battery".

Each of the above tanks is only about the size of a modest “above ground” swimming pool.  Consider a well where the water level is more than 100 feet below the surface. A small windmill could easily during the day fill the pool, providing the evenings power for light and electronics.

Offline tamo42

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Re: Why can't a gravity powered generator work?
« Reply #21 on: July 21, 2012, 12:01:34 PM »
Seems workable if you have the height.

Offline mangyhyena

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Re: Why can't a gravity powered generator work?
« Reply #22 on: July 21, 2012, 08:28:07 PM »
Did someone say to think outside the box?  All right, I'll try.

I've read that a buoyancy/gravity motor is not possible due to water pressure.  (inserting a boyant float into the bottom of a tank will require more energy than gets released as float rises, due to water pressure working against insertion, if I understood correctly.)

What if the float also acted as the weight for the gravity motor?

Float is heavy and shaped like a boat for water displacement, so it will float.  It sits in a container.  When water from a higher location flows in, the boat/weight rises, generating energy.  When water is released from the container, the boat/weight falls, generating energy.  Perhaps the container empties into another container set up the same way.  Height would dictate how many containers could be set up in series.

I don't know if this setup would equal the efficiency of a regular hydro setup.  Maybe in a location where there isn't much in the way of head, it might work out.

Watching the way the ships are "lifted" through locks so they can continue onto a higher body of water gave me this idea.  Ship enters lock, water is released into lock, ship rises as lock fills, then ship leaves lock at a higher elevation than when it entered.


Offline LdMorgan

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Re: Why can't a gravity powered generator work?
« Reply #23 on: July 23, 2012, 02:44:06 PM »
Yup--that's the basic tidal generator, in a nutshell.

A person could anchor a barge, and have the top end of the anchor cable wrapped around a windlass.

When the tide rise, cable pays out, turning a generator. A low tide, just reel in the slack.

Or do the same thing with smaller floats.

If the reel windlass was ratcheted, it could also be a wave generator at the same time.

Offline cottonpatchenergy

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Re: Why can't a gravity powered generator work?
« Reply #24 on: January 09, 2014, 09:36:37 AM »
ok I'm new to this but the short answer is yes. A suspended weight is an excellent way to store potential energy. Gravity driven generators are the same thing as hydroelectric generation. Now for the purpose of this forum pertaining to your own power generation you will have to compile all the stuff you've heard and fix the broken ideas. The falling weight has been used since they built the ancient cities of the past. Here's the basic problem with gravity driven generators you have to reset them in order to complete a cycle. Energy in energy out so you have to have energy to start with but since we are talking about storage to start with the medium is fine. Now that being said there is I believe an idea of making the unit reset or reload the falling weight. One of the post makes me laugh because it is so close to the truth without seeing it, the classical buoyancy drive. The problem is they see the advantage of lifting the weight with buoyancy but just cant seem to figure out how. The key is not to force a buoyant object into a tank of water, it is much easier to just move the air and create the displacement. So without going into great detail here you reset the weight back to the top by floating back up there. You can lift a weight 19 feet in the air with just 8.5 lbs of pressure. That is air pressure. The volume of the air at this pressure will equal the weight in your falling object that you will couple to your gear box and turn your generator. Now here is the kicker the power needed to create the displacement that will lift the weight back to the top of your grandfather clock gravity drive is suspected to be less than the power generated by the falling weight. Here is an example to think about: lets say you have a 400lb weight and your gona lift it to a height of 10 ft. The rules say that the potential energy the weight represents is exactly equal to the amount of energy that can be extracted from the falling object. I agree and it applies in a normal gravitational field but when you throw in another force which negates a portion of the gravitational constant then you end up with a different result. It's a direction of thought that will blow your mind once you get your head around it. Any change in elevation represents energy.

Offline MillenniumMan

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Re: Why can't a gravity powered generator work?
« Reply #25 on: January 09, 2014, 10:42:42 AM »
There's always Heron's fountain. The only problem with that is water eventually evaporates.

The theory is however that if you have a water wheel at the point just below the apex of the fountain, you could use that to constantly run a hydro-electric dynamo. Something like that exists on rivers, but so far no one has bothered implementing it on the fountain.

Offline kckndrgn

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Re: Why can't a gravity powered generator work?
« Reply #26 on: January 09, 2014, 10:56:53 AM »
For the OP, is this what you are looking for?
http://deciwatt.org/

GravityLight™ is an innovative device that generates light from gravity.

It takes only 3 seconds to lift the weight that powers GravityLight creating 25 minutes of light on its descent.

It can be used over and over again with no running costs

While the main purpose of the gravity light is, light, it could easily be set to charge batteries.  The problem, how many times would the system have to be reset to get a full charge on the batteries?

Might be good for keeping a charge on already charged batteries so they are ready for use.

Offline SloSheepdog

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Re: Why can't a gravity powered generator work?
« Reply #27 on: January 09, 2014, 11:03:35 AM »
I like seeing neat mechanical contraptions, but I gotta think that this is the way to go if you're using animal power, or some variation of it. Gear up or down using pullies or gears, connect to generator to battery bank or directly to work load to be done, and pow! Energy!

Wiki says it's a limestone quarry, but the principle remains and can be used for anything.




Offline AvenueQ

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Re: Why can't a gravity powered generator work?
« Reply #28 on: January 09, 2014, 02:11:34 PM »
My physics degree has some use in the prepping world! Though I can only speak from a theoretical, not design standpoint (that's for the engineers  ;) ). If you really want me to explain how gravity and potential energy work I will...but it might be irrelevant to what you're trying to do.

Offline iam4liberty

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Re: Why can't a gravity powered generator work?
« Reply #29 on: January 09, 2014, 07:08:58 PM »
Gravity is a very weak force so it typically takes a lot of mass to store usable amounts of energy. Historically, it has been easier to use other physical means (for example air pressure, rope tension) or chemical means (e.g. battery, fuel) for energy storage.

If you are really interested in this, check out punkin chunkin (www.punkinchunkin.com).  You can see practical gravity (trebuchet), tension (catapult), and air (pressure) storage systems.  Plus it is just so cool   ;D