Methods to use kinetic energy for useful work without a generator? And methods to use kinetic energy to heat water directly?

Edit 07/09/2021: Read this first. Thanks to @PierreB for finding the article. Link to comment.

As expected from Kris De Decker, it is an excellent overview of the subject, amply referenced.

Some quotes:

Generators and batteries and all that goes along with them may cost hundreds or thousands of Euros, perhaps constituting the most significant cost in some systems. So I think it makes sense to try to avoid using them.

What are some ways you can use rotational energy without using a generator?

I am most interested in directly using kinetic energy to heat water, as I think that is the biggest market. What are some products I could buy or make now that would do that and that would end up costing less than using a generator to generate electricity?

As a start:

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Typically you stir water to heat it using shaft power.

The one thing I could foresee is using an existing hydropower plant and pump water into the magazine. This requires a strong coupling to the location of the hydropower plant and wouldnt scale.

When you think of it, electric motors are wonderful machines, that only waste a few % of the power input. After being converted to electricity, you can transport it without loss (almost) to any location provided a grid exists, and even store it relatively cheap using a battery or other means.

I am not sure if this is a problem that needs to be solved

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I’d at least not like it to remain unsolved. More choice is better. Heating water I think is an okay use case, as every household and business needs heating and it is cold in winter when solar is less viable. And heating is the main use of energy/electricity, I think.

For a relatively small or simple system I can easily imagine the cost of the generator + batteries to be a multiple of the cost of the thing in the air. If you can tell your customer, here, stick this heating coil into the water to heat it and pay 80 percent less than the version that generates electricity, that’s interesting I think.

Maybe this is useful to regulate the speed of the turbine in higher winds? What’s the most user-friendly solution? I’m thinking a fully enclosed system that has heating coils or rods coming out of it to submerge in water?

Its true that electric components can be quite expensive. Still, heated water also requires infrastructure in order to be used. Even if you get the heat for free, it is oftentimes (mostly?) not being used (at least here in Norway, with cheap electricity).

Heated water will be worth less than electricity, as it has less utility. It may only be used for heating at a certain location.

In addition, heated water may be used at fewer times: in summer, perhaps cooling is more attractive? Its hard to cool water with a kite. And in any case, there are the periods inbetween where there is no need for either.

I can see an argument for a really cheap AWE rig that is used only during winter (heating something else than water, as it will freeze). I think this is probably not the market that most people would like to be in though. Any slight overhead will kill the profitability (eg training of the user).

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The low value of such heat is discussed in this article, covering the use of heat from Bitcoin mining. In this scenario, you get the heat for free (electricity is primarily exchanged for Bitcoin). Still, modest hardware investments still take 18 months to get to break even. And this kind of rig runs 24/7.


That looks like a use case I was imagining. That’s about 15kWh per day if my math is right. Let’s say you need a multiple of that to consistently provide that, let’s say 50kWh per day. So that’s a 2kW turbine. A five minute search didn’t give me prices for a 2kW generator plus batteries. Let’s say it’s x. Let’s say the cost of the kite is y. And the cost of the dynamometer or similar plus the heat exchanger and all the rest is z.

To be able to make a proper judgement of if doing this makes sense, you’d need to know x, y, z, and the price of electricity, I think. Because we (I) don’t know those yet, it’s a little early to dismiss it I think.

I agree with @tallakt , especially on the hot water case. Also note that hot water is very easy to produce via solar. In hotter countries it’s just a barrel on the roof.

The only potential I see is for gravity energy storage, like this one:

Kinetic energy can be used to smoothen things out but is of course heavy which makes it hardly suitable for anything airborne.

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Sorry, maybe I used the wrong term. With kinetic energy here I meant a rope that is spinning something on the ground.

I also thought about gravity energy storage and AWE after seeing the video. This is potentially a nice combination, as you can lift stuff directly with kites. But - you still have to have electric motors on the crane in order to recover the energy. So you might as well have just put the motor on the AWE rig itself and feed the power to the grid.

Even so, the gravity + AWE does seem to possibly have some cost advantages, as you only need one electric motor, and you get energy storage “for free”.

Plus, the fewer elements there are, the fewer that can break. Lead-acid batteries for example need to be replaced regularly.

Some other ideas:

If that were the case, energy storage would be pointless since it generates electricity from more electricity.^^
With two trolleys on the crane one could be used for lifting by kite (wind -> gravity), and one for letting things down (gravity -> electrical), the rig could give off energy independently from production. If energy needs storing anyway, one can save two conversions by using a mechanical power transfer instead of generating electricity and using that to power the lifting motor.

Not at night, when it’s cloudy, in winter, or on the move for example. The current best practice for solar heating is evacuated tubes, and while that is a great solution, it still is not perfect in every way.

The topic is not asking for an analysis on the market, it is asking for methods and products you can buy or make today, to directly convert movement of a rope into heat, or other useful uses of rotation. This is just brainstorming. The analysis of whether the offered solutions make sense can be made later, for the specific system and location under consideration. For now, for an inexpensive kite, and a generator and batteries that would cost a multiple of the kite, I think it is an interesting thing to think about.

A possible application: you’re going camping in the mountains and it is cold out at night. And you would like to cook some food. You know you will have a quickly moving rope available. What do you bring that could make use of the rope?

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Somewhere in among the yahoo forum tangle was a video link where an American university team (Caltech?) hoisted a large concrete obelisk using a frame and a line tied to a huge kite

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Just keep it in in insulated tank.

Where’s McGyver when he’s needed?
Just clamp the pot really tight and loop the rope around. Wait a long time while your rope will be worn down.
If one would build the most efficient, but obviously expensive machine, it would probably be a specialized reversible heat pump with the compressor run by mechanical energy transfer.
Theoreticall it would be very easy to generate a friction devide. It will always be very efficient!^^ One requirement would be minimal wear. So basically a brake.

As for other (literal) fields in which energy is transmitted mechanically: Power take-off of tractors.
I’ve found fuel pto generators. They come with at least 10kW. So, to illustrate, if one would want to operate such a thing with existing devices one would need 8 or so of Rod’s Daisies. The Power of tractors is scary.
(Off topic: Too many limbs? We can help- video.)

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I was thinking about every stationary machine that nowadays uses a motor. The applications for that are endless. Install the driveshaft somewhere convenient and attach the machine you need to power now to it.

Like this for example:

I don’t like that water has such a low max temperature, you need to have a larger surface area to give off the heat and if you use it for cooking, the temperature difference with the cooking water is absent. Oil might be better despite its lower heat capacity, in some cases.

Other method:

This isn’t going to be so cheap though.

Using the principle of a heat pump?

Heat pump water heaters:

Marine source heat pump:


In power engineering, the ideal is generally to create and use high quality power, usually electricity, and then scavenge the waste heat, or make heat with an electrical heating element. This is more versatile than directly mechancally creating the same thermodynamic amount of heat, and can even be simpler to implement than trying to develop a direct heater.

An interesting aside is the ontological interpretation of heat; its not just an atomic-molecular effect, but also the heat of relative motion of large masses whose body temperatures can measure near absolute zero, unless they collide.