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What can you tell me about Stirling engines? Answered

I'm interested in using a Stirling engine in a solar energy project. From reading around and doing some numbers it looks like I'll need around 1.5 kilowatts, and something in the vicinity of 30% efficiency or upwards would be nice, though I realise this may be overly optimistic. So, what's available, how much will it cost, what temperature differential is ideal, how big and heavy are these things, etc. Any info I get would enormously helpful. Cheers, Daniel.

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LinuxH4x0r

9 years ago

I'm also interested in using solar for sterling engines. I like the idea of using boiling oil or water heated in a parabolic dish or trough.

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SolarFlower_orgLinuxH4x0r

Reply 9 years ago

Parabolic troughs are easy to make and use, but quite inefficient and large. Much more efficient is a parabolic dish, but then you need to keep it very accurately pointed at the sun.

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LinuxH4x0rSolarFlower_org

Reply 9 years ago

Right. But for small homes a less efficient easier method might be more realistic

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SolarFlower_orgLinuxH4x0r

Reply 9 years ago

Yup. Especially if you've got something like a roof where you can take up some space. What information have you found so far? Any numbers?

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LinuxH4x0rSolarFlower_org

Reply 9 years ago

Not a whole lot. Once the snow clears up I'll try tinkering around until I get something. You might be interested in gutting old rear projection TV to get their enormous lenses

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SolarFlower_orgLinuxH4x0r

Reply 9 years ago

Ok, stay in touch with anything you figure out. Good idea bout the lenses, I was wondering where I could source those. Wish it was snowing here in Scotland. Although I did get hailed on sideways yesterday...

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PKM

9 years ago

Yes, I know exactly the website you want. Check out stirling-tech.com first, they sell a commercial cogeneration engine that sounds a lot like what you want.

The tl;dr of their calculations is that you can run the engine, generating about 4kW of electricity and something like 30kW or 115000 BTU/hour (who uses BTU? srsly) of heating from recovered heat, with a heat input of 38kW. This could be achieved by burning 6-10 cords of wood per year (38,000 lbs or about 17 tonnes), but presumably if you can heat the thing externally you might be able to use concentrated solar. A 38kW concentrated solar system in someone's back yard would be a sight to see :)

This site (translated from German) appears to sell what you are looking for (a 500W Stirling) with exposed heat receiver so you could presumably heat it however you want to. I have no idea if the site is still current or not but it looks quite promising. His old site (again might be abandoned but has more information).

This site, difficult to read but an absolute treasure trove, has possibly everything practical you'd ever want to know about Stirling engines and heat engines- it's where I found the link to stirling-tech and all sorts of other obscure stuff.

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PKMPKM

Reply 9 years ago

Am I to assume that you want to build some sort of solar-stirling power generator? Additional stuff that I forgot just then- 30% efficiency is pretty optimistic in terms of heat to shaft power. For a commercial high-temperature-differential engine figure more like 10-20%, for a home-built one it will be less. Them's the rules, it seems.

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SolarFlower_orgPKM

Reply 9 years ago

Wow... that's... terrible.
Luckily, before this information had a chance to get me too frightened and depressed, I found this:

http://www.sunpower.com/lib/sitefiles/pdf/productlit/Engine%20Brochure.pdf

Sunpower EG-1000, 30% efficient (or more), 1kW (or more) pretty small.
I'm still trying to find out how much it costs, but at least if these guys have done it means it can be done. Part of their mission statement apparently is doing these things as cheap as poss.

Booyakasha.

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PKMSolarFlower_org

Reply 9 years ago

Cool! I was unaware of that engine, it sounds a lot better for what Linux seems to want anyway. I think the one I described had two main aims, being reasonably cheap to produce (air as working fluid rather than hydrogen, etc), and having an exposed external heat exchanger so you could run it on logs, wood pellets, agricultural waste etc. It's also designed for cogeneration (heat and power from the same fuel) so might be designed to produce enough heat to heat a house simply with electricity efficiency as a secondary aim. The Sunpower unit looks a lot more futuristic, is specifically designed for electricity generation so is better at generating electricity but is probably hellishly expensive, and I'm not sure how well it would take to alternative fuels. Still, they were producing the engines for the Sandia CSP solar farm so the EG-1000 might be great for use with solar. I'd love one of those engines to experiment with...

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PKMPKM

Reply 9 years ago

.. for some reason I thought LinuxHaxor had started this thread, ignore that comment. The EG-1000 sounds much better for what you want to do with it :$

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SolarFlower_orgPKM

Reply 9 years ago

Wow... that's... terrible.
Luckily, before this information had a chance to get me too frightened and depressed, I found this:

http://www.sunpower.com/lib/sitefiles/pdf/productlit/Engine%20Brochure.pdf

Sunpower EG-1000, 30% efficient (or more), 1kW (or more) pretty small.
I'm still trying to find out how much it costs, but at least if these guys have done it means it can be done. Part of their mission statement apparently is doing these things as cheap as poss.

Booyakasha.

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westfw

9 years ago

Just to be a wet blanket, I hear that Stirling engines make pretty cool looking demos, but it's difficult to get real power out of them. They're dependent on the temperature difference between the hot and cold areas, and it turns out to be HARD to keep a high temperature difference between two pieces of the same motor, especially when you have gas sloshing back and forth. (it seems that it's harder to keep the cool end cool. Heating the hot side is easy :-)

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SolarFlower_orgwestfw

Reply 9 years ago

I'm thinking this will be used in a back-garden kind of setting, which means probably the easiest way to heatsink the engine is just to bury it. ie, run a copper tube or mesh down into a smallish water reservoir a couple of feet under the ground. This should give a fairly consistent temp of about 10 C / 50 F, depending on location. Otherwise, and this may be daft, would it not be possible to run another smaller stirling off the heatloss of the first? I'm not sure how effective it would be at dissipating heat, but it should make the overall setup more efficient? (you could have some kind infinite regress of progressively smaller stirlings, each running off the heat of the last...) There's something weird going on with stirling engines, and I'm not completely sure what it is. It seems like if you want a small toyish one to play with, you're fine, and if you want a huge industrial 25 kW one, you're fine, but if you're just looking for something in the middle to run your home off, then there's very little available. And half the people you ask will tell you they're maybe a bit large, but very efficient and powerful, and half will tell you that it's almost impossible to get anything worthwhile out of them.