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Sterling engine and Solar

D

Drew Cutter

Jan 1, 1970
0
Could someone explain how sterling engines are used in solar power ?
From what i read their are about 4 different type of sterling engines
being offer today.
 
B

Blue Cat

Jan 1, 1970
0
Drew Cutter said:
Could someone explain how sterling engines are used in solar power ?
From what i read their are about 4 different type of sterling engines
being offer today.

A few solar operated Sterling engines were used in the early 20th century as
irrigation pumps, especially in arid climates.
 
D

Drew Cutter

Jan 1, 1970
0
Can you get by with something else ? The reason why i ask I've been
looking that sunflower 250 . Supposedly it comes without a sterling to
save money for now. They are trying to figure out a way to save money.
 
J

John Beardmore

Jan 1, 1970
0
Paul <[email protected]> said:
"Drew Cutter" <[email protected]> wrote in message news:[email protected]...
Stirling engines are heat engines. The parabolic dish concentrates the
heat energy
on the hot end of the Stirling engine.

The one I've seen looked more like a generic non tracking solar
collector.

The cold end is the atmosphere.

Or the water being pumped ?

The engine
runs and generates electricity. It is a solar thermal electro mechanical
generator.

The one I saw was direct mechanical drive to a pump.


Cheers, J/.
 
P

Paul Ciszek

Jan 1, 1970
0
Stirling engines are heat engines. The parabolic dish concentrates the heat
energy
on the hot end of the Stirling engine. The cold end is the atmosphere.

Thermodynamic question: "The cold end is the atmosphere"--I could
interpret that two ways, and I am wondering which more accurately
describes a Stirling engine:

1) The cold end of the engine is air cooled, which means that the
*effective* coldside temperature is somewhat above ambient
temperature, just as with an automobile engine.

2) The engine runs "open cycle" and inhales new outside air rather
that try to cool down air that has previously been heated. My
understanding is that steam engines give you more output when run
"open cycle", but they need a constant supply of water since they
exaust the water vapor rather than try to cool it back into liquid
water.

Can a Stirling engine be run "open cycle"? The advantage
is that you come closer to having the ambient outside temperature as
the "coldside" temperature of your heat engine, and are not dependent
on finding a way to shed heat efficiently.
 
S

SJC

Jan 1, 1970
0
Stirling engines are heat engines. The parabolic dish concentrates the heat
energy
on the hot end of the Stirling engine. The cold end is the atmosphere.

Thermodynamic question: "The cold end is the atmosphere"--I could
interpret that two ways, and I am wondering which more accurately
describes a Stirling engine:

1) The cold end of the engine is air cooled, which means that the
*effective* coldside temperature is somewhat above ambient
temperature, just as with an automobile engine.

2) The engine runs "open cycle" and inhales new outside air rather
that try to cool down air that has previously been heated. My
understanding is that steam engines give you more output when run
"open cycle", but they need a constant supply of water since they
exaust the water vapor rather than try to cool it back into liquid
water.

Can a Stirling engine be run "open cycle"? The advantage
is that you come closer to having the ambient outside temperature as
the "coldside" temperature of your heat engine, and are not dependent
on finding a way to shed heat efficiently.

I do not think that is possible, but you would have to ask some one
with more knowledge of Stirlings than I.
 
D

daestrom

Jan 1, 1970
0
Paul Ciszek said:
Thermodynamic question: "The cold end is the atmosphere"--I could
interpret that two ways, and I am wondering which more accurately
describes a Stirling engine:

1) The cold end of the engine is air cooled, which means that the
*effective* coldside temperature is somewhat above ambient
temperature, just as with an automobile engine.

2) The engine runs "open cycle" and inhales new outside air rather
that try to cool down air that has previously been heated. My
understanding is that steam engines give you more output when run
"open cycle", but they need a constant supply of water since they
exaust the water vapor rather than try to cool it back into liquid
water.

Can a Stirling engine be run "open cycle"? The advantage
is that you come closer to having the ambient outside temperature as
the "coldside" temperature of your heat engine, and are not dependent
on finding a way to shed heat efficiently.

Well, you can run a 'heat engine' open cycle, drawing in cool air,
compressing it, heating it, then expanding it and finally exhausting it.
Such a cycle is known as a Brayton cycle, so strictly speaking, it wouldn't
be a 'Stirling' engine. Some form of 'recuperator' to cool the exhaust and
heat the compressed air would aid efficiency.

Since the incoming air is *at* ambient temperature, it would have the
coldest 'cold side' you could get. The calculations regarding heat engines
are based on the temperature the working fluid gets to, not the 'thing' used
to heat/cool it. So if the outside air is 20C and the working fluid cools
to 30C in a closed cycle system, there is 10 degrees C that aren't
available. An open cycle system that drew in air at 20C would use 20C for
it's 'cold side' calculation.

daestrom
 
P

Paul Ciszek

Jan 1, 1970
0
Since the incoming air is *at* ambient temperature, it would have the
coldest 'cold side' you could get. The calculations regarding heat engines
are based on the temperature the working fluid gets to, not the 'thing' used
to heat/cool it. So if the outside air is 20C and the working fluid cools
to 30C in a closed cycle system, there is 10 degrees C that aren't
available. An open cycle system that drew in air at 20C would use 20C for
it's 'cold side' calculation.

That is my point, exactly. So, has this Brayton cycle been tried with
solar heated engines? Does it work any better than the closed
Stiriling engine?
 
D

daestrom

Jan 1, 1970
0
Paul Ciszek said:
That is my point, exactly. So, has this Brayton cycle been tried with
solar heated engines? Does it work any better than the closed
Stiriling engine?

The Brayton cycle is the classic cycle of gas turbines (intake, compression,
heating at constant pressure, expansion, exhaust). But I haven't seen it
used in solar installations. The 'trick' would be to get the air to flow
through the reflector's focus and gain a lot of heat in the very short time
it is there (to get much power, you need a healthy flow rate). But that's
no different than any other open cycle setup.

The closed Stirling can have the air pressurized so that even during the
'low pressure' phase, the air is much denser than STP. The denser air can
absorb heat from the heat exchanger surface better/faster, meaning it can
absorb more of the energy applied to it.

In the Brayton though, you're limited as to how high a pressure the
compression stage can go. Higher compression ratios mean higher temperature
going *into* the heating section from the compressor. Not a problem with
combustion versions, but with fixed temperature heating plates that means
less heat energy can be transferred into the air in the heating section, so
less total power.

And rigging the Brayton's exhaust so it helps heat the compressor outlet
could be a tricky engineering problem. The Stirling does this with it's
recuperator.

daestrom
 
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