Stirling engine for a smal-medium farm

[becker]

Hello!

I don't know if this is the right place to ask, but I wonder if its a good deal use stirling engine for energy production in a small-medium farm.

Thanks for the response.

Edited November 12, 2014 by CésarNoll

[Enthalpy]

There was such a Stirling in the small industry park where I worked years ago. We were in a forest, and wood chips (bark, sawdust, chopped small branches) heated a Stirling to make electricity, so it does work. I ignore how bad the economics of the project are.

 

What I don't grasp at all is the fuss in ecological circles about the Stirling engine. It's nothing more than a converter from external heat to movement, and any vapour machine does that far better: smaller, cheaper, more efficient. Especially a vapour turbine is so much smaller.

 

In a farm, you might also consider the production of methane, for local use or for sale - it's essentially the same as natural gas.

 

A farm may also produce vegetable oil to run engines, either at cars or electricity generators. Though, this one doesn't use waste products. Petrol from vegetable waste would be very nice but isn't operational up to now; science in progress.

[Sensei]

Don't forget also about production of ethanol from wastes of vegetables and plants.

Just put them to tank with yeast and water, don't let oxygen enter tank, distillate it after couple weeks and you have cheap fuel to burn in engine..

Edited November 14, 2014 by Sensei

[overtone]

What I don't grasp at all is the fuss in ecological circles about the Stirling engine. It's nothing more than a converter from external heat to movement, and any vapour machine does that far better: smaller, cheaper, more efficient. Especially a vapour turbine is so much smaller.

Theoretically, no heat engine cycle is more fuel efficient - hence the attraction in ecological circles, in that it can in theory (and so far in practice) capture a much higher percentage of a given solar energy flux for doing work than the alternatives can. As that is the first problem of solar power - getting work out of such an attenuated and low density supply of energy - the Stirling cycle looks ideal at first.

 

And such a power source is intrinsically more efficient than any conversion of biomass to fuel, since one has already lost 95% of the solar energy flux to production of the biomass. That's before considering soil depletion, fuel and fertilizer costs of production, transport, etc.

Edited November 14, 2014 by overtone

[Enthalpy]

Measured efficiency is worse for Stirling engines than for vapour turbines. And since renewables are free but their conversion costs, efficiency isn't the primary concern.

 

In seriously engineered Solar thermal plants, the conversion uses turbines.

 

Ethanol: it would be nice if this already worked practically. Much research is done on the topic. Presently, fermentation of sugar (beetle, cane) gives ethanol, fermentation of vegetables gives methanol, a lower-value poison. Researcher's aim is to get the preferred ethanol from waste rather than food; until this works well, methane is the best fuel obtained from biomass.

[Sensei]

I was talking about from perspective of existing here and now small-farm (what is interesting to Cesar).

It'd be much harder to make methane, and store gas, than with liquid ethanol (or methanol)..
How are you going to liquefy methane at home in continuous process.. ?

Edited November 14, 2014 by Sensei

[becker]

I didn't mention that, but I have a school work to project something ecologic for the city and I and my friends decided to use the concept of Permaculture. Basically, what the stirling engine will do is just provide energy using the sun, a convex lens will concentrate the solar light to one side of the stirling and other side will be cooled with water or something else.

But the responses, I just want to say this: love you guys! You guys thought things that I'd never imagine.

[Endy0816]

Is there any form of flowing water available? That would be simplest for cooling.

 

An alternative option would be to utilize the waste heat for producing hot water(showers, washing, etc). Necessarily the engine output will drop as the heat sink's temperature rises.

 

Otherwise there is always air cooling which while not being as efficient could still work decently enough depending on the temperature difference.

[overtone]

Measured efficiency is worse for Stirling engines than for vapour turbines.

Not in small scale lower temp solar setups.

 

And since renewables are free but their conversion costs, efficiency isn't the primary concern.

Renewables are not free - especially solar, with its low density of supply. Fuel efficiency is critical for solar - top priority.

 

The theoretical efficiency of a Stirling cycle is just too attractive to let go.

 

 

 

Researcher's aim is to get the preferred ethanol from waste rather than food

Redefine sugar cane as non-food, and you're good to go - in Brazil, anyway.

 

Considered as a multistage solar capture, ethanol and the like throws away 90% of the resource before even beginning the conversion. And it uses good land - with water and good soil.

Edited November 17, 2014 by overtone

[Enthalpy]

Answering to my: " Measured efficiency is worse for Stirling engines than for vapour turbines. "

 

Not in small scale lower temp solar setups.

 

Stirling's measured efficiency is worse than a vapour turbine, at any scale. And if a Solar setup provides a low temperature, it's badly conceived. In addition, a Stirling is huge. Wrong choice, whatever the size.

The theoretical efficiency of a Stirling cycle is just too attractive to let go.

 

But the observed inefficiency is an excellent reason to abandon this bad choice.

Renewables are not free - especially solar, with its low density of supply. Fuel efficiency is critical for solar - top priority.

 

Yes they are. Nobody pays for sunlight nor wind.

 

The collecting area does cost, and a turbine makes best use of it.

Considered as a multistage solar capture, ethanol and the like throws away 90% of the resource before even beginning the conversion. And it uses good land - with water and good soil.

 

But since sunlight is free, and land is much cheaper than a sunlight concentrator, comparing the necessary area doesn't bring farther. The net result is that ethanol from sugar cane is cheap enough to run cars with it at the scale of Brazil, while other renewables don't propel cars up to now.

[becker]

But isn't a Stirling engine at low cost alternative rather than vapor turbine? Remembering that is a small-medium farm, this "farmers" can't spend much money. I thought that Stirling engine could be a good power generator using the sun.

[Enthalpy]

It'd be much harder to make methane, and store gas, than with liquid ethanol (or methanol)..

How are you going to liquefy methane at home in continuous process.. ?

 

Methane is produced on a daily basis in many farms. That's existing technology. As opposed, methanol has presently no broad commercial circuit because it's a poison, and ethanol is not obtained from waste up to now.

 

If it were any necessary, methane could be liquified. That was difficult in the 19th century, not now.

But isn't a Stirling engine at low cost alternative rather than vapor turbine? Remembering that is a small-medium farm, this "farmers" can't spend much money. I thought that Stirling engine could be a good power generator using the sun.

 

A 1 ton piston engine cheaper than a 10kg turbine? No.

[overtone]

Stirling's measured efficiency is worse than a vapour turbine, at any scale.

Depends on the specific setups compared. The best smaller Stirlings have passed 30% photon-to-grid conversion,

 

 

 

 

Yes they are. Nobody pays for sunlight nor wind.

The collecting area does cost,

 

You might as well say nobody pays for coal - although the collecting does cost.

 

But since sunlight is free, and land is much cheaper than a sunlight concentrator, comparing the necessary area doesn't bring farther. The net result is that ethanol from sugar cane is cheap enough to run cars with it at the scale of Brazil

Compared with a concentrated solar collection setup, the cost of the specific example you present there omits very large externalized costs - beginning with the setup for liquid fuel to power internal combustion car engines, continuing with the environmental and opportunity costs of the land use not represented in the price of the land, et al, ending with the fact that comparison of well-understood commercial operations in mass production already with new and boutique setups not well integrated into existing economies misleads. QWERTY phenomena abound in this field.

And that theoretical efficiency still beckons, no? You've got something that routinely hits 50% of its theoretical at low temps even now in the early stages, and its theoretical at higher temps is over 90%. So its attraction is no mystery.

 

A 1 ton piston engine cheaper than a 10kg turbine? No

That's misleading. Compare total weights to total weights.

And note - the pistons are not only less high tech and expensive to maintain than the turbines, but not even necessary: diaphragm designs exist, in operation and in near prospect: http://www.al-ruh.org/page1.html

Edited November 18, 2014 by overtone

[Enthalpy]

You've got something [the Stirling engine] that routinely hits 50% of its theoretical at low temps even now in the early stages, and its theoretical at higher temps is over 90%. So its attraction is no mystery.

 

Pure nonsense. 90% efficiency demands a hot source >10 times hotter than the cold sink, that is, >3000K on Earth. No materials enables a piston engine at 3000K.

[Answering to my: "A 1 ton piston engine cheaper than a 10kg turbine? No"]

 

That's misleading. Compare total weights to total weights.

And note - the pistons are not only less high tech and expensive to maintain than the turbines, but not even necessary: diaphragm designs exist, in operation and in near prospect: http://www.al-ruh.org/page1.html

 

That's bare fact. In a turbocharged piston engine, the turbocharger passes about the same power as the reciprocating part of the engine, but it's nearly 100 times lighter. A Stirling engine is much bulkier and heavier than a gasoline engine.

 

A turbine needs far less maintenance than a piston engine. That's exactly why airliners switched to turbines. Power and mass were perfectly acceptable with piston engines. As for the high tech, you should check what kind of effort was needed before seal rings could be made for the pistons, or bearings between the crankshaft and the rods, and so on.

 

Again: I had a Stirling engine 100m from my employer and observed it often enough. It's bigger than a truck engine for just over 10kW. The comparison with a turbine is immediate.

[overtone]

 

You've got something [the Stirling engine] that routinely hits 50% of its theoretical at low temps even now in the early stages, and its theoretical at higher temps is over 90%. So its attraction is no mystery.

 

Pure nonsense. 90% efficiency demands a hot source >10 times hotter than the cold sink, that is, >3000K on Earth. No materials enables a piston engine at 3000K.

50% of theoretical 90% would be 45% solar efficiency - the research models hitting those numbers (and better - 60% +) use liquid nitrogen as an initial sink, iirc - a substantial source of their loss of efficiency, but a tech necessity for reducing the material demand you note.

 

 

 

A turbine needs far less maintenance than a piston engine. That's exactly why airliners switched to turbines.

Depends on the turbine and piston you are comparing - the Rankine turbine solar pumps that demonstrate such reliability are very expensive. The cheaper ones are not as maintenance free, or as reliable.

 

And of course pistons are not required, in Stirling engines. There are diaphragm engines with 8000 hours continuous on them, still running.

 

But the initial question, if you recall, was about the attraction of the Stirling cycle - the theoretical efficiency, an advantage so apparently close to being realized, was my nomination for the reason. There are working solar Stirling generators over 30% photon to line right now. This is a draw, an attraction. The upside potential is there, and seems to explain the attraction.

 

 

Again: I had a Stirling engine 100m from my employer and observed it often enough. It's bigger than a truck engine for just over 10kW. The comparison with a turbine is immediate

Why the obsession with weight?

Edited November 22, 2014 by overtone

[Enthalpy]

Your font size is getting as unnecessarily fat as a Stirling engine.

Stirling engines are inefficient and huge, that's why sensible designs avoid this fashion.