Geothermal/Solar Stirling Generator ??

[Methusela]

I was tottering around the internet the other night when a rather interesting idea struck me...

Would it be possible/feasible to build a Generator (Most likely 12v or so, bit scared of bodging up a 240v supply ) Using a Stirling engine as the driving force.

If you're not sure what a Stirling Engine is you can check it out here:

http://en.wikipedia.org/wiki/Stirling_engine

I was thinking about it and thought that perhaps you could bury one cylinder in the ground and take advantage of the fairly stable temperatures there and have the other above ground, painted matt black or somehow set up to gather heat from the sun (can you tell i'm still working out the kinks ? ).

If it could be set up this way then in the Summer the sun could heat the cylinder above ground whilst the cylinder buried in the ground would remain cooler, but also in the winter the buried cylinder would (hopefully) be warmer than the cylinder up in the cold and continue to provide energy (via some kind of generator) all the year around.

So, part from it being a horribly ambitious build idea... as an intellectual exercise at least, what are your thoughts??

Discuss

Paul

[MKG]

No reason why a Stirling engine wouldn't work - if you could get the top chamber hot enough and the bottom chamber cold enough. The temperature differential between normal sunlight and the soil wouldn't be enough, I think. You'd need a parabolic mirror to concentrate the sunlight and you'd need something to carry away waste heat at the bottom - the soil certainly wouldn't do that, I feel, and even pumped water cooling may not be enough (and where does the energy come from to power that pump anyway?)

But it's a nice idea - carry on exercising the intellect!

Mike

[Methusela]

(and where does the energy come from to power that pump anyway?)

Well i never claimed it was perfect ;)

[MKG]

Actually, I take it all back. Your post made me go and have another look at Stirling engines, and I see that you can now get low temperature-differential models. They're very small, but they illustrate the principle nicely. So yes, you could run such an engine directly from sunlight. The only question, then, is how much power it would develop - enough to turn a generator? I don't know.

Then, of course, there are other heat sources - the middle of a good compost heap gets hot, as does a pile of grass clippings.

You may actually be onto something!

Mike

[dave45]

research "Whispergen" - this was going to be a world-changing technology based on combining a normal C.H. boiler with a stirling engine to create a hugely energy-efficient system...UK trials were happening ...
I put my name on the list... but they've gone awfully quiet.

[Methusela]

The only question, then, is how much power it would develop - enough to turn a generator? I don't know.

As i understand it producing much in the way of torque is a real issue for Stirling engines... as yet i have no idea on figures or anything like that but i imagine something could be done with the right gearbox.... of course finding the right gearbox is another mission all of it's very own...

I originally thought the thing up as a supplement to existing wind/solar LV systems rather than being able to provide enough eletricity all on it's own

You may actually be onto something!

Thanks for the vote of confidence :) now where did i put that lathe?