200-400w wooden fired Stirling engine?

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200-400w wooden fired Stirling engine?

Postby skands » Sun Oct 04, 2009 7:49 am

For my cabin up in the mountains, I'm thinking of building a Stirling
engine to help charging my battery pack. I also have a solar panel,
and I'm hoping to reduce the need for my combustion generator, which
is (apart from being very effective), noisy polluting and a bit
costly.. besides the fuel needs regular transportation from some gas
station, and it smells etc..

I also use my cabin in the winter, and it is not that much to get from
the sun if I stay more than a few days (draining my battery pack).
But, I have two wood stoves running all day, and outside my walls it's
freezing cold! I need about 300-400 watt in average (daytime when I'm
firing). So if I can get 200w out of each one, i will be happy (as I'm
also planning for a 200w Savonius wind generator).
I need power for my electronic gadgets (laptop, phone, weather station
etc.). I often do some of my working up there (in total concentration
and peace :)

So my plan is to take advantage of heat pipes to bring heating and
cooling to the both ends of the engine. I will drill holes in the back
of my stoves, (near the bottom), and place heat pipes inside (on the
stove "floor" covered by some metal plate). The Stirling engine is
placed outside the cabin wall, above the stove floor (for gravity
assisting heat pipe fluid). Pipes runs thru wall, and is attached to
the hot Stirling engine end (bottom of engine). Top of engine (cold
end) is attached to a vertical heat pipe, heat sink radiator (alcohol
vaporizes). It is often -10 to -20 degree celcius in winter, and snow
will further assist the cooling!

I'm not sure though, if I can get as much as 200w out of each
generator attached to the engines..? If I can get 100w from each, I
will still get 80w more than from my solar panel at peak level.

Type of generator is another concern. If I make the Stirling engines
as powerful as possible, I might find a proper generator to fit my
needs and parameters..?

Or maybe a free piston type engine is ideal for this heat pipe/
Stirling engine project?

If I can melt snow for tap water with the heat pipe radiator, it will
be perfect :)

I know there are certain calculations need to be done, but I would not
enter such a project if it was not for the fun part of it.

Hmm, so I wonder, is this at all possible? (I can afford the costs for
fine machinery).

And sorry for my poor english..
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200-400w wooden fired Stirling engine?

Postby stan.hornbaker » Sun Oct 04, 2009 11:40 am

The problem with your use of a Stirling engine to generate 200-400 watts is in the availability of a suitable Stirling engine.

Such an engine is not available on the market and building one yourself is for the most part a matter of self education to the point of being able to determine the detailed specifications and to design the Stirling engine that you will have to eventually fabricate.
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Response to 200-400w wooden fired Stirling engine?

Postby bptdude___2569 » Sun Oct 04, 2009 6:13 pm

One possible suggestion, if you have available funds, and can build small machines yourself, and willing to violate probably the warranty, ... *grins* ...

There a Stirling sold by a company WhisperGen. They are not really having great success, yet, but they sell a setup for a marine yacht.

I came back to this, when trolling about yachts for fun, and realized I would need to heat it to go out with the New England fisherman in winter, and whatever I got would have a good diesel engine.

There is a WhisperGen unit for the yacht that burns diesel, and supplies heat and hot water, very much like thier CHP unit for home.

For a cabin, I would prob try the yacht unit.

All you have to do, is figure out how to use a real wood furnace to heat the Stirling to the same level as the diesel. You will have a nice industrial strength 800 watt generator.

Well, maybe.
Please post if you try it and it works.

If is is a complete disaster, I don't know you!

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Worth a try?

Postby skands » Mon Oct 05, 2009 2:49 pm

Thank you both for answering my questions.

@ Joe.
Yes I will use money (and time) on this project if it turn out possible to achieve proper results. I've been searching around to find good engines that is already "in the market". Alas, there are disappointingly few.. I've seen kit/plans for building the Viebach ST 05. Some guy said it was possible to buy one for around 4000 € (?)
This one one is quite interesting. ..And of course there is SunMachine and WhisperGen. The latter I think could be modified (and as long at is works well under default conditions, I don't care about the warranty :), but I don't think I have enough firepower to run it. The Viebach is a 350 watt. Like a small wind generator, maybe producing 150 - 250 watt as long as i need heat from the stoves.

With proper heat piping I can maybe reach the 600ºC needed for running.. or about 2000 watt. I can then bear a heat loss of some 100-300ºC.. But trying to transfer that amount of energy will be challenging. I estimate at least 2000w input for the generator. The stoves produce from 3-6 Kw, so maybe I must scale down a bit.

If the heat pipe system can't deliver the right level of temperature to the Viebach (or similar) at the evaporizing end, I must face the challenge of stepping in to the community and designing and building my own hot air engine :)
NASA will truly be in space fitted with some Stirling engines, but for efficiency, and precision, anyone can build one of their own nowadays. Equipment/ tools assortment is head away into space age just around the corner. And to make a prototype is not that costly. So maybe..? Do I have what it takes? Dunno.. yet. Just theory and thoughts for the moment.

The heat piping is it's own project of course. I will anyway use the heat pipes directly for heating water if I can't get an engine/ generator up and running.

If there is a way to take advantage of the heat from wood firing regarding to battery charging, it will be the Stirling engine. I can't think of anything better. - Both heat and electricity.. and some hot water too!
Not talking about big things, but enough to power some equipment/ gadgets.

..If not.. I may try to attach a LPG system to my combustion generator.. No wait, I build a couple of more of those Savonius rotors.. ;-)
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Response to 200-400w wooden fired Stirling engine?

Postby stan.hornbaker » Mon Oct 05, 2009 5:44 pm

IF you have your heart set on using a Stirling engine, GO FOR IT.

Other wise I would suggest that you consider a small reciprocating steam engine of modest size to run a generator to fulfill your needs for electricity. They are readily available at reasonable prices in either ready to run or kit versions from several sources on the internet.
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Response to 200-400w wooden fired Stirling engine?

Postby jol.andre » Thu Jan 14, 2010 12:31 am

Can you correct me on this Mr. Hornbaker?

I believe that small steam engines have efficiencies much lower than could be expected from a ''reasonably well made'' Stirling. (I mean home-built with some careful design, trial and error) Am I overly optimistic?

The problem being that even small steam engines require much more heat than one would normally use to heat a building, and so they require burning a lot of extra fuel just to provide a little electricity, which probably also requires setting up a larger furnace for the boiler.

Then the steam exhaust has to be dealt with, either by wasting it out to the outside, or by condensing it to recuperate the heat. Then one must address the problem of either feeding the boiler with pressurized water, or running the engine on an intermittent basis...
Steam doesn't seem so simple in the end.

If a small, very moderate-performance Stirling has a little better efficiency than a steam engine, then it might run on the heat from the building's existing furnace, and make a simple and economical source of electricity.

Going from 1% to just 3% or 5% in efficiency makes a huge difference in the quantity of fuel that's needed.

If not a Stirling, I would think Indium Telluride thermoelectrics as the 2nd best option, however an expensive one. I find that commercial InTe modules (Tellurex) would cost over $2000 to generate around 150W.

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Response to 200-400w wooden fired Stirling engine?

Postby priler1 » Sat Jan 16, 2010 1:29 pm

I think it's worthy having a look at www.precer.com Those swedish guys develope such engines, even a stirling-electric car running on pellets. I'm not sure though their products are on the market.
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