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Author Topic: Closed chamber Stirling engine generator.  (Read 70867 times)

Offline Groundloop

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Closed chamber Stirling engine generator.
« on: February 29, 2008, 01:04:12 PM »
Hi All,

I have got an idea on how to convert solar heat to electricity. My proposal is to use an completely closed cycle Stirling engine and convert the solar heat direct to electricity by the use of a powerfull Neo magnet and a pickup coil. The Stirling engine has just one moving part. The engine is cooled by water and the hot water byproduct can be used to heat your home or for hot water usage. The Stirling engine can use other gasses than air. Hydrogen, Helium, Nitrogen is some. The solar energy can be collected by a parabolic disk or by Fresnel lens.

I have not build this motor generator and probably never will because I lack the tools and skills to do that. In any case, this is open source information. I hope that someone with the right tools, materials and skills can take this idea into reality.

Groundloop2003.
« Last Edit: February 29, 2008, 06:06:57 PM by Groundloop »

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Offline Groundloop

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Re: Closed chamber Stirling engine generator.
« Reply #1 on: February 29, 2008, 04:36:27 PM »
All,

At mid day in the summer the Sun will provide approx. 800 Watt of energy pr. square meter area.
A solar panel of approx. a square meter area will give you approx. 100 Watt of energy. An Stirling
engine is very effective. Maybe it is possible to convert more of the 800 Watt to electricity when we
compare the area exposed to the Sun.  What do you think?

Groundloop.

Offline tinu

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Re: Closed chamber Stirling engine generator.
« Reply #2 on: February 29, 2008, 04:36:55 PM »
Hi Groundloop,

Stirling usually needs two pistons. One piston variation can be imagined, though.
However, in the variant proposed I think the piston will barely move at best (very small amplitude and tiny motive force) and if it does move at all it will end stuck to the right (cold) side. I can?t see why it would leave that position once getting there.

I?ve also got excited over the time by the idea of solar-heat-electricity but shortly afterward I realized that the efficiency of a thermodynamic engine will be limited to approx. 10% (max. Carnot) considering a reasonable temperature difference of 30Celsius that can be achieved. 10% of >1Kw/sqm of solar energy may not sound too bad on paper but it actually poses a lot of technical challenges in practice because of the cumbersome cylinder and pistons which will weight proportionally to their size (about 1sqm for the displacer), thus generating a lot of friction especially also when considering the sealing requirements for the main piston. Also because at smaller temperature gradients the heat transfer is much slower, any engine of this kind will have a very low RPM ? another nightmare to be overcome.

I?ve seen enough movies of various Sterling engines but not a single one to run on solar energy, although many seemed to happily work above a cup of coffee. I wonder why.

Anyway, I am open for contributing to a thoroughly debate regarding solar-heat-electricity conversion if enough interest exists. After all, solar energy is quite abundant and at about 5USD/W in photovoltaic panels there is at least a theoretical chance to come with something cheaper.

Cheers,
Tinu
« Last Edit: February 29, 2008, 10:39:42 PM by tinu »

Free Energy | searching for free energy and discussing free energy

Re: Closed chamber Stirling engine generator.
« Reply #2 on: February 29, 2008, 04:36:55 PM »
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Offline Groundloop

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Re: Closed chamber Stirling engine generator.
« Reply #3 on: February 29, 2008, 05:16:24 PM »
@tinu,

First, you havent seen much I bellive.  ;D

http://www.sandia.gov/news/resources/releases/2004/renew-energy-batt/Stirling.html

The difference with my design is that there is just ONE moving part.

Next, the temprature difference will be some 1000 Degrees or more in a solar powered Stirling.
The cold side will be approx 90 Degrees Centigrade. (Water cooling, remember.)

A closed cycle Stirling with one piston is no problem to manufacture.


Before you "doom" a project please get some information first!

Groundloop.

Offline tinu

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Re: Closed chamber Stirling engine generator.
« Reply #4 on: February 29, 2008, 05:41:37 PM »
@ Groundloop,

Don?t be that sensitive, now!
Figures are welcome. One moving part is great but it won?t make it workable more than 1RPD (rotation per day) or 1 RPC (per cloud  ;D). I know it because I?ve also designed my own stirling 1 moving part variant. It simply takes more than what's depicted in the above schematic.

Your project is not doomed. Who said it was? Instead, just keep elaborating on it and developing the subject to see how far it/you can go.
As about competing with Sandia that would be another story?

Cheers,
Tinu

Free Energy | searching for free energy and discussing free energy

Re: Closed chamber Stirling engine generator.
« Reply #4 on: February 29, 2008, 05:41:37 PM »
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Offline AhuraMazda

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Re: Closed chamber Stirling engine generator.
« Reply #5 on: February 29, 2008, 05:48:17 PM »
The guy in this video demonstrated an engine like the one you talk about. I am not sure if this is that specific video.

http://youtube.com/watch?v=ofsxZfu9rW0&feature=related

AM

Offline Groundloop

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Re: Closed chamber Stirling engine generator.
« Reply #6 on: February 29, 2008, 05:53:56 PM »
@tinu,

I did put a big smile in there, did I not?  ;D I'm terrible at math. Are you able to compute
approx. how much energy we can get from a temperature difference created from a 1 sq. meter
parabolic disc focused on the hot side of a Striling engine? What I mean, how big must the motor be to
get approx. 300 Watt from the sun? How big is a 1/2 horse power Stirling engine?

One advantage I see with my idea is the closed one piston engine. No need to use any complicated seals etc.
The piston can be made of very light material so the only weight will be the axle and magnet.

Groundloop.

Free Energy | searching for free energy and discussing free energy

Re: Closed chamber Stirling engine generator.
« Reply #6 on: February 29, 2008, 05:53:56 PM »
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Offline Groundloop

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Re: Closed chamber Stirling engine generator.
« Reply #7 on: February 29, 2008, 05:58:33 PM »
@AhuraMazda,

No, the video you posted is not related.

This video is.
http://youtube.com/watch?v=3O1xacAu4jA

My big difference is to get rid of the loss by not using flywheels.
Also since the engine is closed there is no need for exspensive and difficult seals etc.

Groundloop.
« Last Edit: February 29, 2008, 06:52:16 PM by Groundloop »

Offline Gearhead

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Re: Closed chamber Stirling engine generator.
« Reply #8 on: February 29, 2008, 06:16:07 PM »
In the 1970's there was a closed, sealed, free piston stirling engine with a parabolic mirror being offered for sale in Popular Science Magazine that was claimed to be able to produce 100 watts.  I remember the story about how they kept experimenting with different weights of pistons until they got a resonant system that worked.

Free Energy | searching for free energy and discussing free energy

Re: Closed chamber Stirling engine generator.
« Reply #8 on: February 29, 2008, 06:16:07 PM »
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Offline Groundloop

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Re: Closed chamber Stirling engine generator.
« Reply #9 on: February 29, 2008, 06:30:42 PM »
@Gearhead,

Thank you for the information. Do you remember where or who? Maybe a web link?

I have decided to try out my idea, making a prototype. I will use a 46 cm parabolic mirror.
I will also use water cooling on the "cold" part of the engine. The maximum temperature
with a small parabola like that will be 400 - 600 degrees Centigrade on the warm side of
the motor. Depending on how much help I will get on this forum my project will take from
some few weeks to a year to complete. I have computed the total cost of this project
to be approx. 4500,- NOK. (865USD). My goal is to beet the output of a solar panel of
equal area as a 46cm parabola.

Groundloop.

Offline Groundloop

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Re: Closed chamber Stirling engine generator.
« Reply #10 on: February 29, 2008, 07:04:38 PM »
@All,

Take a look at this video:

http://youtube.com/watch?v=kYKOjnCwmG8&feature=related

Groundloop.

Free Energy | searching for free energy and discussing free energy

Re: Closed chamber Stirling engine generator.
« Reply #10 on: February 29, 2008, 07:04:38 PM »
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Offline dutchy1966

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Re: Closed chamber Stirling engine generator.
« Reply #11 on: February 29, 2008, 09:36:48 PM »
Hi groundloop,

I've been pondering about the same sort of stuff lately. I mainly came to the conclusion that a parabolic trough is too expensive/complicated for an amateur scientist. On the other hand Fresnel lenses are cheap and easily obtainable.
The question then becomes what best to do with the focussed sunlight. It has enormous heat potential. We can either use it through a stirling cycle as you suggested or use solar panels (not so efficient). I'm still looking at oscillating steam engines to use. The oscillations can then be used to generate power by a magnet/coil combo (as in your stirling design).

I have made a little drawing which shows a way to maximize the use of fresnel lenses in a for amateur doable way.

Maybe it is usable for your plans or it will give u some new ideas

btw the picture shows an evacuated solar tube in the center but it could also be the hot side of a stirling engine. The yellow lines are supposed to be the rays from the sun.....



regards

Robert

Offline tinu

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Re: Closed chamber Stirling engine generator.
« Reply #12 on: February 29, 2008, 10:00:06 PM »
@Groundloop,

Late reply. I was out for dinner and I?m a bit lazy now so it won?t be a very elaborate answer.

First: I?m not an expert in Stirling engines, neither in thermodynamic ones. So, may views are subject to human errors and surely to various improvements.
Second: Pretty much like most endeavors, the burden rests on the inventor/initiator. This is said to take my views as coming from the side.

I deduce you?re from Norway. First issue would be to decide whether focusing the sun-light or not. It dry or very arid/desert area it seems more advantageous to vote for focus. But there are great disadvantages: tracking the sun (energy and money; good control mechanisms are needed), provide good mirrors often in not common geometrical shape (hard to manufacture and expensive) and keep those mirrors clean; increased risks (birds, fires, burns etc); very narrow window of high efficiency, easily affected by light clouds and other phenomena. I know that for Europe most solar water heaters are not-focused or just lightly focused using small mirrors behind collectors. My option would go into that. But if you decide to focus, well be it. However, on a large body that absorbs heat and transfer it to a sink (like a stirling engine does) 400-600Celsius will require large mirrors. How large? That can be told only after the engine is designed because it will give the amount of heat transferred from the hot to the cold side per each stroke. Also, the hot area of such setup shall be placed in vacuum for minimizing loses and also under some kind of one-way reflexive layer (but these can be bought as they are already manufactured and widely used for various purposes).

For power estimates, I'd go at a maximum of 1.2kW/sqm. It is highly arguable and subject to local conditions. That?s what I used so far. Assume 90% eff for mirrors and you have 1080W (maximum) focused on a given surface. Now a whole bunch of questions arise. Getting to the equilibrium temperature depends on each choice: surface area, color, heat capacity, heat transfer, black-body radiation. I?d go for simple experiments using a 1-2KW heater versus mirrors on a ?Stirling dummy?, starting from Q=C*Delta(T) and drawing a graph. It will go flat toward high temperatures, thus giving a better estimate about 400-600Celsius . My actual guess would be more like 200-300Celsius for a homemade setup.

How big is a 300W Stirling?
It depends on the working pressure. Higher the gas pressure, smaller the engine. It resides in p*V=N*R*T and W=p*Delta(V) as long as p can be approximated as constant.
http://youtube.com/watch?v=BBZDJn6B0cs might actually be around 300W (?) but I don?t think it will suit you. ;)

The only issue I have is that the motor you drew above will not work. Please take a closer look at it. There is nothing to make the piston to move back and forth. You still need to provide a mechanism for that. Also, please have a look on Stirling theory and also at practical devices. There is not a single one that takes power from the displacer. Displacer is always powered (usually by the piston through a flywheel) and it is used to circulate part of the working gas between hot and cold side, thus ensuring the required cycling.  Not only that the displacer (which is not air/gas-tight in respect to the cylinder) is always powered by the main piston, but the main piston is as air-tight as it can be. But in your drawing, if I understand it correctly, the gas will simply pass through the space between the displacer and the cylinder if there is such space. Very little work is transferred by the almost freely passing gas to the displacer and this gas-flow is only temporarily (until thermal equilibrium is reached). No work.
On the other hand, if I misunderstood the drawing and there is not such space and you rightfully put the name ?piston? where it is, the piston will indeed be forced to move by the developing pressure inside the gas due to heating. The piston will indeed be pushed back when you heat the hot side and will do some work in the process but then it will stay there forever, or at least until the heating cease. You need a mechanism either to stop the heating or to increase the cooling, otherwise the piston will not move from that position.
So, either way I really don?t see how it can possibly work. That was the only issue I raised in my first post.

Guess we?ll talk more tomorrow. It?s already late here.

Cheers,
Tinu

Offline dutchy1966

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Re: Closed chamber Stirling engine generator.
« Reply #13 on: February 29, 2008, 10:15:40 PM »
Hi groundloop,

You might wanna look at this nasa slide presentation about free piston sterling engines:

http://www.grc.nasa.gov/WWW/tmsb/stirling/intro_stirling/Slidepage.html

hope it is useful

regards

Robert

Offline AhuraMazda

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Re: Closed chamber Stirling engine generator.
« Reply #14 on: February 29, 2008, 11:56:28 PM »
@dutchy
Could you please post whatever is there? I am told I need a NASA pass to look at the page.

AM

 

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